By: Javier A. Pinzón
Photos: Scientifics courtesies, Caroline Powers y Substation Curaçao
What might happen if humans were able to explore the ocean floor beyond the limits imposed by diving? What surprises await scientists in the deep, hitherto unfathomable coral reefs? Dr. Ross Robertson, who has spent a lifetime studying reef fish, was able to explore deep coral reefs in a submarine and, in just five years, he has discovered, with the help of his team, two-dozen new species – 25% of the fish collected– at depths of between 425 and 1,000 feet. He also discovered a new area of deep-sea coral reefs.
The Australian biologist gets tremendous enjoyment from finding, studying, and describing things others have never seen before. This began as a child, when he attended a rural boarding school in Australia, where he learned not only about farms, but also about the forests, rivers, and wild animals around him, which fascinated him and marked the course of his life. While working on his masters, he studied freshwater fish and later, his doctorate focused on reef fish.
Robertson spent three years on an island in the Great Barrier Reef of Australia, studying a small fish that cleans other fish by “tickling” them and then picking up the parasites they release. Most interesting of all, this little animal can change its sex. Each male moves within a 50-foot territory that includes females, each with its own territory as well. The male makes daily visits to copulate with each of them. If the male dies and fails to return, in just one hour the largest female, realizing that something is wrong, begins to behave like a male and in the space of a week its spermatogonia, previously hidden, begin to develop, expand, and eventually replace the ovaries. Observations such as these from the hidden book of nature can only be made by an acute eye and require a solid scientific background and rigorous discipline.
No wonder then that upon finishing his PhD, Robertson was awarded funding in Australia that allowed him to choose any place in the world to conduct his research. He chose Panama, where the Smithsonian Tropical Research Institute (STRI) is headquartered and, because of the region’s abundance of tropical fish, is his area of interest. With this goal in mind, he spent a year exploring the Guna Yala reefs, after which he was offered a position as a scientist at STRI. Since then, he has traveled the world studying fish and published guides to coastal fishes in the tropical eastern Pacific (https://biogeodb.stri.si.edu/sftep/es/pages) and the Caribbean and vicinity (https://biogeodb.stri.si.edu/caribbean/en/pages) downloadable as apps.
In 2013, Robertson had a fortuitous encounter in Curaçao. A tourism industry investor, fish enthusiast, and amateur explorer purchased the Curasub submarine to satisfy his curiosity about what lies beyond the limits of scuba diving. In fact, very little is known about what goes on below 165 feet, the limit for scuba diving. Even the “rebreather,” which makes it possible for divers to descend to 500 feet, isn’t sufficient for this research, due to the limited time one can remain that deep. Since then, Ross has worked with Dr. Carole Baldwin from the National Museum of Natural History, who was awarded funding for deep-sea studies.
The submarine has allowed them to descend to 1,000 feet, stay below for several hours, and travel long distances. The submarine’s two robotic arms use a pump to suck up the fish, guide them through a compartment where they are anesthetized, and then store them in an aquarium.
Exploration using this submarine has resulted not only in the discovery of new species for science; during the period of this study, Ross and his collaborators also uncovered a new area of coral reefs. Prior to this, only two areas had been identified: one, 0 to 130 feet below the surface, where shallow-water (altiphotic) coral is very common (altifóticos); and another, from 130 to 425 feet, where other mesophotic (light-dependent and low-light penetration species) coral reefs form. Submarine explorations discovered different species of fish related to the same family living between shallow and deep areas of 425-1,000 feet. They found that typical reef fish descended much deeper than the reefs themselves. This area, labeled “rariphotic,” doubled the known area for reef fish families and genres in general.
Ross and Carol wondered if the reef fish they discovered in deep-sea areas around Curaçao were present elsewhere in the Caribbean. To find out, they secured another submarine, the Idabel, in Roatán (Honduras), designed and manufactured by the submarine’s pilot. Because this submarine was not designed for scientific purposes, it had to be outfitted with their fish collection system, but the sub is now Ross’s “right-hand man.”
And because water temperatures in Roatán, on the opposite side of the Caribbean from Curaçao, are warmer, it proved the perfect place to search for answers to their questions. The scientists were interested in studying the exact location of these fish on the reef slope, whether the community of fish changes at different depths, and the factors (light or temperature) that determine the depth at which each species lives. Given the temperature difference between the two zones, it is also possible to compare the depth range of common fish between the two locations to determine whether this factor affects distribution. A comparison with the Bahamas and Bermuda remains to be done, since temperatures in these waters are even warmer, reaching 68° F instead of 51° F.
How important are these studies, beyond satisfying a very valid scientific curiosity? The world is changing. With global warming, the oceans will continue to get warmer. If water on the surface heats up a lot, and the deep waters heat up only a little, can the species nearer the surface move into the depths? Knowing how a certain species functions at different depths, and at different temperatures, can give us an idea of the importance of temperature in determining the proper depth for each species.
Descending to these depths has made it possible to detect another important problem: the lionfish, an invasive species responsible for the mortality of a large number of fish in shallow areas, is larger at depths below 425 feet and therefore able to lay more eggs. Carole and Ross hope to study their reproduction and whether their offspring are rising to the surface. Could these deep-water populations sustain the shallow-water populations currently being hunted to control their population?
The scientists need to estimate the population, measure the size of the fish at various depths (using a laser), and study the contents of their stomachs by analyzing their DNA to find out what the lionfish eat in deep waters. This DNA can be identified through a DNA library developed by the Smithsonian over the years.
Another idea is to use stable isotopes or ratios of isotopes of carbon, oxygen and nitrogen. Every organism keeps a permanent record of what it eats. Using this method, scientists can compare information regarding the isotopes in lionfish living near the surface with those living in deep waters to determine whether their diets differ over a long period of time. The results will tell us if these fish remain in the depths or migrate from top to bottom.
There is still much to discover on our planet and in these deep-water reefs, only a fraction of which have been explored. The problem, as always, is funding; submarines are expensive. However, thanks to the efforts of these scientists, we continue to marvel at the discovery of new species.