Scientists at the Australian Institute of Marine Science (AIMS) have found that some fast-growing coral species on the Great Barrier Reef slow down their growth rates when they are exposed to warmer water.
The study, published in the Proceedings of the Royal Society, shows they are likely to experience a double whammy with high mortality during acute heat stress events and significant reductions in growth due to an increasingly warming ocean.
Fast-growing table corals (Acropora species) cover the reef surface on the southern Great Barrier Reef. Image: Ian McLeod
Fast-growing tabling coral species are common on the Great Barrier Reef, providing essential shelter for other marine life, but at the same time, they are some of the most susceptible to marine heatwaves, bleach easily, and can break during storms.
Recent surveys for AIMS’ Long Term Monitoring Program found that increases in hard coral cover in northern and central regions were largely driven by these species.
Fragments of individual coral colonies from four species were held at 10 different temperatures for a month during the experiment in the AIMS National Sea Simulator. Image: Juan Ortiz
Limited potential for adaptation
“Our results demonstrate that these fast-growing table corals, critical for reef recovery, have evolved strategies that are perfect to maximize growth in their current environment,” said Dr. Juan Ortiz, senior author of the study. “But these initial findings may indicate that they have limited potential for adaptation to future hotter conditions.”
The study is believed to be the first to quantify the relationship between coral growth and temperature. The growth of four coral species from one reef on the central Great Barrier Reef was tracked over a month period, across 10 different temperatures between 19°C and 31°C in the AIMS’ National Sea Simulator.
Fragments of coral colonies in an aquarium during the month-long experiment in the AIMS National Sea Simulator. Image: Juan Ortiz
Dr. Mariana Alvarez Noriega, the lead author of the study, was surprised by how consistently individual colonies of the same coral species responded to temperature. “We were expecting different species to have different responses and we confirmed that but we were not expecting to find such a consistent thermal response between individuals of the same species,” she said.
“While individuals of the same species grew at vastly different rates, the temperature at which they grew fastest was remarkably similar.”
Isabella Marrable, co-author of the paper and research assistant at AIMS, prepares colonies of table corals for the month-long experiment in the National Sea Simulator at AIMS in Townsville. Image: Juan Ortiz
“Low variability in their response to temperature could make it harder for corals to naturally evolve higher thermal tolerance,” Dr.Ortiz added. “This was a technically challenging and ambitious study made possible by the unique facilities and controlled environment of the National Sea Simulator. To gain more insights, we need to understand what is happening at a bigger scale and across more species.”
“These results, together with the follow-up experiments are critical to developing models that will help us predict the future state of the Reef under different climate change scenarios. This work will also help us understand the potential benefits of different interventions.”
