The ecology of chaetognaths in the estuarine system of Goa

Abstract

Incidence, seasonal fluctuations and breeding of chaetognaths in the Mandovi-Zuari estuarine system were studied at twelve stations during the year 1971 to 1972. Chaetognaths constitute an immigrant fauna from the sea to the estuary and salinity appears to be the major factor controlling their distribution in the estuarine system. At the stations close to the mouth where annual variations in salinity were relatively less, they were found throughout the year, with maximum abundance from January to May. Towards the upper reaches, chaetognaths were absent during the monsoon period. Eventhough species diversity was greater at Mandovi Estuary quantitatively, Zuari Estuary, on the other hand, sustained a greater abundance of chaetognaths. Possibly the more marine conditions prevailing in the Zuari Estuary could sustain a higher density of chaetognaths. Of the six species encountered in the estuaries, Sagitta bedoti alone could be considered as a true inhabitant of this estuarine system. S. enflata was found during the period of relatively high salinity. Pterosagitta draco, S. ferox and S. robusta were accidental immigrants associated with the incursion of high salinity water into the system. S. pulchra was caught only in the first week of June. S. bedoti breeds throughout the year with three peak periods of heavy spawning