Hydrochemistry and community structure of benthic macroinvertebrates in Ilaje coastal waters, Ondo State, Nigeria

The water chemistry and benthic macroinvertebrates assemblage of fifteen study stations in the Ilaje, coastal waters of Ondo State, Nigeria were studied from October 2013 to March 2015. The spatial variation in salinity, conductivity and total dissolved solids showed a transition from saline at stations close to the Atlantic Ocean to fresh water conditions at stations farther away. Except for the total dissolved solids and conductivity that showed a significant difference (p<0.05) among the study stations, other measured parameters were not significantly different (p>0.05). Zero salinity was recorded at Alagbon, Ayetoro and Ugbonla study stations throughout the study period depicting minimal or no tidal influence. Species diversity and richness of the benthic macroinvertebrates were extremely low at stations located at the extremes of the study stretch. This could be attributed to poor euryhaline tendencies of the macrobenthic community. The relatively high abundance of nereid polychaetes and the low abundance of the filter-feeding bivalves and the sensitive arthropod species in the study area may be indicative of organic pollution of the area. The benthic fauna are needed for a balanced energy transfer in the food web and their existence must be guaranteed by ensuring healthy aquatic ecosystem. Benthic studies therefore, need to be intensified in the Niger Delta as adequate baseline reports are lacking.