Are corals becoming more resilient to stress?

Published 2018-08-09

Photo: Ji Hoon Justin Han

In a new study, published in the journal PeerJ, scientists replicate a set of experiments from the 1970s to test whether corals on reefs in the Pacific are acclimatizing or adapting to increased thermal stress. Coral reefs around the globe are experiencing more frequent and severe high temperature events, which can lead to a bleaching response, in which corals lose their symbiotic algae. Bleached corals, which appear white after losing their zooxanthellae, can die if the environmental conditions do not improve.

In the 1970’s, a set of experiments was conducted to determine the temperature threshold of corals at the Hawaii Institute of Marine Biology's (HIMB) Coral Reef Ecology Laboratory in Kane'ohe Bay, Hawai'i and the Mid-Pacific Marine Laboratory (MPL) at Enewetak, Marshall Islands. The results of these studies (Coles, Jokiel & Lewis, 1976; Jokiel & Coles, 1977; Coles & Jokiel, 1978) suggest that the temperature threshold of corals was at +1-2°C above the normal maximum temperature.

More than three decades later, the authors of the 2017 study replicated the methodology to test whether this threshold has increased. They found that bleaching did not occur until corals were exposed to higher temperatures and exhibited higher survivorship growth rates than in the 1970’s. Specifically, survivorship of corals was higher in 2017 (60-92%) than in 1970 (0-40%).

These results suggest that corals in these locations may be acclimatizing/adapting to warmer ocean conditions, but questions still remain on whether this pace matches the rate of change in the environment. As temperatures in the ocean are changing rapidly, mitigation of global climate change is necessary to increase the health of reefs worldwide.

Journal reference:
Coles SL, Bahr KD, Rodgers KS, May SL, McGowan AE, Tsang A, Bumgarner J, Han JH.(2018) Evidence of acclimatization or adaptation in Hawaiian corals to higher ocean temperatures. PeerJ 6:e5347