Temporal changes in lipid biomarkers, especially fatty acids, of the deep-sea crustaceans Boreomysis arctica and Nematoscelis megalops: implications of their biological cycle and habitat near the seabed

Two species of benthopelagic deep-water crustaceans, the suprabenthic mysid Boreomysis arctica and the bathypelagic euphausiid Nematoscelis megalops were analysed in their lipidic composition, with especial emphasis on fatty acids, from specimens obtained in the north-west of Mallorca (Balearic Islands, western Mediterranean) at depths ranging between 650 and 780 m. Temporal shifts were studied seasonally, based on five cruises performed in August and November 2003, and February, April and June 2004, using a Macer-GIROQ suprabenthic sledge (0.5 mm mesh size). Evidences of omnivorous and carnivorous feeding habits were found for both species derived from their fatty acid and other lipid profiles. Boreomysis arctica showed a more varied fatty acid profile than N. megalops. This suggests that B. arctica feeds on a wider range of food sources and is a more opportunistic feeder. The high proportions of 16:1(n-7), 20:5(n-3) and 22:6(n-3) fatty acids in both species suggests a link between surface primary production and deep slope habitats, while markers such as 18:1(n-9) and the 20:1(n-9) and 22:1(n-11) fatty alcohols indicate a predatory activity, likely on calanoids. These components may arrive both via phytodetritus deposition to the seabed and by migratory movements of prey consumed by B. arctica and N. megalops close to the sea bottom. Seasonal changes in the total lipids and fatty acid composition of both species are related to the seasonal dynamics in their food sources, coupled with changes in the physiological or developmental stage of individuals. The proportion of total lipids and polyunsaturated fatty acids in the two species may be related to the different life histories of B. arctica and N. megalops. The mysid has direct development of embryos within brood pouches, so eggs with large amount of vitelum are generated and gonad is well developed. By contrast, the meso-bathypelagic euphausiids generate planktotrophic larvae, with a high number of free developmental larvae stages (from nauplius to Furcilia/Calyptopis), and eggs with poor storage of lipid compounds compared with B. arctica embryos.