The Bioscientist (Aug 2015)
HABITAT DIVERSITY AND SPECIES RICHNESS OF BRACHYURAN CRABS OFF UNIVERSITY OF LAGOS LAGOON COAST, AKOKA, NIGERIA.
Abstract
The habitat diversity and species richness of brachyuran crabs of the University of Lagos Lagoon Coast were investigated from seven study sites. Six crabs species were collected and identified namely; Callinectes amnicola (Lagoon crab), Uca tangeri (Fiddler crab), Ocypoda africana (Ghost crab), Sesarma huzardi (Hairy mangrove crab), Goniopsis pelii (Purple mangrove crab) and Cardiosoma armatum (Land crab). The land crab Cardiosoma armatum showed the highest occurrence of all six species and was observed in all the study sites. Uca tangeri and Ocypoda africana showed low occurrence and low abundance where they occurred while Callinectes amnicola was the least occurring species. Site A had the highest species richness (0.7239) followed by Site B (0.7072), both having the lowest elevations of 13.72m and 11.58m respectively. The highest number of species was recorded at site A and B that had five species each. One crab species was each observed at Sites D and E which was the lowest, however these sites were located on higher elevations which were 21.03m and 18.29m respectively. The number of crab holes per site also followed similar pattern with sites A and B having the highest numbers recorded, 18.7x101 and 17.2x101 respectively and sites D and E having the lowest, 0.8x101 and 0.2x101 respectively. C. armatum had the greatest carapace length and heaviest weight, while C. amnicola the longest carapace width. The difference in mean length between left and right chelae of U. tangeri was pronounced when compared to other crab species. It was observed that high amount of oxygen, neutral or near neutral pH, relatively high salinity (6-80/00) and lower temperatures were preferred by these species of crabs. These physiochemical characteristics were present at most sites hence the relative high abundance of crabs within the University of Lagos campus.
