Coral reef communities and the crown-of-thorns starfish: Evidence for qualitatively stable cycles

The interaction between the crown-of-thorns starfish, Acanthaster planci, and its prey, the coral community, is a major source of disturbance on coral reefs. It displays characteristic dynamics with variable time scales and is found with the same dynamics on reefs with different types of coral communities. The cyclicity and stability of these dynamics agree qualitatively with the stable limit cycles of current ecological theory. We argue that the analogy of these qualitatively stable cycles with stable limit cycles is compelling and warrants the qualitative extension of the theory to inherently variable systems such as coral reefs. We show that the evidence for what drives these cycles is ambivalent. The cycles may be purely endogenous, probably driven by asymmetries in response of prey and predator to each other induced through the archipelagic nature of the reef ecosystem. On the other hand, the cycles may be the result of exogenous perturbations mitigating an otherwise endogenous spiral to a qualitatively stable point-here called a metastable state. The existence of such qualitatively stable cycles and metastable states may cause problems for management of infestations since intervention could produce counter productive results.