RESEARCH POSTER PRESENTATION DESIGN © 2015 www.PosterPresentations.com Sea snakes are an awe worthy and beautiful element to the Earth’s oceans. Some are partially terrestrial while others are entirely marine. They share many traits with their fully terrestrial cousins and possess some interesting adaptations to their life in the water. It is believed that there are 70 species of sea snakes (this number includes fresh water snakes that occasionally enter marine habitats). Of these 70 species, they are broken into four families Hydrophiidae, Laticudidae, Archorchodidae and Colubridae. These animals range from non-venomous to mildly venomous to highly venomous, depending on the species. Those that are venomous are believed to be descended from terrestrial cobras. Different species have evolved different hunting techniques and ways to produce young. They only inhabit tropic and sub tropic waters and rarely travel far distances due to their cold blooded nature. Hydrophis elegans (Mazza) Abstract All marine snakes inhabit tropic and sub tropic waters. The most varied and diversified populations are found in the water of northern Australia, Malaysia and Indonesia. As you travel toward the Pacific, variation in species decreases. Most sea snakes prefer shallow waters close to some kind of land or reef mass, but some have been found in deeper water. Usually if a snake is found in open water, it is due to strong currents. Same species can be found in different environments depending on geographic location (deep water, estuaries or reefs) if they are general feeders. However, snakes like the bar bellied sea snake, have a specific diet of snake eel (and are a favorite food of tiger sharks) so they are found in calm, shallow water near sea grasses. Some sea snakes are partially terrestrial (Nerodia valida) while others will not leave the ocean willingly (Bitia hydroides and Cantoria violcea to name a couple). (Heithaus) Environment Sea snakes, like terrestrial snakes, are scaled reptilians with no limbs or internal girdles. However, while terrestrial snakes have enlarged ventral scales to aid in moving across the ground, sea snakes have no need for this adaptation. Their ventral scales are, normally, the same size as their dorsal scales. The scales surrounding the mouth fit tightly together to prevent sea water intrusion (except for an opening for the tongue). The anal scales extend backward to seal the vent for the same reason. Another adaptation to prevent sea water intrusion are little flaps of tissue that engorge with blood and effectively seal the snake’s nostrils. Despite all these adaptations, salt does make its way into the body, and the snake needs a way to expel the excess. Most snakes (ones that are strictly marine and spent most their time in water) possess an excretory gland in their mouth. This gland is a modified salivary gland, known as the sublingual gland, which excretes excess salt. Though the snake’s body is highly adapted to keep sea water out, they are able to respire through their skin to a degree. The ability to breath under water depends on the species but some are able to absorb 1/5 of their required O 2 through the skin. This adaption is one of the reasons some species are able to stay submerged for, up to, two hours. Some have even been recorded to dive at a depth of 100m (though this is uncommon, as most prefer shallow water). A unique adaptation for sea snakes is that they have a singular, tubed lung instead of two branched lungs. Most sea snakes range from 60 to 80cm long, though some species have been recorded to reach an excess of 200cm (Hydrophis elegens and Hydrophis spiralis). These animals are highly adapted to their marine environment. Many species bodies have a slight lateral compression and their heads are not greatly defined from the body. Certain species also have a notably flattened tail that resembles a paddle, especially ones that live in more current heavy habitats. This flattened tail assists in propulsion through the water, some species’ tails are even light sensitive. Regardless of body shape and size, all sea snakes move through the water with a lateral undulating movement. Sea snakes color ranges from muddy brown (Aipysurus apraefrontalis) to a striking combination of black and yellow (Pelamis platurus). (Heatwole, 1987) Sea Snake distribution (Stammler) Morphology It has not been studied in great depth, but sea snakes do not appear to travel a significant distance in order to mate. Most sea snakes do not travel any further than 200m out of their original habitat (those that have been found that far were carried by a current). Their territories tend to greatly overlap, and they do not appear to be territorial. The only ‘migrating’ that happens is movement to a nearby area that is slightly sheltered and has calmer water (like an estuary) when breeding or giving birth. Most sea snakes mate in the water. Males have copulatory organs known as hemipenes. They have two, but only one is used at a time. Once copulation has begun, the male is stuck to the female and cannot disengage until mating is finished. He is subject to the female’s swimming pattern, so when she surfaces to breath he has to attempt to get some breaths of air too. Mating cycles depend on location, not species. For example, a species that lives in the Philippines might be strictly seasonal but the same species living in Malacca are seasonal. Female sea snakes can be either viviparous or oviparous. Those that are viviparous will give birth in the water and those that are egg laying will do so on land. Oviparous snakes carry their eggs higher in the body than terrestrial snakes so that it does not greatly impair their swimming ability. The amount of time the eggs/young stay within the mother’s body depends on the species. However, overall incubation period for sea snakes is significantly longer than terrestrial snakes (three to four months as opposed to nine months). Most females will produce 10 -15 young depending on species. Some species will produce clutches of less than five (most hydrophiids and laticaudids). The ‘reproductive effort’ spent on natal sea snakes is greater than terrestrial ones (more of the mother’s resources go to producing the young). Mortality rate of young sea snakes is very high. Only 10- 20% of newborns survive their first year, and only 6% of females survive long enough to breed. (Heatwole, 1987) Sea Snake Crevice Hunting (animalstime.com) Yellow Belly Sea Snake ambush hunting (Nelson) Breeding and Migration Feeding Most sea snakes will eat a variety of fish, eels, crabs and other invertebrates. Those that are partly terrestrial sometimes enjoy an even more diverse menu. Some are specialized eaters like the eel eaters (Hydrophiidae family) or strict fish egg eaters (Aipysurus eydouxii and the turtle headed sea snakes). Sea snakes mostly use their sense of smell and sense of vibrations to detect prey. They do not seem to use their eye sight as a tool for hunting. To hunt, sea snakes employ a few different techniques, depending on target prey. A technique used by many snakes is called crevice foraging. This is where the snake actively pokes through cracks in rocks, reefs and other structures to find prey. They have been seen targeting prey in a crevice, wrap their body around the opening to prevent escape and attack their prey (fairly clever for a reptile). Another method is called cruising. This is where they swim along and strike, laterally at a fish who is not paying attention. This method does not generally work on fast moving or far off prey as the snake is not able to quickly pursue a fast prey item. The ambush method has only been known to be used by the yellow bellied sea snake. The snake floats as still as possible, trying to imitate a fallen branch and waits for fish to come to it. Once a fish comes close enough, the snake is able to strike and eat its prey. (Heatwole, 1987) Eating with no limbs or chewing teeth is difficult enough, doing so in the water is even trickier. Once a snake has caught a prey item, he will face the current and then turn his head toward the anterior end of his body. This way the current assists in keeping the prey item aligned during swallowing. The snake has to swallow his prey head first to avoid damage to his own body. A sea snake will carefully chew along the body, turning it until the head is positioned in his mouth. Once this is accomplished he may swallow his prey. Sea snakes have not evolved the ability to drink sea water, they must drink fresh water to survive. Some sea snakes that have terrestrial abilities can go on land to find rain water that has collected in pools or in leaves. This is not so easy for the snakes that do not leave the ocean. They may have to wait months at a time for a drink of water. When it rains on the open ocean, a lens of fresh water will float on top of the sea water for a short period of time. This is where strict marine snakes obtain fresh water for drinking. Some snakes will only drink a few sips of water while others have been recorded to drink up to 25% of their body weight. Due to droughts, there has been less rain fall in recent years. This has caused a decline in sea snakes because they are dying of dehydration. (Lillywhite, 2014) Venom Almost all sea snakes, to a degree, are venomous (with the exception of acrochordids and natricines). Inside the snakes head, they possess venom glands. These are elongated, specialized salivary organs located behind the eyes. There are two parts to the gland. The anterior region is the accessory part and secretes a mucus made of polysaccharides to aid in substance flow. The posterior section is the region that manufactures the toxic proteins and polypeptides. Sea snakes do not possess the impressive swinging fangs that are familiar in land vipers. Rather, sea snakes have short cone shaped fangs that are either hollow or solid and grooved (depending on species). Some sea snakes even have their fangs located toward the rear of their mouth. Most sea snakes possess a combination of different toxins. These toxins fall into the categories of nephrotoxins, mycotoxins, hemotoxins and neurotoxins. The type of toxin depends on the species of snake (and their target prey). Some sea snakes have so little toxin that it would do nothing more to a man than cause slight redness and irritation of the skin while others have enough venom to kill 50 men. Why does a sea snake need such potent venom? There are two answers. Firstly, some target prey of certain sea snake species, have developed a tolerance to sea snake venom ( The same fish may be tolerant to one snake species while susceptible to a snake not normally found in the environment), which caused the snake to develop more and more potent venom over generations. Secondly is for safety and digestion. Eating a struggling animal when you have no limbs can be tricky and dangerous. Some sea snakes have developed a toxin to quickly dispatch their prey and allow easier consumption (neurotoxins and nepthrotoxins). It is also quite hard to digest prey if you are not able to masticate it first (in most animals this allows saliva to thoroughly work into the food matter and break it down for digestion). This is where mycotoxins come in handy. Mycotoxins quickly break down muscle tissue, aiding in the snake’s digestion. (Heatwole, 1987)) Luckily for us, sea snakes are not, in general, aggressive. There are some species that refuse to strike despite heavy harassment (Laticuada family). Others will only strike after heavy harassment. Most bites occur after such interaction. There are a few species that are identified as being outwardly curious of humans and will swim up to a human and crawl on them to investigate (Aipysurus laevis). Even fewer species have been identified as aggressive (Enydrina schistosa, Hydrophis caerulescens). There are almost no existing reports of unprovoked attacks (and even then, the scenario usually involved snakes attempting to breed in the area). The best advice a swimmer or diver can take is to remember you are in their territory, so give them the respect and space they deserve. Works Cited Dusheck, Jennie. Annoying Anemones Shed Light on Coral Reef Biology. Scope, Stanford. 1 Sep 2015. Web. 3 Dec 2015 Heatwole, Harold. Sea Snakes. Malabar. Kreiger Publishing Company. 1987. Print Heithaus, Mike. Shark Bay Ecosystem Research Project. Florida International University. Web. 30 Nov 2015. Lillywhite, Harvey and Spence, Cindy. Sea Snakes Need Freshwater for Drinking, Researcher Finds. University of Florida News. 19 Nov 2015. Web. 28 Dec 2015. Mazza, Guiseppe. Dr. Guiseppe Mazza. Photo Mazza. Web. 3 Dec 2015. Nelson, Kerry. Are There Any Countries Without Snakes? Life is Short but Snakes are Long. 30 Oct 2015. Web. 3 Dec 2015. Stammler, Lukas. General Information on Sea Snakes. VAPA Guide. 2011. Web. 3 Dec 2015. **Picture downloaded from <animalstime.com/sea-snake-facts-sea-snake-diet-habitat/>. I could not access the actual website for content information. When I tried my computer blocked the page with a “malicious content” warning. Elisse Tallerico Sea Snakes
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RESEARCH POSTER PRESENTATION DESIGN © 2015
www.PosterPresentations.com
Sea snakes are an awe worthy and beautiful element to the Earth’s oceans. Some are partially terrestrial while others are entirely marine. They share many traits with their fully terrestrial cousins and possess some interesting adaptations to their life in the water. It is believed that there are 70 species of sea snakes (this number includes fresh water snakes that occasionally enter marine habitats). Of these 70 species, they are broken into four families Hydrophiidae, Laticudidae, Archorchodidae and Colubridae. These animals range from non-venomous to mildly venomous to highly venomous, depending on the species. Those that are venomous are believed to be descended from terrestrial cobras. Different species have evolved different hunting techniques and ways to produce young. They only inhabit tropic and sub tropic waters and rarely travel far distances due to their cold blooded nature.
Hydrophis elegans (Mazza)
Abstract
All marine snakes inhabit tropic and sub tropic waters. The most varied and
diversified populations are found in the water of northern Australia, Malaysia and
Indonesia. As you travel toward the Pacific, variation in species decreases. Most
sea snakes prefer shallow waters close to some kind of land or reef mass, but some
have been found in deeper water. Usually if a snake is found in open water, it is
due to strong currents. Same species can be found in different environments
depending on geographic location (deep water, estuaries or reefs) if they are
general feeders. However, snakes like the bar bellied sea snake, have a specific diet
of snake eel (and are a favorite food of tiger sharks) so they are found in calm,
shallow water near sea grasses. Some sea snakes are partially terrestrial (Nerodia
valida) while others will not leave the ocean willingly (Bitia hydroides and Cantoria
violcea to name a couple). (Heithaus)
Environment
Sea snakes, like terrestrial snakes, are scaled reptilians with no limbs or
internal girdles. However, while terrestrial snakes have enlarged ventral scales to
aid in moving across the ground, sea snakes have no need for this adaptation. Their
ventral scales are, normally, the same size as their dorsal scales. The scales
surrounding the mouth fit tightly together to prevent sea water intrusion (except
for an opening for the tongue). The anal scales extend backward to seal the vent for
the same reason. Another adaptation to prevent sea water intrusion are little flaps
of tissue that engorge with blood and effectively seal the snake’s nostrils. Despite
all these adaptations, salt does make its way into the body, and the snake needs a
way to expel the excess. Most snakes (ones that are strictly marine and spent most
their time in water) possess an excretory gland in their mouth. This gland is a
modified salivary gland, known as the sublingual gland, which excretes excess salt.
Though the snake’s body is highly adapted to keep sea water out, they are able to
respire through their skin to a degree. The ability to breath under water depends
on the species but some are able to absorb 1/5 of their required O2 through the
skin. This adaption is one of the reasons some species are able to stay submerged
for, up to, two hours. Some have even been recorded to dive at a depth of 100m
(though this is uncommon, as most prefer shallow water). A unique adaptation for
sea snakes is that they have a singular, tubed lung instead of two branched lungs.
Most sea snakes range from 60 to 80cm long, though some species have been
recorded to reach an excess of 200cm (Hydrophis elegens and Hydrophis spiralis).
These animals are highly adapted to their marine environment. Many species
bodies have a slight lateral compression and their heads are not greatly defined
from the body. Certain species also have a notably flattened tail that resembles a
paddle, especially ones that live in more current heavy habitats. This flattened tail
assists in propulsion through the water, some species’ tails are even light sensitive.
Regardless of body shape and size, all sea snakes move through the water with a
lateral undulating movement. Sea snakes color ranges from muddy brown
(Aipysurus apraefrontalis) to a striking combination of black and yellow (Pelamis
platurus). (Heatwole, 1987)
Sea Snake distribution (Stammler)
Morphology
It has not been studied in great depth, but sea snakes do not appear to travel a
significant distance in order to mate. Most sea snakes do not travel any further
than 200m out of their original habitat (those that have been found that far
were carried by a current). Their territories tend to greatly overlap, and they
do not appear to be territorial. The only ‘migrating’ that happens is movement
to a nearby area that is slightly sheltered and has calmer water (like an estuary)
when breeding or giving birth.
Most sea snakes mate in the water. Males
have copulatory organs known as hemipenes. They have two, but only one is
used at a time. Once copulation has begun, the male is stuck to the female and
cannot disengage until mating is finished. He is subject to the female’s
swimming pattern, so when she surfaces to breath he has to attempt to get
some breaths of air too. Mating cycles depend on location, not species. For
example, a species that lives in the Philippines might be strictly seasonal but
the same species living in Malacca are seasonal.
Female sea snakes can be either viviparous
or oviparous. Those that are viviparous will give birth in the water and those
that are egg laying will do so on land. Oviparous snakes carry their eggs higher
in the body than terrestrial snakes so that it does not greatly impair their
swimming ability. The amount of time the eggs/young stay within the mother’s
body depends on the species. However, overall incubation period for sea
snakes is significantly longer than terrestrial snakes (three to four months as
opposed to nine months). Most females will produce 10 -15 young depending
on species. Some species will produce clutches of less than five (most
hydrophiids and laticaudids). The ‘reproductive effort’ spent on natal sea
snakes is greater than terrestrial ones (more of the mother’s resources go to
producing the young). Mortality rate of young sea snakes is very high. Only 10-
20% of newborns survive their first year, and only 6% of females survive long
enough to breed. (Heatwole, 1987)
Sea Snake Crevice Hunting (animalstime.com)
Yellow Belly Sea Snake ambush hunting (Nelson)
Breeding and Migration
Feeding
Most sea snakes will eat a variety of fish, eels, crabs and other invertebrates.
Those that are partly terrestrial sometimes enjoy an even more diverse menu.
Some are specialized eaters like the eel eaters (Hydrophiidae family) or strict fish
egg eaters (Aipysurus eydouxii and the turtle headed sea snakes). Sea snakes
mostly use their sense of smell and sense of vibrations to detect prey. They do not
seem to use their eye sight as a tool for hunting. To hunt, sea snakes employ a few
different techniques, depending on target prey. A technique used by many snakes
is called crevice foraging. This is where the snake actively pokes through cracks in
rocks, reefs and other structures to find prey. They have been seen targeting prey
in a crevice, wrap their body around the opening to prevent escape and attack
their prey (fairly clever for a reptile). Another method is called cruising. This is
where they swim along and strike, laterally at a fish who is not paying attention.
This method does not generally work on fast moving or far off prey as the snake is
not able to quickly pursue a fast prey item. The ambush method has only been
known to be used by the yellow bellied sea snake. The snake floats as still as
possible, trying to imitate a fallen branch and waits for fish to come to it. Once a
fish comes close enough, the snake is able to strike and eat its prey. (Heatwole,
1987)
Eating with no limbs or chewing teeth is difficult enough, doing so in the water
is even trickier. Once a snake has caught a prey item, he will face the current and
then turn his head toward the anterior end of his body. This way the current
assists in keeping the prey item aligned during swallowing. The snake has to
swallow his prey head first to avoid damage to his own body. A sea snake will
carefully chew along the body, turning it until the head is positioned in his mouth.
Once this is accomplished he may swallow his prey.
Sea snakes have not evolved the ability to drink
sea water, they must drink fresh water to survive. Some sea snakes that have
terrestrial abilities can go on land to find rain water that has collected in pools or in
leaves. This is not so easy for the snakes that do not leave the ocean. They may
have to wait months at a time for a drink of water. When it rains on the open
ocean, a lens of fresh water will float on top of the sea water for a short period of
time. This is where strict marine snakes obtain fresh water for drinking. Some
snakes will only drink a few sips of water while others have been recorded to drink
up to 25% of their body weight. Due to droughts, there has been less rain fall in
recent years. This has caused a decline in sea snakes because they are dying of
dehydration. (Lillywhite, 2014)
VenomAlmost all sea snakes, to a degree, are venomous (with the exception of
acrochordids and natricines). Inside the snakes head, they possess venom glands.
These are elongated, specialized salivary organs located behind the eyes. There
are two parts to the gland. The anterior region is the accessory part and secretes a
mucus made of polysaccharides to aid in substance flow. The posterior section is
the region that manufactures the toxic proteins and polypeptides. Sea snakes do
not possess the impressive swinging fangs that are familiar in land vipers. Rather,
sea snakes have short cone shaped fangs that are either hollow or solid and
grooved (depending on species). Some sea snakes even have their fangs located
toward the rear of their mouth. Most sea snakes possess a combination of
different toxins. These toxins fall into the categories of nephrotoxins, mycotoxins,
hemotoxins and neurotoxins. The type of toxin depends on the species of snake
(and their target prey). Some sea snakes have so little toxin that it would do
nothing more to a man than cause slight redness and irritation of the skin while
others have enough venom to kill 50 men. Why does a sea snake need such potent
venom? There are two answers. Firstly, some target prey of certain sea snake
species, have developed a tolerance to sea snake venom ( The same fish may be
tolerant to one snake species while susceptible to a snake not normally found in
the environment), which caused the snake to develop more and more potent
venom over generations. Secondly is for safety and digestion. Eating a struggling
animal when you have no limbs can be tricky and dangerous. Some sea snakes
have developed a toxin to quickly dispatch their prey and allow easier consumption
(neurotoxins and nepthrotoxins). It is also quite hard to digest prey if you are not
able to masticate it first (in most animals this allows saliva to thoroughly work into
the food matter and break it down for digestion). This is where mycotoxins come
in handy. Mycotoxins quickly break down muscle tissue, aiding in the snake’s
digestion. (Heatwole, 1987))
Luckily for us, sea snakes are not, in general, aggressive. There are some species
that refuse to strike despite heavy harassment (Laticuada family). Others will only
strike after heavy harassment. Most bites occur after such interaction. There are a
few species that are identified as being outwardly curious of humans and will swim
up to a human and crawl on them to investigate (Aipysurus laevis). Even fewer
species have been identified as aggressive (Enydrina schistosa, Hydrophis
caerulescens). There are almost no existing reports of unprovoked attacks (and
even then, the scenario usually involved snakes attempting to breed in the area).
The best advice a swimmer or diver can take is to remember you are in their
territory, so give them the respect and space they deserve.
Works Cited
Dusheck, Jennie. Annoying Anemones Shed Light on Coral Reef Biology. Scope, Stanford. 1 Sep 2015.
Web. 3 Dec 2015
Heatwole, Harold. Sea Snakes. Malabar. Kreiger Publishing Company. 1987. Print
Heithaus, Mike. Shark Bay Ecosystem Research Project. Florida International University. Web. 30 Nov
2015.
Lillywhite, Harvey and Spence, Cindy. Sea Snakes Need Freshwater for Drinking, Researcher Finds.
University of Florida News. 19 Nov 2015. Web. 28 Dec 2015.
Mazza, Guiseppe. Dr. Guiseppe Mazza. Photo Mazza. Web. 3 Dec 2015.
Nelson, Kerry. Are There Any Countries Without Snakes? Life is Short but Snakes are Long. 30 Oct
2015. Web. 3 Dec 2015.
Stammler, Lukas. General Information on Sea Snakes. VAPA Guide. 2011. Web. 3 Dec 2015.
**Picture downloaded from <animalstime.com/sea-snake-facts-sea-snake-diet-habitat/>. I could not access the actual website for content information. When I tried my computer blocked the page with a “malicious content” warning.
Elisse Tallerico
Sea Snakes
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