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yields fall dramatically and grasses, phragmites and sedges or Derris invade the farms and working the farms becomes a problem. Therefore the farms are usually abandoned after this period. Digging of polychaete worms used as fish bait
in the Sonneratia and Rhizophora zones also result in ecological damage of the mangroves Semesi et al. 1999.
5.5.11 Natural impacts
Among the natural impacts affecting the conditions of mangroves are the diversion of water due to the flood and change of river courses, strong wave action, blocking of normal tidal flow due to sand deposition, and drought
which reduce the ground water seepage and create hypersaline conditions in some mangrove that are located landward. Therefore in places like the Rufiji delta there is a lot of natural changes in some mangroves because
they can be killed by being flooded for too long, but also new ones are continual formed in depositional areas. Besides those mangroves close to the shore where wave action has increased due to unknown factors we see poor
natural regeneration and sediments are washed away exposing some of the roots. This is quite common in Mafia Island, and some parts of Chwaka bay and Kaole mangroves for example. Mangrove die back due to unstudied
courses is also common such as in the Rufiji delta and Kilwa.
5.6 Scientific and management recommendations in the literature
5.6.1 Scientific recommendations
Every thesis and paper published has a list of recommendations. For example Hedman and Strandberg 1999 recommends that nutrient dynamics in different mangrove sediments and the function of mangrove, as natural
wastewater treating facility requires further study. They further caution that it must be kept in mind that the characteristics of a mangrove ecosystem cannot rely on generic model but must be based on local observations.
5.6.2 Conservationprotectionrestricted use recommendations
Since mangrove ecosystems are interlinked with both terrestrial and marine ecosystems, any management practice aimed at handling mangrove separately would probably be ineffective. Therefore Nasser 1994 recommended
that a comprehensive management plan of mangroves of Zanzibar be prepared under a broader plan of integrated coastal zone management that would cover both terrestrial and marine ecosystems. While Semesi et al. 1999
recommended that management which focuses on forest tree products should now be supplemented by considering the ecological services and the role of mangroves on capture fishery. Since assigning a direct
economic value to many and complex ecological services of mangroves is difficult, precautionary approach should be used when converting mangroves for aquaculture, or salt pans. They also recommended that no more
mangroves of Bagamoyo be allocated for prawn culture or salt production; already large areas have been allocated for these activities.
5.6.3 Local awarenessparticipationtraining recommendations
According to Semesi et al. 1999 foresters that are dealing with mangrove management needs training on mangrove ecology so that they can supervise the reforestation of clear felled areas. Government needs to provide
opportunities for the education of hotel developers on the importance of developing ecotourism, thus regarding and making use of mangroves as one of the tourist attractions instead of clearing them for sandy beaches Muruke
et al. 1999. In view of the present rate of exploitation and heavy dependency of the local communities for the economy on mangrove ecosystem, there should be a developed management system that would involve the local
people. The mangrove management plans of 1991 should be studied more carefully and ways of involving communities should be developed.
According to Wagner et al. 2000 monitoring of plantation trials should not only be done by scientists, but should involve citizen monitoring. Scientists should work with villagers and train them to gradually take over most of the
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monitoring work in a simplified form, though scientists should continue to be involved as advisors and to monitor aspects that require expertise.
5.6.4 Other if any recommendations
