Cenotes, natural sinkholes often filled with water, are a distinctive feature of regions like the Yucatán Peninsula. Formed over thousands of years as limestone bedrock collapses, these geological formations connect to vast underground river systems. Many cenotes host various fish species, though their presence and diversity depend on specific environmental conditions.
Common Cenote Fish Species
Cenotes are home to a range of fish species, some adapted to sunlit surface waters and others to the perpetual darkness of underwater caves. In open or semi-open cenotes with ample light, common species include mollies, guppies, and various types of catfish. The Mayan tetra, a small fish with silver scales, is also frequently observed in these calmer waters. Larger species like mojarras and Jack Dempsey fish can also be found. Coastal cenotes, connected to the ocean through underground tunnels, may even host marine species such as snappers and gobies.
In the deeper, lightless sections of cenotes, unique fish species have evolved specialized adaptations. These include blind cave fish, such as the Mexican blind brotula and the blind swamp eel, which have lost eyesight and rely on other senses to navigate their dark environments. The “White Blind Lady fish” and the “Yucatecan Blind Eel” are other examples of these endemic species. These fish often exhibit reduced pigmentation and specialized sensory organs to thrive in their isolated habitats.
Why Fish Thrive or Struggle in Cenotes
The presence and abundance of fish in a cenote are influenced by several environmental factors. Water quality plays a significant role, with salinity, oxygen levels, and temperature determining which species can survive. Many cenotes exhibit a halocline, a distinct boundary where freshwater meets denser saltwater, creating varied habitats. Light penetration is another factor, as open cenotes support plant life and a food web reliant on sunlight, while dark caves necessitate different adaptations for survival.
Connectivity to other water bodies, such as rivers, oceans, or other cenotes through underground passages, allows for the migration and dispersal of fish species. Food source availability, often influenced by aquatic plants and invertebrates, also impacts fish populations. Cenotes with more developed shorelines tend to support a greater richness of fish species due to increased vegetation. The relatively stable environment of cenotes, with less abrupt changes compared to other aquatic systems, contributes to the consistent presence of certain fish species.
Beyond Fish: Other Cenote Inhabitants
Cenotes support a variety of other aquatic life. Invertebrates form a foundational part of the food web, including small organisms like rotifers, copepods, and cladocerans, which serve as food sources for fish. Larger crustaceans such as cave shrimps, crabs, and even lobsters are also found. These often adapt to low-light conditions of the subterranean environment.
Amphibians, including frogs and toads, thrive in the humid environments in and around cenotes. Reptiles like turtles are common, basking on rocks or swimming in the clear waters. In some cenotes connected to larger water systems, crocodiles have been observed. Bats often inhabit cavernous areas, and swallows nest along the sinkhole walls.
Protecting Cenote Ecosystems
The unique ecosystems of cenotes face threats, primarily from human activities. Pollution from untreated sewage, industrial waste, agricultural fertilizers, and solid waste can contaminate the cenotes. Microplastics have also been detected in the water and marine life. Overexploitation of water resources for domestic, agricultural, and industrial use can reduce water levels.
Unregulated tourism poses an additional challenge, with chemical sunscreens and insect repellents contaminating the water. Conservation efforts focus on promoting responsible tourism, which includes avoiding harmful chemicals, not touching formations or wildlife, and properly disposing of waste. Education and community involvement are important for protecting these natural areas, ensuring their biodiversity and water quality are maintained.