Fatty acid compositions of gonadal material and diets of the sea urchin, Psammechinus miliaris: trophic and nutritional implications

The fatty acid compositions of gonadal material was examined for the sea ur chin Psammechinus miliaris (Gmelin) held in aquaria and fed either salmon f eed pellets or the macroalga. Laminaria saccharina for 18 months. Gonadal m aterial was also examined from P. miliaris collected from four field sites, including commercial scallop lines encrusted with the mussel, Mytilus edul is, sea cages stocked with Atlantic salmon Salmo salar and two intertidal s ea-loch sites, characterised by either a fine mud or a macroalgal substratu m. The fatty acid compositions of known and potential dietary material was examined. The proportions of certain fatty acids in the gonads of P. miliar is were significantly affected by diet type and location. Docosahexaenoic a cid (DHA) 22:6 n - 3 was significantly higher in the gonads of the sea urch ins fed salmon feed in aquaria and collected from the salmon cages and scal lop lines than in the gonads of the sea urchins fed L. saccharina in aquari a and collected from the intertidal sea loch sites. The salmon feed and the mussel tissue also contained a high proportion of this fatty acid. Stearid onic acid 18:4 n - 3 and arachidonic acid 20:4 n - 6, however, were found i n significantly higher proportions than DHA in the gonads of the sea urchin s fed L. saccharina and collected from the two intertidal sea-loch sites. L . saccharina was also found to contain high proportions of stearidonic and arachidonic acid. The gonads of the sea urchins collected from the intertid al site, characterised by a mud substratum, and from the scallop lines were found to contain a lower 18:1 n - 9/18: 1 n - 7 ratio and a higher proport ion of branched and odd-chained fatty acids, signifying a high dietary bact erial input, than the sea urchins held in the aquaria and collected from th e salmon cage. 20:2 and 22:2 non-methylene interrupted dienoic fatty acids (NMIDs) were found in P. miliaris fed diets lacking there fatty acids sugge sting de novo biosynthesis. These results, therefore, suggest that the prop ortions/ratios of certain fatty acids in the gonads of P. miliaris could he used to give an indication of the predominant diet type of this species in the wild. (C) 2000 Elsevier Science B.V. All rights reserved.