ALBERT

Description: Highlights: • We manipulated burial levels and burial durations in a field experiment. • We found strong effects even at low burial level (5 cm) and short duration (4 weeks). • Higher shoot mortality, and delayed growth and flowering, lower carbohydrate storage. • Relative rather than absolute sediment burial levels determined plant survival. • Management implications of our findings are discussed. Seagrass meadows, one of the world's most important and productive coastal habitats, are threatened by a range of anthropogenic actions. Burial of seagrass plants due to coastal activities is one important anthropogenic pressure leading to the decline of local populations. In our study, we assessed the response of eelgrass Zostera marina to sediment burial from physiological, morphological, and population parameters. In a full factorial field experiment, burial level (5–20 cm) and burial duration (4–16 weeks) were manipulated. Negative effects were visible even at the lowest burial level (5 cm) and shortest duration (4 weeks), with increasing effects over time and burial level. Buried seagrasses showed higher shoot mortality, delayed growth and flowering and lower carbohydrate storage. The observed effects will likely have an impact on next year's survival of buried plants. Our results have implications for the management of this important coastal plant.

Description: To investigate patch selectivity in aspidochirotide holothurians, individuals of five species (Holothuria (Halodeima) atra Jäger, H. (H.) edulis Lesson, H. (Microthele) nobilis Selenka, Stichopus chloronotus Brandt and S. variegatus Semper) were subjected to multiple choice experiments. As a food source, sediments were pre-cultivated in petri dishes under different light and nutrient regimes. This resulted in four sediment treatments with different levels of microalgal biomass (measured as chlorophyll a and phaeophytin concentrations). Only two sediment treatments were used for experiments with H. nobilis and S. variegatus. The sediments were offered simultaneously to individual holothurians (six per experiment), and the weights of the sediment in each petri dish at the start and after 48 h were used to calculate a selection index together with confidence intervals for each food type. In experiments with H. atra and H. edulis, the animals exhibited no preference for any food type. In contrast, S. chloronotus significantly selected sediments with the highest contents of microalgae and avoided the sediment with the lowest pigment concentrations. These results were supported by field collections of sediments found directly underneath holothurians. Sediment underneath H. edulis did not differ from the average sediment of the habitat, while H. atra was found on sediments only slightly higher in chlorophyll a. Chlorophyll a concentrations underneath S. chloronotus were distinctly higher than in the adjacent sediment and that underneath H. atra. H. nobilis showed only a weak preference for sediments with higher pigment concentrations in aquarium experiments, and no patch selectivity in this species was found in the field. Stichopus variegatus exhibited a very distinct patch selectivity towards sediments with more nutritional value in both aquaria experiments and field measurements. Thus members of the genus Holothuria had no, or only a weak, tendency to select their food source, whereas both Stichopus species appeared to carefully select the sediment patch to feed on.

Description: Most conceptual marine eutrophication models predict that ephemeral and epiphytic macroalgae will become substantially more abundant with increasing nutrient richness. This expectation is based on the fact that most of these fast-growing algae possess high requirements for inorganic N and P and, therefore, suffer from nutrient limitation under nutrient poor conditions. We tested the hypothesis that nutrient enrichment will stimulate the abundance of ephemeral macroalgae by studying the abundance and species composition of these algae on several types of substrata along an artificial nutrient gradient. The total biomass of ephemeral macroalgae differed considerably among different types of substrata. The total ephemeral load was significantly higher on consolidated substrata than on large perennial algae, but we were unable to detect any systematic increase in the abundance of these ephemerals with increasing nutrient richness. We found, however, indications that the composition of the ephemeral assemblage changed with nutrient richness. Hence, corticated filamentous algae (mostly red algae) were more abundant at low nutrient richness while thin foliose algae (mainly green species) tended to become more abundant with increasing nutrient richness in most of the surveyed assemblages.

Description: Highlights • Anthropogenic nitrogen (N) inputs are a global problem, but difficult to quantify. • We tested the use of eelgrass δ15N as proxy of such inputs in the Baltic Sea. • The method revealed distinct spatial patterns in sewage N across a eutrophic bay. • Traditional eutrophication measures corroborated the results from δ15N values. • Eelgrass δ15N ratios have high potential as proxy of sewage-derived N in the Baltic. Eutrophication is a global environmental problem. Better management of this threat requires more accurate assessments of anthropogenic nitrogen (N) inputs to coastal systems than can be obtained with traditional measures. Recently, primary producer N isotopic signatures have emerged as useful proxy of such inputs. Here, we demonstrated for the first time the applicability of this method using the widespread eelgrass (Zostera marina) in the highly eutrophic Baltic Sea. Spatial availability of sewage N across a bay with one major sewage outflow predicted by eelgrass δ15N was high near and downstream of the outflow compared to upstream, but returned to upstream levels within 4 km downstream from the outfall. General conclusions were corroborated by traditional eutrophication measures, but in contrast to these measures were fully quantitative. Eelgrass N isotope ratios therefore show high potential for coastal screens of eutrophication in the Baltic Sea, and in other areas with eelgrass meadows

Description: In an investigation of the fauna using the red algae Delesseria sanguinea, Phyllophora pseudoceranoides and Ceramium rubrum as substrata, samples were analysed from two subtidal sites near Helgoland (North Sea), one (semi-) exposed to currents, and the other protected from strong water movement. There were clear differences in the abundances of the gammaridean amphipods Jassa falcata and Jassa marmorata between these sites suggesting strong preference for water movement for J. falcata and a preference for more sheltered habitats for J. marmorata. In laboratory experiments both species preferred current to still water, but J. falcata was stricter in its choice than J. marmorata. Both species differed in their choice of habitat algae in the field and in the laboratory. These results emphasise the importance of taxonomic distinction in ecological studies of the congeners that often have been confused or subsumed in former ecological research.

Description: Stress regimes defined as the synchronous or sequential action of abiotic and biotic stresses determine the performance and distribution of species. The natural patterns of stress to which species are more or less well adapted have recently started to shift and alter under the influence of global change. This was the motivation to review our knowledge on the stress ecology of a benthic key player, the macroalgal genus Fucus. We first provide a comprehensive review of the genus as an ecological model including what is currently known about the major lineages of Fucus species with respect to hybridization, ecotypic differentiation and speciation; as well as life history, population structure and geographic distribution. We then review our current understanding of both extrinsic (abiotic/biotic) and intrinsic (genetic) stress(es) on Fucus species and how they interact with each other. It is concluded that (i) interactive stress effects appear to be equally distributed over additive, antagonistic and synergistic categories at the level of single experiments, but are predominantly additive when averaged over all studies in a meta-analysis of 41 experiments; (ii) juvenile and adult responses to stress frequently differ and (iii) several species or particular populations of Fucus may be relatively unaffected by climate change as a consequence of pre-adapted ecotypes that collectively express wide physiological tolerences. Future research on Fucus should (i) include additional species, (ii) include marginal populations as models for responses to environmental stress; (iii) assess a wider range of stress combinations, including their temporal fluctuations; (iv) better differentiate between stress sensitivity of juvenile versus adult stages; (v) include a functional genomic component in order to better integrate Fucus’ ecological and evolutionary responses to stress regimes and (vi) utilize a multivariate modelling approach in order to develop and understand interaction networks.

Description: Protecting the ocean has become a major goal of international policy as human activities increasingly endanger the integrity of the ocean ecosystem, often summarized as “ocean health.” By and large, efforts to protect the ocean have failed because, among other things, (1) the underlying socio-ecological pathways have not been properly considered, and (2) the concept of ocean health has been ill defined. Collectively, this prevents an adequate societal response as to how ocean ecosystems and their vital functions for human societies can be protected and restored. We review the confusion surrounding the term “ocean health” and suggest an operational ocean-health framework in line with the concept of strong sustainability. Given the accelerating degeneration of marine ecosystems, the restoration of regional ocean health will be of increasing importance. Our advocated transdisciplinary and multi-actor framework can help to advance the implementation of more active measures to restore ocean health and safeguard human health and well-being.