Effects of tides and seasons on the zooplankton of the Warri River, Niger Delta, Nigeria

Abstract

A field study was conducted between July 2014 and February 2015 on the Warri River, Delta State, Nigeria, to determine the effects of seasonal variation and tidal regimes on the zooplankton community structure of the water body. Zooplankton samples were collected from five (5) stations to cover high and low tidal regimes during the wet and dry seasons. A total of 20 zooplankton samples were sorted and organisms identified. Statistical analysis was carried out to ascertain the effects of tidal regimes and seasonal variation on the zooplankton community. Zooplankton comprised 43 species and 2180 individuals/m³ of water sampled. Cyclopoida (71%) were dominant, followed by Calanoida (20%) and Harpacticoida (9%); Diplostraca and Rotifera were less than 1 % each. The density of Calanoida, Cyclopoida, Diplostraca and Rotifera was significantly higher (P<0.001, P<0.05) during the high tide than in the low tide and during the dry season than in the wet season. Harpacticoida was however significantly higher during the low tide. The Bray Curtis and Jaccard similarity indices revealed that zooplankton samples were affected by tidal and seasonal dynamics. In general, seasonal variation and tidal regimes influenced the zooplankton of the Warri River. Results are therefore more authentic and holistic when sampling in coastal tidal rivers takes into account, tidal and seasonal variations. It is therefore recommended that sampling for environmental baseline data acquisition in tidal rivers be carried out to cover high and low tidal regimes and also the dry and wet seasons.

Keywords: baseline data, zooplankton, tides, seasons, dynamics, Warri River