Humans have been lured to the ocean for millennia. With an environment that allows for fishing, shipping, defense, recreation, tourism, and many other human activities, coastlines and seas have been vital for human development and have sparked the imagination. However, for some of us, this fascination with the sea is also balanced by an innate fear of the unknown. A flick through a marine life book can reveal alarming diagrams of gulper eels, anglerfish, black-swallowers, and colossal squid that dwell in the inky abyssal depths. Yet, of all oceanic organisms, surely the shark frighten us the most: But are these fears justified?
Fatal shark attacks make headlines, igniting a primal fear of these alleged blood-thirsty beasts. Undeniably, the razor sharp teeth embedded in the broad, robust jaws of a great-white or tiger shark are impressive. Even so, according to the International Shark Attack File, less than half of the 5,213 globally reported shark attacks since 1958 were unprovoked, and only about a quarter were fatal. When you consider the number of people who enter coastal regions every year, that number is surprisingly low. Although few other animals have the threatening physical form of a great-white, there are many other marine life-forms that you are more likely to come across, which can be far more harmful and yet do not invoke such fear and dread.
Jellyfish, corals, and sea anemones belong to one of the simplest animal groups, which possess specialized stinging cells, or nematocysts, for defense and ensnaring other animals for feeding. Despite their simplicity, however, these animals are not all harmless, and a few species possess stinging cells laden with potent venoms, such as the Portuguese man-o-war.
This animal comprises a gas-filled buoyancy float, below which trail a stream of tentacles, some up to six meters long. These tentacles support small structures called polyps, some for feeding, others for reproduction or defence. The venom that is discharged by the man-o-war’s stinging cells, however, also causes immense pain to swimmers who blunder into the drifting tentacles. There are also many dangerous jellyfish: Some are vast, such as the lion’s mane jellyfish, which can be over two meters across and have tentacles over 30 meters long, bearing harmful stinging cells.
Others are smaller, such as the Indo-Pacific box jellyfish, which are less than 10cm in diameter and yet possesses stinging cells than can kill an adult in minutes.
Some venomous marine worm species can be found higher up the evolutionary tree, such as the fire worm and bristle worms, which are protected by hollow spines, called setae, capable of causing burning or numbness.
Another large group of invertebrates are the mollusks: Soft bodied animals usually protected by external shells, such as snails and clams, or internal structures as in cuttlefish and squid. All venomous mollusks are marine, and the most dangerous are often of the most beautiful. On the tropical beaches of the South Pacific live the attractive cone shells, which are often collected by unaware beach combers. Feeding on fish at night, these sea snails harpoon their prey with their radula – a hollow, dart-like tooth, loaded with venom. These radula-darts are fired from the cone shell to catch passing fish for feeding, or for deterring a threat, such as a human.
Depending on the species, the venom from a cone shell can vary from a mild sting, to muscle paralysis, to heart failure, or even death. The geographer cone and textile cone are among the most dangerous, and some reports suggest that a quarter of all darts are fatal. Another dangerous mollusk is the blue-ringed octopus of Australia.
When these animals bite, saliva containing the neurotoxin tetrodotoxin is released to paralyze prey. When handled by unsuspecting nature enthusiasts, however, a bite from these small (less than 15cm across) and attractive octopuses can cause numbness, paralysis, and death.
Other invertebrates that are harmful include some starfish, such as the crown-of-thorns, which feed on corals in the Indo-Pacific region.
If a swimmer or snorkeler steps on the spiny skin of these starfish, any cuts or wounds will be injected with a toxin that causes vomiting or fever. Sea urchins are related to starfish, and can also be extremely painful if stepped on: The black long-spined sea urchins have hollow, venom laden spines. Another relation of the starfish is the sea cucumber, some of which have toxic skins and respiratory trees that can be expelled to form a sticky, entangled net to deter predators; these toxins are also known to cause blindness, and can be very poisonous if eaten.
Possessing a supporting spinal column, the higher animals or vertebrates, also include an array of potentially harmful marine species, including the cartilaginous fishes, such as sharks and rays. Yet of the 360 or so species of shark, only a handful, including the great-white, bull, and tiger, threaten human life. Rays are placid by nature, but stingrays possess a serrated venom-filled barb on their tails. On average, some 750 people in the U.S. are stung by stingrays each year; some rays produce venom that can be fatal. There are also electric rays that live in shallow water alongside sandy shores; if a bather steps onto these rays, an electric shock of over 200 volts can be generated, which can stun an adult.
More advanced fish have bony skeletons, and on a coral reef, many beautiful and flamboyant bony fish bear venomous spines, including the lionfish that has long barbs radiating from each fin filament, and bold colored surgeonfish that possess scalpel-like protrusions on their tails. Many reef fish exude potent toxins through their skin and internal organs, including puffer fish, triggerfish and boxfish. The famed fugu puffer fish, an expensive Japanese delicacy, contains these powerful toxins in its tissues.
Diners claim to enjoy the tingling sensations that can occur when eating the few edible parts of this fish; if too much toxin is consumed, however, a person can experience dizziness, rapid heartbeat, paralysis, suffocation, or death. These puffer fish toxins are now being used by scientist to research the nervous system, while in West Africa, these toxins are apparently used in voodoo to turn victims into zombies. Other dangerous fish include the toadfish and stonefish, which are often stepped on by swimmers, and European weaver fish that lie in the sand with dorsal barbs pointing upwards, causing excruciating pain to tourists who step on them.
Another main group of potentially dangerous animals are the reptiles. The formidable jaws of a saltwater crocodile are obviously concerning; and there are several sea snakes that are extremely venomous, despite having mild temperaments.
This list of harmful and venomous animals is not designed to frighten or terrify readers from entering the sea. It is just to show that there are many other sea animals that are dangerous, (in addition to the few large, predatory sharks,) yet we rarely consider these other life-forms to be threats. In fact, while on the beach or in the sea, you are more likely to encounter sunburn or rip-currents than a dangerous animal; your best chance for seeing the animals listed above is in an aquarium.
Statistically, crossing a road is more dangerous than meeting a shark, and the most dangerous place a person is likely to go during an average day is a kitchen. The animals that inhabit marine systems should be enjoyed rather than feared, and efforts should now be in place to conserve the oceans and protect these vulnerable ecosystems before they are damaged by overfishing, pollution, or climate change. Very little is known about the ocean, and each time a deep sea submersible explores the abyss, new species are discovered; many of which possess substances vital for modern medicine.
When in the sea, you are in the domain of marine species, and you should respect these creatures, rather than decimate them -- which often happens with sharks. The vast majority of shark species are completely harmless to humans, and attacks usually occur only when the larger, predatory species are provoked. Today, we live in an age where the likelihood of encountering a shark is lower than ever, due to increased shark culling and fishing, primarily to fuel the East Asian shark-finning industry, which has resulted in the dwindling numbers of many shark species. Moreover, many sharks are key apex predators that are vital for stabilizing many marine ecosystems – remove them, and the surrounding ecosystem can unravel.
This Shark Week, try to view sharks – and the rest of the marine environment – as intriguing and fascinating inhabitants that constituent our planet, and which need to be respected and protected, not feared and destroyed. Cone shells, reef fish and sea cucumbers are often far more harmful than sharks, yet these animals do not conjure them same emotions of dread that sharks do. Some sharks are predators, yet they are not the deadly nemesis of the seas – more often than not, we are. Sharks are graceful and efficient marine inhabitants; so make an effort to leave the blood-thirsty thoughts of man-eating terrors for the world of fiction, which is where these stereotypes surely belong.