Browsing by Author "Johnstone, Ron W."

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    The Development of a Scientific Forum in the Western Indian Ocean Region
    (1998) Kyewalyanga, M.; Francis, Julius; Johnstone, Ron W.
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    Effects of Intensive Seaweed Farming on the Meiobenthos in a Tropical Lagoon
    (Elsevier, 1995) Olafsson, Emil; Johnstone, Ron W.; Ndaro, Simon G. M.
    Open water aquaculture of the seaweed Eucheuma spinosum, imported to Zanzibar from the Philippines in 1989, is presently a large scale operation on the island, with algal farms covering around a 1000 ha of the intertidal area. To assess the effects of the farming on benthic communities both field and laboratory studies were conducted. Two field studies conducted at different times showed that all major meiofaunal taxa were found in significantly lower numbers within the farm area compared with control areas. Multidimensional scaling ordination of nematode species, genera and family abundance data separated samples from farmed and control areas. There was a significant difference in the nematode assemblage structure among areas in pairwise comparisons using ANOSIM. The trophic structure of the nematode assemblage was characterised by a high number of epistrate feeders in all areas ranging from 73 to 96% of total numbers in the samples. To test the hypothesis that toxic substances excreted by the seaweed were responsible for lower abundance inside the farm area, a laboratory experiment was conducted. Eucheuma plants were added to several microcosms and allowed to grow there for 40 days. The results indicated no effects of the seaweed on the density of the major infauna taxa as no significant difference was found among the treatments. It is concluded that other factors such as increased predation by benthic feeding fish and the mechanical disturbance of the sediments may better explain the observed differences in infauna abundance inside and outside the algal culture farms.
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    The Status of the Coral Reefs of Zanzibar: One Example of a Regional Predicament
    (1998) Johnstone, Ron W.; Muhando, Christopher A.; Francis, Julius
    Coral reefs are an important resource base for many coastal communities throughout the Western Indian Ocean region (WIO). With the continued growth of coastal populations and the concomitant increase in the need for marine resources, coral reefs stand at the face of overexploitation in many countries, and are being subjected to widespread degradation due to destructive fishing practices and pollution. Within this setting, the islands of Zanzibar exhibit almost all of the problems seen throughout the WIO, and so serve to exemplify some of the issues involved. Zanzibar has extensive coral reefs, which are actively used as a resource base by an increasing coastal population. At the same time, the expansion of urban areas and the development of coastal tourist facilities means that the coral reefs are coming under increasing pressure to provide even more resources than they have historically been required to deliver. At the same time, they are recipients of increasing levels of pollutants from expanding human populations, and they are subject to a range of physically destructive activities. In general terms, the reefs of Zanzibar are in comparatively good condition although there are clear areas of significant perturbation adjacent to certain urban areas and areas of high visitation. The main anthropogenic threats to the coral reefs of Zanzibar include overexploitation, destructive activities (fishing and anchor damage), and pollution. There are indications that overfishing of key species may be leading to a decline in certain economic species as well as ecological shifts in the benthic communities of some reef areas. As is often the case regionally, the lack of historical data limits attempts to resolve the true impact of some of these factors. In line with perceived local problems, a number of activities have been undertaken in Zanzibar to address specific coral-reef related issues, and these are discussed here in the light of the larger regional setting. Some discussion is also centered around the basic issues that undermine the sustainable management of coral reefs in Zanzibar, and how these problems are being dealt with in other parts of the WIO.