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 Meganyctiphanes 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 carnivory. 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 proteinase 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.

Physiology and Metabolism of Northern Krill (Meganyctiphanes norvegica Sars)

“…Sargent and Falk-Petersen (1981) found that more than the half of total lipids in M. norvegica caught during winter (November/December) in Balsfjorden near Troms occurred as TAG and Saether et al (1986) found more than 70% TAG in the total lipids. Their contents varied strongly and (Kreibich et al, 2010;Saether et al, 1986) which shows that TAG serve as the major fraction of storage lipids in M. norvegica. Other lipid classes were present in amounts of less than 5% of the body dry weight.…”

“…The stomach and the midgut gland of M. norvegica are also rich in proteolytic enzymes (Buchholz, 1989). According to inhibition assays, the majority of endopeptidase activity results from serineendopeptidases, including trypsin-like enzymes (Dittrich, 1992b;Kreibich et al, 2010). A set of various digestive hydrolases was detected by Donachie et al (1995) in the stomach and in the midgut gland (Table 4.1).…”

“…Laboratory experiments showed that these bacteria seem to contribute to a lesser extent to the production of a range of enzymes, including chitinolytic and proteolytic Proteolytic enzymes Total proteinase (alk.) Azocasein Spindler and Buchholz (1988), Buchholz (1989), Donachie et al (1995), Kreibich et al (2010), Kreibich (unpublished), Saborowski (unpublished) Trypsin BAPNA, TAME Båmstedt (1988), Dittrich (1992a,b), Kreibich et al (2010), Kreibich (unpublished), Saborowski (unpublished Fevolden (1982), Donachie et al (1995) Valine arylamidase L-Yalyl-2-naphthylamide Donachie et al (1995) Cysteine arylamiadse L-Cystyl-2-naphtylamide Donachie et al (1995) Esterases and lipases Esterase (C2) 1-Naphthyl acetate Fevolden (1982) …”

“…norvegica is well suited to digesting food of both plant and animal origin. Moreover, it shows a certain degree of enzyme polymorphism (Fevolden, 1982) and comparatively high levels of enzyme activity (Kreibich et al, 2010). Seasonally elevated levels of activity of trypsin and amylase appear during the spring (Båmstedt, 1988), probably reflecting a higher metabolic energy demand at this time of year.…”

“…The functions of lipids and fatty acids in the physiology and the ecology of M. norvegica were studied either in relation to reproduction, as an energy store for overwintering, or as markers for nutrition. The amount of total lipids in whole body extracts of M. norvegica can range from as low as 7-8% DW (Kreibich et al, 2010;Saether et al, 1986), or 3.5% DW in krill from oligotrophic waters , to up to more than 40% DW . The lipid content and its composition depends strongly on season, location, sex, maturation, and, particularly, on the nutritive state.…”