Biogeochemical Changes in Lipids in a Model Marine Food Chain

Abstract This study investigates the effects of benthic feeding upon the lipid composition of material passing through marine food chains. GC and GC-MS were used to determine the changes in dietary fatty acids and sterols in a laboratory food chain involving the dinoflagellate Scrippsiella trochoidea , the pelagic shrimp Neomysis integer and the benthic mollusc Scrobicularia plana . Herbivory of Scrippsiella by both Neomysis and Scrobicularia involves preferential removal of algal polyunsaturated fatty acids (PUFAs) from the food and addition of branched fatty acids (BFAS) to the faeces. Both species contribute 4-desmethyl sterols and remove some algal 4-methyl sterols. Coprophagy of Neomysis faeces by Scrobicularia involves the addition of further BFAs as well as further animal sterols. There is a net removal of fatty acids and a net contribution of sterol in all feeding experiments. Faeces produced coprophagously have the greatest proportion of contributed animal sterol and branched fatty acids, reflecting the feeding by both species. The results suggest that observed fatty acid and sterol distributions in sediment surface material may result primarily from pelagic crustacean feeding, though benthic molluscan feeding in conditions of a settling bloom may give similar distributions. The coprophagy experiment suggests that the lipid distributions of sediment surface material are at least partially due to successive reworking of that material by benthic animals.