Mesoscale distribution and population structure of the chaetognath Serratosagitta tasmanica (Thomson, 1947) from Southwestern Atlantic Ocean

Abstract

Although Serratosagitta tasmanica is widely distributed, there is little information on how hydrology affects its distribution, abundance and demography. In this study we analyzed the distribution, carbon content and population structure of S. tasmanica in the Southwestern Atlantic Ocean. Samples were collected at 34°–39°S (Northern Argentine Continental Shelf in winters of 1999 and 2000) and at 47°–55°S (Southern Argentine Continental Shelf in spring 2005, summer 2006 and winter 2006). The analysis of more than 8500 individuals showed that its dominance decreased spatially from south to north, whereas biomass (mgC/m 2 ) increased temporally by three orders of magnitude between spring (4.06) and summer (12.7). In the southern area the presence of all maturity stages in all seasons suggests year-round reproduction, with maximum reproductive activity in winter. Body length increased with increasing latitude and decreased with temperature. We detected differences in the morphology of seminal vesicles and ovary length between mature specimens. In the northern area all individuals exhibited short-type ovaries whereas in the southern area individuals had either short or long ovaries, suggesting that some individuals of the latter area had been advected from the Southern Pacific Ocean through the water discharged from the Magellan Strait.