A field study on the physiology of digestion in the Antarctic krill, Euphausia superba, with special regard to chitinolytic enzymes

Abstract

Endo- and exochitinase activities were determined in the stomach and midgut gland of the Antarctic krill, Euphausia superba, along a transect west of the Antarctic Peninsula. Activities were compared with the digestive enzymes protease, cellulase (1,4-β-D-glucanase) and laminarinase (1,3-β-D- glucanase). The chlorophyll and protein contents in the surface water of the corresponding stations were determined. Enzyme activities were characterized by high individual and spatial variations. Chitinolytic activity in the stomach correlated well with all digestive enzymes investigated. In the midgut gland, a correlation with cellulase and laminarinase was evident. The amount of chlorophyll a and phytoplankton protein in the surface water was not correlated with enzyme activity. Specific enzyme activity was higher in the stomach than in the midgut gland, showing individual ratios for each enzyme. Elevated endochitinase activity in the stomach suggests that chitinous food is digested to oligomers in the stomach, while the subsequent degradation to amino sugars occurs predominantly in the midgut gland.