Mollusc communities of tropical rubble shores of Curaçao: Long-term (7+ years) impacts of oil pollution

Mollusc communities of unpolluted and tar polluted rubble shores of intermediate wave-stress in Curaçao, were compared. At unpolluted sites, mollusc densities averaged in excess of 1000 snails, limpets and chitons m−1 of shorefront, while species richness averaged 20.7 species m−1 of shorefront. Shores massively soiled with crude oil in the past, but which have not been directly impacted by oil spills or significant levels of chronic fresh oil pollution since at least 1986, have retained high concentrations of tar principally in the coarse rubble zone at mid-shore level. Average mollusc densities (m−1 of shorefront) at such sites were 20.6% of those encountered at unpolluted sites, while mollusc species richness was 63.8% that of unpolluted sites. Mollusc densities and species richness were, respectively, log-linearly and linearly correlated with percent tar cover. Furthermore, the species composition of polluted shores was characterized by an increased relative abundance of littorinids and tidal bench species to the detriment of two planaxids, several neritids and other mid-shore species preferring the coarse rubble habitat.