Climate: Heat-adapted corals not immune to bleaching

Intertidal Acropora corals exposed to air at low tide.
Intertidal Acropora corals exposed to air at low tide. Photo courtesy Dr. Verena Schoepf.

A matter of degrees …

Staff Report

Even corals living in some of the warmest ocean waters on the planet are susceptible to bleaching and heat stress, according to Australian researchers who studied unique tidal species in the Kimberley region.

When the water gets too warm, it breaks down the symbiosis between coral and their zooxanthellae (the microscopic plants which gives coral most of its colour), which can be fatal for the coral.

In the new study by scientists at the ARC Centre of Excellence for Coral Reef Studies said they were surprised to find that corals around the Kimberley region in north Western Australia are just as sensitive to heat stress and bleaching as their counterparts from less extreme environments elsewhere.“We found that exceeding their maximum monthly summer temperatures by 1 degree Centigrade for only a few days is enough to induce coral bleaching,” said lead author Dr. Verena Schoepf.  “We were surprised because under normal conditions, Kimberley corals can tolerate short-term temperature extremes and regular exposure to air without obvious signs of stress.”

With up to 10m tides, the Kimberley region has the largest tropical tides in the world, creating naturally extreme and highly dynamic coastal habitats that corals from more typical reefs could not survive.

“Unfortunately the fact that Kimberley corals are not immune to bleaching suggests that corals living in naturally extreme temperature environments are just as threatened by climate change as corals elsewhere,” Schoepf said.

“We found that both branching and massive corals exposed at low tide coped better with heat stress than s corals from deeper water,” said co-author Professor Malcolm McCulloch from the Coral CoE. “However this doesn’t mean that they are immune to bleaching,” Professor McCulloch says.

The research, which was carried out in partnership with the Western Australian Marine Science Institution, also found that massive corals had a better chance of surviving and recovering from bleaching than branching corals.

The current strong El Nino weather pattern in the Pacific puts many coral reefs at risk of severe bleaching, and recent weather predictions show that the Kimberley region might be particularly affected in 2016.

“With the third global bleaching event underway, it has never been more urgent to understand the limits of coral thermal tolerance in corals,” says Professor McCulloch.

 

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