Fish help control naked crown of thorns starfish


image: A Red-throated Emperor (Lethrinus miniatus) stares at the camera in front of a cluster of crown-of-thorns starfish on the Great Barrier Reef.
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Credit: Australian Institute of Marine Sciences

Reef fish, such as emperors, tropical snappers and cod, help control the number of thorn-crowned starfish on the Great Barrier Reef, new study from the Australian Institute of Marine finds Science.

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

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

“Over 50 years ago, it was feared that eliminating predators could contribute to starfish outbreaks. However, at the time, only one starfish predator was known, the sea snail. giant sea newt, ”said Dr. Frederieke Kroon, environmentalist and senior author of AIMS.

“Recent studies have revealed that nearly 100 species of coral reef organisms feed on the different life stages of starfish. Eighty of them are fish, including species of Popular seafood such as emperors, tropical snappers and cod.

“Our study is the first to explore how fisheries for 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 reefs open and closed to fishing. On reefs closed to fishing, the biomass of emperors, snappers and cod was 1.4-2.1 times higher and starfish densities nearly three times lower than those for reefs open to fishing .

“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 might influence starfish numbers as well, but our study provides strong evidence that there are fewer crown of thorns starfish on reefs with more predatory fish. “Said Dr Kroon.

Scientists also compared 30 years of reef fish harvest data from the Queensland Department of Agriculture and Fisheries with abundance data of thorn-crowned starfish from long-term monitoring of AIMS reefs during 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 being 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 Crown-of-thorns starfish.

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

“Since adult coral trout do not eat thorn-crowned starfish, we are interested in what may explain this relationship. One possibility is that young coral trout will eat small starfish, as part of their invertebrate diet, ”said Dr Kroon.

“Combined, our results suggest that the removal of emperors, tropical snappers and cod contributes to the increase in starfish numbers.”

The results provided the opportunity to study new tools to control epidemics on the Great Barrier Reef and possibly across the Indo-Pacific, such as targeted fisheries-based management.

“Starfish outbreaks continue to be a major cause of coral loss, but unlike other pressures like climate change, they can be managed at local and regional levels,” said Dr Kroon.

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

Dr Kroon said the findings make 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 starfish quality. water, as they are not mutually exclusive.

“It is most likely not one, but several factors that contribute to epidemics,” she said.

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

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