Jozani biodiversity inventory report 2002 - Coastal Forests of Kenya ...

In Chwaka Bay some fishers use fishing techniques and gears which are illegal including
dynamiting and poison fishing. These techniques are unselective and kill large numbers of
invertebrates that are then not harvested (IUCN, 1990; Salvat, 1987). Some fishing gears that
are illegal in the area include small mesh size fishing nets and harpoon guns. Many marine
organisms, including corals, sponges, molluscs, echinoderms, puffer and tiger fishes are
collected widely for the curio trade and jewellery (IUCN, 1990; Martens, 1992; Wells, 1988).
Physical alteration and habitat loss
Organisms are adapted to specific abiotic environments, the conditions in each place are
crucial in determining the community of species that live there. Dugan and IUCN (1990)
reported that vast areas of mangrove, estuaries and beaches are cleared for activities like
aquaculture a common practice in many developing countries. Since more valuable and
commercially important fish species depend on these coastal habitats as nursery grounds their
survival is thus threatened. Also some fishing methods like beach seining disturb the seabed
and cause physical damage and reduced photosynthesis caused by suspension of sediment
(Salvat, 1987).
In Chwaka Bay there are various activities which cause physical alteration and habitat loss.
The human population increase and increase of the tourism industry are potential threats to
the area. Other activities causing the physical alterations in this area are construction, clearing
for aquaculture, and dynamiting of the coral reefs, which cause serious beach erosion.
Negative impacts of tourism includes trampling, and boat anchoring on the coral reefs
(Martens, 1992).
Pollution: human sewage (together with pathogenic organisms) and aquaculture runoff (with
increasing amounts of inorganic fertilisers) which are rich in nitrogen and phosphorous, form
a major source of pollution of coastal waters.
Chemicals such as trace metals and petrol residues become toxic environmental contaminants
when discharged in excess concentrations. Increased use and disposal of plastics, solid wastes
and debris cause widespread mortality in marine species through entanglement and ingestion
(Carr, 1987).
73