TROPHIC IMPORTANCE OF THE CHAETOGNATHS EUKROHNIA-HAMATA AND SAGITTA-GAZELLAE IN THE PELAGIC SYSTEM OF THE PRINCE EDWARD ISLANDS (SOUTHERN-OCEAN)

Trophodynamics and predation impact of the 2 dominant chaetognaths Euk rohnia hamata and Sagitta gazellae were investigated at 19 stations in the vicinity of the Prince Edward Islands and at a 24-h station occup ied at the sub-Antarctic Front in late summer (April/May) 1996. During the entire investigation, the zooplankton assemblages were numericall y dominated by copepods with densities ranging from 21 to 170 ind. m(- 3) Amongst the copepods, Clausocalanus brevipes, Metridia gerlachei an d M. lucens dominated accounting for >90% of the total. Generally, cha etognaths were identified as the second most important group composing at times up to 30% (mean = 14.7%) of total zooplankton abundance. Of the two chaetognath species. E. hamata was generally numerically domin ant. Gut content analysis showed that both chaetognath species are opp ortunistic predators generally feeding on the most abundant prey, cope pods. No feeding patterns were evident during the 24-h station, sugges ting that both species feed continuously. The feeding rates of E. hama ta ranged from 0 to 0.50 prey ind. day(-1) and between 0 and 0.90 prey ind. day(-1) for S. gazellae. The maximum total predation impact of E . hamata was equivalent to 5.2% of the copepod standing stock or up to 103% of copepod production per day. For S, gazellae the predation imp act was lower, reaching a level of 3.2% of the copepod standing stock or 63% of the daily copepod production. Chaetognaths can, therefore, b e regarded as an important pelagic predator of the Prince Edward Islan ds subsystem.