Heavy metal accumulation of Littoraria scabra in coastal areas of Tanzania
Rashid, R. (2006). Heavy metal accumulation of Littoraria scabra in coastal areas of Tanzania. MSc Thesis. Universiteit Antwerpen/Vrije Universiteit Brussel (ECOMAMA): Brussel. 55 pp.
Samples of Littoraria scabra were collected from five mangrove areas along the Tanzanian coastline. Among those sites, Msimbazi and Maruhubi were polluted while Mbweni, Kisakasaka and Nyamanzi were unpolluted mangrove areas. All periwinkles were morphologically characterized, while their heavy metal content and trematode parasitic loads were determined as well. L. scabra from unpolluted areas were significantly bigger and more elongated compared to those collected from polluted areas. None of the analysed periwinkles were infested with trematode parasites. Determination of heavy metals using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) revealed that L. scabra from polluted areas had higher heavy metal levels in their soft tissues compared to their conspecifics from the unpolluted mangrove areas. The observed heavy metal patterns coincide with the spatial distribution of the shell variability and suggest a close relationship. Obviously, other stressors besides heavy metals may account for the observed shell patterns as well. Compared to the soft tissue metal data obtained in L. scabra from 1999 along the same area, there is an overall reduction of Copper, Manganese, Cadmium, Arsenic, Iron, lead especially in Msimbazi which is the most polluted area in Dar es Salaam city. Zinc, Aluminium and Chromium are still high. However, with the exception of Zinc all other soft tissue metal levels are not as high compared to the soft metal levels that can be found in littorinids that live in industrialized developed countries.It is concluded that the overall reduction of soft tissue metal levels in L. scabra goes hand in hand with governmental efforts which have been undertaken to reduce pollution in Tanzania. Nonetheless, an indirect adverse morphological relationship is still obvious in the polluted mangrove areas. Indeed, the shell size effect can only be eXplained by the fact that mortality rates in the polluted mangroves are higher and/or growth rates are lower.
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