Effect of rainfall cessation on the plankton abundance and diversity in a tidal tropical creek

Abstract

The abundance, diversity and temporal variation of plankton at Ogudu Creek in relation to the hydroclimatic factors were investigated for six months (October 2005 - March 2006). The physico-chemical characteristics of the creek were influenced by the seasonal change in water chemistry. Surface water was characterized by high total suspended solids (≥650 mg/L), low transparency (≤39 cm), high temperature (28.0 °C-35.0 °C), low dissolved oxygen (≤4.6 mg/L), high biochemical oxygen demand (≥260 mg/L) and acidic to low alkaline pH (6.65-7.50) throughout the sampling months. The study site was freshwater to low brackish (0.054 ‰ - 8.980 ‰). Plankton community structure was relatively low throughout the sampling period. Phytoplankton which comprised 37 species from 22 genera was dominated by the diatoms (29 species from 16 genera). Zooplankton had 4 crustacean species from 4 genera and was dominated by the calanoid copepods (44.45 %). A total of five zooplankton taxa were recorded: 78.34 % belonged to the Phylum Arthropoda, while 16.67 % belonged to the Phylum Chordata. Plankton taxa of environmental significance and already implicated to be pollution-tolerant recorded during this study were Nitzschia, Ulnaria, Oscillatoriaand Pinnularia.

Keywords: Organic pollution, physico-chemical characteristics, tidal dynamics, phytoplankton, zooplankton