Hot Coral Gets Relief from Unique Underwater Phenomenon

The temperature fluctuations naturally occurring on coral reefs due to tides, waves and currents can mitigate marine heat waves and may help corals adapt to higher temperatures, according to a new study by the Australian Institute of Marine Science (AIMS) and the University of Western Australia (UWA). ) scientists found.

Dr Camille Grimaldi and a team of researchers studied Mermaid Reef at Rowley Shoals, just offshore from Broome in northwest Australia, for about a year to understand more about how water flow affects temperature and coral bleaching risks in different parts of the remote atolls. A paper about their findings has been published in the journal Coral reefs.

Bleaching is the coral’s response to heat stress, causing it to turn pale or white after expelling the algae that give it its color and give it food. While corals can recover, bleaching can lead to reduced growth, limited reproduction, and an increased risk of disease and even death. Climate change is leading to marine heat waves that are causing coral bleaching.

Lying at the edge of the continental shelf, Mermaid Reef is part of a system known for healthy, resilient coral reef habitats. This system has not experienced any major coral bleaching events since the mid-1990s.

Dr. Grimaldi said they found some large temperature changes in different regions of the mermaid reef occurring on time scales from a few hours to weeks and caused by tides of up to three metres, and large waves of up to two metres.

“We found Mermaid Reef to be a very lively place in some areas and quieter in others in terms of ocean processes such as tides, currents and waves,” said Dr. Grimaldi.

“Calm areas of the reef such as the lagoon are poorly contacted with marine water, which provides a little bit of cooling to these areas. Other parts of the reef, such as cliffs and flats, are exposed to tidal waves, which increases contact with marine cooling. This has contributed to shifting temperatures. The coral reefs in those areas are very large.

“Looking at the future course of coral reefs in a warming climate, understanding this natural variability in the Mermaid Reef will help us identify environmental conditions that promote resilience and recovery more broadly. This is pivotal to enhancing our ability to conserve and manage coral reefs around the world.”

“As the planet warms, the coral reefs with the best chance of survival will likely be those that are best connected to offshore ocean waters through tidal currents. This is where we can focus conservation efforts. ”

To understand how water flow controls reef temperatures and affects coral health, the researchers deployed a series of instruments in the waters around the Mermaid Atolls, including temperature and velocity sensors to track the strength of incoming waves and tides.

They found that because of the large tidal ranges, tidal flows were responsible for temperature changes that occurred within hours (up to 5.6 degrees Celsius in one hour), at locations only a few hundred meters apart.

The resulting flow from waves at Mermaid Reef also led to cooling over several days to weeks, suggesting that waves could provide relief from heat stress over longer periods of time.

Dr Grimaldi added: “This is important because many studies have indicated that fluctuations in temperatures around the clock or shorter periods of time can expose corals to stressful temperatures for periods short enough to avoid coral death, but long enough to drive adaptation.”

“Understanding the subtle temperature changes and their drivers on Mermaid Reef is important because most satellite sea surface temperature (SST) measurements — the standard tool that managers use to monitor reef temperatures — are too coarse to capture changes in temperature. the temperature we recorded.