Preliminary observations on the benthic macrofauna of a polluted coastal lagoon in Ghana (West Africa)
Four species of gastropods (Lymnaea truncatula, Melonoides tuberculata, Turritella annulata. and Biomphalaria sp.) and three of insect larvae (Chironomus sp.. Peltodytcs sp. and Pseudagrion sp.), were sampled during a preliminary survey of the macrozoobenthos of a polluted Ghanaian lagoon (Fosu Lagoon; 1°16’W. 5°07’N) in January 1993. L. truncatula, constituted about 9 1 % of the biomass of tlie community, suggesting that it might be an ‘opportunist’ under the prevailing conditions in the lagoon. The estimated Shannon-Weiner index (H=0.34). and equitability index (J=0. 17), respectively, indicated a low species diversity and uneven distribution of individual numbers among the species comparcd with estimates for the macrozoohenthos in non-polluted or less polluted waters. Anoxic and low dissolved oxygen conditions attrihutahle to organic pollution, and unfavourable salinities, may be the principal factors accounting for the current state of diversity, distribution and abundance of the benthic macrofauna of the lagoon.