Most dangerous sea creatures

Covering 70% of the world’s surface the sea is home to some of the most unusual, mysterious and deadly animals on the planet. As humans are not native to the oceans this makes us easy pickings for many of these creatures, although thankfully we are largely off the menu..

As someone who has spent plenty of time bobbing around on the surface of the sea my mind has often drifted to what lurks below. Fortunately the statistics provide some comfort and it is apparently quite rare to be eaten alive whilst frolicking in the ocean. However, I expect that’s what all those people who did get eaten were thinking, and lets face it, it’s a pretty unpleasant way to go.

In this selection of the world’s most dangerous sea creatures I have tried to balance the statistics with the potential to kill and aggression of these animals. The list contains a huge range of species from tropical jellyfish to killer seals of the Arctic.

10. Flower Urchin


Flower urchin (Toxopneustes pileolus)

Flower urchin (Toxopneustes pileolus) | Photo: Philippe Bourjon / License

Many of you will have come across sea urchins at some point, and some will have found out the hard way what those sharp spines are for – I certainly have. However, the flower urchin (Toxopneustes pileolus) is in a league of its own when it comes to defensive weaponry. Described by the Guinness Book of Records as the world’s “most dangerous sea urchin” this is one echinoderm you don’t want to be standing on.

What makes this urchin deadly is the potent venom it is armed with. This venom contains at least two dangerous toxins; Contractin A, a neurotoxin which causes spasms of the smooth muscles, and peditoxin – a protein toxin which can cause convulsions, anaphalactic-type shock and death. The venom is delivered via the pedicellariae – these are the flower-like structures that give the urchin its name. Once contact is made with the skin the pedicellariae often break off and continue pumping poison into the victim. Apparently the size of these pedicellariae is directly related to the potency of the venom.

The flower urchin has been responsible for a number of deaths over the years. As well as being intensely painful the urchin sting the resulting paralysis, breathing problems, and disorientation can all contribute to drowning. Regarding the pain, here is an account of a sting recorded by a Japanese marine biologist in the 1930s:

At that time, 7 or 8 pedicellariae stubbornly attached themselves to a side of the middle finger of my right hand, detached from the stalk and remained on the skin of my finger.

Instantly, I felt a severe pain resembling that caused by the cnidoblast of Coelenterata, and I felt as if the toxin were beginning to move rapidly to the blood vessel from the stung area towards my heart. After a while, I experienced a faint giddiness, difficulty of respiration, paralysis of the lips, tongue and eyelids, relaxation of muscles in the limbs, was hardly able to speak or control my facial expression, and felt almost as if I were going to die.

9. Barracuda

Great barracuda

Great barracuda

The photo above should be quite self explanatory as to why the barracuda makes it on to our list. Measuring up to 6ft (1.8m) in length and armed with a terrifying array of super-sharp teeth, the torpedo-like barracuda is more than capable of inflicting serious injuries. There are actually 22 species of barracuda but it is only the great barracuda (Sphyraena barracuda) that has been known to attack humans.

The barracuda’s diet consists mainly of small and medium sized fish. It uses its lightning speed and ambush tactics to catch them. Many of the recorded attacks on humans seem to have involved shiny objects such as jewelry or even diving knives. Apparently the barracuda are attracted to these, confusing them with prey fish and strike.
Such attacks can leave the victim with deep gashes, often resulting in nerve and tendon damage or in the worst case severing blood vessels. These injuries can require hundreds of stitches to patch up.

On rare occasions barracudas have been known to leap out of the water and cause serious injury to people in boat. One recent case in Florida left a female canoeist fighting for her life after suffering broken ribs and a punctured lung after a barracuda attack.

If all that hasn’t convinced you the barracuda should be on this list there is one more thing. Barracuda’s may have the last laugh as their flesh sometimes contains the ciguatera toxin which can cause serious symptoms that last for months.

8. Textile Cone Snail

Cone Snail

Textile cone (Conus textile) © Chiswick Chap / License

The cone snail has been a favourite among shell collectors for centuries, but don’t be fooled by its pretty appearance, these snails are killers! Armed with tiny harpoons formed from modified teeth these critters can fire a hollow barb loaded with deadly neurotoxins in any direction. The harpoon of some of the larger species of cone snail is big and powerful enough to not only penetrate human skin, but gloves or wetsuits too.

A single drop of the cone snail’s venom is said to be sufficient to kill 20 men making it one of the most venomous creatures on earth. Known as conotoxins the poison can be highly specific affecting only certain types of nerves. Whilst this may be of medical interest, the stings generally cause intense, localized pain with the life-threatening symptoms sometimes taking several days to present. On the other hand, rapid paralysis of the respiratory system and death can occur shortly after the sting. In fact, one species of cone snail is known locally as the “cigarette snail” on account of there being just enough time to smoke one before you die!

Despite there lethal venom cone snails have only been responsible for a handful of deaths over the years which is why they only occur at number 9 on our list.

7. Leopard Seal

Leopard Seal

Leopard seal

The leopard seal (Hydrurga leptonyx) is actually named for its spotted coat although it could have easily been for its fierce nature. Sitting right at the top of the Antarctic food chain this seal is one of the biggest seals in the southern oceans. Measuring up to 4 m (13 ft) in length and weighing in at up to 600 kg (1,320 lb) the leopard seal is a formidable predator. In addition to its size and speed these seals are also armed with a huge mouth (big enough to fit your head in!) lined with big, pointy teeth set in a head that looks more reptile than seal.

On the leopard seal’s menu are other species of seal, seabirds, penguins and fish, although they are also known to sieve krill and small crustaceans out of the water too. These seals usually hunt by waiting in ambush just below the ice shelf where seals or penguins are entering the water at which point they pounce.

Given that this seal is only found in the frigid waters of the far southern oceans it doesn’t come into contact with humans often at all. This makes it all the more shocking that a leopard seals have killed people.

Back in 1914, during Sir Ernest Shackleton’s Endurance expedition a leopard seal had to be shot as it chased down crew member Thomas Orde-Lees. The seal first chased  Orde-Lees across the ice before diving under the ice sheet and tracking him from below. After the seal popped up ahead of Orde-Lees another member of the team managed to shoot the seal dead.

In 2003 a British scientist was less fortunate. Kirsty Brown, a 28-year-old marine biologist working with the British Antarctic Survey, was snorkelling off the Antarctic Peninsula when she was attacked by a large leopard seal. The seal dragged the scientist deep underwater where she drowned.
Whilst there are many other stories of leopard seals harassing people in boats this is the first recorded fatality.

6. Stonefish


Stonefish (Synanceia)

This grumpy looking fellow doesn’t seem to be too happy about being the most venomous fish on the planet. Armed with a set of 13 needle-sharp spines along its back the stonefish blends into the background perfectly, just waiting for some unfortunate person to stand on it. Just to increase the likelihood of being stepped on the stonefish is capable of surviving out of the sea for up to 24 hours. Whilst this isn’t really what either party intends to happen it certainly gets them noticed. The neurotoxic venom of the stonefish is not only dangerous but unbelievably painful. In fact the sting from this fish is reported to be so excruciating that victims have been said to beg for their leg to be cut off. The quote below sums up the stonefish sting quite graphically:

I got spiked on the finger by a Stonefish in Australia … never mind a bee sting. … Imagine having each knuckle, then the wrist, elbow and shoulder being hit in turn with a sledgehammer over the course of about an hour. Then about an hour later imagine taking a real kicking to both kidneys for about 45 minutes so that you couldn’t stand or straighten up. I was late 20s, pretty fit physically and this was the tiniest of nicks. Got sensation back in my finger after a few days but had recurrent kidney pains periodically for several years afterwards.

For obvious reasons most people get stung on the foot by stonefish. Whilst this may just bring a new definition to pain, those unlucky enough to get stung on the body can be in big trouble. Such stings are potentially fatal with the venom causing respiratory paralysis and possibly heart failure. In serious cases urgent medical attention is required and victims will need treating with the antivenom. In fact this is the second most frequently administered antivenom in Australia and this has meant no one has died of a stonefish sting there for nearly 100 years.