Decline in biodiversity of copepods in coastal waters of Mumbai
Abstract
Coastal waters of metropolitan cities face severe ecological threat due to sewage discharge and effluents from the industries. Copepods being the most abundant component in zooplankton some species can act as signals of alterations of water quality. Analysis of biological communities is adopted as an effective tool for indicating environmental conditions. Baseline studies were conducted on water quality and species composition of copepods along the coastal waters off ThaI (Mumbai), the location proposed for installing large fertilizer plant in 1980's which was repeated after a decade. Hydrography of the water at Thai was normal where 24 species were recorded in the baseline study. But in the post outfall study the suspended load and the nutrient level especially nitrate and ammonia showed marked increase and the number of copepods decreased to 8 species at the discharge point. Copepods were also studied from Mumbai harbour from4 sites namely Thane, Bassien, Versova and Mahim creeks upstream where sewage and other discharges are slowly converting the area into an imperilled ecosystem. Nutrients were high during pre-monsoon; P04, 42.0~k at/I and N03, 43. O~k at/I, being the highest values recorded. The suspended load in the creeks were high namely 87.5mgll during pre-monsoon and 121mgll during post-monsoon. The upper reaches of the creeks sustained high nutrients and suspended load and low density of zooplankton and diversity of copepods. Species diversity was high in the coastal stations away from the mouth of the creeks. From the Bassein sector 33 species were recorded whereas 35 species were observed in Thane sector. Only 10 species were encountered in Versova and Mahim compared to 68 and 46 species recorded two decades back. Bestiolina similis and Acartia spinicuda together accounted for the copepod standing stock in both localities. Average density of copepods at Thai is very high (2716/m<sup>3</sup>) compared to the Mumbai coast (Mahim310/m<sup>3</sup>versova 213/m<sup>3</sup> and Thane 185/m<sup>3</sup>).The hydrographical features point to habitat degradation.
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