Size-related variation in arm damage frequency in the crown-of-thorns sea star,Acanthaster planci

Objective:To examine variation in the frequency of arm damage in different sizes of Acanthasterplanci(A.planci),assess how this damage is inflicted by fish predators,and infer the potential role of predation in population regulation.Methods:and arm damage frequency and severity was assessed.Frequency of arm damage was compared between sizes.Feeding behavior of fish predators was also observed in the laboratory.Results:This study demonstrates that sublethal predation by triggerfishes on A.planci result inDiameters of A.planci collected from three sites in the Philippines were measured extensive arm damage.Overall,60%of A.planci sampled across all sites had sublethal injuries.The frequency of individuals with missing or regenerating arms was highest in medium-sized young adults(11-20 cm),which coincides with the phase where A.planci shift from cryptic to exposed daytime feeding.Conclusions:The high incidence of arm damage within intermediate-sized sea stars indicates that predators exercise some level of regulation on A.planci populations at a local scale.Identification and protection of putative predators that target the most vulnerable life history stages of A.planci are essential in developing population control strategies and reverse sustained declines in coral cover.

Osmotic shock as alternative method to control Acanthaster planci

Objective:To test six osmotic stressors as alternative methods to control Acanthaster planci(A.planci)outbreaks by exploiting their incapacity to tolerate drastic changes in osmolarity.Finding more effective ways to control A.planci outbreaks is one of the most immediate and effective ways by which to reverse rapid declines in the abundance of live coral cover in the Indo-Pacific.Methods:A total of 10 mL of each of the following chemicals:sodium chloride,ethylenediaminetetraacetic acid,sodium carbonate,sodium cholate,sodium deoxycholate,urea and mannitol were injected into individual healthy sea stars to examine which chemicals induced disease and death.Results:Four out of six chemicals used in this study induced disease.Sodium chloride,sodium cholate,sodium deoxycholate and ethylenediaminetetraacetic acid are capable of inducing death in injected sea stars offering an alternative option to control A.planci outbreaks.Conclusions:Hyperosmotic stress is a viable alternative to control A.planci outbreaks as massive cell death results when acute hypertonicity exceeds a certain level.