Some Corals adjust to climate change

Acropora hyacinthus in the National Park of American Samoa Francois Seneca

Graduate student Rachael Bay sampling from and Acropora hyacinths colony in the back reef pools of the National Park of American Samoa © Megan Morikawa

Through an innovative experiment, Stanford researchers led by biology Professor Steve Palumbi have shown that some corals can – on the fly – adjust their internal functions to tolerate hot water 50 times faster than they would adapt through evolutionary change alone. The findings, published April 24 in Science, open a new realm of possibility for understanding and conserving corals.

The back reef lagoons in the National Park of American Samoa have many species of healthy corals © Megan Morikawa

'The temperature of coral reefs is variable, so it stands to reason that corals should have some capacity to respond to different heat levels,' said Palumbi, director of Stanford's Hopkins Marine Station and a senior fellow at the Stanford Woods Institute. 'Our study shows they can, and it may help them in the future as the ocean warms.'

Coral reefs are crucial sources of fisheries, aquaculture and storm protection. Overfishing and pollution, along with heat and increased acidity brought on by climate change, have wiped out half of the world's reef-building corals during the past 20 years. Even a temporary rise in temperature of a few degrees can kill corals across miles of reef.

The healthy back reef on Ofu Island in the National Park of American Samoa © Francois Seneca

American Samoa presents a unique case study in how corals might survive a world reshaped by climate change. Water temperatures in some shallow reefs there can reach 95 degrees Fahrenheit, enough to kill most corals. To find out how native corals survive the heat, researchers in Palumbi's lab transplanted colonies from a warm pool to a nearby cool pool and vice versa.

The researchers found that, over time, cool-pool corals transplanted to the hot pool became more heat-tolerant. Although these corals were only about half as heat-tolerant as corals that had been living in the hot pool all along, they quickly achieved the same heat tolerance that could be expected from evolution over many generations. Corals, like people, have adaptive genes that can be turned on or off when external conditions change. The corals Palumbi's group studied adjusted themselves by switching on or off certain genes, depending on the local temperature.

Acropora hyacinthus colony living in the back reef pools of Ofu Island in the National Park of American Samoa © Rachael Bay

These findings make clear that some corals can stave off the effects of ocean warming through a double-decker combination of adaptation based on genetic makeup and physiological adjustment to local conditions.

'These results tell us that both nature and nurture play a role in deciding how heat-tolerant a coral colony is,' Palumbi said. 'Nurture, the effect of environment, can change heat tolerance much more quickly – within the lifetime of one coral rather than over many generations.'

Graduate Student Megan Morikawa in the field © Rachael Bay

Palumbi cautioned that corals' heat-adaptive characteristics do not provide a magic bullet to combat climate change. They can't respond to indefinite temperature increases and they could be compromised by stressors such as acidification and pollution.

Still, if it holds true for most corals, this adaptive ability could provide a 'cushion' for survival and might give coral reefs a few extra decades of fighting back the harsh effects of climate change, Palumbi said.

The Stanford Woods Institute has supported Steve Palumbi's study of climate change impacts on coral reefs through its Environmental Venture Projects seed grant program.

Aerial view of back reef pools on Ofu Island. These pools vary greatly in their temperature regimes and are an excellent natural laboratory for studying the potential effects of climate change © Rachael Bay

Portable stress tank systems used to measure thermal tolerance in reef-building corals. These tanks allow scientists to carefully control the temperature of corals in order to measure heat stress response © Rachael Bay

Rachael Bay puts an identification tag next to a coral colony so that researchers can find the same colony later © Steve Palumbi