We know that some reptiles love the water. Alligators,
turtles, snakes, the swamps are crawling with them. But what about the ocean?
Are there any reptiles that use saltwater habitats?
Of course. Sea turtles are well-known for spending their lives in the ocean (aside
from their brief trips to the beach to lay eggs). Not technically a sea turtle
but another turtle also using the sea is the Diamondback Terrapin (Malaclemmys terrapin).
Several species of crocodiles frequent salty habitats: the Saltwater
Crocodile (Crocodylus porosus) comes to mind. There are a handful of Sea Snakes
that are adapted to ocean-life, they feed on marine fish. Finally, don't forget marine iguanas. Brackish habitats, those areas where swamps
and rivers meet the sea that are not quite freshwater but not quite saltwater either, may contain many more reptiles than the open ocean.
But
overall, few reptiles use salty areas. Why is that? Saltwater habitats are
stressful environments. The biggest problem is the lack of drinking water. Just
like us, animals needs water. And, just like us, salt water is not
exactly thirst quenching. Because salt water is so…salty, most vertebrates are
simply not equipped to process it physiologically; it can be very hard on the kidneys.
Vertebrates that live in the ocean don't have it easy. Some seals either rarely drink water or eat snow instead. We don’t even have a very good understanding of how whales and dolphins manage to get the water they need. So, it should not be too much
of a surprise to hear that many species of wildlife, reptiles included, avoid these saltwater environments.
Cottonmouths
(Agkistrodon piscivorus) are an example of a water-loving species that can
sometimes be found in brackish and estuarine habitats. If freshwater isn't available to drink, it’s likely that they
can extract enough water from the other animals they eat. But pure
saltwater is too much for Cottonmouths to handle and they do not live in the ocean.

Any animal on the open ocean is vulnerable, to the sun
and to marine predators like sharks; most animals you see floating in the open
ocean or either just popping up for a breath or can fly away. Cottonmouths are
not deep-divers and they can’t fly either (although some commenters might
disagree) so I think it is safe to say that this animal is out of its element. I think that this
unlucky Cottonmouth had taken an exploratory crawl around the beach and got
swept away by a wave. Right now,
it looks like it’s just floating around and not under its own power, just like
the balloon next to it. Currents are probably controlling the movement of the
Cottonmouth, just as they are controlling the movement of the balloon. I think
this Cottonmouth’s days are numbered.
So,
what was the snake doing on the beach in the first place if the ocean is such
an inhospitable place? We can look to some very interesting research conducted
on the Cottonmouths of Seahorse Key, Florida for the answer. Seahorse Key, a
small island off the shore of Florida and in the Gulf of Mexico, contains a
very unusual population of Cottonmouths. Although the species can be found on
many islands, there is no fresh water on Seahorse Key, and the Cottonmouths there
are considered terrestrial.
The
Cottonmouths on Seahorse Key rely heavily on large colonies of nesting birds.
When the adult birds feed fish to their young, some of the fish fall to the
ground, where they are consumed by waiting snakes. This is a very seasonal
resource, of course, and when there are no nesting birds, the Cottonmouths are
left looking for something else to eat. During these times, the snakes may
wander to the intertidal zone searching for dead fish that have washed onto
shore. Because the species does it there, they probably do it elsewhere from time to time too. Cottonmouths generally don’t crawl around on the open beach or enter the
ocean, they are too vulnerable to predators there. But, perhaps they are also
vulnerable to being hit by a rogue wave? I suspect at least one was.
Ever seen an animal in the ocean that did not belong there, such as a Cottonmouth? Let us know below.
Want to read more?
H.B. Lillywhite, C.M. Sheehy III, & F. Zaidan III (2008). Pitviper scavenging at the intertidal zone: an evolutionary scenario for invasion of the sea BioScience, 58 (10), 947-955 DOI: 10.1641/B581008
Rasmussen AR, Murphy JC, Ompi M, Gibbons JW, & Uetz P (2011). Marine reptiles. PloS one, 6 (11) PMID: 22087300
Rasmussen AR, Murphy JC, Ompi M, Gibbons JW, & Uetz P (2011). Marine reptiles. PloS one, 6 (11) PMID: 22087300
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