Cave Corals Project

Cave Corals Project

This is the story of a cave diver in love with corals who started a science project, and became the crazy coral lady. It’s hard to pinpoint the moment it started. Growing up I spent a lot of time by the water, in a part of Mexico somewhat isolated from the rest of the country. My town was a sleepy fishing village on the coast of Quintana Roo with no phones, no movie theater, and no shopping mall - nothing to speak of in terms of modern conveniences. I spent most of my days in the water and in the sand, digging for crabs, worms, corals, and shells. I have always believed the Ocean is where I belong.

The region of the Yucatan Peninsula is known for the Cenotes, these are geological wonders in the shape of pristine blue and crystal clear pools spread everywhere in the jungle. These ground water openings lead to horizontal cave developments thanks to the dissolution of the limestone rock. This type of caves and landscapes is called Karst.

Caves are exotic places. For most people, the perception of caves varies from fear to awe, from claustrophobia to wonder. They can also be seen as the most gorgeous places on the planet, or the most hostile and dangerous spots on earth. Even if some people say that flooded caves are “just wet rocks”, for me, caves are the place where I found the Ocean once again.

In Quintana Roo, families usually head to the Cenotes for a leisurely change of scenery and to flee the incessant heat of the Mexican summer. My parents weren’t the exception back then, they used to organize outings to spend the day at the Ruta de los Cenotes in Puerto Morelos with other friends and neighbors. I remember that fossils decorated the walls and ceilings of the Cenotes with prints of corals, and they would pave the paths through the jungle with fossilized conch and shells visible on the bare limestone.

Being inside the Mexican flooded caves is like being in a museum. I have fallen in love with the language the cave speaks, and learning this language has become my passion. If you look closely, and you know what to search for, you will learn a lot, but you’ll also come out with more questions than answers. This is what happened the first time I dove a Cenote in 2013. On that dive I became extremely curious about the fossils because I was submerged in a cave - how did coral fossils get here? Having seen them outside around the Cenotes had never stuck me as strongly as when I saw them underwater; the setting, the color, the texture. It made me sigh. I was eager to get out of the water to ask questions. The entire Yucatan Peninsula was once covered by the ocean, they told me.

Photo courtesy of Jeronimo Aviles.

A few years passed before I finally became a cave diver. I had been part of the tourism community for years and knew that the communal knowledge did not include much about coral reefs today, let alone paleo reefs. Those that existed hundreds of thousands (or even millions) of years ago and that now lay fossilized, preserved in the caves. I noticed that most of my dive buddies weren’t interested in marine fossils. While I was able to recognize slate pencil urchin spines, queen conch, brain coral, sand dollars, and sea biscuits, they were constantly looking for big bones. I started a collection of coral photos that barely made justice to the beauty of the coral fossils, this was the only evidence I had of my findings.

A proper search for information began as I looked for resources to be able to identify the fossils I was finding during my cave dives.

In the process, I learned that some of the fossilized reef crests I encountered most probably thrived during the last interglacial period, 130-116 thousand years ago when sea level is estimated to have been up to 6m higher than it is today. I learned that many of the coral species haven’t changed much since, hence I was able to ID them somewhat accurately with the naked eye. They looked exactly the same as the ones on the reef or the fragments we used for reef restoration, or even more like the pieces of coral skeleton washed up on beaches. However, visiting caves further inland would mean looking at coral fossils that appeared much older. Estimations from other scientists looking at the Yucatan Peninsula geological history estimated some could belong to the Miocene-Pliocene at least 5 million years ago. Much to the frustration of my dive buddies I started moving at a snail’s pace through the caves, documenting every coral fossil I saw, my obsession growing.

Photo courtesy of Jeronimo Aviles.

Like a girl scout selling cookies, I started knocking on doors and reaching out to different people with what had become my foremost question - where could I find a list of the fossilized coral species in the caves of Quintana Roo? I got redirected from person to person, resource to resource. At the time I didn’t know that I was looking for a document that did not exist yet. It is uncommon to find other cave divers that share the amazement for these tiny invertebrates. I realized most coral scientists do not dive caves, and most cave divers aren’t coral experts. I had created a unique niche being one of the fewer people who had extensive knowledge about corals and caves.

As luck would have it, two fundamental events helped me in my journey to the Cave Corals Project as it exists today. The first one was an invitation to dive for a restoration project in the Maldives where I was able to expand my knowledge of coral species, without expecting that later in a Mexican cave I would come across something very similar to what I had worked with on the island. A coral fossil of what I believed belonged to the genus Pocillopora. Secondly, I was given the contact of a scientist that had already produced a list of fossil coral species in Quintana Roo. His research had taken place at an excavation site for an amusement park in the early 2000s.

I decided to approach him with an idea. As far fetched as it seemed, I pitched to him the possibility to begin collecting data on the coral fossils of the caves to be able to build a catalogue with photo identification of fossilized Scleractinian corals (also known as stony corals). Corals are sessile invertebrates that most of the time growth into colonies. Each tiny individual called polyp contributes to secreting a calcium carbonate (CaCO3) skeleton that grows rather slowly, and the coral tissue covers that skeleton. Coral reef structures are mainly built by stony corals, and these grow over older coral skeletons, making for thousands of years of layered Calcium Carbonate rock structures. In some places, corals are responsible for building massive reef framework structures (like Cozumel - a world renown dive spot).

Photo courtesy of Tamara Adame.

The skeleton of each species of coral has a different colony form and shape pattern made of valleys and grooves. The cavity where the polyp is fixed is called corallite, and has a specific number and shape of septa. Each septum is a vertical blade-like plate that holds the animal in place within the cup-shaped cavity of the corallite. The soft tissue of the animals connects on the surface of the coral between each individual, covering the skeleton entirely. The skeleton looks like white rock when the animal dies because the color of a coral is provided by the Zooxanthelae (a symbiotic algae that lives in the coral’s soft tissue) and not by the coral polyp itself. The skeleton can then be used to identify the species even when the coral tissue is gone.

By analyzing, counting, and looking at the septa and the corallite, we can tell which species it belongs to. Because of this, when I discovered coral fossils in the caves, it seemed practical to conduct the identification with a simple method such as macro photography. The word simple does not do justice to the process of taking a macro photo of a coral fossil in a flooded cave (in neutral buoyancy with reduced light and finite source of gas with minimum or no help while sediment snows down on you disturbing the visibility). But in theory, if I was able to obtain good closeups of the coral fossils, I would be able to identify them. The corallites vary in size, but I soon found myself taking photos of a 2mm subject. There was a great deal of learning about photography and lighting too.

Photos courtesy of Jeronimo Aviles.

In my pitch, I also included some information about the alleged Pocillopora fossil I had seen and recognized after diving in the Maldives. Was it possible to have found this coral in a cave in Quintana Roo but not in our modern reefs? The answer blew my mind. This coral genus (Pocillopora) is currently absent from the Caribbean, but still present in the Pacific, so I had found and visually identified a fossil of a species that is extinct in our region! This had been documented before so it definitely set me off on the right path. Curiosity had paid off. My new contact confirmed no one (that he knew of) had ever attempted a comprehensive collection of data for identification of coral fossils in the caves of our state. Something similar had been done at an excavation but not in a cave, and that meant my project had huge potential to create something new. It felt like it was meant to be. And the Cave Corals Project was born.

The Cave Corals Project is a one woman show but has received countless support from the diving community. In the beginning, the project consisted of learning as much as I could about fossils in general. Projects like this often take years to launch but in my case, a third lucky event provided for one of the most valuable resources this project needed - time during lockdown.

Photo courtesy of Jeronimo Aviles.

I am not a scientist, but science is a method that I needed to understand and apply to solve the questions I constantly had been accumulating. One of the first things I looked up was “Scientific Method”. I remembered high school so vividly and wished for a second that I had had more interest in sciences growing up. My searches went from “What is a fossil?” to “Types of fossils” to “Dinosaur fossils” to “Types of dinosaurs”. It is easy to spend the day Googling and browsing research data bases during a pandemic lockdown. Entire days went by and multiple documents kept popping on my desktop labeled “For later”.

Fossils form in a variety of environments and conditions. In the case of the coral fossils in the flooded caves, a replacement process is what originates most of them. The skeleton of the coral is buried in sediment, while buried, water flows through, imbibing it and replacing the minerals of the skeleton (in this case Calcium Carbonate) with the minerals present in the water. To my amusement, the groundwater geochemistry of the Yucatan peninsula varies largely and the replacing minerals depend of the cave location. The water itself will dissolve the original minerals that compose the coral skeleton and because the sediment that covered it has hardened, a fossil print or mold is created. Furthermore, the mold can then produce a cast if it gets filled with sediment, which would produce a fossil that looks exactly like the original skeleton. When the hardened sediment that envelops it erodes, the new fossil (made out of crystalized sediment) would be exposed. I felt fascinated every day.

Photos courtesy of Tamara Adame.

With what I had learned about fossils and my previous experience in reef survey, I decided to produce a data collection method and sheet. This meant measuring the fossils (and finding adequate scales for the job!), describing their color, their size, the type of coral they would have been and the type of fossil we were looking at. The data sheet was reviewed by other scientists and mentors who found the project fun and interesting. Eventually it was translated into an online database where I would be able to store the information, images, and analyze and compare the information. The project includes surveying the exact locations of the coral fossils I photographed in order to be able to go back if we need to take more information, or if special fossils that need to be collected for study would be found. The database also makes it possible to share the information with coral experts and palaeontologists who could contribute with the identification process, and other divers could learn the method for data collection and be able to contribute as citizen scientists to the Cave Corals database.

Photo courtesy of Jeronimo Aviles.

The Cave Corals Project is still considered to be in its early stage but in a short time dozens of academics, institutions, scientists, and cave divers have supported me to be able to conduct research without originally being a scientist. The ultimate objectives of the project are to provide organized information in a baseline study that will help understand and preserve the caves of Quintana Roo as they hold an important part of the fossil record of our region, and to motivate the conservation of the aquifer by acknowledging that the pieces of natural history that it holds may one day disappear due to overdevelopment of the land. It will take years before we are able to understand the exact distribution of the species of corals that once thrived over the Yucatan Peninsula and that we now observe in the form of fossils during our cave dives. As divers, we have the possibility of gathering that information bit by bit and painting a picture with every coral fossil recorded, bringing cave divers closer to science.


Written by Tamara Adame

Tamara is a self taught underwater naturalist from Puerto Morelos, Mexico. She has spent most of her life around water and is an Open Water Scuba Instructor and cave diving guide. She holds a BSc in Communication and a Scientific Diving diploma which has allowed her to work in environmental conservation projects and motivated her to launch the Cave Corals Project in 2020.