Description: The concept of the marine ecological community has recently experienced renewed attention, mainly owing to a shift in conservation policies from targeting single and specific objec- tives (e.g. species) towards more integrated approaches. Despite the value of communities as dis- tinct entities, e.g. for conservation purposes, there is still an ongoing debate on the nature of spe- cies associations. They are seen either as communities, cohesive units of non-randomly associated and interacting members, or as assemblages, groups of species that are randomly associated. We investigated such dualism using fuzzy logic applied to a large dataset in the German Bight (south- eastern North Sea). Fuzzy logic provides the flexibility needed to describe complex patterns of natural systems. Assigning objects to more than one class, it enables the depiction of transitions, avoiding the rigid division into communities or assemblages. Therefore we identified areas with either structured or random species associations and mapped boundaries between communities or assemblages in this more natural way. We then described the impact of the chosen sampling design on the community identification. Four communities, their core areas and probability of occurrence were identified in the German Bight: AMPHIURA-FILIFORMIS, BATHYPOREIA-TELLINA, GONIADELLA-SPISULA, and PHORONIS. They were assessed by estimating overlap and compactness and supported by analysis of beta-diversity. Overall, 62% of the study area was characterized by high species turnover and instability. These areas are very relevant for conservation issues, but become undetectable when studies choose sampling designs with little information or at small spatial scales.

Description: The present compilation is the first attempt to generate a comprehensive list of all macrozoobenthic species recorded at least once in the German regions of the North Sea and Baltic Sea including non-indigenous species and freshwater species which occurred in brackish waters (estuaries, bays, fjords etc.). Based on the data of several research institutes and consultancies, the macrozoobenthic species inventory comprises a total of 1.866 species belonging to 16 phyla including 193 threatened species. The most common groups were: malacostracan crustaceans (21%), Polychaeta (19%), and Gastropoda (12%). Even though the two major marine regions are separated by only 50 km of land, the composition of the respective communities was different. The two seas shared only 36.6% of the recorded species which should have profound and far-reaching consequences for conservation purposes. Considering all macroinvertebrates listed 96 species, or the equivalent of 5.2%, were introduced mainly during the last two centuries. Both seas are heavily affected by human activities and are sensitive to climate change displayed by effects on the faunal compositions. The present checklist is an important step to document these changes scientifically and may act as a base for political and management decisions.

Description: 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.

Description: 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.