Do nothing to stem global warming, and some hardy coral will live on

A stark and dire warning appears in The Sixth Extinction: An Unnatural History (Henry Holt and Co, 2014), which was selected by the New York Times as one of 10 Best Books of 2014. “Our oceans, a crucial food source for billions, have become not only warmer but also more acidic…They struggle to absorb excess heat and carbon pollution…which is why, as [book author Elizabeth] Kolbert points out, coral reefs might be the first entire ecosystem to go extinct in the modern era.

But according to an international collaboration consisting of ecologists from 20 institutions worldwide—including the HBCU University of the Virgin Islands (UVI) in St. Thomas—a more likely scenario is that a warming ocean will lead to “winners and losers,” not just losers. In a 2014 PLOS One paper, the researchers looked to the past, present, and future: They analyzed data from studies of fossilized and living reefs and used them to mathematically model coral-community population changes under greenhouse-gas (GHG) scenarios predicted by the UN’s Intergovernmental Panel for Climate Change.

The simulations revealed that coral species possessing some combination of high thermal tolerance, high growth rate, and long lifespan (or low mortality) will survive even the harshest IPCC scenario—that being business-as-usual GHG emissions between now and 2100. A previous study also predicts winner and losers, but did not actually simulate the outcome, nor did it conduct a longitudinal study to account for temporal affects.

Not surprisingly, the unusually less-than-gloomy climate change forecast has attracted news coverage. ScienceDaily, EurekAlert!, Nature World News, Tech Times, and Phys.org all highlighted the study’s optimistic aspects. And yet, the researchers themselves caution in their paper that “…our analyses do not imply a ‘rosy’ future for tropical coral reefs.”  That’s in part because their mathematical model does not explicitly account for other predicted environmental changes, such as “…increasing ocean acidity, increasing frequency and/or intensity [of] hurricanes or typhoons, changing herbivory, nutrient runoff, over fishing, etc.”

Coral reefs are garden-like underwater superstructures primarily made by the marine invertebrate scleractinian (or “stony”) coral. Scleractinia excrete calcium-carbonate exoskeletons that connect to form the backbone of a coral reef. Like any animal, reef coral grow, feed, and die; fossilized reefs are composed of dead coral. Although occupying a tiny fraction of the ocean surface, coral reefs–the so-called rainforest of the sea–is home to more than 25% of the ocean’s marine life. Reefs also protect island shorelines by dampening the force of powerful incoming waves.

Already, climate change has wreaked havoc on coral reefs, as evidenced by increasing reports of  large-scale coral bleaching, a phenomenon that occurs when algae-like organisms growing symbiotically within the coral tissue are expelled as the result of some stressor, most often increased water temperatures. The reefs literally lose their color and turn whitish. Large-scale bleaching is akin to a rainforest being burned to the ground.

Although this study presents a somewhat surprising prediction that some reef coral are tough enough to survive the anticipated climate scourge, other papers and reports continue to warn humans of the need to protect our reefs before it is too late.  For example, results from a major report released last year–Status and Trends of Caribbean Coral Reefs: 1970-2012–show that the Caribbean corals have declined by more than 50% since the 1970s (see the video below). But even that report presents an optimistic twist: The authors claim that restoring parrotfish populations (which graze on coral reefs), and reducing coastal pollution and overfishing could lead to reef recovery.

This paper’s lead author and study designer, biologist Peter Edmunds, and most of the 23 researchers in the study, are affiliated with the National Center for Ecological Analysis and Synthesis based at the University of California Santa Barbara. Reefs studied and sampled were located in the Indo-Pacific and Caribbean regions: near Mo’orea (French Polynesia), Taiwan, Hawaii, Australia’s Great Barrier Reef, and Kenya, Belize, and the US Virgin Islands, in the backyard (metaphorically speaking) of coauthor and UVI associate professor Tyler Smith. He is also research coordinator of UVI’s Coral Reef Monitoring Program in the university’s Center for Marine and Environmental Science.