Look, But Don't Touch!
4 Venomous Sea Creatures You Don’t Want to Mess With
In every good pre-dive briefing, dive professionals emphasize the importance of not touching anything underwater. While this is primarily to protect the fragile ocean ecosystems, it’s also for your own protection.
As divers, we always say we are guests underwater. Yes, the ocean is a beautiful, mystical place that we as divers have the privilege to explore. But it is also full of creatures with natural venomous defense mechanisms that can harm, or even kill, humans.
Here we will introduce some of the most extraordinary venomous sea creatures you might encounter scuba diving. But not to worry, while all these little guys can pack a big punch, they’re not out to attack you. Just remember to keep your hands to yourself!
The Blue-ringed Octopus
One of the most venomous subcategories of octopi is the blue-ringed octopus. They are famously named for the neat iridescent blue markings that appear on their bodies when threatened. There are at least four different species of blue-ringed octopus, all of which live in the Pacific and Indian oceans.
Blue-ringed octopi are only 5cm big on average and, with their arms, can be up to 10cm. They spend most of the day tucked away in tiny crevices and come out at night to hunt for injured fish, shrimp, and other small crustaceans.
Despite its size, the blue-ringed octopus is an incredible hunter. The venom it injects into its prey is called tetrodotoxin, which blocks the nerves from transmitting messages resulting in full motor paralyzation within minutes. Unfortunately for its victims, tetrodotoxin’s effects also lead to respiratory arrest.
These venomous octopi are commonly found in tidepools close to the shore, where people will pick them up because they’re so beautiful. But watch out! These little guys can take you out in a matter of minutes.
However, they are generally shy creatures and will only attack humans out of self-defense. And considering they hide during the daytime, you would have to be messing around in their hiding place to encounter one.
Fun Fact: The blue-ringed octopus’s venom is 1000 times more potent than cyanide, and its little body holds enough tetrodotoxin to incapacitate 26 adult humans. There is no known antivenom.
Enjoying this post? Tell your friends! Ocean Pulse is a global newsletter for divers, by divers
The Stonefish
While it might not look like much, the stonefish is the most venomous fish in the world. However, it only employs its venom in self-defense. The name “stonefish” is derived from its appearance underwater, where it looks like an encrusted rock or piece of coral. They mostly live in the Indo-Pacific and are experts in camouflage.
Stonefish are ambush predators that prey on small fish and crustaceans. Therefore, most incidents with stonefish actually occur because someone unexpectedly steps on one. They can live in both shallow waters and deeper down on coral floors, so it’s hard to predict where one might be lurking.
When the stonefish perceives a threat, it will defend itself by releasing a potent neurotoxin from the spines on its dorsal fin. This venom can lead to respiratory weakness, paralysis, and even necrosis of the affected area.
In a worst-case scenario, stonefish venom can result in death within an hour. However, this is only if left untreated. Luckily, applying hot, but not scalding, water to the area helps, and antivenom is available.
Fun Fact: The amount of pressure applied when stepping on or touching a stonefish correlates directly with the amount of venom it releases.
Other Venomous Relatives of the Stonefish
The scorpionfish is a smaller cousin to the stonefish and has similar habitats and behavior. Although a scorpionfish sting is not lethal in most cases, it sure isn’t pleasant.
Remarkably enough, the lionfish also belongs to the same tribe of fish as the stonefish and scorpionfish. However, lionfish do not lie in wait but actively hunt. They have venomous spines located around their bodies to protect themselves from predators. Lionfish venom is not considered lethal to humans but is still painful.
Fun Fact: The lionfish doesn’t have many natural predators and can survive in both cool and tropical water. This adaptability has helped them spread quickly as an invasive species. Many dive operations even organize lionfish spear hunting sessions to reduce their overpopulation.
To learn more about venomous lionfish, check out the Ocean Pulse articles The Tremendously Invasive Lionfish and Save the Ocean by Hunting Invasive Lionfish.
The Cone Snail
The cone snail is a mollusk that lives inside beautiful cone-shaped shells. Their shell homes can have all kinds of patterns and colors, which often leads to humans picking them up.
They typically live in warm tropical waters, but some of the 900 different species of cone snail are adapted to survive in colder waters. All cone snail species are venomous and utilize a toxin to disable their prey before feeding on it. As bottom feeders, they prey on smaller fish, mollusks, worms, and even other cone snails in this way.
People will often pick up cone snails, believing they are just pretty shells. However, the cone snail will retaliate by biting you with its envenomed barbed tooth. This can feel similar to a bee sting for the smaller cone snail species. However, the larger species of cone snail, particularly the Geography Cone, carry a more potent venom that can be fatal to humans.
The larger species of cone snails can also penetrate exposure equipment, such as your wetsuit and gloves. So, definitely don’t pick try and pick these guys up. What lies in the ocean belongs there, after all.
Fun Fact: A cone snail’s tooth used to hunt is called a harpoon and discarded after use. A cone snail can have up to 20 of these harpoons growing in its body simultaneously.
Enjoying this post? Tell your friends! Ocean Pulse is a global newsletter for divers, by divers
The Australian Box Jellyfish
The box jellyfish, also called the sea wasp, might not be the most venomous jellyfish. However, it is considered the deadliest. As the name implies, its main body is shaped like a box. They can grow up to 20cm, and from each corner of its body flows 15 tentacles that can reach lengths of up to 3 meters.
This beautiful but deadly jellyfish is native to the Indo-Pacific Ocean. In contrast to most jellyfish, it can swim, reaching speeds of up to 2 meters a second. Box jellyfish have 24 eyes, and anything they see gets processed through a ring of nerves in their body. It also actively hunts for fish, rather than floating in wait, and can temporarily shrink itself if it does not eat enough.
Each box jellyfish tentacle is laced with half a million cnidocytes, which inject venom into their victims. Their venom contains toxins that attack the nervous system, heart, and skin. Depending on how much venom is released, this can kill an adult human within a few minutes.
The stingers of a box jellyfish are only triggered by a contact reaction with organic tissue. This is why clothing, stinger suits, and wetsuits can protect you from being stung.
Fun Fact: Not all species of box jellyfish have a lethal venom dosage.
Staying Safe Around Venomous Sea Life
Now that you’ve learned a bit about these fascinating venomous sea creatures, it’s important to note that none of these will come and seek you out underwater. Instead, any incidents are either a freak accident or because someone was not following best practices by getting too close or pestering said marine life.
As long as you maintain your distance, you should be perfectly safe while observing these magical but deadly creatures. You can also check out DAN’s hazardous marine life first aid reference guide for more information.
Enjoying Ocean Pulse? Subscribe for more stories for divers by divers.