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Dangerous Marine Animals
The What, Where, Avoiding and Otherwise Dealing with Biological Stinger, Biters, Pokers as a Diver.

Look, Don’t Touch. Dangerous Marine Animals: An Overview   


by Robert Fenner  


            Amongst the seas denizens that can potentially be harmful to divers, there is a vast array of stingers, biters, venomous and poisonous animals; ranging from microscopic to boat size organisms. Recognizing them becomes easier with time diving as well as above water instruction; and avoiding dangerous marines is mainly a matter of your dive skills in buoyancy control and body awareness.

            Here is presented a necessarily brief glance at some of the major sources of scuba and skin-diving hazardous life to be best un-encountered in the sea.

About Marine Microbes:

            Unbeknownst to most all people are the many microorganisms that are found in even the “cleanest” of seawater. There are some viruses, funguses, bacteria (including Blue Green “algae”) and Protists in every drop of the sea; sometimes a great deal; but most are innocuous to humans; not being pathogenic (disease-inducing) nor even raising a rash (dermatitis) on your skin from immersion.  

Definitions: Dangerous How?

            Getting chemically “stung” appears straightforward; as does getting bitten, poked by sharp processes; but there is an ongoing need to define toxicity in terms of poison versus venom. Poisonous situations arise when toxic biological materials are ingested; when they are taken in by mouth; whereas venomous occurrences are a matter of simple touch or envemonized (via puncture). As an example, you can get stung (venom) as well as poked by the spiny rays of Lionfishes; but they’re definitely not poisonous. In fact, they’re delicious to eat.




Beware of the spiny portions of Scorpionfish’s dorsal and pectoral fins, but don’t pass on the opportunity to consume their tasty flanks in entrée and hors d'oeuvres  offerings. Though they have large heads, not much body meat, Lionfishes and kin are very edible fishes.


     With the invasion of two species in the tropical West Atlantic, folks in the US are learning what much of the world already knew, Lions are delish!


Pictured; a Pterois volitans off the Queensland coast.








There are several, from the Middle English meaning “many” other venomous fishes. For instance, a darling of the marine catfishes, the Coral Cat, Plotosus lineatus is very painful to get stuck and envenomized via its forward pectoral and dorsal fin spines. Think about this next time you’re crouching down low in front of a group for a close up photo or video.


There are many other venomous organisms to be found in the sea and amongst diverse groups. Several Octopus and some Cowries are notorious for their bites and deadly injections.





Of the better known venomous snails the Textile cone (Conus textile), here in the Red Sea) and Geographic cone have been known to cause human deaths. They should not be handled of course.



There are a few octopuses whose bite is very venomous; but none likely better known than the few species of “Blue Rings”. Here a four inch bodied Hapalochlaena lunulata scoots out of the way of divers in Bali, Indonesia.

     All Octopodes can bite, not all are venomous.




Oh ho! Imagine my surprise; when after years of encouraging folks to put Flamboyant Cuttlefish in their hand for a photo, I came to find that they are dangerously venomous!

     Here’s a female Metasepia pfefferi out hunting in Mabul, Malaysia.


Punctures: Easily Done

            Sharp processes are more the rule than exception as defense mechanisms go for aquatic life. With or sans toxic venom, these wounds have the very real potential for infection… and they REALLY hurt.


Tangs, Surgeonfishes, Doctorfishes are delicious food fishes all over their worldwide tropical reef distribution; but spear fishers need beware of their namesake scalpel-like caudal peduncle (the part of the body right before the tail fin) “tang”… A super-sharp saber that these fishes can and do know well how to wield. Shown, the tasty Kole or Yellow-Eyed Tang (Ctenochaetus strigosus) in Maui. A fave to shoot and eat as it “makes its own oil” when cooked whole in a pan.



Related Rabbitfishes, or perhaps the better common name, Spinefoots are also preferred human fare, and similarly spiny. Their anterior dorsal and anal fin rays are dangerously spiny and are lifted into defensive action if would-be predators or fishers get too close. Here is the aptly named Siganus puellis in Wakatobi; S. Sulawesi.

Oh, how few of us have NOT been stuck by Sea Urchins…. Whether from hapless drifting to the bottom, betting pushed about by currents adrift at night or trying our best to not get poked while framing that keeper image or video for posterity? Here is a non-toxic Diadema antillarum in St. Thomas, USVI, and the unwary author with a few spines in his knee…



Biting: Rare, But Can Happen

            The vast majority of incidents where divers are bitten are due to human prompting. Feeding wild, predaceous animals of size (e.g. Sharks, Barracudas, Moray Eels….) is a foolish and dangerous exercise.



A common customer at tropical West Atlantic “shark feeds”, the Caribbean Reef Shark, Carcharhinus perezii waiting their turn for frozen, impaled chunks of mostly the fish species below doing what they do. There are places in the world that hand feed sharks and more. Make no mistake; sharks are not domesticated… and can do make little distinction twixt the food item being offered and the object holding it.

Below; the largest and most common member of the family (worldwide distribution in warm shallow seas) the Giant Barracuda; Sphyraena gigantea. A whole one in the Bahamas and a close up down in S. Sulawesi (Wakatobi). Showing its impressive dentition. Are attracted to shiny objects already; no need to tempt by feeding.



You’re in the mood for what? A moray? These are wild animals; NOT able to be made into pets. Every year finds “mangled accidents” amidst well-meaning divers and folks who just aren’t careful where they place their hands. Do NOT feed wild animals.


     There are smaller species (under a foot in length), and some that eat crabs and shrimps that lack sharp teeth; but there are some humongous species that are piscivorous… one, the Java Moray, Gymnothorax javanicus (here in French Polynesia, though found in Hawai’i, all the way to the Red Sea) gets to some 3 meters/ten feet in length!






Stings A ‘Plenty:

            Scratches, bruises, contusions and piercings from rough encounters with the living and abiotic environment are all too common when you’re a new diver, during night dives and in high current settings. Adding insult to these physical injuries is the realm of stinging; and this is a HUGE category.


Amongst the most familiar diver-stingers are the Hydrozoans; small, polyped kin of corals, sea fans and other Cnidarians. At right, the all-too familiar Fire Coral, Millepora. Worldwide in tropical seas. Below; one of the “Christmas Tree” like Hydrozoans, Aglaophenia, and the author’s arm after coming in contact; not paying attention while making photos in Bali in 2014.



And of course, the many Scyphozoans, “Jellies”; Medusoid animals that can pack a wallop even if you don’t see them. Here’s a stinging Nettle, Chrysaora quinquecirrha at a British Columbia Aquarium.


Combo! Bites/Spikes PLUS Venom!

            Yes; there are animals that render venom through their biting humans; albeit almost always in defense. These dual threats range from not so serious to possible real trouble. We’ll mention by example, the range here.


Fang-Tooth Blennies aren’t often recognized for their danger to divers; until you’ve been bitten! These little (to about four inches) buggers have sharp rear teeth that they use to ambush other fishes, tearing off scales and flesh for nutrition; and do “try out” people at times; rarely with consequence.


     Shown; a Plagiotremus ewaensis in Hawaii. There are several other species of Sabretooth Blennies in Indian and Pacific Oceans.




Seasnakes similarly have small heads with fangs toward the back of their throats; and are even less inclined to bite divers; but occasionally someone gets too close and gets stuck between their fingers. Here is a Laticauda laticauda in Bunaken, N. Sulawesi.


Of the more than eighty known venomous species of Echinoderms (spiny skinned animals), the toxic Sea Urchins are way under appreciated. I have seen many divers picking them up underwater, perhaps believing that due to their shorter spines that they’re not dangerous. Not so. These Echinoids can both puncture your hand and envenomize you painfully. Shown; a Toxopneustes pileolus in Puerto Vallarta, Mexico’s Pacific side.


Many folks get poked and painfully injected while “trying to save the reefs” in well-intended Crown of Thorns Starfish collecting efforts. Other than Triton Snails (Charonia) and some predaceous small shrimps; there’s not much to counter the C o T periodic population explosions and stony coral predation. Do not touch with your bare skin!


     Shown: an Acanthaster planci in Kona, Hawaii.



Back to Poisoning: Ciguatera and More!

            As I’ve mentioned; poisonous refers to ingesting toxic organisms. Poisonous fishes in particular are common in tropical reef areas around the world. The general term given to their toxic ingestion is Ciguatera poisoning. There are a bunch of defining terms here; some for the target tissues affected by their biotoxins (neurotoxin for the nervous system, hemotoxic for blood, cardiotoxic for the heart…).

            Ichthyotoxism (poisoning from ingesting fish) is often linked to bio-accumulation of toxins from “top” predators consuming fishes in turn that forage on toxic algae. We’ll have more to say regarding this category of danger in a piece dedicated to the topic; but suffice it to state that these fishes, Ciguatera, shellfish poisoning and more can be avoided by being informed by local folks. They will know what organisms are poisonous to eat.


            To avoid troubles underwater divers should be aware of hazards, perpetually observant of their surroundings and, avoiding contact with potentially or really dangerous marine organisms. The best course of action is to avoid touching any organism period; as you will find that there are many marines that can cause humans woe.

            In successive articles we’ll review in depth the who and what of sources of biological dangers one should be aware of, how to recognize and hopefully avoid them; and in the event/s of contact, what course of action one can and should take to alleviate pain and infection.

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