Marine Biology

A look at the most Dangerous Ocean Reef Predators

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"A look at the most Dangerous Ocean Reef Predators"
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Dangerous predators lurk in the waters of ocean reefs. From some not so humble crustaceans, to the secretive stonefish, to sharks, the natural cycles of marine life demand that there be predators and prey. It's all about living, instinctive living. But ocean reefs have one specially dangerous predator. One who doesn't even live on the reef!

Ocean reefs, found in tropical and semi-tropical waters, may be fringe, barrier or atoll reefs. They are also known collectively as coral reefs. 25% of marine life dwells on reefs. The largest reef in the world is the Great Barrier Reef, stretching 2,300kms along the north east Australian coastline. It covers an area of 345,000km, with more than 2,900 reefs around 940 islands and cays. But being big does not equate with a strong defense. The Great Barrier Reef, just like other reefs worldwide, is subject to dangerous predators, including the specially dangerous one.

Dangerous predators will be limited to those that threaten the delicate balance of the coral reef ecosystem. Crustaceans, like the coral crab, that uses its strong claws to crush sea urchins and clams, will not be included because it is part of the usual predatory-prey life cycle of the coral system. Crustaceans, in turn, are a delicacy for an octopus. If the coral crab population wiped out the sea urchin population, then it would become a dangerous predator.

Since the late 20th century, the crown-of-thorns star fish has hit the dangerous predator "most wanted" list worldwide. This unusually large starfish can grow up to 1m in diameter, has up to 21 arms and its whole body is wrapped in poisonous spines. It is the bitter enemy of coral. If there is a high population outbreak of this starfish, an intense competition for food begins. A coral reef can take up to 10 years to recover from such a feeding frenzy. "Predators of adult crown-of-thorns starfish include the giant triton snail, the humphead maori wrasse, starry pufferfish and titan triggerfish." But there is insufficient data to identify if feeding rates of predators can impact on birthrates of this starfish.

The whitetip reef shark usually hunts alone, but it can join other sharks on a night feed and aggressively "will thrash through coral reefs looking for food", obviously breaking fragile coral in its path. Sometimes, it will be so intent on winning the hunt, it will wedge the front half of its body in a crevice and stay there till its prey emerges. It is easy to see how this predator, with a hungry belly and a support army could easily slip higher on the dangerous predator list. For now, they only represent occasional setbacks for the coral reef.

To unsuspecting divers in a coral reef, the stonefish can be the most dangerous predator. It is recorded as the most venomous fish in the world, with 13 highly toxic spines and an incredible ability for camouflage. "The venom causes intense pain and is believed to have killed many Pacific and Indian Ocean islanders. No deaths have been recorded in Australia since European arrival (Underhill, 1987). An antivenom developed in 1959 further reduces the likelihood of death." Sharks and rays are natural predators of this fish, so, for now, the stonefish remains mainly a threat to man.

But it is man who is the real, ongoing dangerous predator of ocean reefs; particularly coastal reefs near densely populated areas of coastline. Man's needs and man's activities are killing coral reefs. "In Sri Lanka and India, whole portions of the reef have been covered in cement. Ships also destroy many reefs through anchoring or contact." Overfishing, careless tourism, coral mining, the dumping of urban and industrial waste offshore and sedimentation from logging carried by rivers to the sea are just a few threats man offers the coral reef system. Combine that with El Nino effects, global warming and the odd tsunami or hurricane, it is easy to see that the fragile reef systems worldwide are in great danger of total obliteration.

Somehow, the mention now of another dangerous predator, the garishly coloured nudibranch, a sea slug, pales into insignificance. This slug has toxic glands all over its skin and, after digesting sea anemones, corals and jellyfish, retains the stinging cells of some its prey in a sac on its back. At least this slug has the decency to wear extremely bright colours to warn potential predators. Again, only an outbreak of this species will place it high on the dangerous predator list.

It seems humanity is the real "crown-of-thorns" for the ocean reef environment. "Coral reefs may recover from periodic traumas caused by weather or other natural occurrences. If, however, corals are subjected to numerous and sustained stresses including those imposed by people, the strain may be too much for them to endure, and they will perish." Ironically, humanity loves the beauty of this natural treasure, the coral reef, the ocean's reef. But does humanity love it enough to make sacrifices to save it?

More about this author: Gemma Wiseman

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