Chapter 6:Marine Reptiles

marine iguana

A marine iquana from the Galapagos Islands

Classification of Marine Reptiles

Kingdom Animalia
Phylum Chordata
Class Reptilian
Order Testudines (Turtles)
Squamata (Snakes and Lizards)
Crocodilia (crocodiles)
Families Testudines
Dermochelyidae (leatherback sea turtles)
Cheloniidae (all other sea turtles)

Squamata
Hydrophiidae (all sea snakes)
Iquanidae (marine iguanas)

Crocodilia
Crocodylidae (salt water crocodiles)

Sea Turtles

hawksbill turtleReptiles once dominated the sea, much as they did the land. Today there are only a few dozen species of reptiles that still thrive in the sea.  Certainly one of the most interesting and charismatic groups are sea turtles.  Sea turtles differ from their land counterparts by having flattened shells and flippers in the place of legs.  Like most reptiles they are cold-blooded; their body changes temperature with the surrounding environment.  Despite being quite ancient, sea turtles are only partially adapted to life in the water.  They have lungs and regularly need to come to the surface to breath air.  They have heavy shells and are slow swimmers.  Once they reach reproductive maturity, the females will return to land every 2 or 3 years to lay their eggs in the sand.

There are eight species of sea turtle.  Leatherback sea turtles (Dermochelys coriacea) are the largest and most distinctive (they are the only member of family Dermocheliydae.)  Leatherback sea turtles have a leathery shell, and are the only turtle that does not have its spine fused to its shell.

The others are the green turtle (Chelonia mydas),  the Eastern Pacific green turtle (Chelonia agassizii), the loggerhead turtle (Caretta caretta), the Kemp's ridley turtle (Lepidochelys kempii), the olive ridley turtle (Lepidochelys olivacea), the hawksbill turtle (seen above, Eretmochelys imbricata), and the flatback turtle (Natator depressus.)  Click on any of the links for video of these turtles.

Reproduction and Navigation

newly hatched leatherbacksOver their lifetime, most sea turtles migrate long distances, traveling on the ocean's currents.  We are not exactly sure how they navigate, but much like birds, they seem to have a "sixth sense" that allows them to track magnetic field lines.  Each female sea turtle will return to the very same beach where she was born to lay eggs.  There, she will dig a hole in the sand, above the high tide line, and deposit her eggs.  When she is done she will head back out to sea never to see her offspring again.

Feeding    

Depending on the species, sea turtles may be carnivorous (eating meat like jellyfish, tunicates, sea sponges, or arthropods like shrimp), herbivorous (algae or plan eating), or omnivorous (eating both meat and plants). The jaw structure of many species is adapted specifically for their diet.    Click here to read about the diets of individual sea turtles.

Conservation

Every species of sea turtle is considered endangered.  Turtles are long-lived and reach reproductive maturity late in life.  Sea turtles are slow swimmers and vulnerable to accidental catch by long-lines and fishing nets.  However, what threatens sea turtles more than anything else is their reproductive habits.  Eggs are sometimes taken for food and beaches have been destroyed or developed.

Sea Snakesyellow-bellied sea snake

There is not very much written about sea snakes.  What is known is that there are a 62 species that inhabit the Indian and Pacific Oceans.  They are highly adapted to life in the ocean.  Their bodies are compressed latterally which makes them much better swimmers but makes it impossible for many of them to move on land.   Unlike eels (which are fish) they lack gills and must periodically come to the surface to breathe air.   Most sea snakes feed on fish that inhabit warm coral reefs.  Most sea snakes are highly venomous, including the yellow-bellied sea snake to the right, but rarely aggressive towards humans. They use their venom to help subdue their prey.  Unlike sea turtles sea snakes do not lay eggs on land but rather give birth to live young in the water. Click to read more about sea snakes.

Marine Iguanas of the Galapagos 

The marine iguanas of the Galapagos are the only species of lizard that will spend much of its time in the ocean.  Marine Iguanas are certainly among the most unusual creatures in the Galapagos.  The males, which are larger than the females, may grow to a length of 4 feet or more (almost half of which is tail). They look fearsome (Darwin called them "hideous"), but are quite harmless. These herbivores feed exclusively on algae growing on rocks near the shore. When feeding, they can remain submerged for up to an hour, though dives of 5 to 10 minutes are more common. The water in the Galapagos is often quite cold and being cold-blooded, iguanas spend much of their time restoring body heat by sunning themselves on the rocks adjacent the shore. Text taken from Marine Iguanas, click to read the rest.  You can also click here to watch Video of Galapagos Marine Iguanas feeding.

Saltiessaltie

Earth’s largest living crocodilian—and, some say, the animal most likely to eat a human—is the saltwater or estuarine crocodile. Average-sized males reach 17 feet (5 meters) and 1,000 pounds (450 kilograms), but specimens 23 feet (7 meters) long and weighing 2,200 pounds (1,000 kilograms) are not uncommon.

Saltwater crocs, or "salties," as Australians affectionately refer to them, have an enormous range, populating the brackish and freshwater regions of eastern India, Southeast Asia, and northern Australia. They are excellent swimmers and have often been spotted far out at sea.  Text taken from National Geographic.com click on the link to read the rest.

Questions to Research:

  1. Species: Watch some of the video clips featured for the eight species of sea turtles.  Pick your favorite species and tell me why its your favorite.

  2. Take the turtle quiz from the Sea Turtle Conservancy.  Write one true statement for each answer
  1. Nesting: Watch the linked video clip about leatherback sea turtles.  Explain the process by which Sea turtle's lay their eggs..  You can also look at a map to see where different sea turtles nest.
  1. Navigation: What have researchers found out about sea turtle navigation?  
  1. Migration: Check out the various tracking maps of some of the turtles involved in the link to the Georgia loggerhead tracking project.  Which direction do they all seem to be headed?  Why would that be?  Think about what you learned last semester about currents off of the Atlantic Coast.  If that doesn't help you think about the sea turtle scene from Finding Nemo.
  1. Metabolism: Not all sea turtles are truly cold blooded.  Describe what it means to be a Gigantotherm. (Once you get to TOPP's page, click on the turtle face in the bottom right.)
  1. Conservation: Pick three species of turtles and talk about threats to the survival (and conservation) of each?  Use Turtles.org as an additional resource if you need it.
  1. Hatchlings: When baby sea turtles hatch, they normally do so during full moons.  If you remember back to our section on tides, the a full moon means higher tides, and that means they don't have to crawl so far to the water.  They also instinctually go towards the light.  The development of Florida's beach fronts has made this attraction to the light problematic.  Read the attached article, and explain what some part of Florida are doing to help the hatchlings along. National Geographic - Saving the sea turtle
  1. Sea snakes are not eels and eels are not sea snakes:  Sea snakes are reptiles while eels are fish.  Even though they may look alike, they are very different.  Explain three differences you find between the examples below.

  2. Adapting to Life at Sea:   Take a look at this article from Natural History Magazine. Explain the connection between sea snakes diet, the way in which they eliminate nitrogenous waste, and their need for freshwater. Then explain why this makes life (at least in one way) difficult for them in the ocean.