10 Jun Cave Biology: Deep, or not, Life Inside Mammoth Cave
Oh, hello again! Welcome back to my blog. I’m calling in from a small fraction of Mammoth Cave’s (greater than) 420 miles of cave passages to report on some cave critters I’ve seen, and mention some that are infrequently seen! The cave ecosystem has captivated me since day one. I am very excited to share this post and hopefully, educate others (and myself) on cave adaptations, ecosystem nutrient flow, and the most important critters in Mammoth Cave’s food web!
Life inside the cave is not easy for these critters, but most have specialized adaptations for life in the cave. The cave environment is fairly constant, with a steady temperature of 54 F (12 C), generally low nutrient input, lack of sunlight and deep passages with high CO2 concentrations. So, why would any living being want a life within the cave? Cave critters exhibit genetic and/or behavioral adaptations, favored to exploit the limited resources available, while possibly seeking less competition (in comparison to the surface ecosystem).
This harsh ecosystem is home to a variety of different phylum (specific animal groups) including Arthropoda, Chordata, Crustacea, Platyhelminthes (flatworms), and Mollusca! Different organisms within the
cave systems have developed various adaptations to coping with the cave ecosystem! Some have long antenna to detect nearby prey in a greater surface area. Other organisms have completely lost their ability to see! Since there’s no light in the cave, why keep eyes? The cave fish, Typhlichthys subterraneus, exists today with vestigial eyes, meaning the eye parts are still present and don’t fully function! I really hope to see these critters live with my own eyes someday. Other adaptations to this environment include small body size, slowed metabolism, depigmentation, and further adaptations to deal with oxygen deprivation and high-water pressure at further depths in the cave river!
Can you see the vestigial eyes on Typhlichthys?
Each organism found in cave passages can be split into three major groups: cave guests, cave lovers, and cave obligates. Cave guests (aka trogloxene, for terminology folks) only use the cave for certain periods of their life cycle. For example, a tree roosting bat species may only use the cave during winter torpor or for maternal roosting. Other organisms who are guests to the cave system include daddy long-legs, large spiders (such as wolf spiders), and even birds simply using cave entrances to nest and incubate offspring.
A cave cricket, Hadenoecus subterraneus, is well adapted to life in the cave and serves as a very important member of the cave food web. The cave cricket has long antennae and legs, as well as less pigmentation than its surface relatives. Though Hadenoecus is a cave guest, they have the highly important task of consuming nutrients found on the surface, outside the cave, and returning once they’ve had their fill. The cave cricket supplies nutrients through their excretory products (poop), which is home to many microscopic organisms! Along with that, the cricket can spend great lengths of time inside the cave before needing a meal! This allows them to enter deeper areas of the cave and bury their eggs in sandy areas.
Now you may be thinking, “Those eggs are well hidden from the other hungry cave critters,” and you would be right… and wrong. The cave beetle, Neaphaenops tellkampfi, specializes in digging up the crickets’ eggs (and eating them)! This tiny beetle is troglobitic, a cave obligate, so they are well adapted to cave life. Supported by heightened senses to detect cricket eggs, these beetles are likely found on most cave tours!
The cave salamander, Eurycea lucifuga, is a cave lover (troglophile) and rarely enters the deep cave. I was lucky enough to see these shiny guys before they crept into hiding.
UNDERGROUND AQUATIC ECOSYSTEM
There is nothing more exciting than finding cave critters on a tour, but it’s easy to forget not to touch them. While on an educational cave tour with a college class, we were instructed to flip rocks in search of tiny cave creatures. I would like to state, this should not be done when on regular cave tours! Most areas within the cave are harmed by the human touch, whether intentional or not, it’s much safer to look with your eyes than with your hands!
While flipping over rocks in a cave stream to search for the smallest cave inhabitants, I found a small flatworm (Platyhelminthes)! Gross… but so cool. Cave streams are home to a variety of organisms including but not limited to cavefish, crayfish, Amphipods, crustaceans, snails, and cave shrimp! I couldn’t explore the aquatic cave ecosystem firsthand, so I turned to specimens housed in curatorial! Below I have pictures of well-adapted cave critters, an Amphipod, the crayfish Orconectes pellucidus, and the flatworm I found earlier! The crayfish can be found in streams too small to support cavefish and can grow up to 8 cm long! I look forward to continuing research and exploring further in the cave to update this post as I learn more!