Higher temperatures may help protect coral reefs: Study

Higher water temperature, which increases the aggressiveness of some fish, may lead to better protection of some coral reefs, a study claims.

It is well established that higher water temperatures lead many corals to die, according to the study published in the journal Behavioural Ecology.

Over the past century, global temperature has increased by one degree, said researchers from McMaster University in Canada.

Meanwhile, research has shown that coral recovery can be significantly influenced by the behaviour of species living around coral reefs, they said.

Researchers evaluated the relationship between fish behaviour and coral performance using a farmerfish-coral system.

Farmerfish are aggressive damselfish found around coral reefs in tropical climates that defend gardens of algae from intrusion by other fish.

The study tested the relationship between coral recovery rates and the level of aggression exhibited by farmerfish groups when defending their gardens.

The researchers did so by planting small coral fragments into farmerfish territories with different levels of aggressiveness.

They collected data from 29 farmerfish colonies in French Polynesia from 2016 and 2017.

The researchers evaluated the average aggressiveness of each farmerfish group as well as the group's reaction when intruders entered the farmerfish group's territory.

They found that more branching corals resided in the territories of aggressive farmerfish groups.

In addition, corals experimentally planted into the territories of non-aggressive farmerfish suffered 80 per cent more damage than the corals planted into the territories of aggressive groups.

Researchers also found that farmerfish groups composed of larger animals were more aggressive. However, follow-up analyses showed that group aggressiveness mattered more than group member size in determining coral success.

Fish aggressiveness is therefore likely to be an important part of how coral reefs will grow and survive in future environments.

While warming oceans negatively impacts a variety of biological processes, this study hints that warmer temperatures, which often increase fish aggressiveness, could enhance the protective function of farmerfish for nearby corals.

"Predicting the future of corals will require a systems approach. Failing to account for broader ecological processes, such as species interactions, could lead us to issue the wrong predictions about how some corals will fare in future environments," said Jonathan Pruitt from McMaster University.

"Heating up many corals even mildly can negatively impact a variety of physiological processes. However, this study shows that small increases could provide greater protection by resident fishes.

"Obviously this can't go on for forever, though. At some point, all the protection in the world won't matter anything if the corals can't feed themselves," Pruitt said.