Vertical distribution of zooplankton in relation to thermocline

Abstract

The influence of thermocline on the distribution of zooplankton was studied off the south-west coast of India based on the samples collected from the top most layer of the thermocline up to the surface and from 150 m below to the thermocline up to the thermocline depths. The thermocline depth varied from 30 to 125 m. Invariably, zooplankton biomass was high in the collections taken above the discontinuity layer. Copepods, chaetognaths and decapod larvae were all caught in higher numbers above the thermocline. Fish eggs showed a better representation below the thermocline and in the case of fish larvae, the difference was not very conspicuous. The general pattern of zooplankton distribution indicated a southward increase in their abundance. The role of thermocline in the distribution of zooplankton is discussed