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  • Other Sources  (64)
  • Wiley  (32)
  • Taylor & Francis  (19)
  • IAHS Press  (13)
  • Univ. Bochum
  • 2010-2014  (64)
  • 1980-1984
  • 1925-1929
  • 2012  (64)
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  • 2010-2014  (64)
  • 1980-1984
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  • 1
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    Computer-aided identification of coelacanths, Latimeria chalumnae, using scale patterns (2012)
    Taylor & Francis
    In:  Marine Biology Research, 8 (3). pp. 300-306.
    Details
    Publication Date: 2017-06-20
    Description: Despite coelacanths, Latimeria chalumnae, being listed as either endangered by CITES or critically endangered by the IUCN, their population size within South Africa is unknown and still needs to be estimated. Their conservation status unfortunately excludes the use of conventional tagging to mark individual animals for a possible mark–recapture experiment. This study shows that because coelacanths have a unique spot patterning it is possible to quickly and accurately identify specific individuals photographically using computer-aided identification software. Without any manual intervention by an operator, the software accurately identified between 56 and 92% of the individuals. Indentification success increased to 100% if the operator could also manually select from other potential matching photographs. It was also shown that fish exhibiting a yaw angle not exceeding 60° could be accurately identified in photographs, although the percentage of fish correctly identified without operator-intervention decreased rapidly with increasing yaw angle. Computer-aided identification should therefore facilitate future coelacanth research as it is both efficient and accurate while also reducing potential stress on the animals observed.
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  • 2
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    Robustness of random forests for regression (2012)
    Taylor & Francis
    In:  Journal of Nonparametric Statistics, 24 (4). pp. 993-1006.
    Details
    Publication Date: 2018-03-26
    Description: In this paper, we empirically investigate the robustness of random forests for regression problems. We also investigate the performance of six variations of the original random forest method, all aimed at improving robustness. These variations are based on three main ideas: (1) robustify the aggregation method, (2) robustify the splitting criterion and (3) taking a robust transformation of the response. More precisely, with the first idea, we use the median (or weighted median), instead of the mean, to combine the predictions from the individual trees. With the second idea, we use least-absolute deviations from the median, instead of least-squares, as splitting criterion. With the third idea, we build the trees using the ranks of the response instead of the original values. The competing methods are compared via a simulation study with artificial data using two different types of contaminations and also with 13 real data sets. Our results show that all three ideas improve the robustness of the original random forest algorithm. However, a robust aggregation of the individual trees is generally more profitable than a robust splitting criterion.
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  • 3
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    Influence of positional accuracy, sample size and scale on modelling species distributions: a review (2012)
    Taylor & Francis
    In:  International Journal of Geographical Information Science, 26 (11). pp. 2083-2095.
    Details
    Publication Date: 2020-07-28
    Description: Species distribution models (SDMs) are an important tool in biogeography and ecology and are widely used for both fundamental and applied research purposes. SDMs require spatially explicit information about species occurrence and environmental covariates to produce a set of rules that identify and scale the environmental space where the species was observed and that can further be used to predict the suitability of a site for the species. More spatially accurate data are increasingly available, and the number of publications on the influence of spatial inaccuracies on the performance of modelling procedures is growing exponentially. Three main sources of uncertainty are associated with the three elements of a predictive function: the dependent variable, the explanatory variables and the algorithm or function used to relate these two variables. In this study, we review how spatial uncertainties influence model accuracy and we propose some methodological issues in the application of SDMs with regard to the modelling of fundamental and realized niches of species. We distinguish two cases suitable for different types of spatial data accuracy. For modelling the realized distribution of a species, particularly for management and conservation purposes, we suggest using only accurate species occurrence data and large sample sizes. Appropriate data filtering and examination of the spatial autocorrelation in predictors should be a routine procedure to minimize the possible influence of positional uncertainty in species occurrence data. However, if the data are sparse, models of the potential distribution of species can be created using a relatively small sample size, and this can provide a generalized indication of the main regional drivers of the distribution patterns. By this means, field surveys can be targeted to discover unknown populations and species in poorly surveyed regions in order to improve the robustness of the data for later modelling of the realized distributions. Based on this review, we conclude that (1) with data that are currently available, studies performed at a resolution of 1–100 km2 are useful for hypothesizing about the environmental conditions that limit the distribution of a species and (2) incorporating coarse resolution species occurrence data in a model, despite an increase in sample size, lowers model performance.
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  • 4
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    Rediscovery of Cereopsis studeri Koch, 1891, a forgotten Mediterranean soft coral species, and its inclusion in the genus Nidalia Gray, 1835 (Octocorallia, Alcyonacea, Nidaliidae) (2012)
    Taylor & Francis
    In:  Marine Biology Research, 8 (7). pp. 594-604.
    Details
    Publication Date: 2017-06-20
    Description: Cereopsis studeri was described by G. von Koch in 1891 with material from Naples. However, it was subsequently synonymized, erroneously identified, and overlooked in subsequent soft coral literature of the twentieth century. After the original description, this species was not recorded or correctly described for 120 years. The study of newly collected material from the North Western Mediterranean permits the re-description of this forgotten species and its assignation to the genus Nidalia in the family Nidaliidae. The main features of Nidalia studeri com. nov. are: colony torch-like, a capitulum light orange in colour, not laterally flattened, dome-shaped and not distinctly projecting beyond the stalk, introvert with sclerites transversally placed in two longitudinal rows per interseptal space, anthocodial crown with 28–38 sclerite rows, points separated from polyps distally, formed by 6–9 pairs of sclerites, and the presence of intermediate points (secondary points) between principal (interseptal) ones. Nidalia studeri is here compared with its closest congeners, especially with the Indonesian species N. simpsoni, species from the West Indian Region N. dissidens, N.occidentalis, N. deichmannae, and the recently described Nidalia aurantia from the Mid-Atlantic Ocean. This is the first time that the genus Nidalia and the family Nidaliidae have been reported with certainty for the Mediterranean Sea.
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  • 5
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    Three new compounds from the marine-derived fungusTrichoderma atrovirideG20-12 (2012)
    Taylor & Francis
    In:  Journal of Asian Natural Products Research, 14 (7). pp. 647-651.
    Details
    Publication Date: 2018-01-24
    Description: Three new compounds, 4′-(4,5-dimethyl-1,3-dioxolan-2-yl)methyl-phenol (1), (3′-hydroxybutan-2′-yl)5-oxopyrrolidine-2-carboxylate (2), and atroviridetide (3), have been isolated from the marine-derived fungus Trichoderma atroviride G 20-12. Their structures were determined on the basis of chemical and spectroscopic methods.
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  • 6
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    Bias-corrected random forests in regression (2012)
    Taylor & Francis
    In:  Journal of Applied Statistics, 39 (1). pp. 151-160.
    Details
    Publication Date: 2018-07-13
    Description: It is well known that random forests reduce the variance of the regression predictors compared to a single tree, while leaving the bias unchanged. In many situations, the dominating component in the risk turns out to be the squared bias, which leads to the necessity of bias correction. In this paper, random forests are used to estimate the regression function. Five different methods for estimating bias are proposed and discussed. Simulated and real data are used to study the performance of these methods. Our proposed methods are significantly effective in reducing bias in regression context.
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  • 7
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    Reproductive biology of the shore crabCarcinus maenas(Decapoda, Portunidae): a macroscopic and histological view (2012)
    Taylor & Francis
    In:  Invertebrate Reproduction & Development, 56 (2). pp. 144-156.
    Details
    Publication Date: 2018-04-11
    Description: A histological study of the reproductive cycle of male and female shore crabs, Carcinus maenas (Linnaeus), was performed monthly on the South West coast of Ireland (from December 2006 to July 2008). The calculated sex ratio deviated from equality, 1:0.53, revealing a strong male bias. A system was devised, based on screening of tissue sections, to describe and stage gametogenic development. Histological examinations revealed that ovarian development occurred biannually, with a primary winter cycle in which the larger crabs reproduced and a secondary summer cycle, when smaller crabs reproduced. An association was observed where more of the larger specimens were caught in the summer months and the smaller specimens in the winter months, which inversely correlated with the segregated breeding cycles. There was strong evidence that mature male crabs could potentially copulate year round since all mature specimens, collected throughout the year, contained viable spermatozoa. Developmental stages of oogenesis and spermatogenesis were described to develop a practical gonadal index for this portunid crab, providing information on the biology of this species, which will be of benefit for fisheries management.
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  • 8
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    Global analysis of satellite tracking data shows that adult green turtles are significantly aggregated in Marine Protected Areas (2012)
    Wiley
    In:  Global Ecology and Biogeography, 21 (11). pp. 1053-1061.
    Details
    Publication Date: 2017-12-14
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  • 9
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    Temporal and spatial patterns in the abundance of jellyfish in the northern Benguela upwelling ecosystem and their link to thwarted pelagic fishery recovery (2012)
    Taylor & Francis
    In:  African Journal of Marine Science, 34 (1). pp. 131-146.
    Details
    Publication Date: 2018-01-16
    Description: There has been debate in the literature about whether jellyfish abundance has increased in the northern Benguela upwelling system, or not, over the past five decades and what impact they are having on pelagic fish. Here we review old expedition literature as well as more recent spatial and temporal patterns in distribution of jellyfish off Namibia at a number of different scales, using both published and previously unpublished data. Specifically, we have used data from fishery-dependent sources of both the demersal (359 638 trawls) and pelagic fisheries (11 324 purse-seine sets) that cover the period 1992–2006, supported by data from fishery-independent demersal (6 109 trawls) and pelagic trawls (1 817 trawls) from 1996 to 2006. Using frequency of capture as an index of abundance, it is clear that jellyfish are not randomly distributed within the northern Benguela ecosystem, but show specific areas of concentration that broadly reflect regional oceanography and the distribution of other zooplankton. Although jellyfish are present throughout the year, peaks in abundance are shown that often coincide with peaks in the spawning activity of fish of commercial importance. Interannual changes in jellyfish abundance observed from all sources do not agree, with some showing increases, others declines, and still others showing no change, which suggests caution should be exercised in their interpretation. Based on the multiple lines of evidence synthesised here, we conclude that jellyfish abundance has increased concomitant with a decline of pelagic fish stocks. We conclude that future recovery of the pelagic fishery off Namibia is likely to be considerably challenged because of significant overlaps in space and time between fish and jellyfish, and through the effects of competition and predation effects of jellyfish on fish.
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  • 10
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    Comparison of cyanobacterial and green algal growth rates at different temperatures (2012)
    Wiley
    In:  Freshwater Biology, 58 (3). pp. 552-559.
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    Publication Date: 2018-01-29
    Description: 1. The hypothesis that cyanobacteria have higher optimum growth temperatures and higher growth rates at the optimum as compared to chlorophytes was tested by running a controlled experiment with eight cyanobacteria species and eight chlorophyte species at six different temperatures (20–35 °C) and by performing a literature survey. 2. In the experiment, all organisms except the chlorophyte Monoraphidium minutum grew well up to 35 °C. The chlorophyte Chlamydomonas reinhardtii was the fastest-growing organism over the entire temperature range (20–35 °C). 3. Mean optimum growth temperatures were similar for cyanobacteria (29.2 °C) and chlorophytes (29.2 °C). These results are concordant with published data, yielding slightly higher mean optimum growth temperatures for cyanobacteria (27.2 °C) than for chlorophytes (26.3 °C). 4. Mean growth rates of cyanobacteria at 20 °C (0.42 day−1) were significantly lower than those of chlorophytes at 20 °C (0.62 day−1). However, at all other temperatures, there were no differences between mean growth rates of cyanobacteria and chlorophytes. 5. Mean growth rates at the optimum temperature were similar for cyanobacteria (0.92 day−1) and chlorophytes (0.96 day−1). However, analysis of published data revealed that growth rates of cyanobacteria (0.65 day−1) were significantly lower than those of chlorophytes (0.93 day−1) at their optimum temperatures. 6. Although climate warming will probably lead to an intensification of cyanobacterial blooms, our results indicate that this might not be as a result of higher growth rates of cyanobacteria compared with their chlorophyte competitors. The competitive advantage of cyanobacteria can more likely be attributed to their ability to migrate vertically and prevent sedimentation in warmer and more strongly stratified waters and to their resistance to grazing, especially when warming reduces zooplankton body size.
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  • 11
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    Drained behaviour of cemented sand in high pressure triaxial compression tests (2012)
    Taylor & Francis
    In:  Geomechanics and Geoengineering, 7 (3). pp. 159-174.
    Details
    Publication Date: 2018-04-17
    Description: In this paper, drained behaviour of cemented sand under high pressure is studied. A recently developed high pressure triaxial apparatus is used. The test results indicate the significance of degree of cementation and confining pressure on the isotropic compression, volumetric change, stress-strain behaviour and stress-dilatancy relationship of cemented sand at high confining pressures. The results suggest that the influence of cementation is greater at low confining stresses and it reduces with increasing confining stress where the effect of the confining pressure becomes dominant. A Scanning Electron Microscope analysis has also been included in the paper. It revealed that the particle and cement bonding breakage at high pressure is dependent on the stress level and the cement content. The higher the confining pressure the more significant particle and cement bonding breakage is observed. The higher the cement content the fewer sand particles and cement bonds are broken.
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  • 12
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    Varying sediment sources (Hudson Strait, Cumberland Sound, Baffin Bay) to the NW Labrador Sea slope between and during Heinrich events 0 to 4 (2012)
    Wiley
    In:  Journal of Quaternary Science, 27 (5). pp. 475-484.
    Details
    Publication Date: 2020-07-20
    Description: Core HU97048-007PC was recovered from the continental Labrador Sea slope at a water depth of 945 m, 250km seaward from the mouth of Cumberland Sound, and 400km north of Hudson Strait. Cumberland Sound is a structural trough partly floored by Cretaceous mudstones and Paleozoic carbonates. The record extends from 10 to 58 ka. On-board logging revealed a complex series of lithofacies, including buff-colored detrital carbonate-rich sediments [Heinrich (H)-events] frequently bracketed by black facies. We investigate the provenance of these facies using quantitative X-ray diffraction on drill-core samples from Paleozoic and Cretaceous bedrock from the SE Baffin Island Shelf, and on the〈2-mm sediment fraction in a transect of five cores from Cumberland Sound to the NW Labrador Sea. A sediment unmixing program was used to discriminate between sediment sources, which included dolomite-rich sediments from Baffin Bay, calcite-rich sediments from Hudson Strait and discrete sources from Cumberland Sound. Results indicated that the bulk of the sediment was derived from Cumberland Sound, but Baffin Bay contributed to sediments coeval with H-0 (Younger Dryas), whereas Hudson Strait was the source during H-events 1–4. Contributions from the Cretaceous outcrops within Cumberland Sound bracket H-events, thus both leading and lagging Hudson Strait-sourced H-events.
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  • 13
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    Changes in climate and weather extremes in the 21st century (2012)
    Wiley
    In:  Wiley Interdisciplinary Reviews: Climate Change, 3 (2). pp. 115-129.
    Details
    Publication Date: 2015-10-06
    Description: Climate and weather extremes are sporadically recurring events that may have major local or regional impacts on the society and the environment. These events are typically related to unusually high or low temperature, prolonged dry or wet conditions, heavy precipitation, or extreme winds. Extreme events are part of the overall climate and weather alongside average conditions and variability, and thus are not unexpected as such. Climate change is expected to affect not only means but also variability and extremes. Some inferences can be based on past and present observations, but analyses of especially rare events are hampered by the availability of long time series. Over time, depending on how far the on-going global warming takes us from the present and the past climate conditions, the weather and climate statistics may well come to shift in ways that are well outside observational data. This may lead to shifts in frequency, intensity and geographical distribution of different extremes. Indeed, projected changes in some extremes over the 21st century are quite robust, such as generally increasing warm and decreasing cold extremes. Possible changes in some other aspects, for example storms, remain much more uncertain. Science-based information both on robust findings and on relevant uncertainties on changing extremes can provide useful information for sectorial planning, disaster risk prevention and overall reduction of societal vulnerability related to climate and weather
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  • 14
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    On the spatial scale of dispersal in coral reef fishes (2012)
    Wiley
    In:  Molecular Ecology, 21 (23). pp. 5675-5688.
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    Publication Date: 2015-09-14
    Description: Marine biologists have gone through a paradigm shift, from the assumption that marine populations are largely ‘open’ owing to extensive larval dispersal to the realization that marine dispersal is ‘more restricted than previously thought’. Yet, population genetic studies often reveal low levels of genetic structure across large geographic areas. On the other side, more direct approaches such as mark-recapture provide evidence of localized dispersal. To what extent can direct and indirect studies of marine dispersal be reconciled? One approach consists in applying genetic methods that have been validated with direct estimates of dispersal. Here, we use such an approach—genetic isolation by distance between individuals in continuous populations—to estimate the spatial scale of dispersal in five species of coral reef fish presenting low levels of genetic structure across the Caribbean. Individuals were sampled continuously along a 220-km transect following the Mesoamerican Barrier Reef, population densities were estimated from surveys covering 17 200 m2 of reef, and samples were genotyped at a total of 58 microsatellite loci. A small but positive isolation-by-distance slope was observed in the five species, providing mean parent-offspring dispersal estimates ranging between 7 and 42 km (CI 1–113 km) and suggesting that there might be a correlation between minimum/maximum pelagic larval duration and dispersal in coral reef fishes. Coalescent-based simulations indicate that these results are robust to a variety of dispersal distributions and sampling designs. We conclude that low levels of genetic structure across large geographic areas are not necessarily indicative of extensive dispersal at ecological timescales.
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  • 15
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    An (U-Th)/He age for the shallow-marine Wetumpka impact structure, Alabama, USA (2012)
    Wiley
    In:  Meteoritics & Planetary Science, 47 (8). pp. 1243-1255.
    Details
    Publication Date: 2020-07-01
    Description: Single crystal (U-Th)/He dating was applied to 24 apatite and 23 zircon grains from the Wetumpka impact structure, Alabama, USA. This small approximately 5–7.6 km impact crater was formed in a shallow marine environment, with no known preserved impact melt, thus offering a challenge to common geochronological techniques. A mean (U-Th)/He apatite and zircon age of 84.4 ± 1.4 Ma (2σ) was obtained, which is within error of the previously estimated Late Cretaceous impact age of approximately 83.5 Ma. In addition, helium diffusion modeling of apatite and zircon grains during fireball/contact, shock metamorphism, and hydrothermal events was undertaken, to show the influence of these individual thermal processes on resetting (U-Th)/He ages in the Wetumpka samples. This study has shown that the (U-Th)/He geochronological technique has real potential for dating impact structures, especially smaller and eroded impact structures that lack impact melt lithologies.
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  • 16
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    Dimethylsulphopropionate (DMSP) and proline from the surface of the brown alga Fucus vesiculosus inhibit bacterial attachment (2012)
    Taylor & Francis
    In:  Biofouling, 28 (6). pp. 593-604.
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    Publication Date: 2019-09-23
    Description: It was demonstrated previously that polar and non-polar surface extracts of the brown alga Fucus vesiculosus collected during winter from the Kiel Bight (Germany) inhibited bacterial attachment at natural concentrations. The present study describes the bioassay-guided identification of the active metabolites from the polar fraction. Chromatographic separation on a size-exclusion liquid chromatography column and bioassays identified an active fraction that was further investigated using nuclear magnetic resonance spectroscopy and mass spectrometry. This fraction contained the metabolites dimethylsulphopropionate (DMSP), proline and alanine. DMSP and proline caused the anti-attachment activity. The metabolites were further quantified on the algal surface together with its associated boundary layer. DMSP and proline were detected in the range 0.12–1.08 ng cm−2 and 0.09–0.59 ng cm−2, respectively. These metabolites were tested in the concentration range from 0.1 to 1000 ng cm−2 against the attachment of five bacterial strains isolated from algae and sediment co-occurring with F. vesiculosus. The surface concentrations for 50% inhibition of attachment of these strains were always 〈0.38 ng cm−2 for DMSP and in four cases 〈0.1 ng cm−2 for proline, while one strain required 1.66 ng cm−2 of proline for 50% inhibition. Two further bacterial strains that had been directly isolated from F. vesiculosus were also tested, but proved to be the least sensitive. This study shows that DMSP and proline have an ecologically relevant role as surface inhibitors against bacterial attachment on F. vesiculosus.
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  • 17
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    Ocean acidification weakens the structural integrity of coralline algae (2012)
    Wiley
    In:  Global Change Biology, 18 (9). pp. 2804-2812.
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    Publication Date: 2018-05-17
    Description: The uptake of anthropogenic emission of carbon dioxide is resulting in a lowering of the carbonate saturation state and a drop in ocean pH. Understanding how marine calcifying organisms such as coralline algae may acclimatize to ocean acidification is important to understand their survival over the coming century. We present the first long-term perturbation experiment on the cold-water coralline algae, which are important marine calcifiers in the benthic ecosystems particularly at the higher latitudes. Lithothamnion glaciale, after three months incubation, continued to calcify even in undersaturated conditions with a significant trend towards lower growth rates with increasing pCO2. However, the major changes in the ultra-structure occur by 589 μatm (i.e. in saturated waters). Finite element models of the algae grown at these heightened levels show an increase in the total strain energy of nearly an order of magnitude and an uneven distribution of the stress inside the skeleton when subjected to similar loads as algae grown at ambient levels. This weakening of the structure is likely to reduce the ability of the alga to resist boring by predators and wave energy with severe consequences to the benthic community structure in the immediate future (50 years).
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  • 18
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    Synergistic effects of ocean acidification and warming on overwintering pteropods in the Arctic (2012)
    Wiley
    In:  Global Change Biology, 18 (12). pp. 3517-3528.
    Details
    Publication Date: 2018-05-17
    Description: Ocean acidification and warming will be most pronounced in the Arctic Ocean. Aragonite shell-bearing pteropods in the Arctic are expected to be among the first species to suffer from ocean acidification. Carbonate undersaturation in the Arctic will first occur in winter and because this period is also characterized by low food availability, the overwintering stages of polar pteropods may develop into a bottleneck in their life cycle. The impacts of ocean acidification and warming on growth, shell degradation (dissolution), and mortality of two thecosome pteropods, the polar Limacina helicina and the boreal L. retroversa, were studied for the first time during the Arctic winter in the Kongsfjord (Svalbard). The abundance of L. helicina and L. retroversa varied from 23.5 to 120 ind m−2 and 12 to 38 ind m−2, and the mean shell size ranged from 920 to 981 μm and 810 to 823 μm, respectively. Seawater was aragonite-undersaturated at the overwintering depths of pteropods on two out of ten days of our observations. A 7-day experiment [temperature levels: 2 and 7 °C, pCO2 levels: 350, 650 (only for L. helicina) and 880 μatm] revealed a significant pCO2 effect on shell degradation in both species, and synergistic effects between temperature and pCO2 for L. helicina. A comparison of live and dead specimens kept under the same experimental conditions indicated that both species were capable of actively reducing the impacts of acidification on shell dissolution. A higher vulnerability to increasing pCO2 and temperature during the winter season is indicated compared with a similar study from fall 2009. Considering the species winter phenology and the seasonal changes in carbonate chemistry in Arctic waters, negative climate change effects on Arctic thecosomes are likely to show up first during winter, possibly well before ocean acidification effects become detectable during the summer season.
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  • 19
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    Mantle subducting slab structure in the region of the 2010 M8.8 Maule earthquake (30-40°S), Chile (2012)
    Wiley
    In:  Geophysical Journal International, 191 (1). pp. 317-324.
    Details
    Publication Date: 2016-06-22
    Description: We present a new tomographic model of the mantle in the area of the 2010 M8.8 Maule earthquake and surrounding regions. Increased ray coverage provided by the aftershock data allows us to image the detailed subducting slab structure in the mantle, from the region of flat slab subduction north of the Maule rupture to the area of overlapping rupture between the 1960 M9.5 and the 2010 M8.8 events to the south. We have combined teleseismic primary and depth phase arrivals with available local arrivals to better constrain the teleseismic earthquake locations in the region, which we use to conduct nested regional–global tomography. The new model reveals the detailed structure of the flat slab and its transition to a more moderately dipping slab in the Maule region. South of the Maule region, a steeply dipping relic slab is imaged from ∼200 to 1000 km depth that is distinct from the moderately dipping slab above it and from the more northerly slab at similar depths. We interpret the images as revealing both horizontal and vertical tearing of the slab at ∼38°S to explain the imaged pattern of slab anomalies in the southern portion of the model. In contrast, the transition from a horizontal to moderately subducting slab in the northern portion of the model is imaged as a continuous slab bend. We speculate that the tearing was most likely facilitated by a fracture zone in the downgoing plate or alternatively by a continental scale terrane boundary in the overriding plate.
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  • 20
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    Experimental systems in aquatic ecology (2012)
    Wiley
    In:  In: eLS Citable Reviews in the Life Sciences [Encyclopedia of Life Sciences]. Wiley, ..
    Details
    Publication Date: 2014-01-30
    Description: The main experimental approaches in aquatic community and ecosystem ecology will be presented along a gradient of scale: unenclosed field experiments, mesocosms with a natural mix of species, microcosms with an artificial mixture of species from cultures, and single species experiments in batch and continuous culture. Experimental manipulations usually consist of the addition or removal of (supposed) key organisms, addition of chemicals or alterations of the physical environment. Selecting the appropriate scale of experimentation is not only a question of technical and financial feasibility but also it has to consider the inevitable trade-offs between realism and control. Conclusions will be more widely accepted, if they are supported by experiments at a variety of scales. Key Concepts: The choice of the appropriate experimental scale has to face an inevitable trade-off between realism and control. Unenclosed field manipulations have the highest degree of realism but the least degree of control. Mesocosms operate with natural species assemblages, permit replication and control of experimental manipulations but are limited in temporal scale (weeks). Microcosm experiments operate with artificial communities assembled from cultures, offer a high degree of control, but lack the pre-history a mutual adaptation of the participating species. Experiments with single or few species rely on the 'model organism' concept. Small-scale experiments are biased against the detection of slow and space requiring processes.
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  • 21
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    Approximations for the 2-D coast effect on marine magnetotelluric data (2012)
    Wiley
    In:  Geophysical Journal International, 189 . pp. 357-368.
    Details
    Publication Date: 2019-09-23
    Description: Marine natural source electromagnetic data acquired on continental margins are often of considerable scientific and commercial interest. However, the large conductivity contrast between the ocean and coast causes this type of data to be severely distorted. For a 2-D coastal model, this distortion is most pronounced for the marine magnetotelluric and geomagnetic response function derived from induced currents flowing parallel to the coast. A maximal distortion occurs for a given period at a specific distance from the coast and causes severe anomalies in the magnitude and phase of the response functions. Based on a modelling study, we empirically relate the characteristic period and characteristic distance to physical parameters such as the ocean depth and the host resistivity. Based on a simple analytical approach, we test these approximations and show that maximum distortion occurs when destructive interference between the ocean and host response is at its highest. While the coast effect causes a large distortion in the marine responses we show through a resolution analysis that it does not mask subsurface conductivity anomalies but in fact increases the sensitivity to the seafloor.
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    Three dimensional lithospheric structure of the western continental margin of India constrained from gravity modelling: implication for tectonic evolution (2012)
    Wiley
    In:  Geophysical Journal International, 190 (1). pp. 131-150.
    Details
    Publication Date: 2019-01-22
    Description: This paper describes a 3-D lithospheric density model of the Western Continental Margin of India (WCMI) based on forward modelling of gravity data derived from satellite altimetry over the ocean and surface measurements on the Indian peninsula. The model covers the north-eastern Arabian Sea and the western part of the Indian Peninsula and incorporates constraints from a wide variety of geophysical and geological information. Salient features of the density model include: (1) the Moho depth varying from 13 km below the oceanic crust to 46 km below the continental interior; (2) the lithosphere–asthenosphere boundary (LAB) located at depths between 70 km in the southwestern corner (under oceanic crust) and about 165 km below the continental region; (3) thickening of the crust under the Chagos–Laccadive and Laxmi Ridges and (4) a revised definition of the continent–ocean boundary. The 3-D density structure of the region enables us to propose an evolutionary model of the WCMI that revisits earlier views of passive rifting. The first stage of continental-scale rifting of Madagascar from India at about 90 Ma is marked by relatively small amounts of magmatism. A second episode of rifting and large-scale magmatism was possibly initiated around 70 Ma with the opening of the Gop Rift. Subsequently at around 68 Ma, the drifting away of the Seychelles and formation of the Laxmi Ridge was a consequence of the down-faulting of the northern margin. During this second episode of rifting, the northern part of the WCMI witnessed massive volcanism attributed to interaction with the Reunion hotspot at around 65 Ma. Subsequent stretching of the transitional crust between about 65 and 62 Ma formed the Laxmi Basin, the southward extension of the failed Gop Rift. As the interaction between plume and lithosphere continued, the Chagos–Laccadive Ridge was emplaced on the edge of the nascent oceanic crust/rifted continental margin in the south as the Indian Plate was moving northwards.
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    Influence of Temperature, Hypercapnia, and Development on the Relative Expression of Different Hemocyanin Isoforms in the Common CuttlefishSepia officinalis (2012)
    Wiley
    In:  Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 317 (8). pp. 511-523.
    Details
    Publication Date: 2019-09-23
    Description: The cuttlefish Sepia officinalis expresses several hemocyanin isoforms with potentially different pH optima, indicating their reliance on efficient pH regulation in the blood. Ongoing ocean warming and acidification could influence the oxygen-binding properties of respiratory pigments in ectothermic marine invertebrates. This study examined whether S. officinalis differentially expresses individual hemocyanin isoforms to maintain optimal oxygen transport during development and acclimation to elevated seawater pCO2 and temperature. Using quantitative PCR, we measured relative mRNA expression levels of three different hemocyanin isoforms in several ontogenetic stages (embryos, hatchlings, juveniles, and adults), under different temperatures and elevated seawater pCO2. Our results indicate moderately altered hemocyanin expression in all embryonic stages acclimated to higher pCO2, while hemocyanin expression in hatchlings and juveniles remained unaffected. During the course of development, total hemocyanin expression increased independently of pCO2 or thermal acclimation status. Expression of isoform 3 is reported for the first time in a cephalopod in this study and was found to be generally low but highest in the embryonic stages (0.2% of total expression). Despite variable hemocyanin expression, hemolymph total protein concentrations remained constant in the experimental groups. Our data provide first evidence that ontogeny has a stronger influence on hemocyanin isoform expression than the environmental conditions chosen, and they suggest that hemocyanin protein abundance in response to thermal acclimation is regulated by post-transcriptional/translational rather than by transcriptional modifications
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    Adult exposure influences offspring response to ocean acidification in oysters (2012)
    Wiley
    In:  Global Change Biology, 18 (1). pp. 82-92.
    Details
    Publication Date: 2014-10-08
    Description: It is essential to predict the impact of elevated Pco2 on marine organisms and habitats to anticipate the severity and consequences of future ocean chemistry change. Despite the importance of carry-over effects in the evolutionary history of marine organisms, few studies have considered links between life-history stages when determining how marine organisms will respond to elevated Pco2, and none have considered the link between adults and their offspring. Herein, we exposed adults of wild and selectively bred Sydney rock oysters, Saccostrea glomerata to elevated Pco2 during reproductive conditioning and measured the development, growth and survival response of their larvae. We found that elevated Pco2 had a negative impact on larvae of S. glomerata causing a reduction in growth, rate of development and survival. Exposing adults to elevated Pco2 during reproductive conditioning, however, had positive carry-over effects on larvae. Larvae spawned from adults exposed to elevated Pco2 were larger and developed faster, but displayed similar survival compared with larvae spawned from adults exposed to ambient Pco2. Furthermore, selectively bred larvae of S. glomerata were more resilient to elevated Pco2 than wild larvae. Measurement of the standard metabolic rate (SMR) of adult S. glomerata showed that at ambient Pco2, SMR is increased in selectively bred compared with wild oysters and is further increased during exposure to elevated Pco2. This study suggests that sensitive marine organisms may have the capacity to acclimate or adapt to elevated Pco2 over the next century and a change in energy turnover indicated by SMR may be a key process involved.
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    Divergent selection on locally adapted major histocompatibility complex immune genes experimentally proven in the field (2012)
    Wiley
    In:  Ecology Letters, 15 (7). pp. 723-731.
    Details
    Publication Date: 2017-02-23
    Description: Although crucial for the understanding of adaptive evolution, genetically resolved examples of local adaptation are rare. To maximize survival and reproduction in their local environment, hosts should resist their local parasites and pathogens. The major histocompatibility complex (MHC) with its key function in parasite resistance represents an ideal candidate to investigate parasite-mediated local adaptation. Using replicated field mesocosms, stocked with second-generation lab-bred three-spined stickleback hybrids of a lake and a river population, we show local adaptation of MHC genotypes to population-specific parasites, independently of the genetic background. Increased allele divergence of lake MHC genotypes allows lake fish to fight the broad range of lake parasites, whereas more specific river genotypes confer selective advantages against the less diverse river parasites. Hybrids with local MHC genotype gained more body weight and thus higher fitness than those with foreign MHC in either habitat, suggesting the evolutionary significance of locally adapted MHC genotypes.
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    Population genetic dynamics of three-spined sticklebacks (Gasterosteus aculeatus) in anthropogenic altered habitats (2012)
    Wiley
    In:  Ecology and Evolution, 2 (6). pp. 1122-1143.
    Details
    Publication Date: 2019-01-22
    Description: In industrialized and/or agriculturally used landscapes, inhabiting species are exposed to a variety of anthropogenic changes in their environments. Genetic diversity may be reduced if populations encounter founder events, bottlenecks, or isolation. Conversely, genetic diversity may increase if populations adapt to changes in selective regimes in newly created habitats. With the present study, genetic variability of 918 sticklebacks from 43 samplings (21.3 ± 3.8 per sample) at 36 locations from cultivated landscapes in Northwest Germany was analyzed at nine neutral microsatellite loci. To test if differentiation is influenced by habitat alterations, sticklebacks were collected from ancient running waters and adjacent artificial stagnant waters, from brooks with salt water inflow of anthropogenic and natural origin and adjacent freshwater sites. Overall population structure was dominated by isolation by distance (IBD), which was significant across all populations, and analysis of molecular variance (AMOVA) revealed that 10.6% of the variation was explained by river catchment area. Populations in anthropogenic modified habitats deviated from the general IBD structure and in the AMOVA, grouping by habitat type running/stagnant water explained 4.9% of variation and 1.4% of the variation was explained by salt-/freshwater habitat. Sticklebacks in salt-polluted water systems seem to exhibit elevated migratory activity between fresh- and saltwater habitats, reducing IBD. In other situations, populations showed distinct signs of genetic isolation, which in some locations was attributed to mechanical migration barriers, but in others to potential anthropogenic induced bottleneck or founder effects. The present study shows that anthropogenic habitat alterations may have diverse effects on the population genetic structure of inhabiting species. Depending on the type of habitat change, increased genetic differentiation, diversification, or isolation are possible consequences.
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    Paleocene MORB and OIB from the Resolution Ridge, Tasman Sea (2012)
    Taylor & Francis
    In:  Australian Journal of Earth Sciences, 59 (6). pp. 953-964.
    Details
    Publication Date: 2018-06-08
    Description: Altered lavas have been dredged from three locations on the Resolution Ridge, west of New Zealand's South Island. On the basis of whole-rock geochemistry, Sr, Nd and Pb isotope data and Ar–Ar ages, they can be divided into two suites: 62–60 Ma enriched mid-ocean ridge basalt (E-MORB), and 57 Ma trachybasalt and trachyandesite of ocean island basalt (OIB) affinity. The E-MORBs from the Resolution Ridge are only the second place from which Tasman Sea abyssal oceanic crust has ever been sampled, they have Indian MORB-like isotope compositions, and their ages support a recent interpretation of a 100 km sinistral offset of the southern part of the Tasman Sea spreading ridge. The slightly younger OIB suite erupted shortly after oceanic crust formation and has FOZO to HIMU source characteristics similar to the well-known SW Pacific Diffuse Alkaline Magmatic Province (DAMP). The close occurrence and isotopic mixing relationships of both Paleocene volcanic suites on the Resolution Ridge may be explained by a heterogeneous upper mantle in which the more fertile OIB component was extracted during a later melting event away from the spreading ridge. The dredged lavas predate formation of Southeast Tasman oceanic crust that borders the Resolution Ridge to the south.
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    Ostracod palaeoecology and environmental change in the Laptev and Kara seas (Siberian Arctic) during the last 18 000 years (2012)
    Wiley
    In:  Boreas, 41 (4). pp. 557-577.
    Details
    Publication Date: 2017-01-24
    Description: Fossil ostracod assemblages were investigated in five AMS 14 C-dated cores from various water depths of the Laptev and Kara seas ranging from the upper continental slope (270?m) to the present-day shelf depth (40?m). Six fossil assemblages were distinguished. These represent the varying environmental conditions at the North Siberian continental margin since about 18?ka. In the cores from the shelf the ostracod assemblages reflect the gradual transition from an estuarine brackish-water environment to modern marine conditions since 12.3?ka, as induced by the regional early Holocene transgression. The core from the upper continental slope dates back to c. 17.6?ka and contains assemblages that are absent in the shelf cores. The assemblage older than 10?ka stands out as a specific community dominated by relatively deep-water Arctic and North Atlantic species that also contains euryhaline species. Such an assemblage provides evidence for past inflows of Atlantic-derived waters from as early as c. 17.2?ka, probably facilitated by upwelling in coastal polynyas, and a considerable riverine freshwater influence with enhanced surface water stratification owing to the proximity of the palaeocoastline until early Holocene times. In all studied cores, relative increases in euryhaline species dominant in the inner-shelf regions are recorded in the midlate Holocene sediments (〈7?ka), which otherwise already contain modern-like ostracod assemblages with relatively deep-water species. This observation suggests euryhaline species to be largely sea-ice- and/or iceberg-rafted and therefore may provide evidence for a climate cooling trend.
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    Impacts of Saharan dust and clouds on photosynthetically available radiation in the area off Northwest Africa (2012)
    Taylor & Francis
    In:  Tellus B: Chemical and physical meteorology, 64 . p. 17160.
    Details
    Publication Date: 2019-09-23
    Description: Radiation measurements in the area off Northwest Africa (research cruise, February 2008) and at Mindelo (Cape Verde Islands, May 2009) were used to investigate the impacts of Saharan dust and clouds on solar irradiance and on photosynthetically available radiation, to derive a relationship between dust aerosol optical depth (AOD) and photosynthetically available radiation and to determine the annual variations of photosynthetically available radiation. Three different kinds of atmospheric conditions were considered: cloudy skies, which decreased or increased the irradiance and dusty skies. The reduction by clouds was up to 67.2% at 400 nm and up to 84.4% at 700 nm. Enhancements of up to 21.9% at 400 nm and 34.0% at 700 nm were observed. The decrease by dust was up to 19.7% at 400 nm and up to 4.1% at 700 nm. Clouds decreased or increased the photosynthetically available radiation by up to 79.9% or up to 31.2%. The reduction by dust depended on the dust AOD and was between 3.6% and 12.3%. A linear relationship confirmed a decrease of photosynthetically available radiation of 1.2% by an increase of dust AOD of 0.1.
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    Spatial management of marine resources can enhance the recovery of predators and avoid local depletion of forage fish (2012)
    Wiley
    In:  Conservation Letters, 5 (6). pp. 486-492.
    Details
    Publication Date: 2019-01-21
    Description: The eastern Baltic cod stock has recently started to recover, after two decades of severe depletion, however with unexpected side effects. The stock has not re-occupied its former wide distribution range, but remains concentrated in a limited area in the southern Baltic Sea. The biomass of forage fish, i.e., sprat and herring, is historic low in this area, which in combination with increasing cod stock results in locally high predation mortality of forage fish and cannibalism of cod. In line with low prey availability, body weight and nutritional condition of cod drastically declined. In the southern Baltic Sea, cod competes with pelagic fisheries for the limited resources of sprat and herring, while the largest biomass of these species is currently found outside the distribution range of cod. Accounting for spatial overlap between species is crucial in developing ecosystem based fisheries management to enhance the recovery of predator stocks.
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    No stimulation of nitrogen fixation by non-filamentous diazotrophs under elevated CO2 in the South Pacific (2012)
    Wiley
    In:  Global Change Biology, 18 (10). pp. 3004-3014.
    Details
    Publication Date: 2019-09-23
    Description: Nitrogen fixation by diazotrophic cyanobacteria is a critical source of new nitrogen to the oligotrophic surface ocean. Research to date indicates that some diazotroph groups may increase nitrogen fixation under elevated pCO2. To test this in natural plankton communities, four manipulation experiments were carried out during two voyages in the South Pacific (30–35oS). High CO2 treatments, produced using 750 ppmv CO2 to adjust pH to 0.2 below ambient, and ‘Greenhouse’ treatments (0.2 below ambient pH and ambient temperature +3 °C), were compared with Controls in trace metal clean deckboard incubations in triplicate. No significant change was observed in nitrogen fixation in either the High CO2 or Greenhouse treatments over 5 day incubations. qPCR measurements and optical microscopy determined that the diazotroph community was dominated by Group A unicellular cyanobacteria (UCYN-A), which may account for the difference in response of nitrogen fixation under elevated CO2 to that reported previously for Trichodesmium. This may reflect physiological differences, in that the greater cell surface area:volume of UCYN-A and its lack of metabolic pathways involved in carbon fixation may confer no benefit under elevated CO2. However, multiple environmental controls may also be a factor, with the low dissolved iron concentrations in oligotrophic surface waters limiting the response to elevated CO2. If nitrogen fixation by UCYN-A is not stimulated by elevated pCO2, then future increases in CO2 and warming may alter the regional distribution and dominance of different diazotroph groups, with implications for dissolved iron availability and new nitrogen supply in oligotrophic regions.
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    Bacteria associations with co-occurring macroalgae: Host, epiphyte and environmental factors (2012)
    Taylor & Francis
    In:  European Journal of Phycology, 46 (sup1). pp. 45-50.
    Details
    Publication Date: 2017-01-04
    Description: Bacteria associated with 2 macroalgae growing in the Kiel Fjord (Baltic Sea) were investigated seasonally over two years by scanning electron microscopy and cultivation methods. Seasonal variations and significant differences between both macroalgal species with respect to the associated bacteria were observed. 166 bacterial strains were isolated from the macroalgae and classified by phylogenetic analysis of 16S rRNA gene sequences. The strains formed 82 phylotypes according to sequence similarities of499.0%. Samples from Fucus vesiculosus revealed 43 and from Delesseria sanguinea 57 bacterial phylotypes. They affiliated to Actinobacteria, Alphaproteobacteria, Bacilli, Betaproteobacteria, Flavobacteria, Gammaproteobacteria, and Sphingobacteria. Following the assumption that chemical interactions rule the bacteria-macroalga associations, we tested the biological activity of both macroalgae and isolated bacterial strains against a panel comprising standard and ecologically relevant microorganisms (Gram-positive and Gram-negative bacteria, including macroalgal pathogens and surface associated strains, and a yeast). Both macroalgae presented inhibitory activity against at least one microorganism, but overall the inhibitory activities were low. In contrast, all extracts stimulated growth of many of the tested bacteria. While growth stimulation was common concerning bacteria associated with macroalgae, no stimulation was shown for the standard set of bacteria (with exception of one case of stimulation of the plant pathogen Erwinia amylovora). Regarding the potential biological activity of microorganisms associated with macroalgae, more than 60% of the bacterial phylotypes inhibited the growth of at least one microorganism. A higher proportion of strains showed antimicrobial activity against the set of bacteria associated with macroalgae as compared to standard set of microorganisms. Certain phylotypes are consistently found as epiphytes, suggesting their specific association with macroalgae. The presented positive and negative effects of macroalgal extracts on growth of macroalga-associated bacteria, significant bacterial activity against macroalgal pathogens and competitors, and potential degradative capabilities support the assumption that complex chemical interactions shape the bacteria-macroalga relationships.
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    New(t)s and view from hybridizing MHC genes: introgression rather than trans-species polymorphism may shape allelic repertoires (2012)
    Wiley
    In:  Molecular Ecology, 21 (4). pp. 779-781.
    Details
    Publication Date: 2019-07-09
    Description: One of the key features of major histocompatibility complex (MHC) genes is the frequent occurrence of trans-species polymorphism, that is the passage of allelic lineages from ancestral to descendant species (Klein 2007). Selectively maintained ancestral polymorphism may, however, be hard to distinguish from introgression of MHC alleles between hybridizing species (Fig1). In this issue of Molecular Ecology, Nadachowska-Brzyska (2012) present data that suggest that the latter can be observed in two closely related species of newts, Lissotriton vulgaris (Lv) and L.montandoni (Lm) from south-east Europe. Strikingly, allelic MHC variation displayed more structure between geographically separated populations of L.vulgaris than across species in the hybrid zone. This suggests that high MHC variation in L.montadoni may result from mainly unidirectional gene flow between species, while differentiation between northern and southern populations of L.vulgaris might reflect local adaptation.
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    Seasonal changes in vertical distribution patterns of cod (Gadus morhua) in the Bornholm Basin, central Baltic Sea (2012)
    Wiley
    In:  Fisheries Oceanography, 21 (1). pp. 33-43.
    Details
    Publication Date: 2017-01-09
    Description: Hydroacoustic single fish detection and corresponding hydrographic measurements were used to study seasonal changes in vertical distribution of adult cod (Gadus morhua) in relation to ambient environmental conditions in the Bornholm Basin, central Baltic Sea. Sampling was conducted in April, June and August covering the years 2006–2009. Vertical distribution of individual fish was resolved from hydroacoustic single-target detection in combination with a fish-tracking algorithm and related to ambient hydrographic conditions. Based on a generalized linear effect model, both salinity and oxygen concentration were identified as key parameters affecting cod vertical distribution. Results also showed a clear seasonal effect with a more shallow distribution as the spawning season progressed and oxygen concentrations in the deep parts of the basin deteriorated. The upper limit of the distributional range was mostly constituted by the halocline and remained rather constant, whereas increasing oxygen depletion in the deep water layers lifted the lower boundary of the vertical distribution, leading to the observed upward shift in the overall distribution pattern. The results presented in this study highlight a significant shortcoming of the assessment survey design established for this species, as the observed shift in vertical distribution is not taken into account, thus introducing a potential bias into a data series used to tune the ICES standard stock assessment of this species.
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    Stoichiometric responses of phytoplankton species to the interactive effect of nutrient supply ratios and growth rates (2012)
    Wiley
    In:  Journal of Phycology, 48 . pp. 539-549.
    Details
    Publication Date: 2018-05-30
    Description: Three species of phytoplankton, Rhodomonas sp., Phaeodactylum tricornutum Bohlin, and Isochrysis galbana Parke, were cultivated in semicontinuous culture to analyze the response of carbon (C):nitrogen (N):phosphorus (P) stoichiometry to the interactive effect of five N:P supply ratios and four growth rates (dilution rates). The relationship between cellular N and P quotas and growth rates fits well to both the Droop and Ågren’s functions for all species. We observed excess uptake of both N and P in the three species. N:P biomass ratios showed a significant positive relationship with N:P supply ratios across the entire range of growth rates, and N:P biomass ratios converged to an intermediate value independent of N:P supply ratios at higher growth rates. The effect of growth rates on N:P biomass ratios was positive at lower N:P supply ratios, but negative at higher N:P supply ratios for both Rhodomonas sp. and I. galbana, while for P. tricornutum this effect was negative at all N:P supply ratios. A significant interactive effect of N:P supply ratios and growth rates on N:P biomass ratios was found in both Rhodomonas sp. and P. tricornutum, but not in I. galbana. Our results suggest that Ågren’s functions may explain the underlying biochemical principle for the Droop model. The parameters in the Droop and Ågren’s functions can be useful indications of algal succession in the phytoplankton community in changing oceans.
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    Growth, length-weight relationship and biological information on the clearhead icefish (Protosalanx hyalocranius Abbott, 1901) in Lake Khanka (Xingkai) (2012)
    Wiley
    In:  Journal of Applied Ichthyology, 28 (5). pp. 842-844.
    Details
    Publication Date: 2017-07-03
    Description: This paper reports the growth pattern and length-weight relationship and summarizes biological data for the clearhead icefish (Protosalanx hyalocranius) in Lake Khanka (Xingkai), on the border between China and Russia. The von Bertalanffy growth was estimated as SL = 20.3(1 − e−2.93 (t − 0.21)). The length-weight relationship was W = 0.00448 SL2.99 for juveniles, and W = 0.000896 SL3.59 for adults. P. hyalocranius mature in December and spawn in January, when the lake is still covered with ice, then die after spawning. The larvae hatch in March. Juveniles feed mainly on zooplankton whereas adults also feed on other fishes.
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    Using empirical mode decomposition to process marine MT data (2012)
    Wiley
    In:  Geophysical Journal International, 190 . pp. 293-309.
    Details
    Publication Date: 2019-09-23
    Description: Magnetotellurics (MT) uses a frequency-dependent impedance tensor estimated from the spectra of associated time-varying horizontal electric and magnetic fields measured at the Earth's surface to image the sub-surface of the Earth. Most current methods use Fourier transform based procedures to estimate power spectral densities and, therefore, assume that the signals are stationary over the record length. Stationarity in geomagnetic data, however, is not always ensured given the variety of source mechanism causing the geomagnetic variations at different time and spatial scales. Additional complication and bias may arise from the presence of noise in the recorded electric and magnetic file data. Sophisticated MT data processing account for a potential bias through windowing of the time series as well as robust estimates of the impedance. We explore a new heuristic method for dealing with the non-stationarity of MT time series based on empirical mode decomposition. It is a dynamic time series analysis method, in which complicated data sets can be decomposed into a finite and small number of simple intrinsic mode functions. In this paper, we use the empirical mode decomposition method to decompose MT data into intrinsic mode functions and calculate the instantaneous frequencies and spectra to determine the impedance tensor. We investigate the reliability of the impedance estimates on synthetic data by comparing the results to those obtained by analytical methods. Finally, we apply our processing scheme to data measured from the Costa Rica subduction zone, and compare the results from our new method to the frequently-used BIRRP processing method.
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    HOAPS precipitation validation with ship-borne rain gauge measurements over the Baltic Sea (2012)
    Taylor & Francis
    In:  Tellus A: Dynamic meteorology and oceanography, 64 (18486).
    Details
    Publication Date: 2016-06-14
    Description: Global ocean precipitation is an important part of the water cycle in the climate system. A number of efforts have been undertaken to acquire reliable estimates of precipitation over the oceans based on remote sensing and reanalysis modelling. However, validation of these data is still a challenging task, mainly due to a lack of suitable in situ measurements of precipitation over the oceans. In this study, validation of the satellite-based Hamburg Ocean Atmosphere Parameters and fluxes from Satellite data (HOAPS) climatology was conducted with in situ measurements by ship rain gauges over the Baltic Sea from 1995 to 1997. The ship rain gauge data are point-to-area collocated against the HOAPS data. By choosing suitable collocation parameters, a detection rate of up to about 70% is achieved. Investigation of the influence of the synoptic situation on the detectability shows that HOAPS performs better for stratiform than for convective precipitation. The number of collocated data is not sufficient to validate precipitation rates. Thus, precipitation rates were analysed by applying an interpolation scheme based on the Kriging method to both data sets. It was found that HOAPS underestimates precipitation by about 10%, taking into account that precipitation rates below 0.3 mm h−1 cannot be detected from satellite information.
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    Disruption-free imaging by Raman spectroscopy reveals a chemical sphere with antifouling metabolites around macroalgae (2012)
    Taylor & Francis
    In:  Biofouling, 28 (7). pp. 687-696.
    Details
    Publication Date: 2020-06-19
    Description: Investigations of the surface chemistry of marine organisms are essential to understand their chemically mediated interactions with fouling organisms. In this context, the concentration of natural products in the immediate vicinity of algal surfaccs, as well as their biological activity, are of particular importance. Howevcr, due to lack of appropriate methods, the distribution of Compounds within the Chemical sphere around marine algae is unknown. This study demonstrates the suitability of confocal resonance Raman microspcctroscopy for the determination of metabolites around algal surfaces with a micrometer resolution.
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    Challenges and opportunities of metabolomics (2012)
    Wiley
    In:  Journal of Cellular Physiology, 227 (8). pp. 2975-2981.
    Details
    Publication Date: 2020-07-27
    Description: The metabolome is a data-rich source of information concerning all the low-molecular-weight metabolites in a biofluid, which can indicate early biological changes to the host due to perturbations in metabolic pathways. Major changes can be seen after minor stimuli, which make it a valuable target for analysis. Due to the diverse and sensitive nature of the metabolome, studies must be designed in a manner to maintain consistency, reduce variation between subjects, and optimize information recovery. Technological advancements in experimental design, mouse models and instrumentation have aided in this effort. Metabolomics has the ultimate potential to be valuable in a clinical setting where it could be used for early diagnosis of a disease and as a predictor of treatment response and survival. During drug treatment, the metabolic status of an individual could be monitored and used to indicate possible toxic effects. Metabolomics therefore has great potential for improving diagnosis, treatment and aftercare of disease.
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    Hosts are ahead in a marine host-parasite coevolutionary arms race: innate immune system adaptation in pipefish Syngnathus typhle against Vibrio phylotypes (2012)
    Wiley
    In:  Evolution, 66 (8). pp. 2528-2539.
    Details
    Publication Date: 2017-01-04
    Description: Microparasites have a higher evolutionary potential than their hosts due to an increased mutation rate and a shorter generation time that usually results in parasites being locally adapted to their sympatric hosts. This pattern may not apply to generalist pathogens as adaptation to sympatric host genotypes is disadvantageous due to a narrowing of the host range, in particular under strong gene flow among host populations. Under this scenario, we predict that the immune defense of hosts reveals adaptation to locally common pathogen phylotypes. This was tested in four host populations of the pipefish Syngnathus typhle and associated bacteria of the genus Vibrio. We investigated the population divergence among host and bacteria populations and verified that gene flow is higher among host populations than among parasite populations. Next, we experimentally assessed the strength of innate immune defense of pipefish hosts using in vitro assays that measured antimicrobial activity of blood plasma against sympatric and allopatric Vibrio phylotypes. Pipefish plasma displays stronger antimicrobial activity against sympatric Vibrio phylotypes compared to allopatric ones. This suggests that host defense is genetically adapted against local bacteria with a broad and unspecialized host spectrum, a situation that is typical for marine systems with weak host population structure.
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    A novel primer set for multilocus phylogenetic inference in East African cichlid fishes (2012)
    Wiley
    In:  Molecular Ecology Resources, 12 (6). pp. 1097-1104.
    Details
    Publication Date: 2018-11-09
    Description: The cichlid fishes in the East African Great Lakes are a prime model system for the study of adaptive radiation. Therefore, the availability of an elaborate phylogenetic framework is an important prerequisite. Previous phylogenetic hypotheses on East African cichlids are mainly based on mitochondrial and/or fragment-based markers, and, to date, no taxon-rich phylogeny exists that is based on multilocus DNA sequence data. Here, we present the design of an extensive new primer set (24 nuclear makers) for East African cichlids that will be used for multilocus phylogenetic analyses in the future. The primers are designed to work for both Sanger sequencing and next-generation sequencing with the 454 technology. As a proof of principle, we validate these primers in a phylogenetically representative set of 16 cichlid species from Lake Tanganyika and main river systems in the area and provide a basic evaluation of the markers with respect to marker length and diversity indices
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    Impacts of Saharan dust on downward irradiance and photosynthetically available radiation in the water column (2012)
    Taylor & Francis
    In:  Advances in Oceanography and Limnology, 3 (2). pp. 99-131.
    Details
    Publication Date: 2020-04-23
    Description: A semi-empirical approach was used to quantify the modification of the underwater light field in amplitude (magnitude effect) and spectral distribution (spectral effect) by different atmospheric conditions altering the incident light. The approach based on an optical model in connection with radiation measurements in the area off Northwest Africa. Key inputs of the model were parameterized magnitude and spectral effects. Various atmospheric conditions were considered: clear sky, dusty sky without clouds, cloudy sky without dust and skies with different ratios of dust and clouds. Their impacts were investigated concerning the modification of the downward irradiance and photosynthetically available radiation in the water column. The impact on downward irradiance depended on the wavelength, the water depth, the optical water properties, the dust and cloud properties, and the ratio of clouds to dust. The influence of clouds on the amplitude can be much higher than that of dust. Saharan dust reduced the photosynthetically available radiation in the water column. Ocean regions were more influenced than coastal areas. Compensations of the magnitude and spectral effects were observed at special water depths in ocean regions and at atmospheric conditions with definite cloud to dust ratios
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  • 44
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    Role of domestic shipping in the introduction or secondary spread of nonindigenous species: biological invasions within the Laurentian Great Lakes (2012)
    Wiley
    In:  Journal of Applied Ecology, 49 (5). pp. 1124-1130.
    Details
    Publication Date: 2014-08-08
    Description: The most effective way to manage invasive species is to prevent their introduction via vector regulation. While progress has been made in the management of transoceanic ballast water, domestic vessels operating within smaller geographic regions such as the Laurentian Great Lakes, Mediterranean Sea, North Sea or Baltic Sea are often exempt from regulations. We randomly surveyed unmanaged ballast water moved by domestic vessels within the Laurentian Great Lakes and compared the results with that of exchanged ballast water from transoceanic vessels to assess invasion risk of zooplankton transported by these two types of vessels. Total abundance and species richness were significantly different between the two vessel types with mean abundance being two magnitudes greater, and species richness being threefold higher in domestic vessels compared with transoceanic vessels. Abundance of restricted taxa – cumulatively the Great Lakes' indigenous and nonindigenous species (NIS) which do not occur in all five lakes – was also significantly higher in domestic vessels (mean densities were 24 170 and 3421 individuals per m3 for domestic and transoceanic vessels, respectively), whereas the abundance of NIS did not differ between vessels (median densities of 2015 and 850 individuals per m3, respectively). We documented 89 species transported by domestic vessels of which 31 had restricted distribution and eight were NIS. While most NIS were already established in all five lakes, Cercopagis pengoi, a NIS of global concern, and Nitokra hibernica have not been identified from Lake Superior, and both were sampled from ballast water destined for discharge in Lake Superior. Beside the risk of spread of NIS between lakes, domestic shipping can act as a vector for homogenization of indigenous taxa, with at least 21 native species (99 events) being moved outside their historical distribution. Synthesis and applications. Our study indicates that management of invasive species should consider ecological, not geographical or political boundaries. Domestic vessels operating within a limited geographic region have high potential to introduce or spread species with restricted distribution, demonstrating importance of intraregional ballast water management. Results presented here should interest policy makers and environmental managers who seek to reduce invasion risk.
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  • 45
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    Phosphate transporters in marine phytoplankton and their viruses: Cross-domain commonalities in viral-host gene exchanges (2012)
    Wiley
    In:  Environmental Microbiology, 14 (1). pp. 162-176.
    Details
    Publication Date: 2019-03-05
    Description: Phosphate (PO 4) is an important limiting nutrient in marine environments. Marine cyanobacteria scavenge PO 4 using the high-affinity periplasmic phosphate binding protein PstS. The pstS gene has recently been identified in genomes of cyanobacterial viruses as well. Here, we analyse genes encoding transporters in genomes from viruses that infect eukaryotic phytoplankton. We identified inorganic PO 4 transporter-encoding genes from the PHO4 superfamily in several virus genomes, along with other transporter-encoding genes. Homologues of the viral pho4 genes were also identified in genome sequences from the genera that these viruses infect. Genome sequences were available from host genera of all the phytoplankton viruses analysed except the host genus Bathycoccus. Pho4 was recovered from Bathycoccus by sequencing a targeted metagenome from an uncultured Atlantic Ocean population. Phylogenetic reconstruction showed that pho4 genes from pelagophytes, haptophytes and infecting viruses were more closely related to homologues in prasinophytes than to those in what, at the species level, are considered to be closer relatives (e.g. diatoms). We also identified PHO4 superfamily members in ocean metagenomes, including new metagenomes from the Pacific Ocean. The environmental sequences grouped with pelagophytes, haptophytes, prasinophytes and viruses as well as bacteria. The analyses suggest that multiple independent pho4 gene transfer events have occurred between marine viruses and both eukaryotic and bacterial hosts. Additionally, pho4 genes were identified in available genomes from viruses that infect marine eukaryotes but not those that infect terrestrial hosts. Commonalities in marine host-virus gene exchanges indicate that manipulation of host-PO 4 uptake is an important adaptation for viral proliferation in marine systems. Our findings suggest that PO 4-availability may not serve as a simple bottom-up control of marine phytoplankton. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.
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    Light scintillation in oceanic turbulence (2012)
    Taylor & Francis
    In:  Waves in Random and Complex Media, 22 (2). pp. 260-266.
    Details
    Publication Date: 2019-12-02
    Description: The scintillation index of plane and spherical light waves as well as of a Gaussian beam, propagating in the clear-water weakly turbulent ocean, is revealed. The results are of utmost importance for underwater optical communications and sensing. An analysis of the threshold between the weak and strong regimes of oceanic turbulence is made, with the accent on the contribution from salinity-induced turbulence. It is found that strong oceanic turbulence can occur at distances as short as several meters, in striking contrast with atmospheric studies for which the typical distances are on the order of a kilometer.
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    Structure of the reproductive system and hectocotylus in males of lesser flying squid Todaropsis eblanae (Cephalopoda: Ommastrephidae) (2012)
    Taylor & Francis
    In:  Journal of Natural History, 46 (29-30). pp. 1761-1778.
    Details
    Publication Date: 2021-08-20
    Description: This paper introduces new data on Todaropsis eblanae morphology, morphometry and functional aspects of the male reproductive system and hectocotylus. Spermatophores differ in specimens from the Atlantic Ocean (average length, 18.28 ± 1.45 mm, 15.63 ± 0.8% of mantle length; weight, 2.0–12.0 mg) and the Indian Ocean (average length, 24.8 ± 2.85 mm, 16.9 ± 2.1% of mantle length; weight, 35.0–39.6 mg) (t = 3.14; p 〈 0.01 for absolute sizes and t = 0.711; p 〉 001 for relative sizes). An additional important distinctive trait is the form of connection of the cement body with the ejaculatory tube. In recent years, T. eblanae has been regularly caught in the Barents Sea, meaning its range has extended to subarctic waters. The morphology and morphometry of the spermatophoric complex of organs did not vary in investigated parts of its range. Hectocotylus patterns and some important spermatophore traits distinguish Todaropsis from other Ommastrephidae.
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  • 48
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    Vacuolar respiration of nitrate coupled to energy conservation in filamentous Beggiatoaceae (2012)
    Wiley
    In:  Environmental Microbiology, 14 (11). pp. 2911-2919.
    Details
    Publication Date: 2016-12-12
    Description: We show that the nitrate storing vacuole of the sulfide-oxidizing bacterium Candidatus Allobeggiatoa halophila has an electron transport chain (ETC), which generates a proton motive force (PMF) used for cellular energy conservation. Immunostaining by antibodies showed that cytochrome c oxidase, an ETC protein and a vacuolar ATPase are present in the vacuolar membrane and cytochrome c in the vacuolar lumen. The effect of different inhibitors on the vacuolar pH was studied by pH imaging. Inhibition of vacuolar ATPases and pyrophosphatases resulted in a pH decrease in the vacuole, showing that the proton gradient over the vacuolar membrane is used for ATP and pyrophosphate generation. Blockage of the ETC decreased the vacuolar PMF, indicating that the proton gradient is build up by an ETC. Furthermore, addition of nitrate resulted in an increase of the vacuolar PMF. Inhibition of nitrate reduction, led to a decreased PMF. Nitric oxide was detected in vacuoles of cells exposed to nitrate showing that nitrite, the product of nitrate reduction, is reduced inside the vacuole. These findings show consistently that nitrate respiration contributes to the high proton concentration within the vacuole and the PMF over the vacuolar membrane is actively used for energy conservation.
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  • 49
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    Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophelia pertusa (2012)
    Wiley
    In:  Global Change Biology, 18 (3). pp. 843-853.
    Details
    Publication Date: 2018-05-17
    Description: Ocean acidity has increased by 30% since preindustrial times due to the uptake of anthropogenic CO2 and is projected to rise by another 120% before 2100 if CO2 emissions continue at current rates. Ocean acidification is expected to have wide-ranging impacts on marine life, including reduced growth and net erosion of coral reefs. Our present understanding of the impacts of ocean acidification on marine life, however, relies heavily on results from short-term CO2 perturbation studies. Here, we present results from the first long-term CO2 perturbation study on the dominant reef-building cold-water coral Lophelia pertusa and relate them to results from a short-term study to compare the effect of exposure time on the coral's responses. Short-term (1 week) high CO2 exposure resulted in a decline of calcification by 26–29% for a pH decrease of 0.1 units and net dissolution of calcium carbonate. In contrast, L. pertusa was capable to acclimate to acidified conditions in long-term (6 months) incubations, leading to even slightly enhanced rates of calcification. Net growth is sustained even in waters sub-saturated with respect to aragonite. Acclimation to seawater acidification did not cause a measurable increase in metabolic rates. This is the first evidence of successful acclimation in a coral species to ocean acidification, emphasizing the general need for long-term incubations in ocean acidification research. To conclude on the sensitivity of cold-water coral reefs to future ocean acidification further ecophysiological studies are necessary which should also encompass the role of food availability and rising temperatures.
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  • 50
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    Tephra stratigraphy on the North Icelandic shelf: extending tephrochronology into marine sediments off North Iceland (2012)
    Wiley
    In:  Boreas, 41 (4). pp. 719-734.
    Details
    Publication Date: 2016-11-04
    Description: Tephra stratigraphical and tephrochronological studies of marine core MD99-2275 on the North Icelandic shelf have revealed 58 new tephra horizons within the last 7050 cal. a BP, bringing the total number of identified tephra layers to 76. So far, over 100 tephra layers have been identified in the entire core spanning the last 15 000 years. The majority of the newly identified tephra layers are basaltic in composition and originate from the most active volcanic systems in Iceland, namely Grímsvötn, Veidivötn-Bárdarbunga and Katla. A total of 40 tephra layer land–sea correlations have been made within this time period, of which 16 represent absolutely dated tephra markers. In addition, two tephra marker series are revealed in the marine sediments and in the terrestrial tephra stratigraphy, located between c. 2300–2600 and between 5700–5900 years. For the last 15 000 years, 21 tephra markers have been recognized. The marine tephra layer frequency (TLF) reveals two peaks, within the last 2000 years, and between 5000 and 7000 years ago. It shows the same general characteristics as the terrestrial TLF curve in Iceland, which indicates that marine sediments can yield important information about volcanism in Iceland. This is useful in time segments in which terrestrial records are poor or non-existent. The study contributes to a high-resolution tephrochronological framework on the North Icelandic shelf, with core MD99-2275 representing a potential stratotype section in the area, and for the northern North Atlantic–Nordic Seas region, as well as being an important contribution to the Lateglacial–early Holocene volcanic history of Iceland.
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    Amelioration of free copper by hydrothermal vent microbes as a response to high copper concentrations (2012)
    Taylor & Francis
    In:  Chemistry and Ecology, 28 (5). pp. 405-420.
    Details
    Publication Date: 2021-11-04
    Description: We examined the effect of increased copper concentrations (0-10 mu M) on hydrothermal vent microorganisms and the production of copper (Cu)-binding ligands as a response. Hydrothermal vent microbes originated from diffuse fluids at the Lilliput mussel field and the Irina II site in the Logatchev hydrothermal vent field, both on the Mid-Atlantic Ridge. Parallel studies were also conducted with amino acids supplemented to the incubations in order to verify whether dissolved amino acids, present in hydrothermal fluids, can buffer the bioavailable copper and reduce the active production of Cu-binding ligands. In all incubations, ligand concentrations increased with rising copper concentrations, but microbial cell numbers remained constant. This study shows that microbes were able to cope with as much as 10 mu M dissolved copper by buffering the free copper concentration. The presence of amino acids had no significant influence on the active ligand production. Our results imply that mediation of chemical speciation by vent microbes may have an important impact on hydrothermal trace metal fluxes into the ocean.
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    Changing Floods in Europe (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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    Introduction (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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    Historical Floods in Europe in the Past Millennium (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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    Detection of Changes (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS Special Publication 10
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  • 56
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    Detection and Attribution of Changes in Water Resources (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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  • 57
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    Changes in Flood Risk - Setting the Stage (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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  • 58
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    Flood Risk from a Holistic Perspective - Observed Changes in Germany (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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  • 59
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    Floods in Poland (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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  • 60
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    Catalogue of Large Floods in Europe in the 20th Century (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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  • 61
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    Large-scale Flooding in Europe, 1961-2005 (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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    Changes in Flood Risk in Europe (2012)
    IAHS Press
    In:  IAHS special publication
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    Detection and Attribution of Changes in Flood Hazard and Risk (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Detection and Attribution of Climate Change and Its Impacts (2012)
    IAHS Press
    In:  Changes in Flood Risk in Europe | IAHS special publication ; 10
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    Publication Date: 2022-03-21
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