The Diversiity and Density of Macrobenthic Fauna in the Western Part of Lagos Lagoon and Adjacent Creeks
The study area of Lagos lagoon and harbour covers an area of 257sq. km. The spatial distribution of macrofauna was sampled at 30 stations between July 1987 and January, 1990. Six monitoring stations were sampled bimonthly between March 1988 and January 1990, to assess temporal variation in species diversity. Physico-chemical and biological parameters affecting the community structure were discussed. Salinity and sediment types were the major factors controlling macrobenthic faunal distribution in the lagoon and harbour. Faunal composition and diversity was low, and only twenty-three species were collected. Pachymenanis aurita, Aloidis trigona and Neritina glabrata were wide spread in the lagoon, but P. aurita was the dominant member of the faunal community. Nereis succinea was the dominant polycaheta in the harbour. Faunal indices suggest an unstable environment. The number of species in the monitoring stations were variable, but density of individuals was highest at Itedo. The life cycle of dominant species showed maximum reproductive activity during the dry season, between November and May. Recruitments of gastropod molluscs occurred twice a year in March and September, at Ikoyi, Ibase and Oworonsoki. Biomass and production estimates were calculated for the two most dominant species, P. aurita and A. trigona. P. aurita was the most productive, and had a mean annual production which varied between -1.59 and 0.79/0.5m2/yr. The production: biomass ratio varied between 0.02 and 0.12. The mean annual production of A. trigona was between 0.53 and 3.64g/0.5m2/yr. The production: biomass ratio of A. trigona varied between 0.29 and 1.79.