Population outbreaks of crown-of-thorns starfish (Acanthaster planci L.) represent one of the most significant, but also least understood processes, affecting coral reef communities. Several recent outbreaks have ended with rapid and dramatic declines in the abundance of starfish, which preceded depletion of prey resources (corals), suggesting that population declines may have been effected by extrinsic processes, such as predation and/ or disease. The purpose of my PhD research is to document the occurrence of potential pathogens in natural populations of A. planci at both low and high densities, explore the inherent susceptibility of A. planci to bacterial infections (mainly Vibrio species), and also assess the role of bacterial injections in ending outbreaks.
My research has already revealed that A. planci are extremely susceptible to bacterial (Vibrio) infections. Rapid mortality of A. planci occurs following injections of TCBS media culture (nutrients and vitamins) which inhibits the growth of gram-positive bacteria, suppress coliforms and promotes the growth of gram-negative (Vibrio) bacteria, inducing an homeostasis imbalance and activating natural virulence of Vibrio bacteria. Moreover, diseased starfish rapidly infect other A. planci within close contact, suggesting that this leads to activation of virulence factors (through quorum sensing) within their natural (normal) Vibrio bacteria microflora. This research suggests that Vibrio bacteria that naturally occur on and within A. planci may be responsible for rapid population collapse following some outbreaks. Further research is however, still required to assess how the virulence factors of their natural Vibrio bacteria are activated in the wild.