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Diversity and spatial distribution of zooplankton in the intertidal regions of Calabar River, Cross River State, Nigeria

Okorafor Kalu A., Andem Andem B., Mowang Dominic A. and Akpan Unyime U.

Studies on the diversity and spatial distribution of zooplankton in the intertidal regions of Calabar River in Adiabo River System were carried out for three months (September to November, 2012). A total of 28 species of zooplankton belonging to 23 genera and 9 taxonomic groups were identified. The most abundant zooplankton group at all stations was Calanoida (with 20 individuals at station 1, 32 at station 2, 30 at station 3 and 30 at station 4), thus constituted 48.2% of the zooplankton community observed in this study. Overall contribution of Cladocera was 14.71%, Chaetognatha 12.7%, Decapoda 9.64%, Lamellibranch 2.54%, Mysidae 4.06%, Rotifera and Salps contributed 3.04% respectively. Echinodermata was the least zooplankton group with 1 individual (1.02%). Species richness, diversity and evenness were assessed. Margalef index (R) varied between 6.377 and 7.256 indicating a slight variation in richness in all stations. Shannon-Weaver (H) ranged between 1.241 and 1.383 and Equitability between 0.376 and 0.420 showing that the species were evenly distributed in all stations sampled. The population of Zooplankton was generally high in the river system during the study period. This study provides vital details on zooplankton distribution and abundance along the intertidal regions of Calabar River, Nigeria which may unravel the information on the energy turnover of the river ecosystem. It will also serve as useful tool for further ecological assessment and monitoring of the river ecosystem.