The crown-of-thorns starfish (COTS) is a natural predator of corals in the Indo‐Pacific region, including the Great Barrier Reef (GBR). While they are native to the region, COTS are a leading cause of coral loss on the GBR. Since the 1960s, the Reef has experienced four recorded major outbreaks of COTS, with populations erupting approximately every 15 years.
As with the previous outbreaks, the fourth outbreak is thought to have started on reefs between Cairns and Lizard Island, and spread south, with outbreaks now found south of Townsville. In addition, an apparently independent wave of COTS outbreaks exists in the Swains, where there is currently significant coral loss due to COTS reported. Recent under water surveys and eDNA techniques suggest starfish numbers are building in areas north of Lizard Island, likely the initiation of the fifth recorded outbreak.
Crown-of-thorns starfish research during Great Barrier Reef spawning
During the spawning season, we conduct multiple experiments in which we raise COTS larvae until they can settle onto specific crustose coralline algae (CCA) in aquarium tanks. Most of these experiments test the importance of food (small algae) in the survival of the COTS larvae to investigate if increased nutrient runoff from land use changes or natural nutrient sources may cause COTS outbreaks, as well as testing global change-related factors.
Little is known of the natural diet of COTS larvae due to their small size - it is difficult to determine what food larvae have ingested using traditional methods such as microscopy. Following our success with eDNA based methods to identify larvae in the wild, we are testing whether these methods can allow us to also identify which algae they actually eat.
We also study the starfish's preferred diet during the little-known juvenile stages from when the larvae settle on rubble to the transition from algae eating to coral-eating starfish. Once we raise the young starfish for a few months, we also test which reef invertebrates are important predators of this species.
With help of SeaSim staff, we have developed a flow through larval culture system which allows raising larvae under more natural conditions. Larvae cultured in the SeaSim also assist in other COTS research, such as developing eDNA approaches to monitor COTS larvae and adults.
