a woman holds a petri dish with very small starfish in it. The camea is looking up through the petri dish at the sky, and up to the woman's smiling face.

Understanding crown-of-thorns starfish outbreaks

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 three recorded major outbreaks of COTS, with populations erupting approximately every 15 years.

A fourth outbreak is now in progress.  As with the previous outbreaks, it started on reefs between Cairns and Lizard Island, and spread south, with large numbers 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.  

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.

We also study their preferred diet during the little-known juvenile stages from when the larvae settle on rubble to the transition from algae eating to coral eating seastar. Once we raise the young starfish for a few months, we also test which reef invertebrates are important predators of this species. 

stage of COTS lifecycle under microscope
The crown-of-thorns starfish lifecycle

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. 

In 2023, we will have several visitors from the university of Otago who will work with us studying COTS larvae and juveniles metabolism.