Coral Bleaching Is Not a Tell-Tale Sign of Imminent Extinction

Climate alarmists seem to be working overtime these days to persuade the public to support legislation to combat dangerous climate change, which they claim will occur unless CO2 emissions are drastically reduced. And after nearly two decades of over-predicting global warming (there has been little to no global warming since the late 1990s), they are getting awfully desperate in their attempts to convince the public that there is an imminent climate catastrophe on the horizon.

The rhetoric-of-choice is good old-fashioned fear mongering. The latest example is a New York Times article by Michelle Innis entitled “Climate-Related Death of Coral Around World Alarms Scientists.” In a nutshell it’s a lot of one-sided reporting in making the case that unless climate change is stopped (i.e., fossil fuel use is reduced rapidly), highly important underwater coral ecosystems will be consigned an awful death due to coral bleaching. There’s a substantial literature on coral resilience that somehow was ignored. Surely an oversight!

Coral bleaching is one of the most frequently cited negative consequences projected to result from CO2-induced global warming. It is a characterized by a loss of color in certain reef-building corals that occurs when algal symbionts, or zooxanthellae, living within the host corals are subjected to various stresses (usually higher than normal ocean temperatures) and expelled, resulting in a loss of photosynthetic pigments from the coral colony. If the stress is mild, or short in duration, the affected corals often recover and regain their normal complement of zooxanthellae. However, if the stress is prolonged, or extreme, the corals eventually die, being deprived of their primary food source.

In her article, Innis reports that corals bleached at many locations this year as a result of warmer ocean temperatures associated with El Niño, so therefore if something isn’t done to stop global warming (note to the author: that is impossible), these incredible underwater species will go extinct. 

As noted above, there’s a substantial literature showing that corals are pretty resilient. Consider the recently published work of Guest et al. (2016), who reported on the status of a coral community on a highly disturbed reef site south of mainland Singapore before, during and after a major warming event that occurred throughout the Indian Ocean and Southeast Asia in 2010, leaving in its wake many severely bleached coral reefs. And in so doing, they discovered the following intriguing facts.

First of all, the 13 scientists note that approximately two thirds of the coral colonies bleached; but that “post-bleaching recovery was quite rapid and, importantly, that coral taxa that are usually highly susceptible were relatively unaffected.” Secondly, they note that “there was no significant change in coral taxonomic community structure” as a result of the bleaching. Third on their list of discoveries was the fact that “several factors may have contributed to the overall high resistance of corals at this site, including Symbiodinium affiliation, turbidity and heterotrophy.”

Taken together, all of these observations led the thirteen researchers to ultimately conclude that “turbid shallow reef communities may be remarkably resilient to acute thermal stress.” And they conclude that their results (1) “suggest an under-appreciated resilience in disturbed impacted reef systems” and that (2) “corals that have been classified as losers in the face of climate change may have a greater capacity for adaptation and/or acclimatization than previously supposed.”

The findings of Guest et al. are not unique and many other researchers have reached similar conclusions (see dozens of references in the chapter on Aquatic Life in Idso et al., 2014). As one other example, Guzman and Cortes (2007) studied coral reefs of the eastern Pacific Ocean, which “suffered unprecedented mass mortality at a regional scale as a consequence of the anomalous sea warming during the 1982–1983 El Niño.” At Cocos Island (5°32’N, 87°04’W), in particular, they found in a survey of three representative reefs, which they conducted in 1987, that remaining live coral cover was only 3 percent of what it had been prior to the occurrence of the great El Niño four years earlier (Guzman and Cortes, 1992). Based on this finding and the similar observations of other scientists at other reefs, they predicted “the recovery of the reefs’ framework would take centuries, and recovery of live coral cover, decades.” In 2002, therefore, nearly 20 years after the disastrous coral-killing warming, they returned to see just how prescient they might have been after their initial assessment of the El Niño’s damage, quantifying “the live coral cover and species composition of five reefs, including the three previously assessed in 1987.”

With respect to the subject of thermal tolerance, the most interesting aspect of their study was the occurrence of a second major El Niño between the two assessment periods. In fact, Guzman and Cortes state “the 1997–1998 warming event around Cocos Island was more intense than all previous El Niño events,” noting that temperature anomalies “above 2°C lasted 4 months in 1997–1998 compared to 1 month in 1982–83.” Nevertheless, they report “the coral communities suffered a lower and more selective mortality in 1997–1998, as was also observed in other areas of the eastern Pacific (Glynn et al., 2001; Cortes and Jimenez, 2003; Zapata and Vargas-Angel, 2003),” which is indicative of some type of thermal adaptation following the 1982–83 El Niño.

Corals are much more resilient to the stress of bleaching than many people have supposed, and that is an inconvenient truth for the coralline alarmists.



Cortes, J. and Jimenez, C. 2003. Corals and coral reefs of the Pacific of Costa Rica: history, research and status. In: Cortes, J. (Ed.) Latin American Coral Reefs. Elsevier, Amsterdam, The Netherlands, pp. 361–385.

Glynn, P.W., Mate, J.L., Baker, A.C. and Calderon, M.O. 2001. Coral bleaching and mortality in Panama and Ecuador during the 1997–1998 El Niño-Southern Oscillation event: Spatial/temporal patterns and comparisons with the 1982–1983 event. Bulletin of Marine Science 69: 79–109.

Guest, J.R., Low, J., Tun, K., Wilson, B., Ng, C., Raingeard, D., Ulstrup, K.E., Tanzil, J.T.I., Todd, P.A., Toh, T.C., McDougald, D., Chou, L.M. and Steinberg, P.D. 2016. Coral community response to bleaching on a highly disturbed Reef. Scientific Reports 6:20717, DOI: 10.1038/srep20717.