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Ecology

Animal Forests

These creatures build forests in the immense marine desert and serve as a habitat for numerous species that are important both to the ocean’s ecology and as a food source for humans; they are as colorful and multi-shaped as flowers, and although they don’t seem like it, they are animals. They are octocorals, the great strangers of science, whose basic qualities are only now beginning to be researched. It is unknown how they will react to the warming and acidification of the oceans, so the race is on to understand their importance for marine balance and guaranteeing human food security. Scientists are also researching the possibility that they contain basic elements capable of curing diseases.

Text and fotos: Fundación Azul-Verde-Azul

The sea is beautiful when we see it from the beach: different shades of blue, sometimes calm as a swimming pool, sometimes stormy, with waves and currents; every day it attracts millions of tourists. However, underneath that magical surface, which covers 80% of the Earth and serves as the primary food source for a third of the world’s population, lies a world practically unknown to science. There are totally unexplored territories and living beings with completely unexplored natural histories. Some of the marine ecosystems most interesting to scientists are those formed by corals. These animals form reefs or underwater forests, creating a home for many other species: turtles wander among their branches, thousands of colorful fish congregate, and a multitude of crustaceans and mollusks hide within. Many of the living beings that inhabit the ocean are born –and spend their first stage of life– in these ecosystems.

Not all corals are the same: some are hard and others are soft. The hard ones form reefs; they are called hexacorals because each of their polyps has six tentacles. Although those tentacles help them catch some of their food (small organisms in the plankton), most of their nutrients come from a symbiotic relationship with small algae called zooxanthellae that live inside each polyp. The algae photosynthesize and share nutrients with the coral; in return, the coral provides a place to live. The survival of algae, however, requires calm, shallow, and crystalline waters and a delicate balance of temperature. This close relationship now finds itself in danger: increased carbon emissions are causing the temperature of the water to rise, which kills the algae and, as a result, the corals. This phenomenon has been of great interest to the scientific world and most of the research on corals has been dedicated to studying this type of coral.

However, there are also the lesser-known soft corals, also called octocorals (because they have eight tentacles in each of their polyps), of which there are more than a hundred species. These corals live in the tropical eastern Pacific (a biogeographic region between Baja California and northern Perú), where the waters are very active due to strong ocean currents. To reach some of their colonies, it’s necessary to practice what is known as “flag diving,” where scientists lower themselves, holding onto an anchor, while their bodies whip around like a flag. It is not surprising then that little is known about octocorals, and even now in the 21st century, their basic qualities are just beginning to be studied.

The reason soft corals can grow in such inhospitable places is that, unlike hard corals, soft corals do not depend on algae because they use their tentacles to catch their food. The octocorals, moreover, do not form reefs. Their colonies adhere to rocks, allowing them to conquer space from the surface down to depths greater than 328 feet, where they grow in the shape of a tree, with a trunk and many branches. This allows them to play a fundamental role in the oceans, fostering life in areas that otherwise would be true deserts. Microscopic crabs, brittle stars, and mollusks live in the branches of these corals. Under their canopy, small fish and many invertebrates take refuge, and above, large fish such as snapper congregate, often forming a food source for humans. The cluster of colonies are known as the “animal forests,” and they make up a true oasis in the middle of the immense ocean, as well as guarding valuable information as yet unread by humans.

The work of learning more about these species, identifying them and naming those that have not yet been described, was begun almost ten years ago by the scientists Héctor Guzmán, of the Smithsonian Tropical Research Institute (STRI), and Odalisca Breedy, of the Center for Research in Marine Sciences and Limnology (CIMAR) at the University of Costa Rica. Since then, they have described 34 new species, most of which originate from the Panamanian and Costa Rican Pacific.

Once the species were described, they began researching the basic biology and ecology of these corals. After thorough field work in the Panamanian Pacific, led by Catalina Gómez during her doctoral studies at McGill University, we now know how the octocorals reproduce, factors that limit their recruitment (the process that enables new octocorals to join the community), and how this is linked to annual changes in temperature and the competition for space with other sessile organisms (those that grow attached to a substrate).

For example, Leptogorgia alba polyps, which have thin, white branches, produce just three or four eggs each year and have high recruitment and mortality rates. On the other hand, the Muricea austere, with thick, cream-colored branches, produces about thirty eggs per month throughout the year. Gómez also quantified the recruitment, survival, and death probabilities of the most common species. Through the use of a mathematical model, she calculated that one species is replaced by another every one to five years, and that it would take  21 to 34 years for a coral to return to its original state after a disturbance, depending on the environment in which it is found.

Studying the basic biology of these species is just the beginning of understanding a complex and unknown ecosystem. Many invertebrates live in the octocorals and their life cycles are interdependent. This is where many of the species that provide food for human beings congregate and they also house bacteria that are resistant to diseases, such as cancer and malaria, according to a group of researchers led by Marcelino Gutiérrez of the Center for Biodiversity and Drug Discovery at the Institute for Scientific Research and High Technology Services (INDICASAT).

The studies by Guzmán, Breedy, Gómez, and Gutiérrez are just the beginning of a story that is beginning to take shape. We now know the basic qualities of these animals, but there is still much to research. We do not know, for example, how these species will react to the warming and acidification of the oceans. Everything seems to indicate that they are more resistant than hard corals, but experiments to prove it still need to be conducted. Octocorals provide just one example of how little we know about the oceans and this fascinating world that lives beneath the water’s surface.