This next installment of the Darwinian Coral Reef Theory series moves on to explore the discovery of coral reefs and other theories people had at the time.

English: English map of the Voyage of the Beag...

English: English map of the Voyage of the Beagle, a circumnavigation travel with Charles Darwin. Deutsch: Deutsche Karte der zweiten Reise der Beagle, die Weltumrundung mit Charles Darwin (Photo credit: Wikipedia)

Beginning in the 1700s, the days of early ocean exploration, it was inevitable that ocean explorers would run into coral reefs, as they inhabit the upper waters of the ocean. This led scientists, geologists, naturalists, and gentlemen of the navy to eventually discover coral reefs (Dobbs, Chapter 11). The position of reef structures on the ocean shelf made running into them, as ships could run aground, an imminent danger. According to William Schaffer, a professor in the biology department at the University of Arizona, Charles Darwin supported this theory of coral reef atoll formation by searching for dead corals he found on bottoms of lagoons “below the 120 foot limit” (Schaffer, “Darwin’s Theory of Atoll Formation”). This “limit” refers to the fact that corals can only survive within the top 120 feet of ocean water; at greater depths or above the oceans’ surface the small soft coral organisms, known as polyps, die and become the hard rock-like pieces that can be found on beaches, or in Darwin’s case, at the bottom of lagoons. In The Voyage of the Beagle, Darwin explains that the polyps’ “upward limit of growth is determined by that of lowest water at spring tides.” He explained this finding of dead corals on the bottom of lagoons as evidence for his position that the sea floor encompassing volcanic islands frequently subsides (Schaffer). Darwin also speculates in The Voyage of the Beagle that the water level of a lagoon tends to rise due to strong winds washing seawater up and over the barrier reef. He continues to explain that “for the water within the lagoon not only is not increased by currents from the outside, but is itself blown outwards by the force of the wind. Hence it is observed, that the tide near the head of the lagoon does not rise so high during a strong breeze as it does when it is calm.” Darwin believed that even this small difference in sea level was what caused the corals to die (Darwin, 481).

In addition to Darwin’s thoughts and research on coral reefs, other theories on their origin contributed to the area of interest and scientific advancement towards finding the answer. One theory was that of early voyagers. According to Darwin himself, they believed that polyps grew in the circular formation that most reefs are found in because they could better protect their “inner parts” from predators and harsh ocean processes. In The Voyage of the Beagle, Darwin says that this is far from the truth since the coral-building organisms need the shore to be exposed to the open ocean. Where the large coral features of the reef can depend on the outer ocean, the fragile branching corals thrive in the lagoon (Darwin, 485). Similarly, J.R. Forester, one of the naturalists on the second voyage of Captain James Cook in 1770, proposed that the coral animals simply knew that they needed to grow in a circular arrangement in order to create a sheltered surrounding for themselves (Dobbs, Chapter 11). Another theory is that atolls are related to and come from submarine craters. According to Darwin’s journals from the Beagle voyage, this was the most generally accepted theory. The young naturalist discredits it, though, by saying that “when we consider the form and size of some, the number, proximity, and relative positions of others, this idea loses its plausible character”. He then gives examples of atolls of all dimensions, concluding that they and others in the Maldives of the Indian Ocean must not have been formed by narrow reefs, but rather a multitude of small coral atolls separated from each other and growing in the larger lagoon areas (Darwin, 485-488). On the contrary, David Dobbs, author of Reef Madness, argues that the first theory to gain wide acceptance on the subject of coral reef formation was from Johann Eschscholtz of the Russian Empire. Eschscholtz voyaged to the Marshall Islands in 1815-1818 on a Russian expedition captained by Otto von Kotzebue, a German navigator in service to Russia. Eschscholtz theorized that corals grow faster in the seaward direction because they respond positively to the influx of oxygen and nutrients used for food from the open ocean. A third theory mentioned in Darwin’s records from the Beagle, forwarded by Chamisso, a “justly distinguished naturalist”, who believed that the corals exposed to the open ocean on the outer rim of the reef would grow up before the inner rim corals, creating the circular shape of the common atoll structure (Dobbs, Chapter 11). Darwin argues in his journal that the one key component of coral survival has been overlooked—the question of where do these coral creatures build their foundation, since they cannot survive below 120 feet in the water column (Darwin, 485-488). Naturally, Darwin largely doubted these theories since he had his own, although he admitted that it came to him as he was struggling up the side of the Andes Mountains—despite having never seen a coral reef, while looking at the volcanic aspects of the terrain (McCalman, 188).

Sources:

Darwin, Charles. “Keeling Island:– Coral Formations.” The Voyage of the Beagle. N.p.: n.p., n.d. 472-502. Print.

Dobbs, David. Reef Madness: Charles Darwin, Alexander Agassiz, and the Meaning of Coral. New York: Pantheon, 2005. Print.

Schaffer, W. M. “Darwin’s Theory of Coral Atoll Formation.” DarwinReef.htm. N.p., n.d. Web. 8 June 2015. <http://www.blc.arizona.edu/courses/schaffer/182/DarwinReef.htm>.

McCalman, Iain. “Obsession.” The Reef: A Passionate History. Penguin Books, Australia: Hamish Hamilton, 2013. 187-88. Print.