Trophodynamics of chaetognaths in the Subtropical Convergence in the Indian sector of the Southern Ocean

Abstract

Trophodynamics of chaetognaths was investigated during the first Southern Ocean Ecosystem Variability Study within the vicinity of the Subtropical Convergence (STC) in the Indian sector of the SO during austral autumn (April), 2007. Total chaetognath abundance and biomass ranged from 0.37 to 6.88ind.100m-3and from <0.1 to 0.13mg Dwt l00-m3 respectively. Significantly (p<0.001) higher biomass values were recorded south of the front. Neither biomass nor abundance of chaetognathas indicated significant correlations with mesozooplankton biomass and abundance (r = 0.28 and r = -0.07 respectively). Four species of chaetognathas were identified within the study area, Eukrohnia hamata, Sagitta gazellae, S. zetesios and S. maxima. Of the species E. hamata accounted for 45% of total abundance and 18% of total biomass while S. gazellae accounted for 36% and 68%, respectively. Average lengths for E. hamata, S. gazellae and S. zetesios were 36.15 ± 9.85mm, 38.37 ± 8.16mm and 37.46 ± 7.42mm, respectively. The predominance of stages I and II indicated that chaetognaths were sexually immature. The mean feeding rate of E. hamata was estimated at 0.02 prey d-1 and 0.34 prey d-1 for S. gazellae. Combined predation impact of the two chaetognaths was equivalent to <0.1% of the copepod standing stock.