Ecology and toxicology of mangrove fauna in Tanzania. With particular reference to the mudskipper

Abstract

The aim of this study was to investigate the extent of pollution along the coast of Tanzania by studying the effects of pollution on the ecology and physiology of a resident mangrove fish, the barred mudskipper (Periophthalmus argentilineatus). Initially, the position and functioning of the mudskipper in the mangrove community was explored. The amphibious habits of the mudskipper were found to enable this species to minimise competition with other zoobenthivores through resource partitioning. Analysis of the stable isotope signature of various fish and macro-invertebrate species revealed that the mudskipper was the only fish species to which the mangroves presented an important feeding habitat. It was concluded that the mudskippers are the fish species that has the highest risk of exposure to pollutants in the mangroves, because of their exposure through feeding and their intimate contact with mangrove sediments. The mudskipper was identified as a valuable indicator of mangrove pollution. Subsequently, mudskipper populations from six mangroves along the Tanzanian coast were studied. It was found that the mudskipper population of the Mtoni estuary, near the city of Dar es Salaam, had an abnormal growth pattern and included individuals in which only one eye had come to development. These adverse effects indicate the occurrence of genetic damage. The effects were associated with a nearby textile dyeing mill which released highly embryotoxic effluents. The fact that adverse effects were only found in the Mtoni mangroves corresponded to the higher levels of pollution and isotopic enrichment relative to other mangrove sites. The results of this study reveal that the Mtoni Estuary is subject to severe pollution. The impact of pollution is still confined to the mangrove ecosystem, but already stresses the functioning of the mangrove ecosystem. This conclusion emphasises the importance of conservation of the mangrove ecosystem.