Demographic modelling of giant sea anemones: population stability and effects of mutualistic anemonefish in the Jordanian Red Sea

Abstract

Giant sea anemones serve as important hosts for mutualistic anemonefish on Indo-Pacific coral reefs, but their population dynamics and turnover rates remain largely unknown. We used size-based demographic models to determine recruitment, changes in body size and mortality of bulb-tentacle anemones Entacmaea quadricolor and leathery anemones Heteractis crispa over 2years on coral reefs in the northern Red Sea, Jordan. Individuals recruited at consistent rates and grew rapidly until they reached ~300-cm2 tentacle crown surface area, then mostly remained static or shrank. Mortality rate decreased with body size, and the retention of large individuals strongly influenced population size. Individuals of H. crispa were more dynamic than those of E. quadricolor, possibly due to their hosting significantly smaller anemonefish. Both populations were abundant and stable but dynamic in terms of individuals, with estimated turnover times of only ~5 and 3years for E. quadricolor and H. crispa respectively. We conclude that some giant anemones may be short lived relative to their fish symbionts, and that stasis rates of large individuals disproportionately affect their populations. These results have implications for conservation management strategies of these major cnidarians on coral reefs, and indicate wide variation between species in the population-level effects of mutualistic interactions.