Browsing by Author "Akwilapo, Flora Douglas"

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    Distribution and abundance of mangroves and benthic macrofauna in mangrove ecosystems showing different levels of anthropogenic degradation
    (University of Dar es Salaam, 2001) Akwilapo, Flora Douglas
    Five mangrove forest sites (one site each in Kisakasaka, Zanzibar, and Mtoni Kijichi in the Dar es Salaam estuary and three sites in Mbweni, North of Dar es Salaam) having different levels of anthropogenic degradation were compared. Mangroves were sampled using the Transect Line Plots (10-m X 10-m) method and, at random points within each plot, samples were taken for benthic macrofauna and key abiotic factors. All sampling was conducted in the rainy season and repeated in the same plots during the subsequent dry season. Among the five sites, Kisakasaka had the highest density, basal area and species diversity of mangroves which was attributed to the fact that it was the only site which has been protected from cutting in recent years. Probably due to the high abundance of mangroves, this site also had the highest substrate organic matter content and the highest density and diversity of macrofauna. On the other hand, one of the sites at Mbweni, which had been clear cut a few years previously, had the lowest density, basal area and species diversity of mangroves, the lowest organic matter content and the lowest density and diversity of macrofauna. The three other sites, which had been subjected to intermediate levels of human impacts, also had intermediate levels of mangrove and macrofauna abundance and organic matter content. Moreover, over the few months between the rainy and dry seasons, mangrove basal area decreased and stumps increased in the unprotected sites, but there was no change in the protected site. Macrofauna were more abundant during the rainy season than the dry season, probably due to higher quantities of organic matter and lower salinity levels during the rainy season. Crabs were the most abundant taxonomic group in all sites, followed by gastropods, polychaetes, prawns and, finally, mudskippers. The findings of this study point to the severe impacts of human activities on mangrove ecosystems and indicate the urgent need for more stringent protection of the forests. It is also recommended that mangrove ecosystem restoration should be undertaken.