The Effects of Mangrove Habitat Degradation on Fish Abundance and Diversity In Ungwana Bay, Kenya.

Abstract

The inability to acknowledge the indirect economic importance of ecosystem goods and services generated by mangroves (ecological and physical values) is a major driving force behind mangrove degradation. Disturbances and degradation of mangrove ecosystem by human activities such as clear-cutting are increasing. To maintain a balanced ecosystem and sustainable resource use, it is essential to identify the impact such activities have on the ecosystem. Fish and sediment fauna are the natural resources that are affected by disturbances in the mangrove ecosystem. The objectives of this study were to describe fish assemblage and determine fish density in forested and unforested mangrove habitats. Eight microhabitats each 36m2 inside the forested and unforested mangrove sites at Ngomeni were sampled in spring tides using stake nets. Half of the forested and un-forested sites had either muddy or sandy substratum. Plankton and benthos were sampled using plankton net and plastic corer respectively. The mean density of fish ranged from 0.10 fish m-2 to 2.67 fish m-2 while biomass ranged from 0.26 fish m-2 to 10.89 fish m-2 in both forested and un-forested habitats. The data was analyzed to find out if there was any significant difference using ANOVA and means were separated with post hoc test at p < 0.05. There were significant differences in fish densities with respect to substratum type indicating that the fish community preferred muddy bottom forested sites to sandy bottom forested sites. Significantly higher fish abundance, biomass and mean length were observed in forested habitats compared to un-forested habitats. The un-forested sites showed significantly low density of fauna (copepods, polycheates, nematodes) in the sediments compared to forested sites. Muddy substratum sites had the highest fauna density compared to hard substratum ones. The copepods and nematodes were a major component of fish diet and they were also the principal fauna in sediments and water. Based on the findings of this study, abundance, composition, density, biomass and diversity of fish and fauna were higher in muddy substratum sites compared to sand ones, consequently in forested than unforested sites.