Hello marine biology students.
In this video we're going to talk about marine
reptiles.
[Intro Music]
So while there are no marine amphibians, there
are marine reptiles.
Their basic characteristics is that they are
air breathing, they have lungs.
They also have scaly waterproof skin.
They're mostly going to be cold-blooded, so
they are ectotherms, and poikilotherms, meaning
their body temperature will be similar to
their environment.
They will also usually lay their eggs on land.
There are four major groups of marine reptiles.
We have sea turtles, sea snakes, marine iguana,
and saltwater and American crocodiles.
So the first of these, the sea turtles, all
species of sea turtles are either currently
threatened or endangered.
Endangered 
are species that are in danger of becoming
extinct and threatened 
are species that may become endangered because
of low numbers.
The usual threats to sea turtles 
are going to be humans.
This is because turtles can be used as food
by humans.
Their eggs can be eaten by humans and other
animals, turtles can get caught up in drift,
gill, and shrimp nets.
They can end up swallowing plastic bags and
because the beaches are developed into resorts
or residential areas instead of the nesting
areas that they're supposed to be.
The body of a sea turtle is enclosed by a
shell or carapace and the ribs are fused to
the shell.
All sea turtles have powerful jaws and no
teeth.
Like other reptiles, sea turtles are poikilotherms
and ectotherms.
With the exception of the leatherback turtle,
which is an endotherm
because it keeps its body temperature higher
than that of the waters surrounding it.
So it can venture into colder waters, in contrast
to the other sea turtles which are restricted
to the tropics.
Sea turtles feed on sponges, crabs, molluscs,
another invertebrates, except for the green
sea turtle, which is primarily vegetarian,
eating seaweeds and sea grasses.
Leatherback turtles, the largest of all sea
turtles, primarily eat jellyfish, and can
dive to depths of at least 2,000 feet in search
of other prey.
A big problem is that a plastic bag in the
water looks a lot like a jellyfish.
Sea turtles breed at sea.
They have internal fertilization, so copulation
is involved.
Females can store sperm to fertilize eggs
later.
One clutch or group of eggs could have multiple
paternity
as males and females are not monogamous and
females store the sperm from several matings.
Females normally breed every two to four years.
Females must return to land to deposit 
their eggs above the high-tide mark.
They dig a hole in the sand using only their
back flippers.
During their breeding year, females may lay
up to seven clutches of eggs, each of these
clutches of eggs may have more than 100 eggs
in it.
Eggs typically have an incubation period of
around 60 days, although this varies according
to air temperature.
Warm air temperatures mean eggs will develop
faster, whereas cold air temperatures lengthen
the process.
The eggs are leathery and gradually become
more brittle, making it easier for the hatchlings
to emerge.
Sea turtles, like many reptiles, show temperature-dependent
sex determination.
The biological sex of the hatchling is not
genetically-predetermined, but instead, determined
by the temperature in which the eggs are incubated.
For each species there is a temperature 
that will produce 50% males and 50% females.
Temperatures higher than this temperature
will produce more females, where as temperatures
lower than this will produce more males.
A potential problem is global warming.
So here we see a female sea turtle laying
eggs in a nest she dug in the sand.
The next type of marine reptile we'll talk
about are sea snakes.
They have a laterally flattened body with
a paddle-like tail for propulsion through
the water.
There are more than 70 species of sea snakes.
They're found only in the Indian and Pacific
Oceans.
You may wonder how to tell the difference
between a sea snake and an eel.
Well, eels do not have scales like sea snakes
do and sea snakes have lungs instead of gills.
Most species measure three to four feet in
length as adults.
Sea snakes breed at sea and most species are
ovoviviparous, meaning that their eggs remain
internal and hatch within the female’s reproductive
system and the young are born hatched.
Sea snakes are carnivorous 
and feed mainly on fish and fish eggs.
A bite from a sea snake could be fatal for
a human.
Sea snakes are related to cobras and have
very powerful venom, but sea snakes are not
known to be aggressive and they have small
mouths, so the chances of being bitten by
a sea snake are relatively small.
Conversely, saltwater crocodiles are very
likely to attack and bite humans in their
area.
These are found in Australia, Indian oceans,
and some western Pacific Islands.
They can be found in estuaries, mangals or
mangrove forests, rivers and the open ocean.
They are a predatory species that eats all
type of prey, including humans.
Saltwater crocodiles can reach up to 30 feet
long, although individuals over 20 feet are
extremely rare.
The American crocodile is also considered
a marine species because it tolerates seawater
and can be found in lagoons and other coastal
regions.
They are widely distributed in Florida, the
West Indies, the Pacific and Atlantic coasts
of Central America, and northern South America.
Males have been recorded as long as 20 feet,
but the average is 14 feet.
They feed mostly on fish.
The final species of marine reptile we'll
discuss are the marine iguana, one species
of which is found only on the Galapagos Islands.
While they are marine, they only spend a portion
of their time in the water.
They dive to feed on seaweeds and sea grasses
near shore and a large portion of their day
is spent basking on the shore in order to
warm up from their dives in the cold water
surrounding the Galapagos.
That takes us to the end of our discussion
of marine reptiles.
Now, before our next video, the question I
want you to consider is “Do you prefer warm
weather or cold weather?”
We'll talk about that in the next video.
