Rachel Carson is best known for her seminal work Silent Spring (1962), which brought critical attention to the havoc being wrought by pesticides on the environment. But by then she had already published a number of other well-received works, including The Edge of the Sea, a natural history of the shore and its flora and fauna. A marine biologist by training, Carson had a deep affection for shoreline communities of all sorts, and this work is suffused with her enthusiasm for each variety of coastal marine life. Central to the chapter entitled "The Coral Coast" is her fascination not only with the creatures who live among the coral, but with the living organisms who built the reefs themselves.
Coral reefs are built by communities of tiny coral polyps, living animals that extract calcium from the seawater to form a carbonate exoskeleton for support and protection. It is the accumulating structure of these exoskeletons that make up the reef, formed in many cases over the course of hundreds of thousands of years, and creating the underwater environment in which much of the marine life we know today evolved.
The coral polyps live in a symbiotic relationship with simple algae called zooxanthellae, which live inside the exoskeleton with the coral, and exchange nutrients, waste products, oxygen, and carbon dioxide. It is these algae that give coral its exquisite palette of colors.
Coral reefs are known as the "rainforests of the sea" because they provide the habitat for some 25% of marine species, including over 4000 species of fish.1 They also provide coastal protection from violent storms, contribute substantially to the tourism economy of many reef countries, and, like terrestrial rainforests, are the source of many pharmaceutical ingredients. And they are aesthetically magnificent. According to a popular field guide, a reef's "infinite diversity and beauty make it an almost mystical experience."2
Coral reefs are under assault around the globe. The causes for the decline are many. Coastal development, pollution from agricultural runoff and other sources, overfishing, ship strikes, invasive species, and dredging are some of the local sources. Infrastructure projects stir up sediments and reduce sunlight, interfering with photosynthesis by the algae. The shoring up of beaches by bringing in sand from offshore can destroy portions of reefs. Sewage contains high nutrient levels, which trigger algal blooms that suffocate reefs. Even careless tourists and lost fishing gear damage reefs. And El Niño years tend to see a great increase in bleaching events.
Climate change is also taking a vast toll on coral, with its one-two punch of warmer ocean temperatures and greater acidity. Even a very slight warming of the seawater – often as little as 1° Celsius (1.8° Fahrenheit) – can result in coral bleaching,3 in which the algae are expelled from the reef, leading to the rapid death of the coral. And the absorption by the ocean of some of the excess carbon dioxide being pumped into the atmosphere increases its acidity, interfering with the formation of the calcium carbonate that forms the shells, and therefore the reefs.
Even fish living among the reefs are suffering greater predation, presumably because they are far more conspicuous to predators against the stark white of the dead reefs.4 Many species are declining to dangerously low numbers as a result.
In the waters of Florida and the Caribbean, where Carson indulged her love for the magnificent reef ecosystem, coral cover has declined by as much as 80% in the past 30 years.5 And most of what remains is likely to vanish in the next 20, without sufficient efforts to protect it.6 Yet it is entirely possible to do just that. Coral health in this region depends to a great degree on what are known as grazer species, fish that eat the algae that would otherwise overgrow the coral and smother it. The two most important grazer species here have long been the sea urchin and the parrotfish. Yet the sea urchin was essentially wiped out in 1983 by a disease thought to have been brought in from the Panama Canal. The parrotfish has been the victim of a century of overfishing, resulting in local extinctions.
In areas where local authorities have protected the parrotfish by banning damaging fishing practices, populations are still strong, and coral reefs have remained far healthier than their unprotected neighbors. It is believed that many coral reefs are more vulnerable to local threats than they are to climate change, and that if appropriate protections and management strategies are put in place, we can maintain healthy reefs, and even help the recovery of damaged ones. Carl Gustaf Lundin, the director of the International Union for the Conservation of Nature’s Global Marine and Polar Program, says that “the fate of Caribbean corals is not beyond our control and there are some very concrete steps that we can take to help them recover.”7
Yet halfway around the world Australia’s Great Barrier Reef tells a different story. The world’s largest reef system, about the size of Japan, it contains about 400 different types of coral, 1500 species of fish, and several thousand species of mollusk. It has lost half its coral cover since 1988, and many of the reasons appear to be similar to those in the Caribbean, with an emphasis on sediment and agricultural runoff. In this region those conditions encourage the outbreak of Crown-of-thorns starfish, which prey on coral.
But new surveys, whose results were released in 2016, reveal something startling. Not only has mass bleaching very recently occurred in the entire reef system, but the northern reefs, those farthest from sources of human disturbance and long the healthiest of the reefs, show by far the most damage, with 80% severely bleached.8 This calls into question the idea that reefs can be made more resilient to the effects of climate change by minimizing human disturbance.
One especially ironic side note: The United Nations had listed the Great Barrier Reef as a World Heritage site in 1981, but had been considering putting it on its Danger list in 2015. Australia’s vigorous protestations and promises of improved management had circumvented that; but within months, Australia had approved a coal export terminal right alongside the reef. Not only would this require massive dredging, greatly increased ship traffic, and other extreme disturbances, but the coal mine involved, one of the largest in the world, is a major source of the selfsame greenhouse gases that are producing the climate change that gravely threatens what is left of the coral.
The World Heritage Convention is now reconsidering declaring the reef to be in danger, which would put a good deal of pressure on Australia to step up its efforts to protect this unique and extraordinary landscape. Other governmental and non-governmental organizations are taking action to try to save the coral reefs under their jurisdiction. In the U.S., the National Oceanic and Atmospheric Administration (NOAA) has put a number of programs in place to address the threats to the Florida reef system, from monitoring to reducing runoff to finding better ways to manage fisheries. Florida's two most critically endangered coral species, the elkhorn and staghorn corals, were listed as endangered under the U.S. Endangered Species Act in 2006, the first time corals had been placed on that list. Such protections could help reduce harm from local threats, and in some cases increase the resilience of reefs. But to a considerable extent, the fate of the world's reefs will depend on how quickly appropriate action is taken against climate change.
For Carson, the coral islands of the Florida Keys reverberated with the whole deep history, past and ongoing, of the life forms intrinsic to their existence. She could not have imagined how perilous the next chapter in that long history might be, nor that future readers might one day page through her work with more nostalgia than wonder.
1 Mulhall Marjorie. "Saving the rainforests of the sea: An analysis of international efforts to conserve coral reefs." Duke Environmental Law and Policy Forum, 2009: 19(2) pp. 321-351.
2 Kaplan, Eugene H.; Peterson, Roger T.; and Kaplan, Susan L. A Field Guide to Coral Reefs: Caribbean and Florida (Peterson Field Guide). New York: Houghton Mifflin Co., 1982.
3 Australian Government, Great Barrier Reef Marine Park Authority. “Coral Bleaching.” http://www.gbrmpa.gov.au/managing-the-reef/threats-to-the-reef/climate-change/what-does-this-mean-for-species/corals/what-is-coral-bleaching.
4 Coker, DJ; Pratchett, MS; and Munday, PL. "Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes." Behavioral Ecology, 2009: 20(6), pp.1204-1210.
5 Florida Department of Environmental Protection. “Florida’s Coral Reefs.” http://dep.state.fl.us/coastal/habitats/coral/issues.htm.
6 Aldred, Jessica. “Caribbean coral reefs ‘will be lost within 20 years’ without protection.” The Guardian, 2 July 2014. https://www.theguardian.com/environment/2014/jul/02/caribbean-coral-reef-lost-fishing-pollution-report.
8 Slezak, Michael. “UN committee may again consider listing Great Barrier Reef as ‘in danger’.” The Guardian, 29 June 2016. https://www.theguardian.com/environment/2016/jun/30/un-committee-may-again-consider-listing-great-barrier-reef-as-in-danger.