Other Venomous Marine Animals

Venomous marine animals are present worldwide, but are mainly confined to the Indo-Pacific Region. Unlike jellyfish, which inject venom through their tentacles over a large area, other venomous marine animals envenomate by injecting a large amount of venom into a single area. This causes the venom to have a low absorption rate; however, it's the a effective way to envenomate an animal in water. Many marine organisms use venom, including stonefish, stingrays, sea urchins, cone shells, sea snakes and blue-ringed octopuses (Fenner, 2004).

There are two types of stonefish - estuarine and reef. They are brown to sandstone in colour, which allows them to blend in with their surroundings. Envenomation occurs when the fish is stood on. Stonefish have 13 dorsal spines (each with an attached venom gland) that are used defensively, not to catch food. When the stonefish is stepped on, the spines are pushed down and act like an injector, forcing venom into the wound. After envenomation, the puncture mark has a bluish tinge around it. The severe, local pain extends to the rest of the limb, causing severe pain and paraesthesiae (a tingling or burning sensation of the skin). The victim experiences low blood pressure, pale skin, nausea and dizziness. Other fish that are venomous include the bullroot, lungfihs, scorpion fish, and lionfish (Fenner, 2004).

A stonefish (Image 1).

A reef stonefish camouflaged to look like coral (Image 2).

Stingrays are large, flat fish with flaps that enable them to swim gracefully through water. They have a tail with at least one barb on it, but they can have up to seven barbs present. The barbs face backwards and are covered in a friable sheath of tissue. They are often accidentally stood on, as they bury themselves in the sand to rest. When they are stepped on, the stingray's tail whips forward and the barb/barbs easily penetrate the skin of the victim. The pain is instant and severe. Jagged lacerations can occur, and may cause heavy bleeding. The barbs can often break off, become embedded in the tissue or be cleanly withdrawn after the predator was attacked. After the barb penetrates the tissue, the sheath that covers it is torn off, leaving a trail of venom and debris. Envenomation causes localised myolsis (the breakdown of muscle tissue) and inflammation, with local or extended tissue necrosis. If the abdomen or chest of the predator was punctured, there is an increase in morbidity and mortality (Fenner, 2004).

A stingray (Image 3). 

Sea urchins are covered in hundreds of sharp spikes. They live on rocks close to or in shallow waters. When they are stood on, the spikes break off into the victim's foot. The sea urchin's venom is not very toxin, but causes an unpleasant pain (Fenner, 2004).

A sea urchin (Image 4). 

Cone shells are brightly coloured, triangular-shaped shells, with a longitudinal fold or split running the length of the shell. They have a proboscis (a small, hollow, flexible tube) that can emerge from anywhere along the slit. At the base of the proboscis is an area containing a number of barbs, called radicular teeth. These barbs are bathed in a potent venom and are fired at prey and predators. Envenomation causes a localised, sharp pain. There is very little reaction from the body. Some flushing of the skin may be present, and sometimes a rash can form. The worst reactions occur when someone is stung by a fish eating cone, as the venom is more intense. The venom rapidly causes numbness and local swelling, nausea, incoordination, muscular weakness and difficulty breathing due to weakness of the diaphragm and intercostal muscles. Envenomation may lead to respiratory paralysis and death from asphyxia (Fenner, 2004).

A cone shell with its proboscis extended (Image 5).

A cone shell striking a fish (Image 6). 

Sea snakes are common in all oceans (except the Atlantic), but are most common in tropical and sub-tropical Australia. They are similar in appearance to land snakes, except they have a flattened, paddle-like tail to help them swim. They do not have gills, and so must surface to breathe air. They can be divided into two groups - those that have large mouths but rarely bite or envenomate, and those that have small mouths and very potent venom, but are unable to take a large enough bite to envenomate most animals. However, if something is even scratched and envenomated by the extremely potent venom, death is almost certain to occur. Like land based snakes, sea snakes try to preserve their venom, and hence, most bites are dry (don't inject venom).  The bite is relatively painless, but the venom causes drowsiness, nausea and vomiting, weakness, visual disturbances, breathing problems and muscles pains or stiffness (Fenner, 2004). 

A sea snake (Image 7).

Blue-ringed octopuses are yellow to brown in colour, allowing them to blend in with rocky areas, which is where they live. They are found throughout Australia and the Indo-West Pacific ocean. They have eight arms that grow up to 15 to 20 centimetres in diameter. When frightened, angry or in danger, many small, blue rings appear. This often causes the octopus to be picked up by small children, and leads the them being envenomated. Envenomation occurs after a painless bite from the octopus's beak, found under its body. The venom is a salivary toxin that is produced in the salivary glands. The glands are connected to the beak by small ducts. First sign of serious envenomation may occur within 10 minutes. Muscle weakness, difficulty speaking, difficulty swallowing, visual disturbances and respiratory difficulty are all caused by envenomation. The victim may also experience nausea and vomiting, and collapse from muscle weakness is soon seen. Death can occur from respiratory paralysis if resuscitation is not performed (Fenner, 2004). 

A blue-ringed octopus (Image 8).

A diagram of an octopus's beak and mouth (Image 9).

References

Fenner, P. (2004). Venomous marine animals. South Pacific Underwater Medicine Society Journal, 34 (4), 196-202.

Images

Image 1 - http://upload.wikimedia.org/wikipedia/commons/5/57/Stone_Fish_at_AQWA_SMC2006.jpg. Accessed on 31/3/14.

Image 2 - http://upload.wikimedia.org/wikipedia/commons/b/b8/Reef_Stonefish.jpg. Accessed on 31/3/14.

Image 3 - http://lenebaxter.files.wordpress.com/2012/04/stingraystinger.jpg. Accessed on 31/3/14.

Image 4 - http://www.gambassa.com/GambassaFiles/Images/images/JOHNpetrucci/urchin_V1.jpg. Accessed on 31/3/14.

Image 5 - http://grimwade.biochem.unimelb.edu.au/cone/Conus_textile-Paul_Livett.jpg. Accessed on 31/3/14.

Image 6 - http://www.rudyrucker.com/blog/images/sciamcone.jpg. Accessed on 31/3/14.

Image 7 - https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4fl_k6nMjD2X509QMyaiHmNS7hqDeD1AED2OhXDa0NpJ97m_fUrSdGyU2bfNLfpFTt-6sk0pu11GQFoQ5s9t6z7yxJGkywDimT2w7amD3TeD4yrW6BNTmo7uwMY2vg79pN4NV2eZjihg/s640/ular+laut+2.jpg. Accessed on 31/3/14.

Image 8 - https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgZxjFbokMHogT8BUVozupgem6arvyQV1j3HmyES7brGSUVLvgxx4a6FZYX5EdlqEdI-VDaE4ca17y31SiQ5irGq9c759e-dgLXdwbjvcq7u1aE_D3jf_A7-1Xog9pbY47KDSewz50B06g/s1600/HLfemalesmoothdisplaymed.jpg. Accessed on 31/3/14.

Image 9 - https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjAwYCfCpy0MVKCjaCTsTpvDghjv53NEIYyfoSF-Oh1T5xaHdMiLAhaIL2QOUx1o0kzD08dknw-hJFMCGWv2Dx4A6AoG-azPhMfBYtrQhv1qctY_P97AbH3wkczHMv6QVs9WjZDTyX56FY/s400/octopus-2.jpg. Accessed on 31/3/14.