Assimilation of Dietary Sterols and Faecal Contribution of Lipids by the Marine InvertebratesNeomysis Integer, Scrobicularia PlanaandNereis Diversicolor

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Abstract
Feeding experiments were conducted to characterise the contribution of fatty acids, sterols and fatty alcohols to the faeces produced during feeding on starch by the marine invertebrates Neomysis Integer (Leach), Scrobicularia plana (da Costa) and Hediste (Nereis) diversicolor (O.F. Muller). The contributed fatty acids are generally less unsaturated than those in the animal tissues, indicating reabsorption or assimilation of fatty acids from lysed gut cells. The results suggest an enteric microbial contribution of fatty acids to the faeces as well as modification of the contributed lipids by digestive processes while still in the gut system. Cholesterol is also reabsorbed by Neomysis and Nereis and there is evidence that dealkylation of the sterols in the lysed gut cells may also occur. In addition, each of three species was fed separate diets of 14C-cholesterol and 14C-dinosterol, confirming that cholesterol is absorbed from the diet but that dinosterol is not. Furthermore, the 4-methyl sterol is not transformed into dinostanol or any other sterol. It is concluded that marine invertebrates make a significant contribution of lipids to their faeces, though the contributed lipids are not necessarily in the same distributions as in the animal tissues. Both dinosterol and dinostanol can be considered provisionally as quantitative dinoflagellate markers in marine food chains.