Zooplankton variability and copepod assemblage in the coastal and estuarine waters of Goa along the central-west coast of India

Abstract

Seasonal variations in zooplankton distribution and community structure of copepod species in coastal and estuarine waters of Goa along the central-west coast of India are compared in relation to water temperature, salinity and dissoved oxygen, which were fairly well mixed in both environments during the seasons. However, at the onset of the southwest monsoon, surface cooling and a sharp drop in bottom oxygen occurred in the coastal waters indicating that upwelling was active, while in the estuary, salinity attained almost limnetic conditions as the monsoon progressed and slowly recovered during the postmonsoon season. These changes have tremendous influence on zooplankton production and copepod species distribution. While the highest zooplankton production was recorded in the coastal waters during the upwelling period (biomass: 2.6 ml.m sup(-3), density: 1047 ind.m sup(-3)), the lowest was recorded in the estuary (biomass: 0.03 ml.m sup(-3) density: 105 ind.m sup(-3)). Large carnivores and some typical coastal water taxa rare in the estuary. Copepods were predominant in both areas, but the coastal water population comprised 45 species against 28 species in the estuary. The estuarine copepod population dwindles during the low salinity period and several species move into the high saline coastal waters. On recovery of the salinity, they repopulate and flourish in the estuary. Copepods are generally grouped on salinity preference, and in this case 3 categories are recognized viz. wide (5-36 ppt), medium (5-26 ppt) and high saline species (26-36 ppt)