What was done
Fringing and barrier reefs of a volcanic island in the Society archipelago of French Polynesia were surveyed for mollusc species in 1971 and again in 1995.

What was learned
Between 1971 and 1995, the number of mollusc species on the fringing reef declined by nearly 50%; but on the barrier reef, there was no statistical difference in species richness between the two observation times.

What it means
Over the quarter-century period between the two sampling dates, the study site was subjected to a number of natural disturbances: starfish plagues in 1980 and 1981, hurricanes and abnormally low sea levels in 1982 and 1983, and major coral bleaching events in 1991 and 1994.  In addition, human coastal populations in some areas increased nearly threefold and hotel capacity fully fivefold, with corresponding increases in waste water discharges into the sea.  Also, a large area just offshore was dredged for sand and rock between 1975 and 1979; and an artificial channel was constructed along the beach between 1977 and 1981, both of which activities increased local water turbidity and sedimentation.

These several natural and anthropogenic challenges severely impacted mullosc species richness on the fringing reef, close to the presence of humans; but they had essentially no effect on the mulloscs further out on the barrier reef.  We thus conclude that the mulloscs that were less prone to direct human impacts (those on the barrier reef) were able to successfully tolerate, or recover from, all of the natural disturbances to which they were exposed over the period of the study, as well as all of the indirect anthropogenic disturbances that might have reached them.  It would thus appear that the direct impacts of humans on mulloscs and their immediate environment are more detrimental than all other types of disturbances to which they are subjected, including periodic coral bleaching.