Features and Explainers

5 Dangerous Under Water Animals You Probably Didn’t Know About

Written by Mihika Hegde

In light of the recent sea lice attack, here are 7 other sea animals you should probably know of before heading into the water.

1. Stonefish

Packing a punch, Stonefish are armed with 13 dorsal fin spines, all contained within a thick sheath of skin until it’s time to attack. Each spine has 2 venom glands at their base, which are activated when Stonefish are threatened. The pain from a Stonefish sting is immediate, excruciating, and can even last for days on end. From there, you can expect muscular paralysis, breathing difficulties, shock, and sometimes heart failure without medical assistance. No one has died from  a Stonefish sting in Australia for over a 100 years, but the anti-venom used to counteract it is the second most frequently administered in the country.

How bad are they really? You’d think an animal that doesn’t commonly top 50cm in length might not be a pressing concern but Stonefish have a history of making waves. Take reports from the Gold Coast City Council for example, who are currently considering draining an entire lake after 2 phases of an initiative to find the deadly fish failed.

Where to look out for them: Northern Australia, Shark Bay (WA), Tweed River (NSW). More broadly, Stonefish can be found just about everywhere- from bays, estuaries, and reef flats, they usually nestle themselves around aquatic plants, fallen trees, rocks, and coral. Keep an eye out to make sure you don’t catch them at a bad moment.

So how can you make sure Stonefish and their solitary glory are kept that way? Footwear. If you’re not sure what’s on the bottom of a body of water, take caution… or just stick to an air-conditioned room.

Not just a pretty face, Stonefish (pictured) are the most venomous of all fish.

2. Fire Coral

These organisms look suspiciously similar to your run-of-the-mill coral that decks out our very own Great Barrier reef but touch them and you’d can expect anything from mild irritation, severe pain, nausea and vomiting.

The kicker? Fire Coral have invisible tentacles from which they can deliver a hefty sting. That means you don’t actually have to come in contact with these organisms as much as be near enough to their stingers. Interestingly, they’re closely related to jellyfish and anemones (hence the similar method of defence).

On the plus side, these organisms are also easily identifiable (marine biology degree strictly optional). Being a bright yellow-green in colour means they stick out like a sore… coral in reefs.

Thanks to pollutants, environmental damage, and overfishing, Fire Coral are critically endangered so the change of you bumping into them are extremely low. Given how threatened the species is, they’re not one to look out for, but if you do stumble across them, keep your distance (for their sake, and yours!)

Where to look out for them: Fire Coral appear in small brush-like growths on rocks and coral.

Fire Coral (pictured): Finding Nemo’s Anemone has competition

3. Cone Snail

An ornate shell makes the Cone Snail a camouflaging expert. This animal carries a tiny harpoon of neurotoxins that it uses to quickly spear and kill fish. Ever the adaptable hunter, these harpoons can pierce through wetsuits in a flash. Known to have been responsible for approximately 30 human deaths, the Cone Snail isn’t a garden variety organism.

The bright(er) side? Their venom includes a general pain killer that immobilises its target. If you’re unlucky enough to get caught by a sting, urgent treatment is vital. It’ll involve using pressure/ immobilisation, CPR and further urgent medical assistance.

Cone Snails usually only grow to be 120mm long, but thanks to their distinctly patterned outer shells, they tend to be a point of interest. Their markings can range slightly so if you’re unsure, might be best to visit a souvenir shop for some (vetted) shells.

Where to look out for them:  Although they are most widespread in tropical and subtropical areas (Queensland) they also occur in the temperate waters of southern Australia.

One sting from a Cone Snail has the potential to kill 15 healthy adults within hours.

4. Bristle Worm

The Bristle Worm can grow a considerable length of up to 20cm long. It’s large, thick, a pretty easy to spot because of bright red gills, purple spots, and large bundles of yellow, translucent bristles.

Though quite the eye catching sight, the Bristle Worm is not one to be handled. If threatened, the organism releases its bristles, causing mild to severe skin irritation. Once stung, you can expect anything from redness, to burning, swelling, and a rash. Medical attention to remove any bristles lodged in skin may be required along with a course of antibiotics to prevent infection.

Though a pretty rare sight, Bristle Worms are best taken in from afar.

Where to look out for them: The Bristle Worm is widespread across Australia but you’ll find concentrated numbers in tropical and subtropical areas of the country (particularly Queensland). The sea creature occupies a variety of substrates from fine sands, to mud and gravel.

Bristle Worms (pictured) are colourful, but make sure you exercise caution.

5. Stinging Hydroid

The Stinging Hydroid is found in feathery colonies on inshore reefs in shallow water from 3-25 metres depth. They can reach 45cm high, making them relatively easy to spot.

Also known as the White Stinging Sea Fern, these organisms look light and delicate but pack a powerful sting.

When threatened, Stinging Hydroids use tiny, barbed, needle-like structures to inject toxin into their target. This happens whenever the Hydroids sense danger or nearby prey in a reaction that is said to be one of the fastest cellular responses in nature- toxin can be released within 3 milliseconds of contact with a target.

Stings can cause painful blisters and rashes, allergic reactions, and occasionally, infections. Depending on the severity of a sting, medical attention may be required.

Like with other dangerous sea organisms, you can avoid the hassle of a hospital visit by avoiding them. Wearing protective wetsuits, including gloves, even when the temperature doesn’t necessitate it, is also good way to go.

Where to look out for them: Stinging Hydroids are found are found in tropical to warm-temperate seas, and are especially common on the Great Barrier Reef.

Delicate but dangerous, the Stinging Hydroid (pictured) is one to watch out for.

About the author

Mihika Hegde