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.
Polychaete worms: worms named for their bristles or 'Chaetae', which enable them to move rapidly through the water and to burrow. The most common is the writhing Neris, with an undulating fringe of chaetae up to 15cms in length.
(Note: polychaetes are NOT related to the myriapods.)
Molluscs: a large group of unsegmented animals, soft-bodied but often hardshelled. The group includes octopus and squid, but also mussels, oysters, periwinkles and snails.
Zooplankton: tiny animals including many Protozoa, minute crustaceans and the small larvae of larger animals.
Protozoa: single-celled microscopic animals.
Faeces: the residue of foods, bacteria and secretions expelled from the digestive system of animals.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.
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