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Many invertebrate species inhabit coastal areas where loads of plastic debris and microplastics are high. In the current case study, we exemplarily illustrate the principal processes taking place in the Atlantic ditch shrimp, Palaemon varians, upon ingestion of microplastics. In the laboratory, shrimp readily ingested fluorescent polystyrene microbeads of 0.1-9.9 µm, which could be tracked within the widely translucent body. Ingested food items as well as micro-particles cumulate in the stomach where they are macerated and mixed with digestive enzymes. Inside the stomach, ingested particles are segregated by size by a complex fine-meshed filter system. Liquids and some of the smallest particles (0.1 µm) pass the filter and enter the midgut gland where resorption of nutrients as well as synthesis and release of digestive enzymes take place. Large particles and most of the small particles are egested with the feces through the hindgut. Small particles, which enter the midgut gland, may interact with the epithelial cells and induce oxidative stress, as indicated by elevated activities of superoxide dismutase and cellular markers of reactive oxygen species. The shrimp indiscriminately ingest microparticles but possess efficient mechanisms to protect their organs from overloading with microplastics and other indigestible particles. These include an efficient sorting mechanism within the stomach and the protection of the midgut gland by the pyloric filter. Formation of detrimental radical oxygen species is counteracted by the induction of enzymatic antioxidants.

Marine invertebrates inhabiting estuaries and coastal areas are exposed to natural suspended particulate matter (SPM) like clay or diatom shells but also to anthropogenic particles like microplastics. SPM concentrations may reach 1 g per liter and more, comprising hundreds of millions of items in the size range of less than 100 μm. Suspension feeders and deposit feeders involuntarily ingest these particles along with their food. We investigated whether natural and anthropogenic microparticles at concentrations of 20 mg L

Extensive marine benthos surveys have resulted in a solid understanding of the broad distribution pattern of seafloor biotopes in the southeastern North Sea (temperate northeast Atlantic region). However, due to the low spatial resolution of large-scale surveys, specific smaller-scale biotopes with scattered distribution have been insufficiently captured. Consequently, knowledge regarding the environmental characteristics and species inventories of some specific biotopes is still limited. We investigated the habitat characteristics and the macroinfauna (i.e., organisms in samples collected by a sediment grab and retained in a sieve with a mesh size of 1000 μm) of a spatially restricted, patchy coarse sediment (i.e., grain size fraction >500 μm accounting for ≥60% of the total sample mass) biotope in the German Bight over three consecutive years. Habitat and faunal characteristics were contrasted with four other benthic biotopes sampled at the same time to allow for a comparative evaluation. Our study revealed considerable fluctuations in grain size distribution among samples of the coarse sediment, potentially resulting from a frequent redistribution of sediments. A total number of 243 infauna taxa were identified at the 66 stations sampled over three consecutive years (16–33 stations per year) with a considerable proportion of endangered and rare species. The results highlight that previous studies have underestimated the species richness of the biotope. The focus on this previously poorly studied biotope type allowed us to detect species in the study region that were formerly unreported. The macro-infauna in the coarse sediments was characterized by comparatively high abundance and biomass, which may provide a rich food resource for organisms from higher trophic levels. Therefore, coarse sediments likely are an ecologically valuable seafloor biotope despite its limited coverage.

Sediment samples were randomly taken in March and August 2017 at the strandlines of nine locations along the coast of Slovenia (Adriatic Sea, Mediterranean). Microparticles were isolated by density separation in saturated aqueous NaCl-solutions and analysed by infrared spectroscopy (ATR-FTIR). 11.3% of these particles were unambiguously confirmed as microplastics. Another 8.2% showed plastic characteristics but failed ATR-FTIR validation. 4.3% were naturally organic. The rest was unidentified material (76.2%). The average microplastic densities were 0.5 ± 0.5 MP kg−1 in March and 1.0 ± 0.8 MP kg−1 in August. The microplastics comprised fragments, fibres, films, and foams. The characteristics of the microplastics suggest origin from single-used plastic products and from aquaculture. Compared to other studies and sites, the microplastic pollution of the Slovenian coast appeared low. The validity of the results is discussed with respect to microplastic distribution and patchiness, sampling strategies, methodology, and scientific claims.

Globally, marine subtidal hard-substrate habitats provide important ecological functions to a variety of sessile and mobile taxa. The southern North Sea is a marine environment with relatively low amounts of hard-substrate areas. Surveys with high taxonomic resolution on the associated hard-substrate epifauna, e.g. by diving observations, are challenging in this region because of strong tidal currents and considerable water depths. Therefore, the characteristics and functions of hard-substrate habitats in the North Sea remain poorly understood. The goal of this study was to extend the knowledge on sessile taxa assemblages in four hard-substrate areas within the German Bight (SE North Sea) using underwater video observations as a straight-forward and visual method to obtain and process detailed data on seafloor characteristics. Still images from drift videos were analyzed to determine the epifaunal assemblages attached to the stones on a presence/absence scale. A subsample of cobbles, boulders and large boulders was further investigated to derive quantitative data on the colonized area for each taxon and stone size. The four areas showed significant differences in sessile taxa richness, with higher numbers of sessile taxa in the deeper far-shore areas than in the shallower nearshore areas, despite a generally high similarity in the sessile animal taxa spectrum. Within the areas, cobbles were mainly dominated by short-lived taxa ( 5 years) like Metridium dianthus, Flustra foliacea and Alcyonium digitatum. Most of the stones were typically covered by epifauna by more than 50%. The differences in the sessile taxa spectrum between the areas were interpreted as a consequence of reduced abiotic stress and higher habitat complexity in the far-shore areas. The dominance of short-lived taxa on cobbles, in comparison to long-lived taxa on boulder-sized stones, possibly reflects the frequency of disturbance and the competitiveness of these taxa.

Comprehensive empirical data to inform benthic species distribution models for marine hard-substrate-dominated environments, are pivotal. However, such data are difficult to obtain. These data are crucial to the definition and demarcation of protected areas and for assessment of the ecological status and function of hard-substrate habitats. In this study, underwater video-observations of hard-substrate habitats within four target areas in the sand-dominated German Bight (SE North Sea) were investigated to obtain comprehensive information on hard-substrate distribution patterns, on the amount and sizes of stones and on the presence of sessile organisms. Based on three size classes (cobbles, boulders, large boulders) three hard-substrate distribution classes were identified: (1) widely scattered stones, (2) accumulations of stones and (3) dense stone fields. The ratios between cobbles, boulders and large boulders differed significantly between the investigated areas. Boulders and large boulders were largely colonized by sessile organisms, whereas cobbles in coastal areas were least frequently colonized. Physical disturbances of epibenthos resulting from abrasion and coverage by mobile sediments are discussed as a possible explanation for the proportional differences in the colonization of stones. Hard substrates in shallower, coastal areas appeared to be strongly influenced by sand abrasion because of higher current velocities and storm-induced waves. In deeper areas, located further offshore, disturbances caused by migrating sandy ripples mobilized by storm-events seemed to be more relevant. Habitat modelling of hard substrates and resultant ecological studies require sound information on the probability of epifaunal colonization for different substrate sizes, hard-substrate distribution patterns combined with hydrodynamic and physicochemical properties of the marine environment to produce valid results. We used a structured approach for the video-based analysis of hard-substrate habitats and present estimates of the colonization probability of differently-sized stones. Our study shows that the analysis of drift videos provides basic data at a suitable resolution to contribute to the monitoring and modelling of marine ecological processes.

Bio-based polymers have been suggested as one possible opportunity to counteract the progressive accumulation of microplastics in the environments. The gradual substitution of conventional plastics by bio-based polymers bears a variety of novel materials. The application of bioplastics is determined by their stability and bio-degradability, respectively. With the increasing implementation of bio-based plastics, there is also a demand for rapid and non-elaborate methods to determine their bio-degradability. Here, we propose an improved pH Stat titration assay optimized for bio-based polymers under environmental conditions and controlled temperature. Exemplarily, suspensions of poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) microparticles were incubated with proteolytic and lipolytic enzymes. The rate of hydrolysis, as determined by counter-titration with a diluted base (NaOH), was recorded for two hours. PLA was hydrolyzed by proteolytic enzymes but not by lipase. PBS, in contrast, showed higher hydrolysis rates with lipase than with proteases. The thermal profile of PLA hydrolysis by protease showed an exponential increase from 4 to 30 °C with a temperature quotient Q10 of 5.6. The activation energy was 110 kJ·mol−1. pH-Stat titration proved to be a rapid, sensitive, and reliable procedure supplementing established methods of determining the bio-degradability of polymers under environmental conditions.

Increasing anthropogenic activities on land and at sea underline the demand for easily applicable indices to effectively predict human mediated changes in ecosystem functioning. Here, we propose a novel bioirrigation index (IPc) that is based on body mass, abundance, burrow type, feeding type and injection pocket depth of bottom dwelling animals. The index was validated with combined field (in situ communities) and manipulative (single species) experiments. Results from both community and single-species experimental incubations indicate that IPc is able to predict the bioirrigation rate in different sediment types (mud, fine sand, sand). The trait-based index thus demonstrates robustness in the prediction of animal-mediated functional processes that support biogeochemical functions under variable environmental conditions. Accordingly, we argue that trait-based indices provide a useful tool for the quantitative prediction of ecosystem processes as effect traits provide a direct link to the behavioral mechanisms that drive ecosystem functioning.

Microplastic fibers represent a significant share of the global marine micrcroplastic pollution, particularly in coastal areas. In controlled laboratory experiments, we offered fluorescent microplastic fibers (40–4400 μm lengths, median 150 μm) and spherical microplastic beads (9.9 μm O) together with commercial fish food to the Atlantic ditch shrimp Palaemonetes varians. The shrimps ingested fibers and beads along with the food. Upon ingestion, the beads and the shortest fibers (up to 100 μm) passed from the stomach into the gut and were egested within the fecal strings. The longer fibers first remained in the stomach but were regurgitated, i.e. extruded through the esophagus, within 12–14 h. Regurgitation is an evolutionary adaptation of particular crustacean species and other invertebrates to remove large and indigestible food particles from the stomach. Accordingly, the process of regurgitation attained a new task nowadays, i.e. the elimination of anthropogenic filamentous microplastic debris from the stomach to avoid harm. This behavioral feature may represent a selective advantage in view of the continuously increasing environmental plastic pollution.

In coastal waters the identification of sources, trajectories and deposition sites of marine litter is often hampered by the complex oceanography of shallow shelf seas. We conducted a multi-annual survey on litter at the sea surface and on the seafloor in the south-eastern North Sea. Bottom trawling was identified as a major source of marine litter. Oceanographic modelling revealed that the distribution of floating litter in the North Sea is largely determined by the site of origin of floating objects whereas the trajectories are strongly influenced by wind drag. Methods adopted from species distribution modelling indicated that resuspension of benthic litter and near-bottom transport processes strongly influence the distribution of litter on the seafloor. Major sink regions for floating marine litter were identified at the west coast of Denmark and in the Skagerrak. Our results may support the development of strategies to reduce the pollution of the North Sea.

Predation has direct impact on prey populations by reducing prey abundance. In addition, predator presence alone can also have non-consumptive effects on prey species, potentially influencing their interspecific interactions and thus the structure of entire assemblages. The performance of potential prey species may, therefore, depend on both the presence of predators and competitors. We studied habitat use and food consumption of a marine mesograzer, the amphipod Echinogammarus marinus, in the presence/absence of a fish mesopredator and/or an amphipod competitor. The presence of the predator affected both habitat choice and food consumption of the grazer, indicating a trade-off between the use of predator-free space and food acquisition. Without the predator, E. marinus were distributed equally over different microhabitats, whereas in the presence of the predator, most individuals chose a sheltered microhabitat and reduced their food consumption. Furthermore, habitat choice of the amphipods changed in the presence of interspecific competitors, also resulting in reduced feeding rates. The performance of E. marinus is apparently driven by trait-mediated direct and indirect effects caused by the interplay of predator avoidance and competition. This highlights the importance of potential non-consumptive impacts of predators on their prey organisms. The flexible responses of small invertebrate consumers to the combined effects of predation and competition potentially lead to changes in the structure of coastal ecosystems and the multiple species interactions therein. Electronic supplementary material The online version of this article (10.1007/s00442-017-4056-4) contains supplementary material, which is available to authorized users.

Loss of bioturbating key species from marine sediments has been shown to strongly reduce benthic biogeochemical cycling and ecosystem functioning. It is thus of paramount importance to identify key bioturbators and quantify their effect on biogeochemical processes. To do so trait based community and species bioturbation potential (BPc and BPi) was mapped for 423 North Sea stations in the German Bight. Mapping of BPc and BPi identified Amphiura filiformis, Echinocardium cordatum and Nucula nitidosa as major bioturbating species in the German Bight. The effects of these species on benthic nutrient flux (i.e., changing concentrations of silicate ∆[SiO2], ammonium ∆[NH4+], nitrate ∆[NO3−] and nitrite ∆[NO2−]) were quantified in laboratory experiments together with their bioturbation rate (Db) and bioirrigation activity. The experiments indicated that mapped species bioturbation potential (BPi) may be a poor tool for identifying key bioturbators while calculated experimental BPi (expBPi) was a good indicator for species impact on biogeochemical cycling. Out of the three investigated species only E. cordatum significantly influenced biogeochemical cycling, whereas the effect of A. filiformis remained inconclusive potentially because arm damage and regeneration may affect the bioturbation activity of many individuals. The bivalve N. nitidosa showed only little impact on biogeochemical cycling, although this species was found to be an active bioturbator. Accordingly, E. cordatum may be considered one of the most important contributors to biogeochemical cycling at the sediment-water interface in the German Bight.

The Pacific oyster Magallana gigas (formerly Crassostrea gigas) was introduced in the Wadden Sea in the 1980s for aquaculture purposes. Soon after the introduction, oysters escaped from the commercial oyster farms and massively colonized the intertidal beds of the native blue mussel Mytilus edulis. A competitive suppression of the mussel population may have led to the loss of important ecosystem services provided by the mussels. Today, however, both species co-exist in dense mixed beds without substantial change in mussel density and functioning of the Wadden Sea ecosystem. The invasion of the Pacific oyster in the Wadden Sea provides an example of how relatively young ecosystems can integrate non-indigenous species without detrimental implications for ecosystem services.

Brown shrimp, Crangon crangon, inhabit highly productive sandy and muddy grounds of the southern North Sea. The stomachs of the shrimp contain variable and often high numbers of sediment grains. The function of sediment grains inside the stomach and the purpose of their ingestion are only poorly understood. We tested in laboratory experiments whether sediment and associated organic material complement the natural food of C. crangon or if sand grains may be used by the shrimp to support trituration and maceration of ingested food. The shrimp showed no notable preference for sediment with natural organic content over sediment with reduced organic content, limited ingestion of sediment upon starvation, and no additional uptake of sand grains after feeding. Instead, C. crangon took up sediment only while feeding on regular food, suggesting that sand grains are not ingested intentionally but rather incidentally as a side effect of hasty gobbling. This conclusion is supported by the highly variable uptake of sand grains among individuals. Under experimental conditions, sand grains from sediments do not seem to have a crucial function in food processing and digestion in brown shrimp.

Microplastic pollution is an emerging threat to marine biota. Uptake of microplastics can impair nutrition and affect the performance of organisms. However, the vulnerability to microplastics seems to vary between species for yet widely unexplored reasons. We investigated the stomach content of the brown shrimp, Crangon crangon, from the southern North Sea and performed feeding experiments and anatomical studies of the digestive organs to comprehend the distribution of fluorescent microparticles within the shrimp. Shrimp collected in their natural environment contained between 51 and more than 3,000 sand grains and fragments of bivalve shells in their stomachs. Sand grains may have been ingested to exploit the associated biofilm or to support maceration of food. Bivalve shell fragments were particularly abundant in summer when shrimp fed on freshly settled mussels. Shrimps' stomach can be cleaned from ingested particles by regurgitation. In an experimental approach, we administered fluorescent microbeads of 0.1, 2.1, and 9.9 μm diameter. Only the smallest particles (0.1 μm) entered the midgut gland, which is the principal site of nutrient resorption in crustaceans. A fine-meshed chitinous filter system in the stomach of the shrimp prevents the passage of particles larger than about 1 μm. C. crangon appears well adapted to handle natural microscopic particles. This trait might also be advantageous in coping with microplastic pollution.

Respiration of ectotherms is predicted to increase faster with rising environmental temperature than photosynthesis of primary producers because of the differential temperature dependent kinetics of the key enzymes involved. Accordingly, if biological processes at higher levels of complexity are constrained by underlying metabolic functions, food consumption by heterotrophs should increase more rapidly with rising temperature than photo-autoptrophic primary production. We compared rates of photosynthesis and growth of the benthic seaweed Fucus vesiculosus with respiration and consumption of the isopod Idotea baltica to achieve a mechanistic understanding why warming strengthens marine plant–herbivore interactions. In laboratory experiments thallus pieces of the seaweed and individuals of the grazer were exposed to constant temperatures at a range from 10 to 20 °C. Photosynthesis of F. vesiculosus did not vary with temperature indicating efficient thermal acclimation whereas growth of the algae clearly increased with temperature. Respiration and food consumption of I. baltica also increased with temperature. Grazer consumption scaled about 2.5 times faster with temperature than seaweed production. The resulting mismatch between algal production and herbivore consumption may result in a net loss of algal tissue at elevated temperatures. Our study provides an explanation for faster decomposition of seaweeds at elevated temperatures despite the positive effects of high temperatures on algal growth.

We examined long-term variability in the abundance of German Bight soft bottom macro-zoobenthos together with major environmental factors (sea surface temperature, winter NAO index, salinity, phosphate, nitrate and silicate) using one of the most comprehensive ecological long-term data sets in the North Sea (1981–2011). Two techniques, Min/Max Autocorrelation Factor Analysis (MAFA) and Dynamic Factor Analysis (DFA) were used to identify underlying common trends in the macrofaunal time series and the relationships between this series and environmental variables. These methods are particularly suitable for relatively short (> 15–25 years), non-stationary multivariate data series. Both MAFA and DFA identify a common trend in German Bight macrofaunal abundance i.e. a slight decrease (1981–mid-1990s) followed by a sharp trough in the late 1990s. Subsequently, scores increased again towards 2011. Our analysis indicates that winter temperature and North Atlantic Oscillation were the predominant environmental drivers of temporal variation in German Bight macrofaunal abundance. The techniques applied here are suitable tools to describe temporal fluctuations in complex and noisy multiple time series data and can detect distinct shifts and trends within such time series.

The ingestion of microplastics has been shown for a great variety of marine organisms. However, benthic marine mesoherbivores such as the common periwinkle Littorina littorea have been largely disregarded in studies about the effects of microplastics on the marine biota, probably because the pathway for microplastics to this functional group of organisms was not obvious. In laboratory experiments we showed that the seaweed Fucus vesiculosus retains suspended microplastics on its surface. The numbers of microplastics that adhered to the algae correlated with the concentrations of suspended particles in the water. In choice feeding assays L. littorea did not distinguish between algae with adherent microplastics and clean algae without microplastics, indicating that the snails do not recognize solid nonfood particles in the submillimeter size range as deleterious. In periwinkles that were feeding on contaminated algae, microplastics were found in the stomach and in the gut. However, no microplastics were found in the midgut gland, which is the principle digestive organ of gastropods. Microplastics in the fecal pellets of the periwinkles indicate that the particles do not accumulate rapidly inside the animals but are mostly released with the feces. Our results provide the first evidence that seaweeds may represent an efficient pathway for microplastics from the water to marine benthic herbivores.

Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. By contrast, small mesograzers, including gastropods and peracarid crustaceans, are abundant on seaweeds but have low per capita feeding rates and their impacts on marine macrophytes are difficult to predict. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipods Sunamphitoe lessoniophila and Bircenna sp., which construct burrows in the stipes of subtidal individuals of the kelp Lessonia berteroana in northern-central Chile, southeast Pacific. Infested stipes showed a characteristic sequence of progressive tissue degeneration. The composition of the amphipod assemblages inside the burrows varied between the different stages of infestation of the burrows. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. The estimated loss of biomass of single stipes varied between 1 and 77%. For the local kelp population, the amphipods caused an estimated loss of biomass of 24–44%. Consequently, small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue.

The rapid dissemination of microplastics in many habitats of the oceans has raised concerns about the consequences for marine biota and ecosystems. Many adverse effects of microplastics on marine invertebrates are consequences of ingestion. Accordingly, the identification of mechanisms that facilitate the uptake of microplastics is essential for the evaluation of possible implications for marine organisms and food webs. Gastropods produce mucus for locomotion. Gastropod pedal mucus naturally retains formerly suspended micro-organisms, such as bacteria, microalgae, and seaweed spores. The retained organisms are consumed by gastropods that forage on pedal mucus. Here, we investigated the potential of gastropod pedal mucus to retain suspended microplastic particles and make them available for ingestion by periwinkles that forage on the contaminated mucus. In laboratory experiments, mucus of the periwinkles Littorina littorea and Littorina obtusata efficiently retained microplastics. Retention of microplastics varied between mucus from conspecifics of different size but not between mucus from either species. The density of microplastics in mucus trails increased concomitantly with the experimental particle concentration but was independent of incubation time. Aging of mucus and, particularly, desiccation affected the retention of microplastics. Periwinkles ingested microplastics when foraging on the contaminated mucus. Our results reveal a functional link between biogenic accumulation of microplastics and their trophic transfer by marine benthic herbivores into marine food webs.

Ingestion of microplastics can impair nutrition of marine invertebrates. In a laboratory study, we tested whether microplastics affect ingestion rates and gastrointestinal enzyme activities in the marine isopod Idotea emarginata. Isopods were fed for eight days with one out of four different food formulations: natural food (the brown alga Fucus vesiculosus) or synthetic diet consisting of freeze-dried algal powder embedded in agarose, both, with or without microplastic particles (fluorescent polymethyl methacrylate, 10–100 μm) at a concentration of 40 items per mg of food. The isopods accepted both types of food but consumed significantly more (average 3.1-fold) of the agar based synthetic food. I. emarginata responded to the reduced content of digestible organic matter in the synthetic food by a compensatory adjustment of the ingestion rates. Addition of microplastics had no effect on ingestion rates in natural food whereas the feeding rates for synthetic food varied in response to microplastics. Similarly, activity patterns of digestive enzymes, particularly those of esterases, changed significantly in the treatment with synthetic food. Isopods fed with synthetic food alone showed elevated esterase activities in the gut while those isopods fed with synthetic food and microplastics showed elevated esterase activities in the midgut gland but not in the gut. Apparently, not the exposure to microplastic alone, but the combined effects of reduced nutrient availability and microplastic ingestion caused considerable biochemical reactions in the digestive organs of the isopods.

We determined the spatial and seasonal distribution of Floating Marine Debris (FMD) by visual ship surveys across the northern Baltic Sea between Finland and Sweden. FMD density was comparatively low, and we found the highest debris density close to major port cities. The seasonal variation in debris density was not pronounced although we observed more FMD items during the summer surveys. Plastic bags were the most common identifiable litter items, and we also found other consumer items (plastic bottles and cups). Styrofoam items suggest fishing or aquaculture activities as potential sea-based sources of FMD. These are the first data on FMD density in the Baltic Sea, and they are substantially lower than those reported for other coastal waters, which may be due to (i) lower human population densities, and (ii) higher environmental awareness in the Scandinavian countries.

Anthropogenic litter contamination of the oceans is a global problem of growing concern and currently receives strongly increasing attention by policy makers, public authorities, media and the general public. Unlike many other pollutants, marine litter on beaches and its deleterious effects on marine mammals, birds and turtles have attracted much attention as they can be directly observed by stakeholders.

After detachment from benthic habitats, the epibiont assemblages on floating seaweeds undergo substantial changes, but little is known regarding whether succession varies among different seaweed species. Given that floating algae may represent a limiting habitat in many regions, rafting organisms may be unselective and colonize any available seaweed patch at the sea surface. This process may homogenize rafting assemblages on different seaweed species, which our study examined by comparing the assemblages on benthic and floating individuals of the fucoid seaweeds Fucus vesiculosus and Sargassum muticum in the northern Wadden Sea (North Sea). Species richness was about twice as high on S. muticum as on F. vesiculosus, both on benthic and floating individuals. In both seaweed species benthic samples were more diverse than floating samples. However, the species composition differed significantly only between benthic thalli, but not between floating thalli of the two seaweed species. Separate analyses of sessile and mobile epibionts showed that the homogenization of rafting assemblages was mainly caused by mobile species. Among these, grazing isopods from the genus Idotea reached extraordinarily high densities on the floating samples from the northern Wadden Sea, suggesting that the availability of seaweed rafts was indeed limiting. Enhanced break-up of algal rafts associated with intense feeding by abundant herbivores might force rafters to recolonize benthic habitats. These colonization processes may enhance successful dispersal of rafting organisms and thereby contribute to population connectivity between sink populations in the Wadden Sea and source populations from up-current regions.

Plastic pollution is an emerging global threat for marine wildlife. Many species of birds, reptiles and fishes are directly impaired by plastics as they can get entangled in ropes and drown or they can ingest plastic fragments which, in turn, may clog their stomachs and guts. Microplastics of less than 1 mm can be ingested by small invertebrates but their fate in the digestive organs and their effects on the animals are yet not well understood. We embedded fluorescent microplastics in artificial agarose-based food and offered the food to marine isopods, Idotea emarginata. The isopods did not distinguish between food with and food without microplastics. Upon ingestion, the microplastics were present in the stomach and in the gut but not in the tubules of the midgut gland which is the principal organ of enzyme-secretion and nutrient resorption. The feces contained the same concentration of micro-plastics as the food which indicates that no accumulation of microplastics happens during the gut passage. Long-term bioassays of six weeks showed no distinct effects of continu¬ous micro-plastic consumption on mortality, growth, and intermolt duration. I. emarginata are able to prevent intrusion of particles even smaller than 1 µm into the midgut gland which is facilitated by the complex structure of the stomach including a fine filter system. It separates the midgut gland tubules from the stomach and allows only the passage of fluids and chyme. Our results indicate that micro¬plastics, as administered in the experi¬ments, do not clog the digestive organs of isopods and do not have adverse effects on their life history parameters.

Recent data indicate accumulation areas of marine litter in Arctic waters and significant increases over time. Beaches on remote Arctic islands may be sinks for marine litter and reflect pollution levels of the surrounding waters particularly well. We provide the first quantitative data from surveys carried out by citizen scientists on six beaches of Svalbard. Litter quantities recorded by cruise tourists varied from 9-524 g m-2 and were similar to those from densely populated areas. Plastics accounted for >80% of the overall litter, most of which originated from fisheries. Photographs provided by citizens show deleterious effects of beach litter on Arctic wildlife, which is already under strong pressure from global climate change. Our study highlights the potential of citizen scientists to provide scientifically valuable data on the pollution of sensitive remote ecosystems. The results stress once more that current legislative frameworks are insufficient to tackle the pollution of Arctic ecosystems.

For many years, the pollution of the oceans with marine litter received only little attention from the public although the global plastic production has grown steadily. However, since the “discovery” of the oceanic garbage patches and microplastics the littering of the oceans has become a hot topic, which is reflected in strong recent increases in the number of publications. Despite growing research efforts many questions remain unanswered and the new wealth of information does not readily transpire to the general public, which is left unsettled. For example, it is still unclear what the overall extent of ocean pollution is, or how the enormous amounts of oceanic plastics affect marine life and ecosystems. To overcome this uncertainty and make best use of the existing knowledge, we currently develop an online portal for marine litter and microplastic pollution named LITTERBASE. As of early 2017, LITTERBASE will provide access to the current state of understanding of marine litter and microplastics to the general public and stakeholders. Published records of marine litter and microplastics and their impact on marine life will be compiled in a database. The regularly updated information will be displayed in distribution maps and other graphs in an interactive online portal. In the long run, data from citizen scientists may also be integrated into these infographs.

Baztan, Juan ... et al.-- MICRO 2016, 25-27 May 2016, Lanzarote, Spain.-- 5 pages

Mikroplastik stellt eine ernst zu nehmende Belastung fur die Meeresumwelt dar. Neben Quellen und Eigenschaften von Mikroplastikpartikeln werden ihre Auswirkungen auf Meeresorganismen sowie die Herausforderungen bei der Erforschung dieser Form der Umweltverschmutzung besprochen. Aufgrund der geringen Grose der synthetischen Partikel sind ihre Identifizierung und Quantifizierung in der Umwelt technologisch sehr anspruchsvoll. Das Verstandnis der Wirkung von Mikroplastikpartikeln auf die Tiere und Pflanzen des Meeres ist ein Ziel aktueller Meeresforschung.

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80 %) in blade growth rates despite limited loss of kelp biomass (0.5 % per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Within the next few decades, large underwater structures of thousands of wind turbines in the northern European shelf seas will substantially increase the amount of habitat available for mobile demersal megafauna. As a first indication of the possible effects of this large scale habitat creation on faunal stocks settling on hard substrata, we compared selected taxa of the mobile demersal megafauna (decapods and fish) associated with the foundation of an offshore research platform (a wind-power foundation equivalent) with those of five shipwrecks and different areas of soft bottoms in the southern German Bight, North Sea. When comparing the amount of approximately 5000 planned wind-power foundations (covering 5.1 � 10 6 m 2 of bottom area) with the existing number of at least 1000 shipwrecks (covering 1.2 � 10 6 m 2 of bottom area), it becomes clear that the southern North Sea will provide about 4.3 times more available artificial hard substratum habitats than currently available. With regard to the fauna found on shipwrecks, on soft substrata and on the investigated wind-power foundation, we predict that the amount of added hard substrata will allow the stocks of substrata-limited mobile demersal hard bottom species to increase by 25e165% in that area. The fauna found at the offshore platform foundations is very similar to that at shipwrecks. Megafauna abundances at the foundations, however, are lower compared to those at the highly fractured wrecks and are irregularly scattered over the foundations. The upper regions of the platform construction (5 and 15 m depth) were only sparsely colonized by mobile fauna, the anchorages, however, more densely. The faunal assemblages from the shipwrecks and the foundations, respectively, as well as from the soft bottoms clearly differed from each other. We predict that new wind-power foundations will support the spread of hard bottom fauna into soft bottom areas with low wreck densities. 2013 Elsevier Ltd. All rights reserved.

Summary Rising atmospheric CO2-concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca (Linnaeus) to rising CO2-concentrations in a rockpool scenario. U. lactuca was cultured under aeration with air containing either preindustrial pCO2 (280 μatm) or the pCO2 predicted by the end of the 21st century (700 μatm) for 31 days. We addressed the following question: Will elevated CO2-concentrations affect photosynthesis (net photosynthesis, maximum relative electron transport rate (rETR(max)), maximum quantum yield (Fv/Fm), pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1–4) the Seawater Carbonate System (SWCS) of the culture medium could be adjusted to the selected atmospheric pCO2 condition by continuous aeration with target pCO2 values. In the second phase (day 4–31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO2-concentrations, whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO2-concentrations. At low CO2-concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO2-concentrations most thalli remained integer until day 31. Thallus disintegration at low CO2-concentrations was mirrored by a drastic decline in seawater dissolved inorganic carbon and HCO3−. Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO2-concentrations. The accelerated thallus disintegration at high CO2-concentrations under conditions of limited water exchange indicates additional CO2 effects on the life cycle of U. lactuca when living in rockpools.

In the light of the introduction of thousands of large offshore wind power foundations into the North Sea within the next decades, this manuscript focuses on the biofouling processes and likely reef effects. The study explores the macrozoobenthos (biofouling) colonization at an offshore platform which is comparable to offshore wind turbine foundations. A total of 183 single samples were taken and the parameters water depth and time were considered comparing biofouling masses and communities. The blue mussel Mytilus edulis , Anthozoa and the Amphipoda Jassa spp. were the dominant species. The community from the 1 m zone and those from the 5 and 20–28 m zones can clearly be differentiated. The 10 m zone community represents the transition between the M. edulis dominated 1 m and 5 m zones and the Anthozoa dominated 20–28 m zone. In the future offshore wind farms, thousands of wind turbine foundations will provide habitat for a hard bottom fauna which is otherwise restricted to the sparse rocky habitats scattered within extensive sedimentary soft bottoms of the German Bight. However, offshore wind power foundations cannot be considered natural rock equivalents as they selectively increase certain natural hard bottom species. The surface of the construction (1280 m²) was covered by an average of 4300 kg biomass. This foundation concentrates on its footprint area (1024 m²) 35 times more macrozoobenthos biomass than the same area of soft bottom in the German exclusive economic zone (0.12 kg m −2 ), functioning as a biomass hotspot. Concerning the temporal biomass variation, we assume that at least 2700 kg biomass was exported on a yearly basis. 345 × 10 4 single mussel shells of different sizes were produced during the study period. It is anticipated that the M. edulis abundance will increase in the North Sea due to the expansion of the offshore wind farm development. This will result in the enhanced production of secondary hard substrate (mussel shells) and its associated fauna and will intensify filtration rates of the seawater. This predicted ecological system change is coined the ’ Mytilus ation’ of the German Bight.

In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Among these, temperature, irradiance and CO2 availability are major factors influencing the physiological performance of marine macroalgae. To test whether elevated levels of CO2 may remediate the otherwise reduced performance of uncalcified seaweeds under the influence of other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus from Helgoland (North Sea) with two levels of CO2, temperature and irradiance: low and high pCO2 levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis and pigment content. Acclimations of growth and photosynthesis were measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO2 effects on growth and photosynthesis. Significant CO2 effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis had divergent patterns: RGR and biomass significantly increased only under a combination of high pCO2 and elevated temperature; gross photosynthesis was significantly reduced under high pCO2 conditions at low irradiance. Pigment content varied in response to irradiance and temperature, but was independent of pCO2.

On the shore of the rocky island of Helgoland (North Sea) two closely related isopod species, Idotea balthicaPallas, 1772, and Idotea granulosaRathke, 1843, share a similar fundamental niche but inhabit well-separated habitats. Idotea balthica inhabits floating algae at the sea surface and accumulations of decaying algae on the seafloor, whereas I. granulosa primarily occurs in intertidal macroalgal belts. In laboratory experiments on individually reared isopods I. balthica outperformed I. granulosa with regard to growth, reproduction, and mortality in both a fully inundated habitat and in a tidal habitat with 5 h of daily emergence. We hypothesized that habitat segregation in the two isopod species is driven by one or multiple types of biotic interactions: (1) no interaction, (2) cannibalism, (3) intraguild predation, and (4) terrestrial predation. In order to evaluate how habitat segregation can be explained by each of these interaction types we employed a size-structured population model to account for the body-size-dependent predation. Net population growth rates were fitted to the simulations as a measure of population fitness. Experimental results served as database for parameter and process identification. As predation rates were unknown, we performed a sensitivity analysis for these. We found that below 5 h of daily tidal emergence either cannibalism or terrestrial predation sufficed to explain habitat segregation. Intraguild predation, in contrast, advantaged I. balthica in any case. From linear extrapolation of the effects occurring under conditions of 5 h of daily tidal emergence, we predict that contrasting physiological responses in I. balthica and I. granulosa would cause segregation even without any interaction if emergence lasted long enough. Electronic supplementary material The online version of this article (doi:10.1007/s00227-016-2843-9) contains supplementary material, which is available to authorized users.

Our objective for this study was to evaluate the influence of preindustrial and expected future atmospheric CO2 concentrations (280 μatm and 700 μatm pCO2, respectively) on different life-cycle stages of the kelp Laminaria hyperborea from Helgoland (Germany, North Sea). Zoospore germination, gametogenesis, vegetative growth, sorus formation and photosynthetic performance of vegetative and fertile tissue were examined. The contribution of external carbonic anhydrase (exCA) to C-supply for net-photosynthesis (net-PS) and the Chla- and phlorotannin content were investigated. Female gametogenesis and vegetative growth of sporophytes were significantly enhanced under the expected future pCO2. rETR(max) and net-PS of young vegetative sporophytes tended to increase performance at higher pCO2. The trend towards elevated net-PS vanished after inhibition of exCA. In vegetative sporophytes, phlorotannin content and Chla content were not significantly affected by pCO2.