Population dynamics of clownfish sea anemones: Patterns of decline, symbiosis with anemonefish, and management for sustainability

Abstract

Giant sea anemones on Indo-Pacific coral reefs are important ecologically as hosts to obligate clownfish (anemonefish) and cleanershrimp symbionts, and also economically as major components of the global trade in reef invertebrates for ornamental aquaria. The population dynamics of these sea anemones remain poorly understood, but are vital to their sustainable management. I applied size-based demographic models to population information collected intensively during 1996-2000, and then again in 2013-2014, for the 2 major species of clownfish sea anemones on coral reefs at Eilat, Israel, northern Red Sea. High rates of mortality led to highly dynamic populations of both species. In turn, relatively low recruitment caused gradual population decline, which continued through 2014, when the abundances of both the anemone hosts and their fish associates were at all-time lows. The long-term decline of habitable sea anemones observed here significantly altered the anemonefish population structure, creating a negative feedback loop in which the fish changes then impacted their mutualistic hosts. Based on this long-term demographic analysis, including patterns of elasticity and population turnover, I provide recommendations for the sustainable harvest of these giant sea anemones on coral reefs. This demographic study reveals the processes leading to population decline in an important coral reef mutualism, as well as the urgent need for more scientifically-based management to prevent the local extinction of both mutualistic partners on these reefs.