Dangerous Sea Animals On October 24, 1995, Brett Fields wrote:

Dear Captain Nelson,
Do you know anything about sea wasps or Portuguese men-of-war ??? Where do they live ?? Please write me back if you have time. Thank you.

Brett Fields


I'm certainly not an expert on poisonous marine animals, but you are in luck, as we do have a copy of a book on board the MALCOLM BALDRIGE that's entitled "Dangerous Australians" published in 1985 by Bay Books in Sydney, Australia. This book describes the sea wasp and Portuguese man-o-war that interest you, in addition to about 3 or 4 dozen other deadly animals that inhabit the land and sea surrounding Australia, including crocodiles and the great white shark.

We are very interested in these deadly animals, and we want to know about their distribution around northern Australia, because we are just about ready to make our transit from Male, Maldives to Darwin, Australia. The coastal sea inside the barrier reef around Darwin is home to the sea wasp, the Portuguese man-o-war, the blue-ringed octopus, and some pretty nasty salt- water crocodiles. Because all of these marine animals are extremely deadly, we want to avoid any contact with them, which will probably mean absolutely no swimming at the beaches in Darwin while we are there.

I. The sea wasp, or the box jellyfish ( Latin name Chironex fleckeri Southcott) is one of the most deadly stinging animals in the sea. The sea wasp has a large transparent body shaped like a box or a bell, that can be as large as a bucket, and can weigh as much as 2 kilograms. A cluster of 16 long (up to 3 meters in length) semi-transparent, extendable tentacles stream out from under the bell of the box jellyfish. Millions of stinging capsules cover each of the 16 long tentacles. The stinging capsules discharge lethal poison through a penetrating thread into the skin of any creature that touches them.

The sea wasp is found in coastal waters, creeks, and rivers in Australia north from about 22-degrees south latitude. The box jellyfish ranges from the Queensland coast on the eastern coast of Australia into the Northern Territory, and around the northern coast of Western Australia. The sea wasp is most prevalent during the Austral summer months from November to mid- March.

The sea wasp uses its deadly venom to catch prey, which usually consists of prawns. However, when the box jellyfish moves into the coastal areas, rivers, and creeks, particularly during the wet Austral summer season, the sea wasp becomes a deadly menace to swimmers and fishermen in the area. On clear, calm days, the semi-transparent sea wasps can usually be seen and avoided. However, during the wet season, the coastal waterways are often flooded, muddy, and turbid, and the sea wasps are difficult to see until it is too late.

The sea wasp is the cause of numerous deaths to swimmers and bathers along the north Queensland coast of Australia, and because of the potent poison injected by the sea wasp, most children who have been stung by the sea wasp have died within minutes of being stung. The sting of the box jellyfish causes an excruciating pain that increases quickly. Where the tentacles have contacted the skin, large brown or purple lines and welts appear quickly, causing the victim to appear as if he/she has been whipped. The poison injected by the sea wasp causes death by shock to the heart, complete circulatory failure, and respiratory paralysis. If the severe symptoms are not treated quickly, death can occur in minutes, even to an adult. The venom also attacks the victim's red blood cells and severely damages the skin where the poisonous capsules have penetrated the skin. An antivenom for the sting of the sea wasp has been developed, but it must be administered relatively quickly. Because the venom from the sea wasp seriously affects the victim's breathing, it may be necessary to perform continuous CPR to keep a victim alive until professional medical assistance can be obtained.

There are two other cousins to the deadly sea wasp or box jellyfish that are somtimes mistaken for the sea wasp. These are the Carybdea alata Reynaud and the Chiropsalmus quadrigatus Haeckel. Both of these marine animals are also know as sea wasps, but they are not as poisonous or as deadly as the box jellyfish or Sea Wasp (Chironex fleckeri Southcott). As you have learned from this description, we would just as soon not see any sea wasps or box jellyfish in the wild near Darwin. I'm perfectly satisfied seeing these types of marine animals swimming in an aquarium, behind a protective glass barrier.

II. The Portuguese Man-Of War is another stinging jellyfish, and although it is much more widespread and common than the box jellyfish or sea wasp, it is not as deadly as the sea wasp. The Portuguese man-o-war or Physalia physalis, is commonly called the blue-bottle in Australia. It is widely distributed throughout the warmer seas of the world, and its habitat generally encircles Australia and extends to Tasmania, as well. The Portuguese man-o-war is most common in the Austral summer months in shallow, coastal waters, and it is not uncommon to find thousands of Portuguese man-o- war floating in groups off the popular surfing beaches in Queensland, Australia. Various species of the Portuguese man-o-war inhabit the tropical Atlantic, sometimes reaching as far north as the Bay of Fundy, the Mediterranean Sea, the Indo-Pacific region, the ocean around Hawaii, and up to southern Japan. The Portuguese man-o-war is commonly observed in the open ocean and coastal seas, and is often mistaken for a true jellyfish.

Actually, the Portuguese man-o-war is not a single marine animal, but it is a colonial hydroid, consisting of a large colony of smaller marine organisms. The blue-bottle gets its name from the body, which really is a large, gas- filled, bladder-like blue float, that can be up to 30 centimeters in length and rise above the water as much as 15 centimeters. The float has a crest, that is used much as a sail to propel the colony across the water when the wind blows.

Clusters of colonial polyps are attached to the underside of the blue bladder, and very long tentacles (sometimes up to 10 meters in length) extend from each of the polyps. Each of the tentacles has stinging cells (called nematocysts) that are capable of killing fish up to 10 centimeters long. The poison secreted from the nematocysts of the Portuguese man-o-war causes respiratory problems and muscle weakness, and it is through these actions that the Portugese man-o-war captures and kills its prey.

Although the sting from the Portuguese man-o-war is not deadly to humans, a person who comes into contact with a Portuguese man-o-war or blue-bottle will still experience a sharp severe pain. Single or multiple welts will appear on the skin where the tentacles have come in contact with the skin. The sting from the Portuguese man-o-war can cause serious side effects including fever, shock, and circulatory and respiratory problems. The severe pain from the sting may last about two hours, and depending upon treatment, the pain will usually subside and go away in seven or eight hours. The usual, quick but effective first aid treatment for the sting from a Portuguese man-o-war is to pour vinegar over the area of the sting and over the tentacles, before removing the tentacles from the skin. Vinegar neutralizes the poison from the nematocysts on the tentacles. In certain cases, some persons may develop allergic reactions to the sting from the Portuguese man-o-war, and they may require medical treatment at a hospital to treat the pain and side effects from the sting.

III. The blue-ringed octopus is another one of the smaller, but more deadly marine animals that inhabit the coastal waters around Australia. There are two species of blue-ringed octopus: the Hapalochlaena lunulata, which is the larger tropical animal, and the Hapalochlaena maculosa, which is the more common, southern species. These deadly creatures are found throughout Australia and Tasmania, and most often inhabit inshore tide pools around the coast.

The blue-ringed octopus is small, and rarely is larger than about 20 centimeters from the tip of one tentacle across to the tip of the opposite tentacle. The blue-ringed octopus is normally light in color, with dark brown bands over its eight arms and body, with blue circles superimposed on these dark brown bands. When the octopus is disturbed or taken out of the water, the colors darken and the rings turn a brilliant electric-blue color, and it is this color change that gives the animal its name.

The blue-ringed octopus secretes a very deadly venom, either by biting with its parrot-like beak, or by squirting the poison into the water surrounding its prey (usually small crustaceans like crabs). The poison is so strong that it causes immediate respiratory paralysis and death can occur within an hour and a half. The direct bite from the blue-ringed octopus is usually painless, and may not be noticed immediately by the victim, who may have mistakenly picked up an interesting looking octopus while searching through a tide pool. However, the deadly effects of the poison will be noticed immediately. The poison apparently interferes with the body's nervous system. The victim will immediately experience numbness of the mouth and tongue, blurring of vision, loss of touch, difficulty with speech and swallowing, and paralysis of the legs and nausea. If the victim does not receive medical treatment immmediately, full paralysis may occur within minutes, followed by unconsciousness and death due to heart failure and lack of oxygen. There is no antivenom for the poison from a blue-ringed octopus. It is usually necessary to perform continuous CPR on a victim until the effects of the venom have subsided. This may take several hours, but it may mean the difference between life or death for the victim.

IV. Now, there's one more deadly marine animal that I'd like to tell you about. Unlike the sea wasp, Portuguese man-o-war, or the blue-ringed octopus that all use deadly poisons to kill their prey, this particular marine animal kills its prey by brute force and strength. It is the saltwater crocodile of "Crocodile Dundee" fame.

The saltwater crocodile, Crocodylus porosus, inhabits Australia's northern tropical waters, particulary in the Northern Territory region around Darwin. The saltwater crocodile is a highly intelligent marine animal that has few natural enemies, and it is most feared because it is one of the few animals known to man that will attack humans without provocation.

Crocodiles have survived on Earth, substantially unchanged by evolution, for more than 180 million years. Fortunately the saltwater crocodiles don't quite live that long, but their life span is impressive, nevertheless. The saltwater crocodile may live for more than 100 years. So if a young crocodile that has just hatched from its egg is able to avoid being early morning breakfast for some other larger marine predator, that young hatchling may grow into a 20-25 foot long, deadly predator that will continue to prowl the coastal sea, inshore rivers and creeks, and mangrove swamps for the next century, always lurking in the shadows, waiting for its next victim. The adult saltwater crocodile will eat anything that comes too close to it. That includes fish, birds, and mammals of any size, including humans, that venture near the water's edge.

Even though the crocodile looks like it should be clumsy on land, the saltwater crocodile is extremely fast on its feet, and it is, of course, an excellent swimmer and an expert at camouflage. Crocodiles can actually outrun a horse on land in a short sprint (30-100 feet). The crocodile frequently attacks with a loud hissing sound, grasps the victim with a very powerful bite, and if the bite doesn't kill the victim immediately, then in the process of dismembering the victim in the water, the crocodile will make a quick twirling movement of its body and drown the victim instead. The saltwater crocodile is also quite capable of knocking a victim off its feet with a sharp blow from its powerful tail. Often the crocodile will hide the killed animal underwater in the mangroves, and wait until the animal has decayed and fermented in the water before finally consuming the animal.

We have been told that the waters around Darwin are often infested by the saltwater crocodile during the wet Austral summer season. We've also been told that there are excursion boats that will take tourists out into the harbor and rivers around Darwin to "feed" the crocodiles, and that the crocodiles apparently will leap several feet out of the water to snatch dead chickens that are dangled above them on a pole. I'm definitely not going to take that sort of "tourist" excursion while I'm in Darwin. However, several of us do intend to go to Kakadu National Park, which is about 2 hours away from Darwin. There we hope to see crocodiles and other animals indigenous to Australia in their natural environment, hopefully without tempting fate.

Well, I hope that the descriptions that I have provided on the sea wasp, Portuguese man-o-war, blue-ringed octopus, and saltwater crocodile have been interesting and have stimulated your curiosity. Please write again soon.

Your Friend,
Captain Craig S. Nelson, NOAA
Commanding Officer