Biological control of Biomphalaria glabrata, the intermediate host of schistosomes, by Marisa cornuarietis in ponds of Guadeloupe: long-term impact on the local snail fauna and aquatic flora

The efficiency of Marisa cornuarietis, a Venezuelan freshwater prosobranch was tested against Biomphalaria glabrata, a pulmonate snail which plays the role of intermediate host of human schistosomes in the Caribbean area. M. cornuarietis was introduced to 15 experimental ponds in Guadeloupe, while 15 control ponds were left unchanged. Populations of all species of freshwater molluscs as well as representative plant species were followed for the 13 subsequent years in all ponds. B. glabrata rapidly disappeared from experimental sites, probably because M. cornuarietis consumed plant species that constitute its most favorable habitat. Importantly, no other mollusc species was affected by the presence of M. cornuarietis. Moreover, M. cornuarietis remained in the sites of introduction only and did not spread. This species therefore showed little invasive capabilities compared to other possible control agents. Because of its metapopulation dynamics, the occurrence of B. glabrata may decrease not only in sites where competitors are introduced, but also in sites without competitors, because of lowered overall colonization rates. We discuss the possible importance of this effect and that of various competitors including M. cornuarietis, Biomphalaria straminea, and Melanoides tuberculata, in explaining the long-term collapse of B. glabrata in Guadeloupe over the last two decades. This study shows that M. cornuarietis is a very efficient control agent.