We were recently lucky to be visited by Dr Alistair Sponsel from Vanderbilt University in Nashville, Tennessee. Alistair gave a talk in which he described Darwin’s debt to marine science. This debt took the form of an amphibious approach to natural history that shaped his approach to theoretical reasoning and which was developed by working closely with hydrographic surveyors during the voyage of the Beagle (1831-1836). While this voyage is well known for presenting Charles Darwin with the opportunity for wide geographical exposure to, and comparative work on, the animals, plants and fossils that gave rise to his Theory of Evolution, he also thought a lot about coral reefs on that trip. During this time he also came up with the Theory of Coral Reef Formation. This states that coral reefs evolve through a series of successional stages from fringing reef to barrier reef to atoll, by staying up at sea level through
their upward growth on top of subsiding marine volcanoes.
Alistair described how Darwin’s Theory of Coral Reef Formation was shaped by the activities of the ship’s hydrographic surveyors. These included carrying out many many many (many many!) depth soundings from a lead line. The bottom of this lead line was hollowed out and stuffed with tallow (animal fat), so that interesting things from the seafloor might stick to it and be dragged up from the depths for inspection. Darwin got quite excited about these specimens and we saw some of the notes he made about them in Alistair’s talk (like a true scientist, his handwriting was quite hard to decipher). Moreover, we learned how Darwin had largely deduced his theory of reef formation from maps and topographic profiles before carrying out his first reef surveys. As he later wrote:
“No other work of mine was begun in so deductive a spirit as this, for the whole theory was thought out on the west coast of South America, before I had seen a true coral reef. I had therefore only to verify and extend my views by a careful examination of living reefs.” (The Life and Letters of Charles Darwin, Day 18 of 188).
The next stop on Alistair’s journey is Cocos (Keeling) Atoll in the East Indian Ocean. This was the only Atoll that Darwin visited, where he was able to carry out a careful examination of the reef. He was particularly keen to explore the geographical distribution of different corals across the reef, with a view to answering questions such as ‘why don’t the lagoon corals also grow up to the sea surface?’, ‘are the corals that inhabit the outer periphery of the atoll different to those in the lagoon and how deep do these outer corals extend?’ and ‘Does a shallower foundation exist or is it possible that these can have grown up from the sea floor?’ The answers to these questions had implications for the validity of his coral reef theory.
I found this all very exciting to hear because last year I did somefieldwork at Cocos. At the time I hadn’t realised how similar my own motivations had been to those of Darwin. I had gone with the intention of mapping the seafloor composition around the atoll and collecting depth soundings with an echo sounder in order to make a 3D model of the reef. My job was much easier because I was armed with a satellite image and I could work from a boat instead of a using a leaping pole to get across the reef flat, as Darwin did (yes! this has been fact checked!).
They are approximately 150 years too late, but you can see the bathymetric model and seafloor maps I made of Cocos in this video. I wonder whether Charles Darwin might have taken an interest in them.