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Does Primary Productivity Affect Benthic Macroinvertebrate Abundance and Diversity in Estuarine Ecosystem? A Case Study in Lagos Lagoon, Nigeria

Whether the level of primary productivity as expressed in the concentration of chlorophyll a (chl a ) in water and sediment affect the abundance and diversity of benthic macroinvertebrates in an estuarine ecosystem was investigated using data generated from a six month study in the Lagos Lagoon, Nigeria. Overall trends in physical variables were relatively inconsistent for study sites. Water transparency varied between 3 – 32 cm with highest and lowest values recorded in stations 1 and 3 respectively. Turbidity values varied inversely as transparency and directly with depth. Values were lowest in station 1 and highest in station 3. Two major macroinvertebrate groups (Annelida and Mollusca) made up of eight species were identified from a total density of 7820 ind/m 2 . Mollusca were the most abundant group with a density of 7800 ind/m 2 and accounted for 99.7 % of the total macroinvertebrate density. Significant difference (ANOVA, F = 8.282, p > 0.05) was observed in the density of benthic macroinvertebrate recorded in study stations. Of the eight species recorded, six occurred in all the study stations while the remaining two species were limited to station 1 (for Neritina glabarata ) and stations 1 and 2 (for Nereis lamellose ). Generally, values of chl a were higher in water samples than in sediment. The concentrations of chl a in water during the study months were significantly different (ANOVA, F = 8.883, p 0.05) during the sampling months with values highest in the month of March.. Relatively higher values of chl a in sediment was recorded in station 2. There was significant and positive correlation between macroinvertebrate density ( r s = 1; p 0.01), diversity ( r s = 0.45; p > 0.01) and chl a in sediment. Transparency of water correlated positively and significantly with chl a in sediment ( r s = 1; p < 0.01) and water ( r s = 0.8; p < 0.01). Turbidity and depth of water related negatively but significantly with chl a in water and sediment. Results obtained in this study suggest that primary production may influence benthic macroinvertebrate abundance and diversity in estuarine ecosystems.