The productivity, nutrients status and ichthyofauna of the Imo River estuary

Abstract

The productivity, nutrient status and ichthyofauna of the Imo River Estuary at Ikot Abasi, Akwa Ibom State, Southeastern Nigeria, were studied to establish the primary production, nutrient load and the predominating pathway of organic carbon production. Monthly sampling was done at fishing grounds designated as upper, middle and lower course of the estuary in the wet months of April to September 2011. The mean primary productivity of organic carbon was 1.2 x 109 gC/m²/day. Sediment nitrate and phosphate levels were 7.04 mg/kg and 1.28 mg/kg respectively. TOC was 7.194%C, representing 12.438% organic matter. Sixteen fish and shellfish species from twelve families including Chrysicthys nigrodigitatus, Tilapia niloticus, Lutjanus agennes, Ethmalosa fimbriata and Cynoglossus senegalensis were observed. The middle course had significantly higher primary productivity of 2.034±0.277gC/m²/day, nitrates in water (7.25±0.218 mg.l^-1), nitrate in sediments (12.198±0.365 mg.kg^-1), phosphate in water (1.457±0.180 mg.l^-1) and TOC in sediments (3.715±0.060 %C) than other locations (p<0.05). Autotrophic-heterotrophic production pathways of organic carbon were significantly different (P<0.05).

Key words: Productivity, nutrient status, ichthyofauna, Imo River estuary