Crown of thorns thrives in warmer seas

Increasing ocean temperatures are supporting a boom in crown of thorns (COTS) numbers, a venomous starfish that poses one of the most significant threats to the Great Barrier Reef (GBR).

The research, most of which was carried out in the National Sea Simulator by scientists from the Australian Institute of Marine Science (AIMS), the University of Sydney and the University of Otago, has revealed that rising sea surface temperatures are contributing to the survival rate of the coral-eating seastar Acanthaster planci.

The COTS is native to coral reefs in the Indo-Pacific region. On healthy coral reefs, the starfish plays an important role, as it tends to feed on the fastest growing corals such as staghorns and plate corals, allowing slower-growing coral species to form colonies and helping to increase coral diversity.

“Warmer sea temperatures were found in this study to enhance COTS survival along with other, cumulative pressures on the reef,” said AIMS scientist Dr Sven Uthicke.

A 2°C increase in sea temperature can increase the probability of survival of COTS by 240% under certain conditions - such as the availability of nutrients for COTS larvae to feed on.

Recognising the synergistic effects of increased nutrient flows and sea surface temperatures on COTS survival will help scientists better understand COTS outbreaks.

COTS outbreaks place a significant stress on the survival of corals on the GBR. Research indicates that COTS outbreaks are a major contributor to the estimated 50% decline in coral cover during 1985 and 2012.

“Given that the most moderate climate change scenarios predict a 1-2°C increase in average sea temperatures, the present study further demonstrates the value of taking a holistic, multivariable approach to understand better how cumulative factors affect the survival of species such as COTS,” Uthicke concluded.

The study has been published in Scientific Reports.