Juvenile Crown-of-Thorns Starfish (CoTS) Research

Juvenile CoTS on hard corals

Crown of Thorns Starfish are a natural coral predator within the Great Barrier Reef, however they can occur in outbreaks which devastate coral communities. In an outbreak the population of COTS can increase from <1 starfish per hectare to >1000 starfish per hectare. In these proportions they can devastate large sections of coral reefs.

Our observant team of Marine Biologists at GBR Biology, during their storytelling and reef health monitoring, noticed increasing numbers of these notorious starfish in 2008. In the following years after this 4th recorded outbreak on the Great Barrier Reef. Our team noticed that the number of CoTs was increasing, but there were more juveniles than Adults at our Reef Magic Site.

Interested to know why this section of reef was so high in juvenile numbers, we started our juvenile CoTS research project. In that time from the ~13,000 juvenile CoTS (<150mm) collected we have learnt:

• That our average juvenile size was ~70mm
• 3mm animal was the smallest collected
• Densities were greater than 100 individuals per hectare
• Densities started to decrease after the 2017 summer
• Individuals grow very fast when there is plenty of coral
• Individuals smaller than 70mm prefer one type of coral, the Bottlebrush corals.

This long-term juvenile research programme provides information on juvenile CoTS ecology that may be useful to innovative programmes involved with suppression of future outbreaks.

Juvenile CoTS on hard corals