If you can’t take the heat, get out of the ocean? Or adapt….

By Amanda Jacobson

Coral reefs, also known as the tropical rainforests of the ocean, are refuges of marine diversity. Sadly, bleached white corals have become the poster child for global warming and the effects on ocean life.

Major coral bleaching events occur due to the loss of the symbiotic nutrient-producing algae (zooxanthellae) residing within the corals. Corals themselves are clear, but receive their coloration from the algae living within their tissues.

Loss of the zooxanthellae, and subsequent coral bleaching, can be induced by a variety of factors causing stress to the algae, rising ocean temperature being one of them. Different coral species have variable susceptibility to thermal stress. It has been hypothesized that hardier, slow growing coral will replace less hardy species in the future. The increasing occurrence and magnitude of bleaching episodes have led some marine biologists to believe that corals have exhausted their capacity to adapt. 

There may be hope.  James Guest et al., in a recent article published in the journal, PLoS ONE, describe how one type of coral is adapting to the increasingly warming temperatures of the ocean.

The authors of this paper hypothesized that corals have the ability to adapt to elevated sea temperatures.  They expected to find increases in thermal tolerance on reefs that typically experience more thermally variable environments; corals in these environments would bleach less severely during episodes of elevated sea temperature. 

The study assessed the thermal tolerance of coral in South East Asia that underwent a large-scale thermally-induced bleaching event in 2010. The findings of their work suggest that coral populations that bleached during the last major warming event in 1998 have adapted to thermal stress.

The authors conclude that this study does not suggest that coral bleaching is no longer a problem. Most coral reefs are still threatened by imbalanced ecosystems from overfishing, pollution, disease and acidification.

We need to change our ways; Mother Nature is not always going to be able to bail us out. 

Corals developing resistance to bleaching (colored) thrive in warmer water temperatures relative to those corals that do not (white). Photo credit: James Guest

References:

Guest, JR et al. (2012) Contrasting Patterns of Coral Bleaching Susceptibility in 2010 Suggest an Adaptive Response to Thermal Stress. PLoS ONE 7(3):e33353. 

Loya, Y et al. (2001) Coral bleaching: the winners and the losers. Ecol Lett 4: 122–131.

Hughes TP et al. (2003) Climate change, human impacts, and the resilience of coral reefs. Science 301: 929–933.