Tidal Influence on Epiphyton Population of Okpoka Creek, Upper Bonny Estuary, Nigeria

Abstract. Okpoka Creek of the Upper Bonny Estuary in the Niger Delta is a sink under tidal effects. The study investigated the influence of low and high tides on the species composition, diversity, abundance and distribution of epiphyton. The epiphyton samples were collected monthly from May 2004–April 2006 at both tides from ten stations according to APHA methods. Epiphyton 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 (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 129 species of epiphyton were identified. Diatoms (35.4%) dominated the epiphyton population. Diversity indices of epiphyton diatoms were 0.9±0.03 (Margalef) and 0.5±0.01 (Shannon). Pollution-indicator species recorded at either or both tides were Navicula placentula, N. recognita, N. pusilla, N. similis, N. gastrum, Nitzschia bilobata, N. apiculata, N. lanceolata, N. acuta, N. sigma, N. linearis, Synedra ulna, C. menephiniana, Cocconeis placentula (diatoms), Cladophora glomerata, Scenedesmus sp (green-algae), Euglena acus (euglenoid), Anabeana spiroides (blue-green algae) and Ceratium furca (dinoflagellate). The presence of dominant diatoms, indicator species and high levels ammonia and phosphate indicate organic pollution and stress at both tides. Tide contributes to the perturbed condition of this creek. The study therefore suggests frantic environmental surveillance on the Upper Bonny Estuary to reduce the inflow of pollutants from the Bonny Estuary into this Creek caused by tide.