Community structure and bioturbation potential of macrofauna at four North Sea stations with contrasting food supply

Abstract

We investigated the macrobenth~c faunal composition, vertical distnbution, biomass, abundance and trophic structure in 4 North Sea sediments with contrasting quantity and quality of organic matter and with different hydrodynamic environments. The vertical distribution of macrofauna biomass generally followed the TOC (total organic carbon) profiles. The trophic structure reflected differences in relative quality of the organic matter In the high amount-high quality TOC sediment at the German Bight station, most organisms were found at shallow sediment depths (<2 cm), mainly feeding on freshly deposited or (re-)suspended material as interface or suspension feeders. Skagerrak sediments, containing a large amount of refractory organic matter, supported a small-sized deeply penetrating fauna (up to 20 cm) consisting mainly of deep-living deposit feeders and also endobenthic predators. Highest diversity of trophic groups, largest individual sizes and deepest distribut~on were found in sediment with organic matter of intermediate quantity and quality at the Frisian Front. The highly dynamic, coarse-grained Broad Fourteens sediments were very poorly inhabited, probably due to the extremely high hydrodynamic stress and low quantity of TOC. With the aid of a simple dlagenetic model, we analysed the potential effect of bioturbation on the distribution of food in the investigated sediments. The model predicted for a given bioturbation coefficient that total mineralization rate at depth reaches an optimum when the arriving material is of intermediate quality, whereas it is not possible for macrofauna to redistribute the organic matter up to depth when the quality of the arriving mater~al is high. The results of the diagenetic model agreed well with our characterization of the fauna community on the basis of pnncipal bioturbation categories (species causing surface deposition, biodiffusion, conveyor belt transport). Strong mixing by biodiffusion was observed at the station which had organic matter of intermediate quality (Frisian Front) and minimal mixing at the German Bight station, w h c h was charactenzed by the high quality of the arriv~ng organic matter

Marine benthic faunal successional stages and related sedimentary activity

“…Thus, the functional biodiversity, reflected in different feeding modes and mobility, correlated with increased salinity. On 4 stations in the North Sea, with similar salinities, Dauwe et al (1998) found instead that the different composition of trophic groups of the benthic fauna was related to food availability, which also was suggested by Pearson and Rosenberg (1987).…”

“…The brittle star Amphiura filiformis was one abundant species that was favoured by these changing conditions in food supply. In another study in the North Sea, Dauwe et al (1998) similarly found that the distribution of benthic communities was related to bottom dynamic factors and food supply. The highest diversity of trophic groups, largest individual sizes and the deepest distribution were found in sediment with organic matter of intermediate quality and quantity.…”

An approach for the identification of exemplar sites for scaling up targeted field observations of benthic biogeochemistry in heterogeneous environments

“…Activity levels are very low (Fig. 14) across the Celtic Sea shelf compared to other UK shelf areas (Dauwe et al 1998;Teal et al 2008), and similar across all sediment types observed. The median ( f-SPI L med , typical shortterm depth of mixing), maximum ( f-SPI L max , maximum extent of mixing over the long-term) and mean ( f-SPI L mean , time dependent indication of mixing) mixed depths of particle redistribution are presented in Table 6.…”

Benthos and demersal fish habitats in the German Exclusive Economic Zone (EEZ) of the North Sea

“…Species commonly found in the coastal habitat such as gobies, the pipefish Syngnathus rostellatus or the brittle star O. albida are known to have a high tolerance towards temperature and salinity variation (Ursin 1960;Knijn et al 1993). High nutrient input, together with a relatively long residence time of the water masses in the coastal habitat, could also result in intense algal blooms and, therefore, in increased food supply for benthic fauna (Dauwe et al 1998;Stöck and Kröncke 2001). Generally, most abiotic habitat characteristics changed gradually from the coast towards the Duck's Bill area (Table 4).…”