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Marine Biology (2004) 144: 11731182 DOI 10.1007/s00227-003-1282-6
RESEARCH ARTICLE
S. Fratini V. Vigiani M. Vannini S. Cannicci
Terebralia palustris (Gastropoda; Potamididae) in a Kenyan mangal: size structure, distribution and impact on the consumption of leaf litter
Received: 12 January 2003 / Accepted: 20 November 2003 / Published online: 4 March 2004 Springer-Verlag 2004
Abstract Although the role of macroinvertebrates in the nutrient cycling of the Indo-Pacic mangrove ecosystems is now a paradigm of ecological research, most of the research and scientic assumptions deal with decapod crustaceans alone. However, decapods are not the only representatives of mangrove macrobenthos and in certain mangals they are surely outnumbered by gastropods, especially by potamidids of the genus Terebralia. This paper aims at bridging the gap in the knowledge of the ecological role of the largest and most abundant potamidid species of the Indo-Pacic mangals, the semiterrestrial T. palustris. In particular we studied size structure and distribution in relation to micro-environmental factors and feeding ecology, both in terms of diet composition and grazing rate, of two populations of this gastropod colonising a Kenyan mangrove creek. In contrast to what has been described by various authors concerning other mangals, in our study site juveniles and adults of T. palustris were present throughout the whole forest, from the landward belt to the seaward fringe, locally reaching very high densities at various levels. Both life stages showed a preference for patches characterised by soil with high organic content; thus the habitat of juveniles largely overlapped with that of the adults, although they are known to occupy dierent ecological niches. Indeed, gut-content analysis conrmed that juveniles are detritivorous and adults are mainly leaf-litter consumers. In
situ experiments on the grazing activity of the adult snails showed that, in contrast to the litter-consuming crabs, they feed in every light and tidal condition, for an hourly consumption rate of $0.65 g per snail. Considering an average density of about 10.5 adults m)2,itis estimated that a total of 10.5 leaves m)2 are removed by adult snails in each tidal cycle (i.e. about every 6 h).T. palustris is the only leaf consumer capable of searching for food under water during high tide and is responsible for the removal of a great quantity of mangrove litter. The results...