Understanding the trophic role of the Antarctic ctenophore, Callianira antarctica, using lipid biomarkers

Abstract

To better understand the trophic role of ctenophores in Antarctica during austral fall and winter, a major species of cydippid ctenophore, Callianira antarctica, was collected during April/May (fall) and August/September (winter) 2002 in the vicinity of Marguerite Bay. Lipid content, lipid classes, fatty acids, fatty alcohols and sterols were analyzed in animals, together with lipid biomarkers in krill and copepod species representing potential ctenophore prey. Lipid content in ctenophores collected in winter was slightly higher than from animals in fall (4.8 and 3.5% of dry weight, respectively). Polar lipids were the dominant lipid class in ctenophores, accounting for over half of the lipid content, with significant amounts of free fatty alcohols (more than 10% of total lipid content) detected. Lipid-class composition, however, differed significantly between seasons, with significant amounts of neutral lipid (wax esters and triacylglycerols) only detected in animals from fall. Although the dominant lipid classes in ctenophores varied between fall and winter, individual lipids (i.e., fatty acids, alcohols and sterols) showed only minor changes between seasons. Specifically, long-chain polyunsaturated fatty acids [20:5(n-3) and 22:6(n-3)] found in high abundance in larval krill were also elevated in ctenophores collected in winter. Very high amounts of monounsaturated fatty alcohols, particularly 20:1(n-9) and 22:1(n-11), known to be important components of wax esters in calanoid copepods, were also observed. Multivariate analysis using the suite of lipids found indicated that copepods are an important diet item for ctenophores in the study area. Results further suggest that C. antarctica feed actively year-round, with larval krill providing a food resource during austral winter.