Effects of Tide on Zooplankton Community of a Tributary of Upper Bonny Estuary, Niger Delta, Nigeria

Okpoka Creek is a tidal tributary of the Upper Bonny Estuary in the Niger Delta receiving organic anthropogenic effluents from Trans-Amadi Industrial Layout and the waterfront communities. The study investigated the influence of tide (low and high) on the species composition, diversity, abundance and distribution of zooplankton. The surface water and zooplankton samples were collected monthly from May 2004 – April 2006 at low and high tides from ten stations according to APHA methods. Zooplankton was identified microscopically. Species diversity was calculated using standard indices. Data analyses were done using analysis of variance, Duncan multiple range and descriptive statistics. Phosphate and ammonia exceeded FEPA and USEPA acceptable levels of 0.10 mg/L and 0.10 mg/L respectively for natural water bodies. Phosphate had significant tidal variations (P < 0.05). A total of 85 species of zooplankton were identified. Copepods (43.4%) dominated the zooplankton. Diversity indices of copepods were: 1.0±0.03 (Margalef) and 0.5±0.02 (Shannon). Most of the species were more abundant at low tide than high tide, suggesting retention and settlement in the Okpoka Creek at low tide. The presence of dominant copepods and high levels of nutrients (ammonia and phosphate) indicate organic pollution and stress. Increasing anthropogenic wastes especially dredged materials, slaughter effluents and raw human faeces lead to high organic loads. Concerted environmental surveillance on Upper Bonny Estuary is advocated to reduce the inflow of pollutants from the Bonny Estuary into this Creek caused by tidal influence.