Hydrographic Conditions and the Macrozoobenthos of a Coastal Wetland in Ghana

I. Okyere, J. Blay, J. Aggrey-Fynn

Abstract


The prevailing aquatic environmental conditions and their effects on the composition of the benthic macro-invertebrate community were investigated in a few ephemeral pools in coastal Ghana along the Kakum Estuary (about 2 km west of Cape Coast; 5o 6' N, 1o 18' W). Water and benthic sediments were sampled every month from five pools in the wetland from July 2009 to February 2010, and were analysed for six hydrographic parameters as well as the species composition and mean density of benthos.

Significant changes occurred in hydrographic conditions during the year. Water temperature, salinity, conductivity, turbidity, dissolved oxygen and pH were relatively low in July 2009 (27.9 oC, 0.7‰, 1,503 µS cm 1, 78 mg L 1, 3.5 mg L 1 and 6.9 respectively) but increased progressively to 46.6 oC, 5.7 ‰, 12,777 µS cm 1, 304 mg L 1, 5.7mg L 1 and 8.62, respectively, in January 2010. Chironomid larvae (Diptera) and oligochaetes were the only benthic fauna encountered. These organisms were abundant in the wet season (July –September 2009), with mean density of 258 to 1,375 individuals m-2 for diptera, and 81 to 203 individuals m-2 for oligochaetes. Their abundance and density however declined progressively during the dry season (November 2009 – January 2010) after which they were not found.

The increase in salinity stressed the macrozoobenthic fauna during the dry season leading to their extermination. The ephemeral nature of the environment conceivably resulted in the poor diversity of macro-zoobenthic fauna, and this could limit the development of the fish community.


Keywords


Marsh; Pools; Hydrographic Parameters; Benthic Macroinvertebrates; Species Composition; Population Density

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