An assemblage of 343 species of cryptic, shelled molluscs was identified in three large samples from shallow subtidal and intertidal shelter habitats under rubble and corals at Malololailai Fiji in 1983, 1984, and 1985. One species was a polyplacophoran, 273 were gastropods (38 families), and 69 were bivalves (21 families). Cryptic gastropods were more abundant than bivalves, but showed a reduction in abundance relative to bivalves from 1983 to 1985. The abundances of many cryptic molluscs show dramatic adjustments from 1983 to 1985, chiefly due to hurricanes in 1983 and 1985, showing a decrease in equitability with increased physical disturbance. The abundance and diversity of molluscan predators in the crypts means that predation in these habitats may be substantial.
The gastropod sample diversity showed the greatest change during the 1984 post-hurricane recovery period. The 1985 hurricanes affected the sample diversity by shifting the gastropod diversity closer to what it was after the 1983 hurricane. The bivalves underwent a similar shift in sample diversity, although larger numbers of individuals in proportionately more species survived the hurricanes.
The cryptic bivalves exploited space in new crypts, while maintaining their rate of increase in abundance in the recovery period after the 1983 hurricane and through the two hurricanes in 1985. The gastropods declined in abundance after the 1983 hurricane. They recovered after the 1985 hurricanes by doubling their abundance, showing that they could exploit new resources in crypts. This increase in the gastropod population was not proportional to the increase in available cryptic space. This may mean they were still recovering in August 1985, or they may have been unable to capture their portion of cryptic space in competition with other organisms during recovery.
The 1985 hurricanes did not have much effect on the overall molluscan diversity, a possible result of pruning by the 1983 hurricane of molluscs unable to survive storms. Because there was only a short interval between the hurricanes, many molluscs that survived the 1983 event were still in the population, so that the cryptic molluscs probably were better able to deal with the effects of the 1985 hurricanes than they would have been before the 1983 hurricane. The result was that the sample diversity after the 1983 hurricane increased during the recovery period but did not decline later even though the population was devastated by hurricanes in 1985. This lends support to intermediate disturbance models linking increasing or stable diversity with disturbances spaced at intervals allowing recovery.