Dangerous reef organisms
Dangerous reef organisms hot buttons for dangerous reef-organisms section of BIOLOGY OF CARIBBEAN CORAL REEFS website hot button for irritating chemicals section of BIOLOGY OF CARIBBEAN CORAL REEFS website hot button for bites section of BIOLOGY OF CARIBBEAN CORAL REEFS website hot button for sharp spines/bristles section of BIOLOGY OF CARIBBEAN CORAL REEFS website hot button for poisonous flesh section of BIOLOGY OF CARIBBEAN CORAL REEFS website hot button for stings section of BIOLOGY OF CARIBBEAN CORAL REEFS website

There aren't many Caribbean-reef orgnanisms that will kill you dead, but there are certainly quite a few that can hurt you. CLICK ON an icon to learn about what you should avoid.

NOTE it goes without saying that a good and careful SCUBA diver will be swimming well above the reef and will not be touching anything. For this reason, most dive-boat operators frown on their customers wearing gloves

subtitle icon for poisonous flesh part of BIOLOGY OF CARIBBEAN CORAL REEFS website

Poisonous flesh

Only a few reef animals have poisonous flesh. Pufferfishes, for example, have highly toxic livers containing a potent neurotoxin. Other fishes, most notably large predatory ones like groupers, morays, jacks, triggerfishes, and barracudas, become toxic by eating herbivorous fishes that feed on botton-dwelling dinoflagellates that contain paralytic toxins. The herbivores are generally not poisonous to humans, perhaps because the levels of toxins in their bodies are low. Through concentration from eating many of these herbivorous fishes, though, toxin levels magnify in the "top predators" and may reach levels dangerous for human consumption. The effect of the toxins on the fishes, if there is any effect at all, is not known.

NOTE a type of single-celled photosynthesising protist (formerly known as a protozoan)

photograph of

"Triggerfishes and many other reef fishes are caught and sold as food throughout the Caribbean.  But not this pufferfish!…if it’s like the deadly fugu pufferfishes of Japan it will have toxic flesh which, if prepared improperly, can kill" - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE bandtail puffer Sphoeroides spengleri




The infamous fugu of Japanese cuisine is pufferfish flesh taken from as close to the liver as the chef dares, and usually prepared sashimi style. The liver contains a large amount of tetrodotoxin, which is a deadly neurotoxin, and this diffuses to some extent into the body-wall musculature. Human photograph of sharpnose puffer coutesy Anne Dupont, Floridaresponse to a fugu meal ranges from nothing, to tingling in the lips and fingertips, to respiratory distress and, sometimes, to death. Japanese fugu chefs dance on a tightrope, as afficianados who pay high price for the delicacy (perhaps $500-1000 for a meal), demand to be tingled but, of course, not killed. Little is known of the biological role played by tetrodotoxin in the natural world. Pufferfishes apparently have glands in the skin that secrete the chemical, and its external presence may be repugnant to predators. If a predator eats a pufferfish it may spit it out; however, if the prey is swallowed and digested, the predator may sicken or even die. Photograph courtesy Anne Dupont, Florida.

NOTE lit. "toad toxin". The toxin was originally isolated and characterised from toads. It is a nerve-impulse inhibitor and works effectively to protect the toads from predators


Sharpnose puffer Canthigaster rostrata 1.2X

treatment for fugu (pufferfish) poisoning

1. there is no antidote for pufferfish poisoning.
2. induce vomiting and administer oxygen.
3. seek immediate medical attention, preferably in an emergency room.
4. if in doubt whether or not to eat fugu (prepared by a professional), heed the words of a Japanese sage, "those who eat fugu soup are stupid, but those who don't eat fugu soup are also stupid".




photograph of adult sushi-worms Anisakis sp.
are a type of parasitic nematode normally vectored from marine mammals through fishes and crustaceans.  While not exactly an example of "poisonous flesh", the juvenile sushi-woms encyst for a time in various organs of the host's body, including muscles and, as such, can be eaten by humans, either as sushi or sashimi or other preparations of raw fish. When eaten, the juvenile worms attempt to escape by burrowing through the gut wall and in so doing produce intense ulcer-like pain. Other symptoms include nausea and vomiting. The worms generally don't survive their transit through a human gut, so long-term effects are usually uncommon.

A bundle of preserved sushi-worms Anisakis sp. 1.25X

treatment for sushi-worms

1. go to a doctor for any ulcer-like pain.
2. although the chance of getting a sushi-worm infection has always been small, nowadays all fish for preparation of sushi and sashimi is frozen, which kills the worms.  Also, sushi-worms are apparently not common in reef fishes.  Still, if you should happen to eat raw reef fish, follow your mother's advice and chew it extra-carefully


Ciguatera poisoning


Large predatory reef fishes may contain toxins known as ciguatoxins.  The toxins, usually of several chemical types, are derived initially from consumption of certain single-celled bottom-dwelling dinoflagellates, and then are accumulated up the food chain from herbivorous fishes to carnivores.  The toxins are chemically unchanged through this transfer.  Consumption of uncooked affected fishes can lead to diarrhea, vomiting, muscle aches, and abdominal pain, followed by numbness, tingling of the mouth, itchy skin, burning sensation on contact with something cold like ice, hallucinations and, in extreme drawing of a ciguatera-producing benthic dinoflagellatecases, death from cardiovascular failure.  Ciguatera is found not only in fishes, but also in certain crabs and snails. The toxins, representing several different types, but all producing similar symptoms, are quite heat-resistant, so may be resistant to normal cooking temperatures.

Gambierdiscus toxicus is just one of several ciguatera-poisoning benthic
dinoflagellates, but is one of the commonest in the Caribbean region 250X

  Any of these large fishes may contain dangerous levels of ciguatoxins amplified through the food chain from their origin in bottom-dwelling dinoflagellates...
  photo collage of possible ciguatera-containing reef fishes
  Severe mortality in reef fishes in the Florida Keys during 1993-94 may have originated through consumption of toxic algae or benthic dinoflagellates such as ciguatera-producing Gambierdiscus toxicus.  Landsberg 1995 Dis Aquat Org 22: 83. 

Species commonly affected in the Florida Keys include gray angelfishes, eaters of sponges and gorgonians....




Gray angelfish Pomacanthus arcuatus 0.33X

photograph of gray angelfish
photograph of princess parrotfish

...princess parrotfishes, eaters of bottom algae...





Princess parrotfish Scarus taeniopterus 0.6X 


...and doctorfishes, eaters of bottom algae.




Doctorfish Acanthurus chirurgus 0.33X

photograph of doctorfish

map of Caribbean area showing distribution of ciguatera-causing dinoflagellates Gambierdiscus
Collections of algae throughout the Caribbean Islands disclose high numbers of cells of Gambierdiscus toxicus in regions such as the Virgin Islands that coincidentally are characterised by high incidence of ciguatera outbreaks.  Taylor 1985 Proc 5th Intern Coral Reef Sympos 4: 423.





Numbers (in yellow type-face) of
Gambierdiscus toxicus per live gram
of finely branched, bushy macroalgae

In some areas increased incidence of ciguatera poisoning in herbivorous fishes is correlated with coral-bleaching.  Some species affected are shown here. photo collage of ciguatera bearing herbivorous fishes

photograph of diseased boulder coral Montastrea sp.
The correlation may be explained by the preferential colonization of dead parts of bleached corals such as boulder and staghorn by filamentous algae that are then eaten by the herbivorous fishes. Within the filamentous algae are entrapped ciguatera-causing dinoflagellates.  The fishes shown above are common prey for large piscivores, leading to amplifiction of the toxins through the food chain. Kohler & Kohler 1992 Envir Biol Fish 35: 413.

NOTE lit. “eaters of fishes”

Boulder coral Montastrea sp. with
damaged/diseased portion bearing
a growth of filamentous algae 0.4X


photograph of blue chromis and damselfish
A comparison in Australia of resistance of 2 species of damselfishes to ciguatoxins shows a bottom-feeding species to be more resistant to clinical injections of the toxins than a planktivorous species.  Small, regular meals containing toxins may result in the chemicals being stored (sequestered) in regions of the fish’s body. Capra et al. 1988  Proc 6th Intern Coral Reef Sympos 3: 37.

NOTE lit. "eater of plankton"


Two types of damselfishes on a Caribbean reef crest: blue chromises
Chromis cyanea
and a bicolor damselfish Stegastes partitus 0.2X. 
The chromises are planktivorous (eating mainly copepods) and would
have little contact with ciguatera-containing dinoflagellates.  In
comparison, damselfishes are benthic herbivores and could be regularly
consuming dinoflagellates attached to seaweeds in their gardens

  Let's hear what the chromis and damselfish have to say on the matter:
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treatment for ciguatera poisoning
  1. there is no antidote for ciguatera toxins. Treatment is limited to supportive therapy that usually leads to slow but complete recovery.
2. if symptoms of disabling gut pain are present go immediately to a doctor or hospital.
3. to be certain about not contracting ciguatera poisoning, do not eat reef fishes.
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