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World's Most Dangerous Marine Animals

Batul Nafisa Baxamusa
Beneath the calm surface of the sea, lurks a silent monster. Read about some of the world's most dangerous marine animals here.
The crystal clear water, cool breeze and pleasant sun, tempts one to go for a swim in the sea. One gets into the water without a single doubt about what lurks beneath. There are plenty of dangerous marine creatures which may cause harm. Many swimmers of the deep blue sea have encountered the most dangerous marine animals and lived to tell the tale.
The world beneath the calm surface of the sea and ocean is dramatically beautiful. Yet, it has its dangers that makes their world so magical and intriguing. Here's some truth about these sea creatures. Read on and learn about some of the possible threats to humans living in an aquatic environment.

Dangerous Sea Animals

The following list covers the names of some of the most deadly inhabitants of the oceans and seas around the world. Go through the information provided and learn the painful encounters that one may face, when they come face to face with the dangerous creatures living in the water.

Blue Ringed Octopus

The blue ringed octopus is in no way similar to the German octopus Paul, who predicted the football game results. He does not predict the outcome of a particular game, but makes a difference between life and death.
This creature lives deep in the oceans near Japan to Australia and camouflaged itself with its dermal cells. This makes it very difficult to spot this marine creature as most of the time it hides under the camouflage. But, when disturbed it turns bright yellow in color. It sports bright blue rings that makes it looks quite striking.
It is just the size of a golf ball, but packed with a venom that is powerful enough to kill an adult human. What makes it one of the dangerous sea animals is that there is no anti-venom available for its bite. It injects a neurotoxin into the body that causes paralysis, respiratory arrest, cardiac arrest and other problems like respiratory distress.
A person bitten by the blue ringed octopus requires immediate artificial respiration. The toxins take hours to be flushed out of the body and if timely medical treatment is not available it can lead to sure death.

Box Jellyfish

One of the most venomous creatures in the world is the box jellyfish. Also called the box of death, this creature has about 60 tentacles that are over 5 meters long.
If an adult human comes in contact with just 3 tentacles, he is injected with over 5,000 million stinging cells. It injects a deadly venom. This leads to skin necrosis, excruciating pain and shock. The box jellyfish is totally invisible to the naked human eye. Thus, it is very hard to spot and prevent a sting.
Most of the victims die before they reach the shore for help, due to drowning. The pain is so excruciating that the body goes into a shock and the person drowns. If the person does not drown, he may suffer from a cardiac arrest.

Crown of Thorns

The crown of thorns starfish is a carnivorous predator. It can move around the reef and release digestive enzymes to liquefy the coral tissue. It then extrudes its stomach to absorb the nutrients.
It is a voracious eater and consumes more than 6 square meters of coral reef/year. It has sharp spines on its limbs that look like thorns. It has a crown shape that gives rise to its name. These sharp thorns can pierce through wetsuits and other clothes. They release a chemical that attracts more crown of thorn starfishes to a particular area.
The thorn causes a serious wound to the diver and releases neurotoxins. These neurotoxins lead to a stinging pain for hours, nausea and vomiting. The wound may become dark blue in color and lead to edema. The spines may get embedded in the skin and lead to an infection.


Lionfish belongs to the venomous marine fish genus Pterosis. It is found in the Indo-Pacific region and is known for its showy pectoral fins, venomous spiky tentacles.
Lionfish is a predatory fish and its venom poses danger to fishermen and drivers. The venom causes a negative inotropic and chronotropic effect. It leads to vomiting, fever, sweating and may prove to be fatal in some people.
Lionfish generally do not attack humans, until provoked. If one is stung they should immediately soak the injured part in hot water and seek medical attention.


It is very cute to see a fish suddenly bloat and puff up. But, these cute looking fish carry a deadly poison called tetrodotoxin (TTX).
These toxins prove to be more dangerous than cyanide. If injected into a human it will lead to breathing difficulty and then ultimately death. However, not all pufferfishes carry toxins and many are even consumed in Japan.

Sea Eel

The slippery eels are one of the most dangerous marine animals. They tend to hide in cracks and crevices of rocks during the day. They are nocturnal and hunt for food at night.
Thus, when mariners or divers swim around rocks, they are advised to keep their hands safe from cracks or holes. They have sharp teeth that can give you a very bad bite. This bite leads to serious bacterial infections. Never, ever try to feed these creatures when in water. Or else you will be attacked by a flock of sea eels with razor-sharp teeth.

Sea Urchin

Sea urchins are brightly-colored, oddly-shaped creatures. They have really sharp spines that can penetrate deep into your body. They can even break and remain lodged into your body.
It leads to severe pain and needs to be removed surgically in many cases. The flower urchins are species of sea urchins that are venomous. They appear like a flower, not a thorny creature. They can inject a venom that can lead to paralysis, even death.


'Crocodile Hunter' Steve Irwin lost his life on 4th September 2006, due to a sting by the stingray. These creatures rarely attack humans, but when they feel under threat, they try to defend themselves.
They sting their supposedly aggressor and inject them with a toxin that causes an injury. There are a few stingray species that have a fatal sting. Otherwise they are the most passive creatures and divers can swim along with them in water.
Steve Irwin's death was a tragic incident, that proves nature is unpredictable. If you happen to be on the ocean floor, slide your foot, do not step on the floor. This way the stingray will just flee and not whip its tail if stepped on accidentally.


The stonefish is the master of camouflage. They sport such an excellent camouflage, that they are virtually undetectable until attacked by one.
They live close to the coral reefs and disguise themselves as rocks and thus, known as stonefish. Stonefish are known to be one of the most poisonous fish in the world. They have 13 spikes on their dorsal side that contain an extremely potent venom.
If the sting penetrates deep enough, it could lead to death in a matter of minutes. It causes severe pain, shock and paralysis. If one survives the attack, they are known to develop muscle atrophy due to nerve damage.

Saltwater Crocodile

Crocs, the name says it all. Although not exactly a sea creature, this marine animal is one of the most dangerous since prehistoric times. It is one of the most ferocious predators of the world.
It reaches a size of over 6 feet in length and can weigh over 1500 kg. It attacks a full-grown buffalo, kangaroos, monkeys and even takes on sharks singlehandedly. When the crocodile catches its prey, it takes it down in the water and twirls it around. This paralyzes the already terrorized victim, waiting to be devoured.
The list continues with names of animals like the great white shark, sea serpents, sea lion, yellow-bellied sea snake, marbled cone snail and many more. Do make sure you know well about the dangerous animals in the water you are about to swim. This will help you keep them at arm's length and save yourself from an unpleasant encounter under the sea.