Common Venomous Reef Creatures of the Shallow Seas
Photo StoryPublished : Jun 22, 2021Updated : Sep 24, 2023
Among the multitude of fish on reefs are a vast array of venomous stingers. Though most use their poison in self-defence and to hunt, they will also strike at perceived threats
Text and photos: Vardhan Patankar
Among the multitude of fish on reefs are a vast array of venomous stingers. Though most use their poison in self-defence and to hunt, they will also strike at perceived threats
Imagine feeling totally weightless while gliding above colourful coral reefs in the middle of the sea. Big fish chase small fish. Small fish hide in their burrows and coral crevices. In that world, humans are the curiosity. We are the strangers that don’t belong. The underwater world is so different from our own that we can get lost observing the corals and fishes of different sizes, shapes, and colours. A few corals extend their polyps in a feeding frenzy, others sway gently with the currents. A sea krait swims by, a grouper fish waits to ambush its prey, a shoal of butterflyfish feed on polyps, fusiliers glide in unison and feed on plankton. All are busy in the rigmarole of their daily lives.
Among these reef denizens, there are a vast array of venomous stingers. While most use venom in self-defence and to satisfy their hunger, venom also is a weapon of choice when a threat is perceived. If you accidentally step on them or brush up against them, you are definitely in for a painful — sometimes deadly — and unwelcome surprise.
Researchers have documented the presence of about 1,200 different venomous species worldwide while in India there are about 50 venomous species that are common in our shallow seas. Their venom has a potent chemical composition. Around the world, these creatures are estimated to injure about 50,000 people per year. While none of them is known to release their venom unless threatened, avoiding them is about great buoyancy control and respectful underwater behaviour. Here are a few common venomous creatures that you can watch out for when you are on a dive in India. Getting to explore the underwater world is a true privilege, therefore as a general thumb rule, divers and snorkellers should avoid touching anything underwater to minimise damage to the reef system and themselves.
By far the highest concentration of venom is found in sea kraits. These sea snakes, such as the yellow-lipped sea krait (Laticauda colubrina) pictured here, have distinct black-and-white stripes, a narrow mouth and jaw, and a flattened tail that helps them propel through the water column. Being reptiles, they need to surface every few minutes for a breath of fresh air, which increases the chance of encounters with divers and snorkellers. Although they are non-aggressive, gentle, and only bite in self-defence, their venom is ten times more potent than that of an Indian cobra and that is why it is best to keep a safe distance from them. Cover photo: Bearded scorpionfish (Scorpaenopsis barbata).
Amongst reef fishes, the winner in the most venomous category are stonefish (this one is Synanceia sp.). They are heavily disguised as large coral-encrusted rocks when they lie in wait for prey. Whenever a suitable victim such as a crab or fish is close by, the stonefish lunges forward and engulfs its meal. As a diver, if you disturb one by being oblivious to its presence, it immediately erects 13 venomous spines along its back and if stepped on shoots venom from some or all its spines. Each spine is like a sharp needle, delivering the venom from two sacs attached to it. This results in severe pain, paralysis, tissue death, and can be fatal if not treated.
Scorpionfish, like the devil scorpionfish (Scorpaenopsis diabolus) (above left) and Poss’s scorpionfish (Scorpaenopsis possi) (above right) are perhaps the second most venomous reef fish. Like stonefish, they are also considered masters of disguise. As the name suggests, they have a type of "sting", just like terrestrial scorpions, in the form of sharp spines coated with venomous mucus. While stonefish and scorpionfish can be confusing to identify underwater, an easy way to distinguish them is to differentiate the mouth structure. The stonefish's back fin is bigger and spines thicker. Nonetheless, any resulting wound inflicted by it is acutely painful, and can even be lethal.
The most attractive venomous reef creatures are lionfish, like this longspine lionfish (Pterois sp.), which carry 16 venomous barbs around their fins. Their venom is so painful that it is said to make you wish you were dead. Don’t let their attractive looks fool you and keep a safe distance from those barbs. Having said this, like scorpionfish and their colleagues, they won’t lie in ambush to poke you, rather they will display their spines by swirling around to ensure that you do not get close to them. Unfortunately, because of how attractive they are, they are highly desired by the aquarium trade.
Cone shells such as the cobweb cone shell (Conus araneosus) seen here are unusual suspects among venomous sea creatures. They have conical or cylindrical-shaped shells and a muscular foot. Some cone shells target other snails, while others feast on fish. To sense food, cone shells filter water through a tubelike organ called a siphon, awaiting a whiff of the tell-tale chemicals emitted by their prey. When prey is near, the cone shell extends a proboscis armed with a harpoon-like tip that injects venom filled with special chemicals called “conotoxins”. These toxins stop nerve cells from communicating with each other causing paralysis within seconds and, eventually, death. Their venom is so powerful and painless that victims (human and other prey) often die unaware that they have even been bitten.
The most notorious venomous sea creature is surely the stingray, primarily because of the incident where the famous TV presenter and environmentalist, Steve Irwin died in an unfortunate event. Stingrays like this blue-spotted stingray (Neotrygon kuhlii) camouflage themselves under the sand to hunt for prey, hence they can be hard to spot and easy to step on when on a dive. If threatened, a stingray whips its tail in defence leaving a laceration or puncture wound on your skin. The sheath around each spine then breaks apart and releases venom into the wound and surrounding tissues. To avoid trouble, it is best for anyone entering the area around reefs to be aware of which creatures can cause harm and be perpetually observant of their surroundings.
is a marine biologist working on a range of basic and applied studies in marine systems. He is fascinated by marine life that exists within reefs, but observes life outside with much wonder.
