Our group prepares to leave Lighthouse Cave, San Salvador, Bahamas.
Some marine dwellers have become proficient at luring prey. The angler fish uses this technique to obtain its food. The angler fish has a modified extension on its dorsa fin. At the end of this extension is a fleshy object that may resemble a food source for the prey item. When the unsuspecting fish comes for a closer view, it is quickly eaten by the waiting angler fish. The method of luring is very effective because it does not require the predator to waste valuable energy chasing after its prey.
Much like the trapdoor spider that lies in wait for its prey, some marine organisms have become ambush predators. Many times these predators are found on sandy ocean bottoms or rock crevices that provide concealment from potential prey. Examples of fish that use this capturing technique are: flounders, groupers, and scorpion fish.
I think perhaps one of the most fascinating techniques of capturing prey or defending oneself is the use of poisons or venoms. One group of land animals that seems to be frequently feared are the snakes, possibly due to the fact that poisonous species have been known to kill humans with their bite. Marine organisms of the Caribbean that use poison and venom pose the same risk to both prey and humans alike. Knowing that there are a multitude of poisonous marine organisms, I have chosen just a few to discuss in this paper.
To say an animal is venomous is to say that animal has a certain apparatus to apply the contents of a gland that contains the venom. Some injecting apparatuses are cellular in structure, like nematocysts. Others may be hollow spines that serve the same function of a hypodermic needle. Still other marine organisms inject their venom through biting, such as the octopus or sea snakes.
One common venomous Caribbean reef fish is the lionfish. The lionfish belong to the large family Scorpaenidae. This group of scorpionfish is broken into several families, the lionfish belonging to Pteroiidae. With so many species of Scorpaenidae being broken into smaller families, they all posses one similar characteristic. They have a bony plate that goes from the eye to gill cover across the cheek area. Lionfish are usually brightly colored and have a “lacy” appearance with “fan-like” pectoral fins. Their brilliant appearance is probably one reason they are sought after for aquarium pets.
The members of Scorpaenidae, including the lionfish, can be located in temperate to tropical marine waters. They tend to be bottom dwellers with a preference for rocky crevices. Many venomous species of this family inhabit coral reefs, although some species are deep-water dwellers.
The lionfish seem to be mostly ambush-type predators, using their venom for mostly a defensive mechanism. The lionfish have thirteen dorsal, three anal and two pelvic spines all containing their own venom gland. Their pectoral fins are not associated with any venom glands. These spines are hollow and covered by sections of skin. Upon stinging the skin covering the spines is pushed back and the venom gland empties into the wound. When threatened, the lionfish will confront its aggressor with its dorsal fins. In this position they can quickly strike to envenomate the object.
If stung by a lionfish, the victim will feel an intense sharp, throbbing pain. This pain can last for six to twelve hours, or in some cases days to weeks. In some rare instances, there has been evidence of necrosis around the wound. Systemic effects are rare in this type of envenomation. A major treatment for this wound is to immerse the body part into hot water. Pain medications are usually given and the wound is thoroughly cleaned to prevent secondary infections.
The impact of lionfish on humans seems to be minimal. For the most part injuries are due to the temptation of touching one of these organisms in open waters or poor handling when removing them from a fishing line and hook. Other injuries are typical from the mishandling of these fish by aquarium owners.
Cone shells are another venomous organism of the Caribbean reef. These are marine snails from the phylum Mollusca and the class Gastropoda. They belong to a large family called Conidae, which contains about 400 species. The length of their shells can range from 1-4 inches. Colors of the shells vary from bland grayish/brownish to very brightly colored. The cone shells reside mainly in tropical and subtropical waters. They are mainly shallow water dwellers and are often associated with coral reefs.
The cone shells are mainly nocturnal while hiding during the day on the sandy bottom. Cone shells are predators and are divided into three main groups; the ones that feed on worms, the ones that feed on mollusks and the ones that feed on fish. The latter group, the piscivores, are the most deadly for humans. Cones have modified radular teeth. These teeth are detachable and can act like a spear gun. When the cone makes contact with its prey, its radular tooth is shot out, piercing the victim’s skin and injecting its venom. This venom is very effective at paralyzing and eventually killing the prey before it’s ingested. The most poisonous cone shells have killed humans, while others may have weaker effects. Swelling will usually occur and numbness may spread quickly throughout the entire body. Muscle paralysis has been involved in severe cases. The venom of cone shells is thought to be a competitor for acetylcholine receptors at neuromuscular junctions.
The impact of cone shell envenomation on humans seems to be minimal. The greatest number of reported stings occurs in the Indo-Pacific area. Many stings occur as the result of mishandling by humans. Cones are sought after by shell collectors for their beauty. Some species may bring in $2,000-$4,000 by these collectors.
Puffer fish are a part of a group called tetrodotoxic fish. Named because of their biotoxin, the puffer fish and porcupine fish belong to the families Tetraodontidae and Diodontidae, respectively. Puffers usually travel alone or in pairs, inhabiting coral reefs. They are considered omnivorous in their eating habits and are capable of inflicting severe bites to humans. They are very quick and have the ability to inflate themselves to a spherical shape when threatened. When they are inflated, their spines, usually flattened, become fully extended. They inflate themselves by drawing water into an area of their stomach and holding it there. If the fish is out of water it can inflate itself by drawing in air.
Humans are not inflicted with the poison from a bite or stinger; it is from ingesting the fish as a food source. There has been much research about the origin of the toxicity in puffer fish. Some scientists believe the poison is a direct effect of their feeding habits; feeding on toxic algae, sponges and coelenterates. The theory being that it may be non-toxic when the fish eat the prey, but then converted into a toxic form in their bodies. Another hypothesis is that the poison is a product of sex glands. It has been shown that puffer fish are their most toxic before and during sex organ activity. The female is more toxic than the male fish. The toxin is concentrated in the skin and internal organs of the puffer fish, although the muscle tissue has been found to contain the toxin also. Recent research suggests strongly that tetrodotoxin in puffer fish comes from bacteria in their food source.
Tetrodotoxin (TTX) is considered a neurotoxin. It blocks voltage-gated sodium channels which are essential for nerve cell function. One of the first symptoms of this poisoning is numbness of the lips and tongue, which may spread to the face and other extremities. Death can occur within 4-6 hours, usually due to respiratory distress and cardiac arrhythmia. The severity of symptoms depends on the amount ingested and the toxicity of the fish.
The occurrence of TTX poisoning in North America is rare. Most of the poisonings occur in the Indo-Pacific area, especially Japan. This is because puffer fish, or Fuga as the Japanese call it, is considered a delicacy to eat. The best prevention against TTX poisoning is to abstain from eating puffer fish or related species. If a person is going to eat this type of fish it is best to get rid of all internal organs and the skin. It should be prepared by a licensed fuga chef.
The last topic of discussion is a little different in nature. This poisoning comes in a much smaller form. Ciguatera poisoning is caused by consuming tainted seafood. More specifically it is caused by a marine dinoflagellate. Dinoflagellates are microscopic unicellular protests. Dinoflagellates are commonly known to cause “red tides”. The main dinoflagellate responsible for Ciguatera poisoning is Gambierdiscus toxicus which usually lives on the macro algae of coral. Reef fish eat this algae and then they are eaten by secondary consumers (carnivorous fish). When humans consume these fish the toxin has become very concentrated. This is a good example of how toxins/poisons concentrate themselves at the end of a food chain. The fish are unharmed by the toxins; however, humans can suffer greatly from the effects of this small dinoflagellate.
Ciguatera poisoning is most common in tropical and sub-tropical Indo-Pacific regions along with the Caribbean. The poisonous fish are most commonly associated with the coral reef. Consequently the moray eel is usually regarded as the most toxic ciguatera fish. Ciguatera fish smell and taste normal. High levels of the toxin may cause behavioral changes in these fish. This makes the detection of Ciguatera fish very difficult. Due to the fact that detection is so difficult, Ciguatera poisoning continues to be a big problem.
Depending on the toxicity of the fish, symptoms can occur within 30 minutes or 24-48 hours. The unusual thing about Ciguatera is that it is possible for symptoms to last over a year. The typical time is a few weeks to a few months. Common symptoms include; abdominal pain, nausea and tingling of the lips and extremities. Victims of this poisoning also experience reversal of hot/cold sensations, where cold ice feels as though it is burning the skin. Patients usually don’t die probably due to the fact that the reef fish do not accumulate lethal amounts of toxins before they die themselves.
Osha Gray Davidison did a great job of describing the “braid” of the coral reefs. All the species discussed in this paper have their own place in that braid. Their importance in the food chain and ecosystem could all be discussed further in great detail. The global warming and coral bleaching, along with human actions, that Mr. Davidison described can be linked with an increasing habitat for the Gambierdiscus toxicus. Coral reefs should be regarded and conserved because of their beauty and importance regardless of the venomous species of organisms that may inhabit them. Every ecosystem in the world contains poisonous or venomous organisms. If we respect and study them they become an integral part of the habitat in which they live and not just an item to be feared and destroyed.
Davidson, Osha Gray. The Enchanted Braid. New York: John Wiley & Sons, 1998
Dugan, Ruth. The Ocean World of Jacques Cousteau. The Danbury Press, 1975
Freiberg, Marcos, Walls, Jerry G. The World of Venomous Animals. Neptune City, N.J: T.F.H. Publications, 1984
Halstead, Bruce W. Poisonous and Venomous Marine Animals of the World. Princenton: The Darwin Press, 1978
Lebowitz, Jeffery B., Marcus, Steven., Vetrano, Stephen. “Lionfish Envenomation.” The Journal of Emergency Medicine. May 2002:379-382, Vol. 23
Lehane, Leigh., Lewis, Richard. “Ciguatera: recent advances but the risk remains.” International Journal of Food Microbiology, June 2000: 91-125, Vol. 61.
Lewis, Richard J. “The changing face of ciguatera.” Toxicon May 2000:97-106, Vol.39
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