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  • 1
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    Non-breeding distribution and activity patterns in a temperate population of brown skua (2018)
    Inter Research
    Details
    Publication Date: 2023-09-18
    Description: Brown skuas Catharacta antarctica lonnbergi breed across a broad latitudinal range from the Antarctic to temperate regions. While information on the non-breeding distribution and behaviour for Antarctic and subantarctic populations is known, no data exist for populations breeding at temperate latitudes. We combined geolocation sensing and stable isotope analysis of feather tissue to study the non-breeding behaviour of brown skuas from the temperate Chatham Islands, a population that was historically thought to be resident year-round. Analysis of 27 non-breeding tracks across 2 winters revealed that skuas left the colony for a mean duration of 146 d, which is 64% of the duration reported for Antarctic and subantarctic populations from King George Island, South Shetland Islands, and Bird Island, South Georgia. Consistent with populations of brown skuas from Antarctica and the Subantarctic, the distribution was throughout mixed subtropical-subantarctic and shelf waters. Stable isotope analysis of 72 feathers suggests that moulting takes place over mixed subtropical-subantarctic and subtropical shelf waters. We conclude that brown skuas from the Chatham Islands are migratory, but the year-round mild environmental conditions may reduce the necessity to leave their territories for extended periods.
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  • 2
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    Mapping and modeling eelgrass Zostera marina distribution in the western Baltic Sea (2015)
    Inter Research
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    Publication Date: 2023-03-30
    Description: In the northern hemisphere, eelgrass Zostera marina L. is the most important and widespread seagrass species. Despite its ecological importance, baseline data on eelgrass distribution and abundance are mostly absent, particularly in subtidal areas with relatively turbid waters. Here, we report a combined approach of vegetation mapping in the Baltic Sea coupled to a species distribution model (SDM). Eelgrass cover was mapped continuously in the summers of 2010 and 2011 with an underwater towed camera along ~400 km of seafloor. Eelgrass populated 80% of the study region and occurred at water depths between 0.6 and 7.6 m at sheltered to moderately exposed coasts. Mean patch length was 128.6 m but was higher at sheltered locations, with a maximum of 〉2000 m. The video observations (n = 7824) were used as empiric input to the SDMs. Using generalized additive models, 3 predictor variables (depth, wave exposure, and slope), which were selected based on Akaike’s information criterion, were sufficient to predict eelgrass presence/absence. Along with a very good overall discriminative ability (area under the receiver-operating characteristic curve ROC/AUC = 0.82), depth (as a proxy for light), wave exposure, and slope contributed 66, 29, and 5%, respectively, to the final model. The estimated total areal extent of eelgrass in the study region amounts to 140.5 km2 and comprises about 11.5% of all known Baltic seagrass beds. The present work is, to the best of our knowledge, the largest study undertaken to date on vegetation mapping and the first to assess distribution of eelgrass quantitatively in the western Baltic Sea.
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  • 3
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    Moderate virulence caused by the protist Labyrinthula zosterae in ecosystem foundation species Zostera marina under nutrient limitation (2017)
    Inter Research
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    Publication Date: 2022-05-20
    Description: The nature of many microbe-host interactions is not static, but may shift along a continuum from mutualistic to harmful depending on the environmental conditions. In this study, we assessed the interaction between the foundation plant eelgrass Zostera marina and the frequently associated protist Labyrinthula zosterae. We tested how an important environmental factor, nutrient availability, would modulate their interaction. We experimentally infected naive eelgrass plants in combination with 2 nutrient levels (fertilized and non-fertilized). We followed L. zosterae infection, eelgrass growth parameters and host defense gene expression over 3 wk in large 600 l tanks. Inoculation with L. zosterae and nutrient limitation both reduced eelgrass growth. These effects were additive, whereas no interaction of nutrient treatment and L. zosterae inoculation was detected. Gene expression levels of 15 candidate genes revealed a reduced expression of photosynthesis-related genes but an increased expression of classical stress genes such as Hsp80 in inoculated plants 2 d post-inoculation. However, we found no effects on plant mortality, and plants were able to clear high infection levels within 3 wk to ambient background levels of infection as assessed via specific RT-qPCR designed to quantify endophytic L. zosterae. Thus, we found no evidence that L. zosterae is a facultative mutualist that facilitates eelgrass growth under nutrient-limiting conditions. We suggest that the interaction between contemporary L. zosterae genotypes and Z. marina represents a mild form of parasitism in northern Europe because the damage to the plant is moderate even under nutrient limitation stress.
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  • 4
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    Ecological Assessment of the Sustainable Impacts of Fisheries (EASI-Fish): a flexible vulnerability assessment approach to quantify the cumulative impacts of fishing in data-limited settings (2019)
    Inter Research
    In:  Marine Ecology Progress Series, 625 . pp. 89-113.
    Details
    Publication Date: 2022-01-31
    Description: In fisheries, vulnerability assessments - also commonly known as ecological risk assessments (ERAs) -have been an increasingly popular alternative to stock assessments to evaluate the vulnerability of non-target species in resource- and data-limited settings. The widely-used productivity-susceptibility analysis (PSA) requires detailed species-specific biological information and fishery susceptibility for a large number of parameters to produce a relative vulnerability score. The two major disadvantages of PSA are that each species is assessed against an arbitrary reference point, and PSA cannot quantify cumulative impacts of multiple fisheries. This paper introduces an Ecological Assessment of the Sustainable Impacts of Fisheries (EASI-Fish), a flexible approach that quantifies the cumulative impacts of fisheries on data-limited bycatch species, demonstrated in eastern Pacific Ocean (EPO) tuna fisheries. The method first estimates fishing mortality (F) based on the 'volumetric overlap' of each fishery with the distribution of each species. F is then used in length-structured per-recruit models to assess population vulnerability status using conventional biological reference points. Model results were validated by comparison with stock assessments for bigeye and yellowfin tunas in the EPO for 2016. Application of the model to 24 species of epipelagic and mesopelagic teleosts, sharks, rays, sea turtles and cetaceans and identification of the most vulnerable species is demonstrated. With increasing demands on fisheries to demonstrate ecological sustainability, EASI-Fish allows fishery managers to more confidently identify vulnerable species to which resources can be directed to either implement mitigation measures or collect further data for more formal stock assessment.
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  • 5
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    Potential role of oxygen and inorganic nutrients on microbial carbon turnover in the Baltic Sea (2019)
    Inter Research
    In:  Aquatic Microbial Ecology, 83 . pp. 95-108.
    Details
    Publication Date: 2022-01-31
    Description: Oxygen (O2) deficiency and nutrient concentrations in marine systems are impacting organisms from microbes to higher trophic levels. In coastal and enclosed seas, O2 deficiency is often related to eutrophication and high degradation rates of organic matter. To investigate the impact of O2 concentration on bacterial growth and the turnover of organic matter, we conducted multifactorial batch experiments with natural microbial communities of the central Baltic Sea. Water was collected from suboxic (〈5 µmol L -1) depths in the Gotland Basin during June 2015. Samples were kept for four days under fully oxygenated and low O2 conditions (mean: 34 µmol L-1 O2), with or without nutrient (ammonium, phosphate, nitrate) and labile carbon (glucose) amendments. We measured bacterial abundance, bacterial heterotrophic production, extracellular enzyme rates (leucine-aminopeptidase) and changes in dissolved and particulate organic carbon concentrations. Our results show that the bacterial turnover of organic matter was limited by nutrients under both oxic and low O2 conditions. In nutrient and glucose replete treatments, low O2 concentrations significantly reduced the net uptake of dissolved organic carbon and lead to higher accumulation of more labile dissolved organic matter. Our results therewith suggest that the combined effects of eutrophication and deoxygenation on heterotrophic bacterial activity may potentially favor the accumulation of dissolved organic carbon in the Baltic Sea.
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  • 6
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    Interactive effects of ocean acidification and nitrogen limitation on two bloom-forming dinoflagellate species (2016)
    Inter Research
    In:  Marine Ecology Progress Series, 543 . pp. 127-140.
    Details
    Publication Date: 2021-04-23
    Description: Global climate change involves an increase in oceanic CO2 concentrations as well as thermal stratification of the water column, thereby reducing nutrient supply from deep to surface waters. Changes in inorganic carbon (C) or nitrogen (N) availability have been shown to affect marine primary production, yet little is known about their interactive effects. To test for these effects, we conducted continuous culture experiments under N limitation and exposed the bloomforming dinoflagellate species Scrippsiella trochoidea and Alexandrium fundyense (formerly A. tamarense) to CO2 partial pressures (pCO(2)) ranging between 250 and 1000 mu atm. Ratios of particulate organic carbon (POC) to organic nitrogen (PON) were elevated under N limitation, but also showed a decreasing trend with increasing pCO(2). PON production rates were highest and affinities for dissolved inorganic N were lowest under elevated pCO(2), and our data thus demonstrate a CO2-dependent trade-off in N assimilation. In A. fundyense, quotas of paralytic shellfish poisoning toxins were lowered under N limitation, but the offset to those obtained under N-replete conditions became smaller with increasing pCO(2). Consequently, cellular toxicity under N limitation was highest under elevated pCO(2). All in all, our observations imply reduced N stress under elevated pCO(2), which we attribute to a reallocation of energy from C to N assimilation as a consequence of lowered costs in C acquisition. Such interactive effects of ocean acidification and nutrient limitation may favor species with adjustable carbon concentrating mechanisms and have consequences for their competitive success in a future ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
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    Heme b quotas are low in Southern Ocean phytoplankton (2015)
    Inter Research
    In:  Marine Ecology Progress Series, 532 . pp. 29-40.
    Details
    Publication Date: 2021-04-23
    Description: Heme is the iron-containing prosthetic group of hemoproteins, and is thus required for photosynthesis, respiration and nitrate reduction in marine phytoplankton. Here we report concentrations of heme b in Southern Ocean phytoplankton and contrast our findings with those in coastal species. The concentration of particulate heme b (pmol l-1) observed at the end of the exponential growth phase was related to the concentration of dissolved iron in the culture media. Small Southern Ocean phytoplankton species (〈6 μm in diameter) had heme b quotas 〈1 μmol mol-1 carbon, the lowest yet reported for marine phytoplankton. Heme b was also depleted in these species with respect to chlorophyll a. We calculated the amount of carbon accumulated per mole of heme b per second in our cultures (heme growth efficiency, HGE) and found that small Southern Ocean species can maintain growth rates, even while heme b content is reduced. Small Southern Ocean phytoplankton can thus produce more particulate carbon than larger Southern Ocean or small coastal species at equivalent iron concentrations. Combining primary productivity and heme b concentrations reported for the open ocean, we found that HGE in natural populations was within the range of our laboratory culture results. HGE was also observed to be higher at open ocean stations characterized by low iron concentrations. Our results suggest that low heme b quotas do not necessarily result in reduced growth and that marine phytoplankton can optimize iron use by manipulating the intracellular hemoprotein pool
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  • 8
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    Seagrass wasting disease varies with salinity and depth in natural Zostera marina populations (2018)
    Inter Research
    In:  Marine Ecology Progress Series, 587 . pp. 105-115.
    Details
    Publication Date: 2021-02-08
    Description: In the 1930s the wasting disease pathogen Labyrinthula zosterae is believed to have killed 90% of the temperate seagrass Zostera marina in the Atlantic Ocean. Despite the devastating impact of this disease the host–pathogen interaction is still poorly understood, and few field studies have investigated factors correlating with the prevalence and abundance of L. zosterae. This study measures wasting disease in natural populations of Z. marina, showing a strong correlation between the disease and both salinity and water depth. No infection was detected in Z. marina shoots from low salinity (13–25 PSU) meadows, whereas most shoots carried the disease in high salinity (25–29 PSU). Shallow (1 m) living Z. marina shoots were also more infected compared to shoots in deeper (5 m) meadows. In addition, infection and transplantation experiments showed that Z. marina shoots from low salinity meadows with low pathogen pressure were more susceptible to L. zosterae infection. The higher susceptibility could not be explained by lower content of inhibitory defense compounds in the shoots. Instead, extracts from all Z. marina shoots significantly reduced pathogen growth, suggesting that Z. marina contains inhibitory compounds that function as a constitutive defense. Overall, the results show that seagrass wasting disease is common in natural Z. marina populations in the study area and that it increases with salinity and decreases with depth. Our findings also suggest that low salinity areas can act as a refuge against seagrass wasting disease.
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  • 9
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    Reef sponges facilitate the transfer of coral-derived organic matter to their associated fauna via the sponge loop (2018)
    Inter Research
    In:  Marine Ecology Progress Series, 589 . pp. 85-96.
    Details
    Publication Date: 2021-02-08
    Description: The high biodiversity of coral reefs results in complex trophic webs where energy and nutrients are transferred between species through a multitude of pathways. Here, we hypothesize that reef sponges convert the dissolved organic matter released by benthic primary producers (e.g. corals) into particulate detritus that is transferred to sponge-associated detritivores via the sponge loop pathway. To test this hypothesis, we conducted stable isotope (13C and15N) tracer experiments to investigate the uptake and transfer of coral-derived organic matter from the sponges Mycale fistulifera and Negombata magnifica to 2 types of detritivores commonly associated with sponges: ophiuroids (Ophiothrix savignyi and Ophiocoma scolopendrina) and polychaetes (Polydorella smurovi). Findings revealed that the organic matter naturally released by the corals was indeed readily assimilated by both sponges and rapidly released again as sponge detritus. This detritus was subsequently consumed by the detritivores, demonstrating transfer of coral-derived organic matter from sponges to their associated fauna and confirming all steps of the sponge loop. Thus, sponges provide a trophic link between corals and higher trophic levels, thereby acting as key players within reef food webs.
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  • 10
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    Baltic Sea diazotrophic cyanobacterium is negatively affected by acidification and warming (2018)
    Inter Research
    In:  Marine Ecology Progress Series, 598 . pp. 49-60.
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    Publication Date: 2021-02-08
    Description: Nitrogen fixation is a key source of nitrogen in the Baltic Sea which counteracts nitrogen loss processes in the deep anoxic basins. Laboratory and field studies have indicated that single-strain nitrogen-fixing (diazotrophic) cyanobacteria from the Baltic Sea are sensitive to ocean acidification and warming, two drivers of marked future change in the marine environment. Here, we enclosed a natural plankton community in twelve indoor mesocosms (volume ~1400 L) and manipulated pCO2 to yield six CO2 treatments with two different temperature treatments (16.6°C and 22.4°C, pCO2 range = 360 – 2030 μatm). We followed the filamentous, heterocystous diazotrophic cyanobacteria community (Nostocales, primarily Nodularia spumigena) over four weeks. Our results indicate that heterocystous diazotrophic cyanobacteria may become less competitive in natural plankton communities under ocean acidification. Elevated CO2 had a negative impact on Nodularia sp. biomass, which was exacerbated by warming. Our results imply that Nodularia sp. may contribute less to new nitrogen inputs in the Baltic Sea in future.
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