The increasing ocean temperatures likely influenced by human-induced climate change are affecting and harming coral reefs around the world. In fact, warming ocean temperatures are the main culprit behind coral bleaching, as per many scientists. New research suggests, that not even the deep water corals are entirely protected from the warming ocean temperatures.
These findings are derived from a new study led by scientists at Scripps Institution of Oceanography at the University of California San Diego and the Coral Reef Research Foundation (CRRF) in Palau. The team of scientists introduced a new approach that successfully predicts warm temperature-induced stress in coral reefs, coming from the sea surface, to the deeper expanse between 100 and 500 feet, also known as the mesophotic zone.
Corals that sit at the mentioned depths are thought to be safer from the warming temperatures because they are deeper than other corals that live in shallow water. However, the Scripps Oceanography team discovered that those corals at that depth are also exposed to thermal stress at different intervals compared to the corals near the surface.
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The team used nearly two decades of data collected, including sea level, sea-surface temperature, as well as the temperature measurements between the surface and deep into the mesophotic zone. That way they could develop a forecast tool that would show how corals are stressed by the rising temperatures. The team worked around the island nation of Palau, located in the tropical Pacific Ocean. The team published their findings in the journal Geophysical Research Letters on Aug. 27.
“We’re now adding the dimension of depth into the problem where before we were only skimming the surface of what temperature stress meant for corals,” Scripps Ph.D. candidate Travis Schramek, lead author of the study, said in a statement. “We see that the heat-induced stress penetrates all the way into the mesophotic zone during larger bleaching events.”
The scientists also used a network of reef temperature recorders that are maintained by CRRF divers in locations across Palau going to depths of 295 feet, to observe how the deep water corals are affected. CRRF has been measuring the temperatures at the key locations starting from the surface to the mesophotic reefs since 1999. Moreover, there are not many divers that possess this training routine as well as safety equipment. Pat Colin, who is a rare scientific diver at these locations and CRRF director contributed to the study as a coauthor.
For decades, Colin and his team of divers have conducted dives on a weekly basis to monitor the ocean temperatures over a longer period of time.
They found that there is a coincident between the higher water temperature and coral bleaching in the deep water corals.
“Our understanding of the ocean is really going to continue to be driven by observations. The models are really informative, but the way that we ground them is through observing the Earth system,” said Schramek. “Having observations like what Pat has collected shows the power of actually going and deploying tools and observing Earth in a unique way.”
They combined the sea level and sea temperature data sets to discover that there is a strong indicator that surface ocean levels affect water temperatures tens of feet below. Further on, Schramek developed an algorithm that combined the accepted coral stress algorithms to depths which also include the deeper mesophotic corals, which were often thought to experience less thermal stress.
“A surprising outcome of the study is that the oceanic conditions along the dramatic reef walls that are the boundaries of Palau are very representative of the broader Western Pacific,” said Scripps oceanographer Eric Terrill. “As a result, we had a surprising amount of success in predicting the vertical structure of the temperature fields that the coral communities would be exposed to, even during El Niño conditions.”
He also added that given these results, they can continue to use their methods at other islands in the Pacific region. Also, the team’s insights of the deep water corals being exposed to higher ocean temperatures may help understand more about the different reef systems, and that way develop new ways to cure corals and prevent coral bleaching.
“Now that we’ve observed this ecosystem in a unique way, we can start to better assess how corals in the mesophotic zone are stressed,” said Schramek. “If we can better understand how they’re stressed, then we can better understand how to protect them.”