Source and Fate of Lipids in Polar Gelatinous Zooplankton

Abstract

The presence or absence of accumulated lipids in arctic and Antarctic medusae and ctenophores was determined by visual examination of living specimens with a dissecting microscope. Lipid accumulations were obvious because of their high refractive indices. Lipids were seen in many of the 200+ gelatinous zooplankton specimens collected. They always consisted of various-sized droplets and larger masses within the lumen of the gastrovascular system. No true depot lipids or adipose tissue were present. The accumulation of lipids was observed in feeding animals, suggesting that the prey-derived lipids were unmodified. Disappearance of lipids in starved animals suggested that lipids are taken up and assimilated. In medusae, they occurred in the stomach, ring and/or radial canals. In most ctenophores, lipids were found in the meridional canals below the comb rows. However, in one ctenophore species, Mertensia ovum, lipids are stored in special sacs associated with the tentacle bulbs. Lipids were more frequently observed in arctic than in Antarctic gelatinous zooplankton. A review of the literature suggests that in the Antarctic, the average lipid content of gelatinous predators is about 3% DW (range = 0.4-6%), whereas in the Arctic it is nearly three times higher, about 8% DW (range = 1.5-22%). These differences are probably related to the amounts of lipids in their prey. The abundance of lipid-rich Calanus spp. copepods in the Arctic may be responsible for the high levels of lipids in gelatinous predators.

Key words: lipids, gelatinous zooplankton, ctenophores, medusae, Arctic, Antarctic, polar, feeding, starvation