Quality differences in feeding areas of the red crab, Pleuroncodes planipes stimpson, as reflected from their lipid, fatty acids, and astaxanthin composition

The red crab or "langostilla", Pleuroncodes planipes, is abundant in the Pacific coast upwelling system of Baja California. It feeds both on plankton in the pelagic realm and on detritus in the benthic habitat. Previous studies of stomach contents suggested variations with latitude and depth, and potential differences in productivity. The aim of this study was to use the lipid and astaxanthin contents as well as the fatty acid composition of the red crab as a measure of its nutritional condition and thus of the quality of their feeding areas. Crabs were collected in September 1991 using a shrimp trawl at 6 stations on the continental shelf off the west coast of Baja California between 26° and 24°N. All samples were sun-dried and homogenized by grinding, prior to the extraction of total lipids. Astaxanthin content was also measured at each location. The methyl esters of the total fatty acids were analysed by capillary gas chromatography with flame ionization detection (FID). Lipids and astaxanthin contents varied significantly from shallow to deeper locations, and both organic compounds were significantly correlated (p < 0.05). The C16:0, C16:1, C18:0, C18:1, C18:2n-6, C18:3n-3, C20:4n-6, C20:5n-3, and C22:6n-3 fatty acids were identified and quantified. The most abundant fatty acid was C20:5n-3, ranging from 8.3 to 21.06 g/100 g TL, followed by C16:0 (3.4-14.10 g/100 g TL) and the C20:4n-6 (1.42-7.43). Fatty acids with the least statistical variation between locations were C18:3n-3 and C20:5n-3. Fatty acids from the different locations were found to be grouped into a latitudinal cline, suggesting red crabs are good indicators of areas with distinct food quality.