Evidence of acclimatization or adaptation in Hawaiian corals to higher ocean temperatures

Major findings of the study

  • In the three species of Hawaiian corals retested, bleaching occurred later, with higher survivorship and growth rates than the same species of corals in 1970.
  • Hawaiian corals have acclimatized and/or adapt to increases in seawater temperatures over the last half century.
  • Seawater temperatures are increasing at an alarming rate.
  • We are unsure if the differences in coral temperature tolerance (amount of heating corals can withstand without bleaching) are because of changes in physiological processes (acclimatization) or because of natural selection for the survival of more temperature tolerant corals (adaptation). Until now, it had not been determined how long these processes take. From prior temperature related research on corals we do know that this change is not occurring at a pace rapid enough to adjust to the frequency and severity of current elevated temperature events. Coral in Kāne‘ohe Bay have not kept up with acclimatization evidenced by the 22% mortality from the 2014/15 bleaching event.
  • Some coral species will do better than others. Mortality was first reported for Montipora capitata (rice coral) in 3 days in 1970 but took 15 days in 2017. In 2017 survivorship was 83% higher and growth rates 164% higher than in 1970. Lobactis scutaria (mushroom coral) first mortality occurred at 3 days in 1970 and 17 days in 2017 while survivorship was 92% and growth 99% higher than in 1970. Pocillopora damicornis (lace coral) suffered first mortality in 1970 at 3 days while in 2017 it took 13 days. Survivorship was 60% higher and growth 173% higher in 2017.

Nutrient levels were higher in 1970 in Kāneʻohe Bay when sewage was being discharged into the area. However, these levels were lower than the levels that have been shown to increase the rates of bleaching and mortality in corals. To determine the role elevated nutrients played in the bleaching and mortality of the experimental corals we are currently subjecting the same species of corals used in the acclimatization experiments to the levels of nutrients experienced in 1970.

This work shows that corals have responded to changes in the environmental over the last 50 years. However, the rate of seawater warming is occurring too fast and may lead to the collapse of many coral reefs. We must reduce our use of fossil fuels and lower emissions of CO2 and other greenhouse gases to help slow the rate of warming. One of the main things you can do to lessen the carbon impact is to think of the true cost of everything you buy, the cost to the environment. How was it made, how far away did it come from, will it be recycled? Buy local foods and goods that aren’t associated with the carbon travel costs. This is especially true here in Hawai’i where over 90% of our resources are shipped in.
Eating lower on the food chain will significantly reduce your impact. It takes 10 times more energy each time you go up the food chain. For instance, it takes 10 pounds of corn or soybeans to make one pound of beef or pork and a lot of water. We can become part of the solution by developing, advocating for, and using new earth friendly technology.

Ridge to Reef (Mauka/Makai) Connections

Map showing (a) watershed health indices (WHI), (b) reef health indices (RHI), and (c) the difference between RHI and WHI for watersheds on the islands of Ni‘ihau and Kaua‘i in the main Hawaiian Islands. Index values are scaled from 0-100 for all Hawaiian Islands with a value of 0 representing the worst relative condition (colored in red) and a value of 100 the best (colored in blue). In the lower map (c), negative numbers indicate watershed health is greater than reef health (colored in red), numbers near zero indicate that watershed health and reef health are similar (colored in gray), and positive numbers indicate reef health is greater than watershed health (colored in blue).

Map showing (a) watershed health indices (WHI), (b) reef health indices (RHI), and (c) the difference between RHI and WHI for watersheds on the islands of O‘ahu, Moloka‘i, Lana‘i, Kaho‘olawe, and Maui in the main Hawaiian Islands. Index values are scaled from 0-100 for all Hawaiian Islands with a value of 0 representing the worst relative condition (colored in red) and a value of 100 the best (colored in blue). In the lower map (c), negative numbers indicate watershed health is greater than reef health (colored in red), numbers near zero indicate that watershed health and reef health are similar (colored in gray), and positive numbers indicate reef health is greater than watershed health (colored in blue).

Map showing (a) watershed health indices (WHI), (b) reef health indices (RHI), and (c) the difference between RHI and WHI for watersheds on the island of Hawai‘i. Index values are scaled from 0-100 for all Hawaiian Islands with a value of 0 representing the worst relative condition (colored in red) and a value of 100 the best (colored in blue). In the lower map (c), negative numbers indicate watershed health is greater than reef health (colored in red), numbers near zero indicate that watershed health and reef health are similar (colored in gray), and positive numbers indicate reef health is greater than watershed health (colored in blue).