Impact of thermal stress on the growth, size-distribution and biomass of estuarine populations of a benthic gastropod Pachymelania aurita Müller

Abstract

This paper reports an in-vivo account of the impact of thermal stress on the biomass and sizedistribution of estuarine populations of Pachymelania aurita in Epe Lagoon, Nigeria. Off all physicochemical variables investigated only water temperature was statistically different among study stations. A total of 7626 individuals of the organism comprising 2,371juveniles, 3586 immature adults and 2,034of spawning adults were collected from the study area. Highest populations of juveniles and immature adults occurred in station 3 where the highest water temperature occurred while, station 1 recorded lowest populations of the two size classes. Spawning adults occurred in highest number in station 2 while their lowest population was observed in station 3.Of the total biomass of 2491 g recorded, juvenile population recorded a total biomass of 143.401 g, immature adults contributed 874.424 g while spawning adults recorded 1473.19 g. Highest juvenile biomass (34.7 g) occurred in station 5 while, the least (17.7 g), was recorded in station 1. Station 3 accommodated the highest biomass (233.60 g) of immature adults and the least biomass for this group was observed in station 1.Biomass of the spawning adults was highest (475.08 g) in station 2 and the lowest biomass (162.03 g) for this class was observed in station 3. The elevated water temperature observed in station 3 affected the growth of the organism such that only few individuals developed to spawning adult. It is therefore important that, the regulatory agencies should carry out regular monitoring of cooling water discharge from Egbin Power Station to ensure compliance with stipulated laws.

Keywords: Thermal stress, gastropods, growth, biomass, size distribution