Seasonal occurrence, distribution and diversity of phytoplankton in the Douala Estuary, Cameroon

Abstract

The occurrence and abundance of phytoplankton in the Wouri and Dibamba rivers and the Douala Estuary and their relationships to physico-chemical conditions were studied during the wet and dry seasons of 2008. One-hundredand-sixty-eight species belonging to 67 genera were identified. Ninety-two and 127 species were identified in the wet and dry seasons, respectively, including 51 common species. In the rivers, species richness decreased with increasing salinity, but in the estuary it increased up to salinity levels of 20.43 and thereafter decreased. The Bacillariophyta, including 101 species, was the most prominent division, whilst Euglena anabaena (24.98%) was the most abundant species. Cyclotella bodanica, C. ocellata, C. comta, Navicula sp., Gomphonema sp., Nitzschia sp. and Denticula sp. were present in all samples. Nitrate ranged from 107.5 to 129.9 mg l^–1 in the wet season and from 31 to 44 mg l^–1 in the dry season. Phosphate ranged from 0.04 to 0.38 mg l^–1 in the wet season and from 0.03 to 0.04 mg l^–1 in the dry season. Conductivity, temperature, total dissolved solids, and ammonium (NH₄⁺), nitrate (NO₃–), phosphate (PO₄^3–) and calcium (Ca²⁺) ions, were factors that influenced species diversity in both seasons. Species saprobity was in the ratio eutrophic (39.9%) > oligotrophic (30.4%) > mesotrophic (7.1%). The saprobic index was 0.15, and thus the water was eutrophic.

Keywords: abundance, diversity index, nutrients, rivers, saprobic index, trophic class

African Journal of Aquatic Science 2013, 38(2): 123–133