Journal of the Marine Biological Association of India

Distribution of meroplankton in relation to the thermocline in the western Indian Ocean during day and night

Volume 33 Issue 1&2

T. Balachandran

Abstract

Based on 35 night and 27 day zooplankton collections made from a depth of 200 m to surface and the thermocline layer to surface, the distribution of meroplankton in relation to the thermocline was studied in the western Indian Ocean. The abundance of fish larvae both below and above the thermocline indicated that the thermocline is not a barrier for the distribution of larvae. Fish larvae showed nocturnal abundance. Their diurnal migration indicate that the major factor controlling the vertical migration is light rather than temperature. Fish eggs were found in large numbers in certain areas probably due to congregation of spawners. Larvae of bivalves and Anthozoa indicated nocturnal abundance influenced more by light than temperature. Larvae of sipunculoids and cirripeds mainly present below thermocline and Tornaria above thermocline showed nocturnal abundance. Actinotrocha and phyllosoma larvae were rare. A swarm of stomatopod larvae occurred in one collection. Cephalopod larvae indicating nocturnal abundance preferred the layer below thermocline. In general vertical migration of larvae were more influenced by light than temperature.

Date : 31-12-1991