Episodic mortality of limpets on a shore platform at Rottnest Island, Western Australia

Abstract

Extended emersion of intertidal limestone platforms during periods of calm, hot, dry weather in summer episodically causes mass mortality of molluscs at Rottnest Island, Western Australia. Death of the abundant limpet Patelloida alticostata results in dislodgement from the substratum, revealing the prominent home scar. Empty home scars and empty shells following such an event in January 1991 were analyzed to estimate the prior population density (8-200, x̄=113 m⁻²), mortality rate (81%), size frequency distribution, and size selectivity of mortality on the highest intertidal platform, at Cape Vlamingh. Semiquantitative estimates of other gastropods indicate less severe mortality of 12 additional species. The effects were similar to but probably less severe than from a similar event in 1959. The time course of recolonization and population recovery of P. alticostata remains speculative. Available evidence strongly indicates more than 5 and fewer than 30 years are required, and the latter may overestimate by a factor of at least two. The best estimate of the time from mass mortality to high, persistent population density and size-frequency distribution may be about 10 years.