J. moll. Stud. (1983), Suppl. 12A, 10-26 Proceedings 2nd Franco-British Symposium on Molluscs BIOGEOGRAPHIC AND ECOLOGICAL REMARKS ON MOLLUSCAN DISTRIBUTION IN MANGROVE BIOTOPES.

The mangrove forest ecosystem occupies an important part of the tropical and subtropical coasts of continents and islands. These forests have various biotopes available for molluscs and particularly for gastropods. They colonize roots, trunks, branches or leaves of the trees; but also, they show a zonation on neighbouring muddy substrates from the seaward fringe of the mangrove swamps to its landward one. The present work includes a survey and an analysis of the mangrove gastropods based upon published and unpublished data about world-wide mangroves. Remarks are made on abundance, trophic groups, morphological features and taxonomical relationships of these molluscs. The main conclusions are: —the drawing of a standard distribution schema of the principal families of gastropods for worldwide mangroves, taking into account the presence of vicariant species; —the analysis of the ecological factors responsible for the vertical and horizontal zonations of the faunistic assemblages; —the pointing out that the gastropod fauna of the mangroves is predominantly a soft bottom fauna belonging to the "sheltered muddy sediment community". Mangrove swamps are one of the main ecosystems occurring along the tropical and subtropical coasts. They are characterized by halophilous trees growing at the limit between the marine, freshwater,. and terrestrial environments. Four main types of mangroves are observed: —the large estuarine endbayed mangroves (ex.: Congo, Bangladesh and Amazon; the least studied), —the coastal lagoonal mangroves, —the littoral belt mangroves, and finally, —the TOtal reef flat mangroves (growing generally behind boulder tracks or atoll rim of the island). This peculiar ecosystem is inhabited by various zoo-logical groups; gastropods are among the dominant representatives of its epifauna