Rivalry Among The Reefs: Charles Darwin and a Century of Conflict Over the Coral Reef Problem

It took the threat of nuclear annihilation between the two greatest powers of the 20th century to solve one of the most profound scientific controversies of the 1800s. In 1952 Dr. Harry Ladd, a researcher for the US Geological Survey, convinced the US War Department to drill holes deep into the Bikini and Eniwetok Atolls just prior to their obliteration by hydrogen bombs. The reason for the drilling had little to do with the nuclear tests as part of Operation Crossroads, but was simply to conduct an experiment based on the hypothesis of coral reef formation first proposed by Charles Darwin in 1837.

Coral reefs are formed by the biological activity from millions of tiny cnidarian polyps, sea anemone-like creatures only a few millimeters in diameter, which secrete calcium carbonate as a protective exoskeleton. As each generation of coral dies, a new generation builds upon the bones of their ancestors. Since the coral feed on the energy produced by photosynthetic algae, they can only survive near the ocean surface where there is plenty of sunlight. The abandoned tenements beneath thus serve as the ideal habitat for millions of marine species. While occupying only 0.2 percent of the world's oceans, coral reefs sustain 25 percent of species diversity an oceanographic public works project that has been in existence for 3.5 billion years.

But therein lies a problem. Many of the coral reef atolls are thousands of feet deep, but the algae on which the coral survives only receive enough sunlight for a few hundred. If the polyps that constructed the reef are unable to live so far beneath the ocean surface, how did the bottom layers ever come to be? This mystery captured the attention of a young naturalist while traveling aboard the HMS Beagle, an oceanic journey that would be forever famous for revealing humanity's place in the scheme of existence.

Coral reefs hold an important place in the history of evolutionary theory, as they were the subject of Darwin's first scientific monograph and his official entrance into the scientific community. It was this research, and his eight-year study of barnacles, that led to the Royal Society awarding him the Copley Medal for outstanding achievement in science. Based on depth measurements taken of the coral reefs at Cook, Keeling and Mauritius Islands, Darwin developed his theory of "subsidence" to explain their development. Darwin didn't know just how coral reefs grew, but he was aware that the living coral formed fringing reefs just below sea level along many coastlines. He was also aware of white strips of limestone that encircled volcanoes throughout the South Pacific. Darwin theorized that these were the remnants of fringing reefs that had been raised above sea level by the rising volcano. The same logic should therefore operate in reverse; if the coast were sinking then the coral would continue to grow upwards in order to remain in the warm, sunlit waters. Eventually, once the coastline was completely submerged, all that would remain would be the coral atoll. After arguing away every problem that had previously plagued coral reef formation, Darwin was left with his triumphant conclusion:

On this view every difficulty vanishes; fringing-reefs are thus converted into barrier-reefs; and barrier-reefs, when encircling islands, are thus converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the ocean.

Darwin's finished work, The Structure and Distribution of Coral Reefs, was published in 1842 at just over two hundred pages. The book was immediately hailed as a breakthrough. Even Darwin's mentor Charles Lyell, whose previous theory of coral formation Darwin's book sought to disprove, was impressed with the young man's argument. In one review for the Royal Geographical Society of London, a Colonel Jackson wrote enthusiastically, if a bit florid and verbose, as was the Victorian way:

Mr. Darwin has added his own personal examination of a great many of those interesting structures; and, from the manner in which he has grouped the facts, and then reasoned upon them, the mind remains satisfied that he has detected the law, or rather the process, of nature in their formation . . . Upon the whole, we can safely say we have rarely met with a work every way so satisfactory.

Colonel Jackson ended the review eagerly waiting "with great impatience the works promised by the same talented naturalist on Volcanic Islands and on South America." The scientific community would soon receive these anticipated works, and a great deal that they hadn't anticipated, as Darwin's research pursued ever deeper into the great mysteries of the natural world. As it turned out, Darwin's greatest achievement - his theory of natural selection - would also lead directly into a personal challenge and one of the longest running scientific controversies in history.

Louis Agassiz was a giant of American science. He was a paleontologist, glaciologist, geologist, biologist, a distinguished professor at Harvard University and founder of the Museum of Comparative Zoology. There was little that Agassiz put his mind to that wasn't honored as a work of innovation and authority. He was also a creationist at the height of his professional career when On the Origin of Species was published in 1859. As a hold out against Darwin's theory until the end of his life, Agassiz had the unfortunate experience of watching his stature and reputation erode, like the very geological processes he spent his career studying, as one claim after another was undermined by the brilliance and clarity of Darwin's insights. As just one example of how events had conspired against Agassiz: in his monumental 1863 work Methods of Study in Natural History, he insisted that coral reefs themselves offered the evidence against Darwin's theory. In his detailed analysis of the Florida Keys, he found the same species of coral polyp fossilized at the base of the atoll as were currently alive at the surface, with no evidence of evolutionary change.

What, now, do they tell us of the permanence of the Species by which they were formed? In these seventy thousand years has there been any change in the Corals living in the Gulf of Mexico? I answer most emphatically, No.

Of course, seventy thousand years is little more than an opening act as far as geologic time scales are concerned, there being anywhere from ten to twelve million years for rats and mice to have evolved from their common ancestor. Over the next few years Agassiz watched as all of his students, including his son Alexander, split ranks and became evolutionists themselves. In the end, seemingly bitter and resigned, Agassiz wrote simply, "I have devoted my whole life to the study of Nature, and yet a single sentence may express all that I have done."

However, in those seeds of resentment lay the foundation for a lifelong antagonism. As David Dobbs beautifully relates in his book, Reef Madness, Agassiz left behind a rival that would pursue Darwin for years to come and stoke a controversy that wouldn't be resolved for nearly a century. It was Alexander Agassiz, the son who had watched his father's career in decline, who took over for him at Harvard's Museum of Comparative Zoology. A prestigious naturalist in his own right, he had an endowed chair named after him that has been passed down to such luminaries as Ernst Mayr, Stephen Jay Gould and Richard Lewontin today. In the years after his father's death in 1873, having also just lost his wife to pneumonia, young Agassiz picked up the coral reef problem and pursued it for the next thirty years of his life.

In the midst of tragedy, a fortuitous event brought an inspired idea to the distraught naturalist. A close friend, Sir John Murray, had just returned from a five-year oceanic expedition and relayed to Alex Agassiz that planktonic debris, floating in tropical waters, would be enough to raise underwater mountains over time to a high enough level that coral reefs could form on top. Darwin, usurper of the throne, may have been wrong after all. Alex Agassiz found his opening in the fact that Darwin's theory of subsidence, brilliant as it may have been, was only based on a few observations of coral reefs. He would now use Darwin's strengths against him and accumulate such an abundance of evidence that few could deny the reality.

Terrific argument and speculation continued over the intervening years and, for many, the coral reef problem became a way to tear down Darwin's legacy over their opposition to evolution. After Darwin's death in 1882, and that of his primary advocates in the decades to follow, natural selection as a theory was relegated to a secondary level of interest. It wouldn't become a central pillar of biology until the New Synthesis of the 1930s. Alex Agassiz continued to piece together a global theory of coral reef formation that included a combination of subsidence, erosion, the accrual of debris and geologic uplift that included nearly every coral formation around the world. Upon his death in 1910, his collected evidence hadn't yet been organized into a book and none of his research had ever been published. The true story of coral formation would have to wait.

Having been a prisoner of illness at his home in Down for the past two decades, Charles Darwin wrote about the coral reef controversy less than a year before his death. As was typical of Darwin, his description expresses a humble self-criticism not often found in his adversaries (either then or now):

If I am wrong, the sooner I am knocked on the head and annihilated so much the better. . . I wish that some doubly rich millionaire would take it into his head to have borings made in some of the Pacific and Indian atolls, and bring home cores for slicing from a depth of 500 or 600 feet.

As luck would have it, that "doubly rich millionaire" came in the form of the United States Federal Government. The very institution that had provided Agassiz, both father and son, with research grants to prove Darwin wrong, now ended up funding the solution to a puzzle that had waited more than a century to resolve. After several years discussing the "coral reef problem" with colleagues, geologist Harry Ladd submitted a report to the US War Department proposing "systematic geologic investigations of the Pacific islands now under U.S. military or civil control be undertaken immediately by the Geological Survey." Included in his proposal was a request that thousands of holes be bored into the coral to determine their depth.

This was the final test between Darwin and Agassiz. If Darwin was correct, the drill would need to pass through several hundred feet of coral before connecting with the basalt below. However, if Agassiz was correct, as Ladd suspected he was, then the drill would only need to go through a thin crust before connecting with the underlying foundation. After digging nearly 5,000 feet through the coral of Eniwetok Atoll, the drill finally passed through and hit pay dirt. The atoll had been built up from coral as the land had sunk from view, just as the theory of subsidence had predicted. Tiny organisms, just millimeters across, had pulled themselves up by their own bootstraps to create the largest natural structures ever created by a living being. Just next to the borehole that ended the debate, Ladd erected a small sign that still stands today. It reads, simply "Darwin was right!"

Ironic though it may be, it took a bitter rivalry between nations to find a solution to the rivalry between scientists from centuries past. Today, however, it is far more than a mere reputation that is in decline. Current estimates are that one-third of the world's coral reefs are in imminent danger of extinction. In an international survey of these most diverse ecosystems in our oceans, researchers determined that global climate change is increasing the average temperature of the Earth's oceans. This is killing the photosynthetic algae that has adapted into a pristine symbiotic relationship with their hosts. Coral bleaching on a global scale is the result and mass extinction will be the inevitable conclusion unless this trend is reversed. International conflict may have solved one coral reef problem, but if we're to resolve the next it will take a new spirit of cooperation to protect the oldest living structures ever created in our planet's history.


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Very well written and entertaining article, I enjoyed it very much. Thanks!

I felt I didn't get a very clear picture of Agassiz' alternative theory.

As a graduate student in biological oceanography, this article is appreciated. The concepts that these symbiotic colonial organisms illustrate range from evolutionary theory, ecology, paleoology, geoloy, etc. Corals (shallow zooxthentellate ones as well as their deep-sea calcifying brethren) conduct a delicate biological balancing act that operates at the interplay of biology and geology. They are life acting as a profound geological force. Bermuda too, is built mainly on the foundations of coral skeletons.

However, with the combined menace of ocean acidification and climate change these organisms could die out geologically soon, and the biodiversity of the ocean would suffer greatly for it if the status quo is maintained. Thanks for helping to popularize this issue through your column here.