Comparing recent and abandoned shell middens to detect the impact of human exploitation on the intertidal ecosystem

Abandoned and recent shell middens were compared from Inhaca island, Mozambique, to investigate the impact of human exploitation. The growing human population was expected to increase the exploitation pressure, decrease the mean shell size, and increase the species diversity. Moreover, exploitation-vulnerable species were expected to disappear from recent middens. 29252 shells were collected from 6 recent and 8 abandoned middens, comprising 78 species, the majority bivalves. Pinctada nigra was the most abundant. The mean shell size was significantly smaller in recent middens, and the conspicuous, surface-dwelling gastropod Terebralia palustris showed the largest size reduction. Size reduction was related with the life history of the species. Older, abandoned middens had a larger species richness, refuting the intermediate disturbance hypothesis. The species composition of recent and abandoned middens was relatively similar, which was probably caused by low human exploitation pressure and the substrate characteristics. The disappearance of the mussel Perna perna was thought to be related to overexploitation.[PUBLICATION ABSTRACT]