Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/95

The Brackish Ecozone inundation they also provide the nutrients to start food chains in associated rivers and estuaries.

Detritus-consuming animals include species of nematodes, polychaete worms, molluscs and crustaceans. They feed on the detritus itself and produce faeces; these are in turn consumed by microorganisms, which are themselves another source of food for the larger species. This is only the beginning of a complex but wonderfully productive aquatic system of interrelationships, including the following examples:
 * Small fin-fish feed both directly on the detritus and upon the polychaete worms. Their faeces are in turn a substrate for more microorganisms.
 * These small fin-fish are food for larger carnivorous and omnivorous fish, which are in turn food for even larger fish and for birds.
 * Large zooplankton feed on the larvae of crabs and other arthropods.
 * These zooplankton themselves support fish and prawns.

In this sense the mangroves of the Niger Delta are one of the most productive ecosystems in Africa, and are the beginning of a food chain that supports all the rich fishing grounds of the Bight of Guinea.

At the top end of this food chain, the dominant animals of the BAM ecozone are crustaceans, molluscs and fish. Compared with the neighbouring inshore and freshwater ecosystems, higher animal species diversity is low; comparatively few animals are fulltime residents of the mangrove forest. However, within the ecozone, greatest diversity is found in protected areas where there is strong ebb and flow of tides; here are also found high populations of crabs and mudskippers.

7.6 ANIMAL COMMUNITIES OF THE BAM ECOZONE

The animal groups are distributed as follows:

7.6.1 MOLLUSCS

Oysters (Crassostrea gasar) are found on stilt roots of Rhizophora. Periwinkles (Pachymelania aurita) and other species) are found on the floor of more protected areas. 93