Seasonality in Cyclopoids (Crustacea; Copepoda) and rainfall variation of the Forcados River, Nigeria

Abstract

Investigations into the seasonality of cyclopoid (crustacean: copepoda) with regards to rainfall variations were carried out in Forcados river.  Samples were collected by towing two plankton nets of 55µm and 100µm mush sizes at 5knots for 5 minutes  behind an engine boat.  Meterological station in Warri gave the rainfall data.  Centigrade  thermometer was used for measuring the surface water temperature.  Results showed low temperature range (27.5ºC – 31.5ºC), while that of rainfall was high (25.8-602.6mm).  Eleven cyclopoid species were identified and they exhibited seasonality due to rainfall variations.  High numerical abundance was observed in rainy season months of June to September, with a peak in July.  Thus seasonality in the tropics is due to rainfall variations.