After the Federation’s quarterly Board of Directors meeting in April, some of our board members and staff went tromping around in the marshes of the northern Everglades — at night!
Following consistent rainfall in South Florida over the last several weeks, many depression marshes in the southern part of the state have been covered by at least a few inches of water. These marshes that appear brown and barren during the day become teeming with wildlife once the darkness of night has set in. Present are fish, snakes, crayfish, frogs, diving beetles, salamanders, snails, turtles, wading birds—the list goes on and on!
These marshes are ephemeral habitats, which means that for parts of the year, they are dry. Where do all the animals go? Underneath the muck! The floor of these wetland habitats is covered with a mat of algae, cyanobacteria, plants, and decaying organic matter that scientists call periphyton.
Outreach Coordinator Tasman Rosenfeld is holding an Everglades dwarf siren (Pseudobranchus axanthus belli), which is found nowhere else in the world but the Florida Everglades!
During wet conditions, periphyton acts as a food source for all of the animals in these wetlands. Plus, due to the 3D structure of the mats, complete with floating vegetation and cross-cutting branches, it provides shelter in which most of the invertebrates and smaller vertebrates like fish and salamanders live.
But when the water evaporates, the periphyton creates a crusty layer over the sand bottom (evidence that the present-day sites of these freshwater wetlands were beaches or ocean shallows millions of years ago). Moisture is trapped between the crust and underlying sand, creating a humid layer where the animals enter a period of torpor (slowed metabolism) and patiently wait for the next flooding rains in slimy anticipation. Why slimy? Many inhabitants of depression marshes cocoon themselves in their own mucous to resist dehydration!
The main reason that these marshes are so busy with life after dark is that the animals know they only have so much time left to eat and make babies before their homes dry out.
FWF President Sarah Gledhill holding a two-toed amphiuma (Amphiuma means), one of the seldom encountered species of giant salamander that dwells in these habitat
If interspersed drought periods weren’t drastic enough, these habitats are also threatened by human activities. Development is, of course, a primary threat as depression marshes are filled in and razed across the state for new buildings, roads, and parking lots.
Furthermore, many regions where these wetlands persist are beloved sites for off-road vehicle use. Besides the risk of squishing animals under tires, off-road vehicles also disturb the integrity of the moisture seal underneath periphyton crusts, leading to the dehydration of the aquatic animals that rely on that moisture for survival.
Board member Matt Erpenbeck found an old striped mud turtle (Kinosternon baurii) out hunting for dinner
Most depression marshes also lie within a matrix of fire-dependent flatwoods or scrub, which means that the wetlands also depend on fire to avoid being choked out by woodier aquatic vegetation. Like with many of Florida’s habitat types, fragmentation of the landscape across which wildfires would historically burn and decades of fire suppression has taken its toll.
Of course, the ever-present threat of climate change has implications for depression marshes, too. In the southeastern US, evidence is mounting that seasonal rainfall patterns are shifting or becoming more irregular, meaning that drought periods could last much longer than the animals in these habitats can handle.
Now, let’s take a look at some of the creatures the FWF team encountered!
Two-toed amphiumas (Amphiuma means) is one of the world’s largest species of salamander. From afar, they are much more reminiscent of an eel than a salamander since they are aquatic and appear limbless. Truthfully, however, they still possess all four limbs! They’re just really, really tiny and thus basically useless. They also have quite poor vision, and instead rely on a network of electroreceptors on the dorsal surface of their heads to detect their prey. For a salamander, they have remarkably developed jaws which may have evolved to help them feed on crayfish, whose hard exoskeletons normally make them a tough meal.
The Everglades dwarf siren (Pseudobranchus axanthus belli) is endemic to the Everglades and South Florida, meaning that it is found nowhere else in the world. Interestingly, it is the only amphibian that is unique to the ‘Glades. These aquatic salamanders typically display quite bushy external gills much like an axolotl, though these gills atrophy and sometimes disappear altogether when the marshes dry out and the salamanders retreat to their mucous cocoons under the periphyton crust, only to re-develop during the wet season. Like all other sirens, a family of salamanders restricted to the southeastern US, they possess only their front two limbs.
They also found a small peninsula newt (Notophthalmus viridescens piaropicola), which is another salamander that is found only in Florida.
Peninsula newts (Notophthalmus viridescens piaropicola) are another salamander which is found only in Florida, usually on the edges of stagnant or slow-moving bodies of water. With four fully developed limbs, they are the salamanders with the most familiar form of the four species found in the Everglades.
The greater siren (Siren lacertina) is common in marshes and swamps throughout Florida and coastal plain of the Southeast. Like their cousins, the dwarf sirens, they retain juvenile features like external gills and an underdeveloped palate throughout adulthood. This makes them a prime example of paedomorphy, or evolution towards a juvenilized adult body form, which is a more common theme in salamanders than it is in the evolution of many other vertebrate groups. Sirens, like amphiumas, can grow upwards of three feet long and get as girthy as a human forearm forearm.
About the author: Tasman Rosenfeld is a teacher and active research scientist who has previously served on the FWF Board of Directors and as a staff member.