During this thesis, the epibenthos (demersal fish and macro-invertebrates) of the seagrass beds and mangrove creeks of Gazi Bay were sampled during the day at 30 different locations with a fine mesh beam trawl (mesh width 6 mm). Sampling occurred in the east creek, west creek, connecting creek and the intertidal and deeper parts of the bay. The spatial patterns of the epibenthic communities were investigated by multivariate analyses (cluster analysis, Twinspan, correspondence analysis). In total, 5947 individuals were caught, belonging to 118 fish species and 133 species belonging to other taxa such as Mollusca, Echinodermata, etc. The fish were divided into 8 orders and 30 families. The stations were divided in 6 communities according to density and species composition. A first community was typical for the upstream area of the west creek. This community showed the lowest average density and also a low diversity, and was constantly split off based on the absence of Leptoscarus vaigiensis. The most abundant species in this community was Metapenaeus monoceros. The stream downward sampling locations of the west creek belonged to the second community, but also two stations of the connecting creek namely, BT18 and BT19 belonged to this second community. Community II had the second highest diversity and density. Sebastapistes slrongia is the most abundant, together with Leptoscarus vaigiensis and Siganus sutor. Community III comprised the shallow western region of the bay and showed the highest diversity and density. Arcuatula capensis was the most abundant in this community that was mainly present in BT13. Community IV comprised the shallow eastern region of the bay, and was characterized by a moderate diversity and density. Cypraea annulus and Leptoscarus vaigiensis were dominant species here. Community V comprised the deeper located sampling station and had a relatively low density, but a higher diversity. Leptoscarus vaigiensis was the dominant species. Community VI did not form a contiguous area, because the stations were relatively distant from one another. This community showed a low density and the lowest diversity. Based on the measured lengths of the fish, it can be concluded that all caught fish were in their juvenile phase. This is a strong indication for the importance of the seagrass beds as a nursery. The importance of a nursery can be explained by the habitat structure and the protection against predation, but also the production and availability of food are crucial factors. In the east creek, the first two factors are decisive, while in the west creek the nutrient supply could also play a crucial role. |
