MARS2014 Lecture 9: Unit 9 - Marine Reptiles
Unit 9: Marine reptiles
▪ What are the four extant groups of marine reptiles?
• Marine iguanas
• Saltwater crocodiles
• Sea turtles
• Sea snakes
▪ What are the characteristics of sea snakes?
• Marine
• Cold-blooded
• Evolved from terrestrial snakes
• 2 groups of aquatic snakes
o Laticandida (sea kraits – not fully aquatic)
o Hydrophiidae (true sea snakes)
▪ What are the characteristics of the family Hydrophiidae?
• Evolved approx. 370 MYA
• Fully aquatic
• Slender snakes 1-2m long
• All are venomous
• Are air breathers
▪ What is the diversity and distribution of the sea snakes?
• 54 known species
• Found in the Indo-Pacific, tropical to subtropical
• Found on mostly shallow waters on continental shelves
• They decline in diversity from tropics to subtropics, with most
diversity in equatorial waters
o In the northern GBR there are 16 species
o In the southern GBR there are 7 species
o In Moreton Bay there is 1 species
▪ How do sea snakes move?
• Use a side-to-side motion (laterally compressed) and tail moves as a
paddle
• Most are benthic, but some swim
▪ How do sea snakes breathe?
• Their right lung is proportionally larger than in land snakes
• Vascular nostrils are at the top of snout
• Some use cutaneous respiration (across skin)
▪ How do sea snakes balance their salt?
• Salt is toxic to vertebrate tissue
• Their tongue gland excretes excess salt
▪ How do sea snakes feed?
• Carnivorous
• Some are ambush hunters, others chase prey
• They usually take small long fishes
• Prey detection and recognition through
o Jacobsen’s organ (an olfactory pit in their mouth)
o Well-developed eyes
• Predator detection
o Light-sensitive organs in tail tip
o For nook-and-cranny feeders this is useful, to detect larger
animals that come up behind them
• Prey is swallowed whole
o The venom is a neurotoxin, which immobilises the prey
o Cranial kinesis is dislocation of the jaw
o Teeth are recurve to hold prey
• Have large meals and slow metabolism (eat when they can, but
meals are infrequent)
▪ What is feeding diversity in sea snakes?
• Slender snakes feed on elongate fish
• There are fish egg-eaters with vestigial venom systems
• There are tiny-headed snakes that feed on burrowing eels
• There are wide-gaped snakes that feed on spinous catfish and
toadfish
▪ What is different about the Australian turtle-headed sea snake?
• Specialist feeder on fish eggs
• Unique suctorial feeding
• Have a reduced venom gland and fangs
▪ What is different about Stoke’s sea snake?
• Most aggressive sea snake
• Large and bulky with a large head
• Eats spiny fish and catfish, can deal with the spines and toxins
▪ What is different about the yellow-bellied sea snake?
• Sit on the surface in deep water
• Its body throws a shadow on the floor and fish come up to rest
under the shadow
• Fangs are at the side of mouth, not the front (has a side-swipe
feeding strategy)
• Only one that isn’t a benthic feeder
▪ How do sea snakes reproduce?
• Sexes are separated (female is larger than male)
• Strongly seasonal reproductive patterns
• Internal reproduction
• Viviparous
• Small litters, 4-5
▪ What do we know about sea snake populations of the GBR?
• Little known of their population ecology status
• Reef species can be quite successfully marked and recaptured
• Inner reef species have a low recapture rate and larger movements
• Inshore species can be estimated via trawler by-catch, but we have
no population or density data
▪ What are the threats to sea snakes?
• By-catch in trawlers (is the major threat)
• Possibly habitat loss
