Food utilization of two pelagic crustaceans in the Greenland Sea: Meganyctiphanes norvegica (Euphausiacea) and Hymenodora glacialis (Decapoda, Caridea)

Abstract

Large pelagic crustaceans from Greenland Sea waters, the northern krill Meganyc- tiphanes norvegica (Euphausiacea) and the decapod shrimp Hymenodora glacialis (Caridea), were captured in depths down to 1500 m and studied with respect to their physiological food utilization abilities. Both species showed distinct differences in the amount of total lipids (TLs), lipid class and fatty acid (FA) compositions as well as proteolytic enzyme activities. In M. norvegica, the overall amount of TLs and storage lipids was much lower than in H. glacialis, and triacylglycerols formed the major lipid fraction with a mean of 48% TLs. Major FAs comprised the trophic markers 20:1(n-9) and 22:1(n-11), indicating the ingestion of calanid copepods. Additionally, the FAs 22:6(n-3), 18:1(n-9) and 16:0 prevailed. In H. glacialis, TLs (mean = 44% dry mass) were about twice as high as in krill, with wax esters comprising up to 89% TLs. H. glacialis seems to accumulate these lipids as energy reserves to survive periods of food limitation. Moreover, high lipid levels, particularly wax esters, also help to maintain neutral buoyancy. The major FA in H. glacialis was 18:1(n-9); other dominant FAs were 20:1(n-9) and 22:1(n-11), typical of calanid copepods, as well as the diatom trophic marker 16:1(n-7). Both species showed omnivorous feeding behaviour with a strong tendency towards carni- vory. Total proteolytic activities in midgut gland tissue were higher in M. norvegica than in H. glacialis. In M. norvegica, proteinases were dominated by serine proteinases, whereas cysteine proteinases formed the major group in H. glacialis. High proteolytic activity in M. norvegica indicates a high digestive potential for proteins and efficient utilization of prey. The presence of different pro- teinase classes in both species may be due to different group-specific enzyme expression patterns between euphausiids and caridean decapods. Both species follow highly deviating life strategies, as reflected by their specific lipid and enzymatic characteristics.