Description: This study shows that macrofaunal irrigation traits constitute a valuable complement to sediment reworking traits in estimating macrofaunal impact on nutrient fluxes across the sediment-water interface. We correlated density, biomass, community bioturbation potential (BPc, an index based on reworking traits, body mass and density) and community irrigation potential (IPc, an index based on irrigation traits, body mass and density) with nitrite, nitrate, ammonium, silicate and phosphate flux data under different environmental conditions. Generalized linear models performed best with a combination of environmental conditions and irrigation trait-based indices. This was not only a direct effect of the irrigation traits, but also of the scaling factor 0.75 employed in IPc to infer metabolic activity from body mass. Accordingly, predictive models of nutrient flux across the sediment-water interface will profit greatly from incorporating macrofaunal irrigation behaviour by means of trait-based indices.

Description: Benthic macrofauna in the North Sea is subjected to a wide variety of anthropogenic stressors, which have a significant impact on community composition. In order to understand how these communities react to anthropogenic influences, the effect of natural environmental variation, such as temperature, salinity, or sediment characteristics, must first be understood. It is generally known that natural variation causes differences in the classical biological measures, such as the species diversity of benthic communities, however there is a paucity of studies regarding the response of functional diversity. Due to the tight linkage of functional diversity to ecosystem processes, it is important to understand these functional aspects of community diversity for understanding changes in ecological processes as a whole, and ultimately the effects on vital ecosystem services and goods. This study determined changes in functional diversity of benthic macrofaunal communities along natural sediment gradients on small spatial scales (i.e. ~5 km). Soft-bottom assemblages including infauna and epifauna in the Sylt outer reef area of the North Sea were examined, with functional diversity being based on functional traits. Changes in functional diversity are compared to species diversity and relationships present are discussed. For the first time, this study examines if there are functional changes along sediment gradients on such a small scale. The results thus deliver valuable insight on the potential effects of community changes on ecosystem functioning and process-driven changes in assemblages. Further, the outcomes provide an important framework for ecological monitoring and impact assessments for future North Sea projects.

Description: Benthic food webs are very important as they provide food for higher trophic levels. However, during the last century North Sea benthos has been affected by different types of increasing anthropogenic pressures, such as fishing, windfarms and sand extraction. Studies concerning human activity consequences, especially the trawling effects on benthos, have shown changes in its abundance, biomass and production over various spatial and temporal scales. For fish, a decline in trophic level due to overfishing has been underlined both worldwide and for the North Sea. In general, the effects of human pressures on benthic communities are well understood and some studies have already highlighted that benthic trophic interactions can be regarded as being resilient by opportunistic feeding, i.e. most species being generalists, and trophic redundancy. However, there is still little detailed knowledge on benthic food web structure and trophic interactions of different habitats and communities. In this study, we investigated the trophic levels and food webs of the macroinvertebrates and demersal fish in two different North Sea benthic communities based on stable isotope analysis (13C /12C and 15N/14N ratios). The samples were collected from the Bathyporeia-Tellina and Central North Sea communities in the German Bight. For the first time, the food webs of these two communities were analyzed, by comparing trophic parameters, such as carbon sources, trophic levels and feeding types. Similarities and differences in the trophic structure between the two communities are discussed against the background of natural conditions and anthropogenic disturbances. Thus our results provide valuable knowledge and a sound scientific baseline for understanding trophic functioning in the context of marine management and sustainable use of marine resources.

Description: Understanding the role of biodiversity for ecosystem functioning has become a central research theme in marine ecology. Benthic communities with a higher diversity have been suggested to operate more effectively, which could be quantifiable as a higher secondary production. However, there is no general ecological relationship between diversity and production, not only due to environmental influences, but also because of species-specific effects. Functional diversity has been identified as the key to understanding the link between biodiversity and ecosystem functioning. We are taking a trait-based and large-scale observational approach to relate patterns in macrofaunal secondary production to functional diversity in the southern North Sea, where benthic macrofauna is confronted with many natural and anthropogenic stressors. Functional diversity is expressed in indices based on dissimilarities of species traits such as feeding type, environmental position, and larval development. Production is calculated with taxon-specific empirical productivity models. Patterns of functional diversity were spatially more homogeneous than taxonomic diversity. A handful of species provided the majority of the secondary production. Spatially implicit regressions are used to analyze how secondary production is related to environmental factors and trait diversity. We explore further whether models are improved by including specific key traits potentially contributing to energy flow. Knowledge on the explanatory value of trait composition for maintaining productivity in our system is needed to explore scenarios of anticipated changes in diversity.