A Sea of Grass; Part 11- Reptiles

When snorkeling the grassbeds of the Florida panhandle encountering a reptile has a low probability, but it is not zero.  Of all the reptiles that call this part of the state home, few enter marine waters and most of those are very mobile, moving up and down the coast heading from one habitat to another.  In fact, there are no marine reptiles that would be considered residents of our seagrasses, only transients. 

The one species that you might encounter is the green sea turtle (Chelonia mydas).  This is the largest of the “shelled” sea turtles and has a vegetarian diet.  With a serrated lower jaw, they can be found grazing in the seagrass beds feeding on both the grasses and the species of algae found there.  The carapace length of these large reptiles can reach four feet and they can weigh up to 400 pounds.  Their coloration is similar to that of the loggerhead sea turtle (Caretta caretta) but their heads are smaller and there are only two large scutes between the eyes rather than the four found in the loggerheads.  The colors of the skin and shell have shades of brown, yellow, orange, and some black and can be quite beautiful.  The name “green” sea turtle comes from the color of their internal fatty tissue.  Feeding on a diet of seagrasses, it becomes green in color, and this was discovered by early fishermen who hunted and consumed this species.  It is the one used most often in what is called turtle soup and is actually farmed for this dish in other countries. 

Like all sea turtle species, they are born on the Gulf side of our barrier islands.  If they successfully hatch, they work their way to the open water and spend their early years in the open sea.  Some have been associated with the mats of Sargassum weed floating offshore, feeding on the variety of small invertebrates that live out there.  They will also nip at the Sargassum itself.  As juveniles they will move back into the coastal estuaries where they begin their vegetarian lifestyle.  As adults they will switch time between the open sea and the grass filled bays.  Once unfortunate side effect of feeding in our grassbeds is the frequency of boat strikes.  There are tens of thousands of motored vessels speeding through our grassbeds and the turtles surfacing for air can be targets for them.  Our hope is that more mariners are aware of this problem and will be more vigilant when recreating there. 

Another turtle who IS a resident of the estuary is the much smaller diamondback terrapin.  Though terrapins much prefer salt marshes they will enter seagrass beds, and some spend quite a bit of time there.  Terrapins prefer to feed on shellfish so, moving through the grassbeds it is the snails and bivalves they seek.  Because of their size they feed on the smaller mollusk.  A typical terrapin will have a carapace length of about 10 inches and may weigh two pounds.  They will take small crabs and shrimps when the opportunity is there, and they are known to swim into submerged crab traps seeking the bait.  Unfortunately, being air breathing reptiles, they will drown after becoming entrapped.  It is now required that all recreational crab traps in Florida have bycatch reduction devices (BRDs) on each of the funnel openings to reduce this problem.  Many studies, both here in Florida and elsewhere, have shown these BRDs do not significantly reduce crab catch and so you can still enjoy crabbing – just not while catching terrapins.  Encountering one snorkeling would be a very rare event, but – particularly in the eastern panhandle – has happened. 

A third reptile that has been seen in our grassbeds is the American alligator (Alligator mississippiensis).  Preferring freshwater systems, encounters with alligators in an open seagrass bed are rare, but do happen.  There are plenty of freshwater ponds on some of our barrier islands that the alligators will use.  They have been seen swimming out into the seagrass beds and often will cross the bay, or Intracoastal Waterway, to mainland side.  They have also been seen swimming near shore in the Gulf of Mexico.  Though they can tolerate saltwater, they have a low tolerance for it and do not spend much time there. 

Alligators are top level carnivores feeding on a variety of wildlife.  Like most predators, they tend to seek and capture the easiest prey.  Most often these are fish, reptiles, or small mammals.  But they will take on large birds or deer if the opportunity presents itself.  Despite their natural fear of humans, they have taken pets and also have attacked humans. 

Having only canines in their mouths, they must grab the prey and swallow it.  Lacking molars, they cannot chew.  So, more often than not, they select prey they can swallow whole.  If they do grab a larger animal, they are known to drown the creature in what has been termed the “death role” and cache it beneath the water under a log (or some structure) where it will soften to a point where they can cut small pieces and swallow it.  All of the alligators I have seen in our grassbeds were definitely heading somewhere.  They were not spending time there.  After heavy rains the salinity may drop enough to where they can tolerate being out there longer and encounters could increase.  But they are still rare. 

I will mention here that there are several species of snakes that, like the alligator, are swimming from one suitable habitat to another – crossing the seagrass in route.  All snakes can swim and encounters in brackish water are not unheard of.  I have several photos of diamondback rattlesnakes (Crotalus adamanteus) swimming across the Intracoastal Waterway between the mainland and the islands. 

Encounters with reptiles are rare in our seagrass beds but pretty exciting when they do occur.  There is certainly no need to fear swimming or snorkeling in our bay because they are so rare.  But maybe one day you will be one of the lucky ones who does see one.