Endemic brittle stars discovered in Mexico show how cave fauna has adapted to extreme environments

An unprecedented study led by the National Autonomous University of Mexico (UNAM) detected the presence of cave brittle stars at the “El Aerolito” cave in Cozumel, the first specimens found in Mexico and the third in the world.

Scientists from the UNAM’s Institute of Sea Sciences and Limnology (ICML) along with members of the University of Quintana Roo, observed that this kind of cave brittle stars , found in 2019, have a different pigmentation due to the low light of the cave as well as longer extremities compared to species that live outside that environment.

Cave brittle stars are a member of the echinoderm family, made up of a group of sea animals that include sea urchins, lilies, and sea cucumbers.

“Brittlestars have a small, flattened body made up by a round disc and five thin, long arms that measure between 18 and 20 centimeters and that look like snakes,” explain the scientists. They produce oxygen in the seabed, model the texture of the seafloor, and are part of the diet of other organisms.”

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For their detection, UNAM researchers employed different comparative methods between two other species living at the “El Aerolito”, O. commutabilis and O. reticulate, which are classified as troglomorphic, animals that live in dark areas.

“Troglomorphism is an adaptation to cave life and its been mainly studied in arthropods and vertebrates of water and land caves. It had not been analyzed on echinoderms exclusive to caves; we had only made suppositions regarding their appearance,” added Francisco Alonso Solís-Marín from the ICML.

The UNAM researcher explained in a statement that cave life has conditions such as the lack of light, low amounts of oxygen, and low temperature, as well as lack of food.

Among the characteristics observed “the most notorious one is the length of the ambulatory arms and feet, as well as the system of photoreceptors or light receptors and the peculiar pigmentation with opaque colors such as gray or white, perhaps as a result of the environment they live in, with almost no light,” stressed Solís Marín.

“El Aerolito” is characterized for being a “system with tunnels full of freshwater, whose entry is a cenote; it is 18 meters deep and is in perpetual darkness,” reports UNAM. So specialists think that the Ophionereis commutabilis can produce its own light through a bioluminescence process .

“El Aerolito” is currently in a vulnerable situation because of the development of tourism complex such as the construction of golf fields that require the use of fertilizers that spread inside the sea cave and which could undermine the current state of its habitat.

Over 100 species of sea invertebrates live at the “El Aerolito,” which makes it one of the richest water systems on the planet, hence, Solís-Marín thinks “it is necessary for there to be a plan that protects these fragile environments without harming tourism in the area.”

The academic said that once the coronavirus lockdown is completely lifted, they will continue exploring the cave: “Reporting the results of this work is an achievement for the Institute and the University; it’s the first time there is evidence of the adaptations of these water organisms in caves that feed on microbial mats,” he added.

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Back in February, Francisco Alonso Solís Marín explained that the brittle star arrived at the cave approximately four billion years ago. It was discovered in 2006 but it was revealed until the obtention of its nuclear DNA in 2019. Through years of research, it is believed that the ancestors of this species sent larvae to explore the cave, where they mutated and generated a new species that installed in the depths of the cave.

The ICML representative stressed the relevance of echinoderms who “are important for being a food source, while in the pharmaceutical industry they are studied for having active principles that are able to inhibit the growth of carcinogenic cells.”

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