Reef fish, such as emperors, tropical snappers, and rockcods, help control the number of coral-eating crown-of-thorns starfish on the Great Barrier Reef. –ScienceDaily

Reef fish, such as emperors, tropical snappers and rockcods, help control the number of crown-of-thorns starfish on the Great Barrier Reef, according to a new study from the Australian Institute of Marine Science. Coral.

Published today in Nature Communication, the study found that the abundance of coral-eating starfish increases where the fish species known to eat starfish are suppressed.

Crown of Thorns Starfish (acanthaster spp.) are native to Indo-Pacific coral reefs. They are a major contributor to coral loss when found in large numbers, as they feed on the living tissues of many hard coral species. On the Great Barrier Reef, four outbreaks have occurred since the 1960s – the most recent is still ongoing.

“More than 50 years ago, it was feared that predator removal could contribute to starfish outbreaks. However, at the time, only one predator of the starfish was known, the sea ​​giant newt,” said Dr Frederieke Kroon, AIMS ecologist and lead author. .

“Recent studies have revealed that nearly a hundred species of coral reef organisms feed on different life stages of the starfish. popular seafood species such as emperors, tropical snappers and rockcods.

“Our study is the first to explore how harvests of these fish species may affect starfish abundance.”

First, the team compared long-term data from AIMS on the abundance of coral reef fish and starfish collected from open and closed reefs. On reefs closed to fishing, the biomass of emperors, snappers and cod was 1.4 to 2.1 times higher and densities of starfish almost three times lower than those on reefs open to fishing. the Peach.

“It is well known that no-take marine reserves increase fish biomass and the diversity of large fish. Previous studies have suggested that marine reserves may also influence starfish numbers, but our study provides strong evidence that there are fewer crown-of-thorns starfish on reefs with more predatory fish,” Dr Kroon said.

Scientists also compared 30 years of reef fish harvest data from the Queensland Department of Agriculture and Fisheries with crown-of-thorns starfish abundance data from Long-Term Reef Monitoring. of AIMS over the same period.

Dr Kroon said the relationship between fishery harvests and starfish numbers was striking.

“We found that the density of crown-of-thorns starfish increased in areas where more reef fish biomass was harvested,” she said.

“This relationship was strong for the emperors, especially the robin and star emperors [Lethrinus miniatus and L. nebulosus]both of which are well-known predators of the crown-of-thorns starfish.”

The relationship was also strong for tropical snappers and rockcod, including coral trout (Plectropome spp. and Smallpox spp.).

“Since adult coral trout are not known to eat crown-of-thorns starfish, we are interested in what might explain this relationship. One possibility is that juvenile coral trout eat small starfish, as part of their invertebrate diet,” Dr Kroon said. .

“Combined, our results suggest that removal of emperors, tropical snappers, and rockcod contribute to increased starfish numbers.”

The results provided an opportunity to investigate new tools for controlling disease outbreaks on the Great Barrier Reef and possibly in the Indo-Pacific, such as targeted fisheries-based management.

“Outbreaks of starfish continue to be a major cause of coral loss, but unlike other pressures like climate change, they can be managed locally and regionally,” Dr Kroon said.

“Targeted fishery-based management, in combination with current crown-of-thorns starfish management interventions such as direct manual control, could help further control outbreaks.”

Dr Kroon said the findings made a significant contribution to understanding possible drivers of starfish outbreaks, such as the natural tendency of starfish to reproduce in large numbers and the role of food quality. water, because they are not mutually exclusive.

“It’s most likely not one, but several factors that contribute to outbreaks,” she said.

“Large-scale, long-term data such as those used in this study, along with experimental studies are the best scientific tools we have to help understand the complexity of outbreaks of crown-of-thorns starfish and to implement effective and efficient management interventions for their control.”

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