Benthic grazers and suspension feeders: Which one assumes the energetic dominance in Königshafen?

Abstract

Size-frequency histograms of biomass, secondary production, respiration and energy flow of 4 dominant macrobenthic communities of the intertidal bay of Konigshafen were analysed and compared. In the shallow sandy flats (Nereis-Corophium-belt [N.C.-belt], seagrass-bed andArenicola-flat) a bimodal size-frequency histogram of biomass, secondary production, respiration and energy flow was found with a first peak formed by individuals within a size range of 0.10 to 0.32 mg ash free dry weight (AFDW). In this size range, the small prosobranchHydrobia ulvae was the dominant species, showing maximal biomass as well as secondary production, respiration and energy flow in the seagrass-bed. The second peak on the size-frequency histogram was formed by the polychaeteNereis diversicolor with individual weights of 10 to 18 mg AFDW in theN.C.-belt, and byArenicola marina with individual weights of 100 to 562 mg AFDW in both of the other sand flats. Biomass, productivity, respiration and energy flow of these polychaetes increased from theNereis-Corophium-belt, to the seagrass-bed, and to theArenicola-flat. Mussel beds surpassed all other communities in biomass and the functional parameters mentioned above. Size-frequency histograms of these parameters were distinctly unimodal with a maximum at an individual size of 562 to 1000 mg AFDW. This size group was dominated by adult specimens ofMytilus edulis. Averaged over the total area, the size-frequency histogram of energy flow of all intertidal flats of Konigshafen showed one peak built byHydrobia ulvae and a second one, mainly formed byM. edulis. Assuming that up to 10% of the intertidal area is covered by mussel beds, the maximum of the size-specific energy flow will be formed byMytilus. When only 1% is covered by mussel beds, then the energy flow is dominated byH. ulvae. Both animals represent different trophic types and their dominance in energy flow has consequences for the food web and the carbon flow of the total area. If the energy flow of the macrozoobenthos of Konigshafen is dominated byM. edulis, then the primary energy has to be gained from the pelagic primary production and the total ecosystem will be dependent on energy input from the North Sea and deeper parts of the adjacent Wadden Sea. In the case of a dominance ofH. ulvae, the energy flow of Konigshafen is mainly based on autochthonous primary production.