Journal of the Marine Biological Association of India

Volume 13 Issue 2

Zooplankton distribution along salinity gradient in the Cochin Backwater before and after the monsoon.

K. K. Chandrasekharan Nair and D. J. Tranter

Quantitative studies were made on zooplankton collected along with hydrographic data from ten fixed stations in the backwaters of Cochin during the post and pre-monsoon period and collections were taken both by day and night.

During the post-monsoon period because of the previous heavy monsoonal rainfall and consequent influx of freshwater the estuarine salinity structure shoed a steep gradient (0.17%0-31.3%o ) and zooplankton biomass was high in those stations towards the mouth of the estuary (upto 562 mg/m3).

In the pre-monsoon period because of the lower rainfall and the instruction of sea water into the estuary, the whole system became highly saline with a weaker gradient (28.0%o-34.4%o) and the biomass and the faunal composition at the different stations showed remarkable variations (92-26782 mg/m3).

The temperature did not vary as much as salinity in either season, but slightly from day to night.

The overall changes in temperature-salinity and the associated changes in the biomass inside the system are closely associated with the monsoons and the changes effected by the adjacent coastal waters.

Date : 30-12-1971