Seasonal differences in citrate synthase and digestive enzyme activity in larval and postlarval antarctic krill, Euphausia superba

Abstract

Antarctic krill maintain large population sizes despite dramatic seasonal fluctuations in food availability, but the mechanisms for this are still debated. The aim of this study was to compare seasonal differences in enzyme activity and respiration rates of larval and postlarval krill to provide insights into their overwintering strategies. Respiration rates, activity of the metabolic enzyme citrate synthase (CS), and those of the digestive enzymes laminarinase and total proteinase were measured in austral summer west of the Antarctic Peninsula, and in autumn in the southwestern Lazarev Sea. The 100-fold difference in chlorophyll a concentrations between the two studies is representative of the classic transition from a summer bloom to sparse winter conditions. Correspondingly, adult krill showed reduced respiration rates and CS activity in autumn. However, their digestive enzyme activity was significantly higher, suggesting more efficient assimilation of food at low food levels. Similar-sized larvae showed no summer-autumn differences in respiration rates and enzyme activity, supporting suggestions that they need to feed and grow year-round. However, trends in enzymatic activity varied between the larval stages measured, implying ontogenetic changes in body structure and function.

The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective

“…The respiration rates of freshly caught larvae from mid-winter are comparable with rates of furcilia from late summer and autumn starved for 1 week (Fig. 10a, Meyer et al 2002a). Oxygen consumption increased in larval krill with temperature (Frazer et al 2002a, b).…”

“…Additional evidence of metabolic depression in winter krill was the signiWcantly lower activity of the key metabolic enzyme citrate synthase (Meyer et al 2002a) and malate dehydrogenase (Donnelly et al 2004). Ambient temperature inXuences the metabolic rates of ectotherms (Gillooly et al 2001).…”

“…Larvae show no signiWcant diVerences in metabolic activity, measured as respiration rates, between summer and autumn, ranging from 0.7 to 1.4 l O 2 mg DW h ¡1 (Ikeda 1981;Meyer et al 2002aMeyer et al , b, 2003Meyer et al , 2009, whereas in winter, the respiration rates are only half of those in summer (Frazer et al 2002a;Meyer et al 2009). The respiration rates of freshly caught larvae from mid-winter are comparable with rates of furcilia from late summer and autumn starved for 1 week (Fig.…”

Physiological response of adult Antarctic krill, Euphausia superba, to long-term starvation

“…The homogenate was centrifuged at 5,000g and 4°C and the supernatant transferred into a fresh tube. From this supernatant, maximum activity of malate dehydrogenase (MDH; EC 1.1.1.37) was determined according to Teschke et al (2007), whereas activity of citrate synthase (CS; EC 4.1.3.7) was determined according to Stitt (1984) using previously described modifications (Meyer et al 2002b, Meyer et al 2010). Activities of 3-hydroxyacyl-CoA dehydrogenase (HOAD; EC 1.1.1.35), glyceralaldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) were measured as described in Auerswald and Gäde (1999).…”

Natural and AntHropic Impact Assessment on Biochemical and Histopathological Biomarkers of Fishes and Invertebrates at Coastal Region of Admiralty Bay King George Island

“…The lesions detected in cells, tissues or organs exposed to pollutants represent an integration of the cumulative effects of these substances at the biochemical and physiological levels (Meyer et al, 2002).…”