Bile salts and the single-shot lethal injection method for killing crown-of-thorns sea stars (Acanthaster planci)

Given the threat posed by population outbreaks of Acanthaster planci to coral reefs throughout the Indo-Pacific, significant investment is being made to reduce the number of sea stars and their effects on coral assemblages, both through ongoing direct control programs and indirectly, through targeted improvements in water quality and fisheries management. In Australia, bile salts have recently replaced sodium bisulfate as the chemical used to inject, and thereby quickly and efficiently kill, individual sea stars. This study reports on results of experimental studies conducted prior operationalizing bile salts for widespread use on Australiaʹs Great Barrier Reef, both to optimize doses of bile salts and further examine potential side-effects of administering low doses of bile salts into individual sea stars when found at high concentrations. This study showed that injecting A. planci with 10 mL of 8 g l−1 Bile Salts No. 3 or 12 g l−1 of Oxgall solution into the base of the arm with a new gun adapted with a 16 Gauge x1/2” needle is the most rapid and effective way to kill individual A. planci, which were up to 42 cm in diameter. No immediate flow-on effects on reef fish, corals, and other benthic invertebrates were observed in laboratory experiments and field surveys. Efficient control measures using bile derivatives can offer immediate relief from ongoing COTS predation, and when done in conjunction with improved land use practices that reduce nutrient input and establishment of protected areas to protect predator species, can offer benefits for the resilience of reef ecosystems.