Mollusk Response to Anthropogenic Impacts: An Example from Cross River Estuary, South Eastern Nigeria

The Mollusks of the Cross-River Estuary were sampled monthly between June and August during the rainy season using the direct search and litter-sieving methods. The results show that the extent of alteration of the natural ecosystem from anthropogenic activities could be deduced using the variations in numerical abundance and composition of mollusks in the environment. The most dominant mollusk communities in this study are represented by Neritina glabrata (30.29% during the first sampling and 49.08% during second sampling), Pachymeninx aurita (30.28% during the first sampling and 24.15% at second sampling), Tympanotonus Fuscatus (24.90% and 24.87% during the first and second sampling respectively) and Mactra glabrata (7.00% and 2.00% during the first and second sampling respectively). Low numerical abundance was recorded during the first sampling (241 individuals) as compared to the second sampling (381 individuals) which was attributed to the impacts of silt sedimentation caused by the dredging activities on the estuary in the first month of sampling. The general low diversity of mollusks assemblages recorded in this study reflects the strong impacts of anthropogenic activities. This study has demonstrated the fact that mollusk communities can be utilized as important marker for monitoring anthropogenic impacts and the state of health of the aquatic environment. The study however records various sampling variables due to the nature of the sampling methods. In order to obtain more precise data for a reliable assessment of anthropogenic impacts on the Cross-River Estuary, detailed study of the mollusks communities considering variables such as weather, season and salinity is therefore recommended.