Distribution, abundance and biomass of Chaetognaths off São Sebastião region, Brazil in February 1994

Abstract

The distribution, abundance, biomass, population structure and feeding habits of chaetognaths collected off Sao Sebastiao region, Brazil, in February 1994 are described. Bongo nets were hauled obliquely to collect zooplankton samples. Forty-three samples obtained with the 333 urn mesh were analysed. In this study, 7 chaetognath species belonging to two genera were identified. Sagitta friderici, S. tenuis and S. bipunctata were grouped into the neritic category, and Sagitta enflata, S. hispida, S. minima and Krohnita pacifica into the semi-neritic group. The analysis of the community structure distinguished 3 zones: 1) a nearshore zone evidenced by low richness; 2) an offshore zone evidenced by higher number of species and 3) another offshore zone, located south and south-westward of Sao Sebastiao Island, characterised by higher richness but with dominance of one species. The nearshore zone was dominated by the neritic species S. friderici and S. tenuis, whereas the offshore zone was dominated by S. enflata. Abundance and biomass increase from nearshore toward offshore zones by about two orders of magnitude. Gut content analysis revealed over 90% of empty guts. The chaetognath population was composed mainly of juveniles. The diets among the different chaetognath species was very similar, composed mostly of small copepods and appendicularians.