Diversity and Spatial Structure of Benthic Macro-Invertebrates Community of Calabar River, Nigeria: Implications for Bio-Monitoring of River Environmental Quality

The study was carried out to ascertain benthic macro-invertebrates checklist in the Cross River, Nigeria and using it for bio-indication of the river quality. A total of 186 benthos specimens were collected. The phylum Insecta was most abundant (96) representing 51.61% of total benthos abundance; followed by Oligochaeta 60 (32.25%), Nemertea 10 (5.37%), Hirudiae 8 (4.3%), Cladocera 6 (3.22%), Asteroidea 4 (2.15%), and Gastropoda 2 (1.07%). At the species level, Chironomus was the most abundant (64) representing 34.4% of the total benthos abundance, and this was followed by Limnodrilus sp (11.82%), Tubifex (10.75%), and Eristalis (9.67%). The least abundant species were Myxas glutinosa (1.07%), Hirudo sp (1.07%), and the unidentified Asteroid (2.15%). Overall abundance in sampling stations ranged from 34 (Station 4) to 64 (Station 3) and comprised of 15 species, with the taxon Oligochaeta contributing the highest percentage of species (33.33%). This’was followed by Insecta (26.66%), Nemertea (6.66%), Asteroidea (6.66%), Cladocera (6.66%), Gastropoda (6.66%) and Hirudea (3.33%). Only two species Limnodrilus and Chironomus sp, were found in all the sampling stations. The range of diversity indexes were as follows: Margalef’s index (1,412 in Station 4 to 3.174 in Station 3), Shannon-Weiner Index (1.565 in Station 4 to 2.202 in Station 3), Pielou’s evenness index (0.8 in Station 2 to 0.97 in Station 4), Simpson’s Diversity Index (0.137 in Station 3 to 0.463 in Station 1). The comparative theoretical ranking of unhealthiness (CTRU) ranks station 4 as the best in environmental quality followed by stations 3, 2, and 1 in that order. Data from this study suggests that although Calabar River exhibited fragmentations in benthos species composition, abundance and diversity, the river generally is of satisfactory environmental quality and devoid of any evidence of significant pollution-triggered perturbation that is beyond its carrying capacity. (