Crown of thorns eat their way outside and at home

A world’s first study of the Great Barrier Reef shows that crown of thorns starfish have the ability to find their own way home – a behavior that was previously undocumented – but only when their neighborhood is filled with their favorite food: coral .

Australian researchers watched the starfish emerge from their shelters in the afternoon so they could feed on coral at night before returning home at dawn.

“Crown-of-thorns starfish often partied all night, fell asleep, and only those with a well-stocked pantry found their way home – so it’s a very youthful behavior model,” said lead author Dr. Scott Ling of the Institute for Marine and Antarctic Research at the University of Tasmania.

“Their preferred prey is Acropora corals,” said co-author Professor Morgan Pratchett of the James Cook University’s Coral Reef Studies Center of Excellence (CoralCoE at JCU). Acropora is an important species of coral – they have been the building blocks of reefs around the world for two million years.

“When the Acropora populations declined, the starfish did not return home,” said Prof. Pratchett. “Their behavior is directly related to the local abundance of Acropora.”

The results of the study show that healthy reefs with high coverage of these corals can promote crown of thorns aggregations and eruptions. The eruptions are causing extensive, widespread and sustained coral loss throughout the Indo-Pacific region.

Similar examples of predator infestations that are destroying the environment include sea urchins that graze on kelp forests and coral reef fish that feed through seagrass patches.

The researchers used in situ time-lapse photography to track the movements of 58 starfish in the northern and southern Great Barrier Reef during an eruption in 2015. In the absence of their favorite acropora coral prey, starfish were typically homeless and instead migrated up to 20 meters per day.

“Unlike sea urchins, which can change their diet once they graze in kelp forests, the time-lapse monitoring results suggest that the starfish are consuming available acropora and ultimately feeding themselves outside and at home before looking for new food disperse, “said Dr. Said Ling.

Previous outbreaks on the Great Barrier Reef were recorded in 1962, 1979, 1993 and 2009. Although bulk coral bleaching is the greatest threat to coral reefs worldwide today due to global warming, the combined effects of bulk bleaching and crown of thorns eruptions are potentially catastrophic to coral reefs.

“By better understanding the behavior of these starfish, we can help prevent and control their outbreaks, which will help relieve pressure on coral reefs,” said Prof. Pratchett.

The study is published in the journal Royal Society procedure B..

Hidden Army: How Starfish Can Build Numbers to Attack Coral Reefs

More information:
The homing behavior of destructive crown-thorns starfish is triggered by the local availability of coral prey. Royal Society procedure B., rspb.royalsocietypublishing.or… .1098 / rspb.2020.1341

Provided by the ARC Center of Excellence for Coral Reef Studies