Seasonal chaetognath abundance and distribution in a tropical estuary (Southeastern, Brazil)

Resumen

This study focuses on the seasonal variation of the chaetognath species in the Vitória Bay/Passage Channel estuarine system, Espírito Santo, Brazil, in terms of their abundance and distribution. Specimens of chaetognaths were collected between July 1997 and April 1998 at 10 sampling stations, with a cylindrical-conical plankton net of 200 µm mesh and 30 cm mouth, fitted with a mechanical flowmeter. Five chaetognath species were identified: Sagitta enflata, Sagitta decipiens, Sagitta hispida, Sagitta friderici and Sagitta minima. Most of them were distributed in areas of high salinity (e.g. at the stations closest to the outer estuary). The dominant species, S. enflata and S. friderici, were more frequent in the outer estuary where salinities varied from 32 (wet season - summer) to 28 (dry season - winter). S. friderici was the only species found right in the middle of the Passage Channel, at a station close to the main freshwater input into the estuary. Results showed that chaetognaths only enter the estuary due to the tidal effect, and that they are not typical residents of this system. This is to be expected because the group normally inhabits only truly marine regions.