The Effects of Hypoxia on the Distribution, Abundance and Diversity of Benthic Macroinvertebrates of Lagos Lagoon, Nigeria

Abstract

The Lagos lagoon, Nigeria receives lots of organic wastes from anthropogenic sources. The biodegradation of these wastes by aerobic microbes has resulted in the depletion of the dissolved oxygen. Study of this area of the lagoon was conducted for two years to investigate the impact of hypoxia on the distribution, abundance and diversity of benthic macroinvertebrates. Water and benthic samples were collected monthly along the study stretch and analysed in a standard laboratory. Temporal variation in water physico-chemistry was largely controlled by rainfall pattern while the spatial variation was influenced by proximity to the Harbour as well as the pollution sources and types. A total of 3,159 individuals comprising three phyla, five classes, nineteen families and twenty three species were recorded. Iddo I, Iddo II, Ogudu and Agboiyi monitoring stations recorded very low individuals, but, relatively high number of polychaetes. Benthic macroinvertebrate community was dominated by the molluscs. Margalef's index of species richness ranged from 0.79 to 2.57 while Shannon-Wiener index ranged from 0.40 to 2.19. Species evenness index ranged from 0.29 to 0.80. There was generally low biodiversity indicating the stressed nature of the study area.