The sea covers most of the world's surface, and it teems with life. Your first dive on a coral reef will see you swimming in a colourful garden vibrating with activity. It begs the question: 'Am I swimming with anything dangerous?'
Well, yes, quite frankly it's a bloodbath down there!
Virtually all the life you see under water is animal life. Those gorgeous flowers, that wonderful vegetation, even the curiously shaped rocks, are usually animals or colonies of animals. Everything is hungry, and everything is eating everything else.
For a list of undersea predators, we would have to start with organisms such as coral polyps, which come alive at night and grab smaller planktonic life-forms as they pass on the current. The same goes for those 'flowers'. They are grabbing tiny animals with their feathery petals.
Big fish eat smaller fish. Some are sedentary and lie in wait, enormous mouths waiting to open and then snap shut on an unwary passing prey. Others hunt in packs.
Generally size is the guide as to whether you are eaten or get eaten. Small fish are prey to bigger fish.
So how do the big fish get to be big? By being very cautious and circumspect about other animals, staying safe. It's the same with sharks. Some of them can be quite big, but usually your first encounter with a shark, although adrenaline-charged, may be tinged with a certain disappointment. Most sharks are a lot smaller than you are.
What is the function of a shark? Why are they there? Are they the undiscerning predators usually portrayed in the movies?
You rarely see a dead or dying fish ona coral reef. You never even see an ill or infirm one. Everything bursts with rude health. And that's a clue to the function of the shark. Its role is to maintain the health of the rest of the fish population.
Sharks eat dead and dying fish, and those that are injured or diseased. They are very good at scavenging. There are no epidemics of disease among fish populations if there is a healthy presence of sharks.
Over millions of years of evolution, a strict set of rules has emerged within the sub-aquatic animal population. Everyone knows who eats whom. So where does man fit into all this? Expelling masses of noisy bubbles, we arrived on the scene in any numbers only about 50 years ago, and the animals don't know what to make of us.
We're bigger than most of them, so they are wary. They know that rule about always being eaten by something bigger. They will usually let you approach only so close before beating a speedy retreat.
And those few animals that are bigger than you didn't get to be that size by dashing in and biting anything that took their fancy. The bigger the animal, the more
cautious it is likely to be. As a diver, you really don't have to worry about shark attacks unless you intentionally provoke one to defend itself, and the statistics bear this out. But then, the same goes for any animal.
Sea-lions are pretty well armed with a set of teeth, so don't pester them. Bull sea-lions are usually busy guarding their harems of females. They bark a lot, but their bark is worse than their bite!
An octopus can make short work of a crab because it has a beak that can penetrate any shell. Small fish like titan triggerfish can be aggressive if they think you are threatening their territory, and even a clownfish like Nemo will put up a good fight if it thinks you are endangering it.
So don't go around attacking animals, because they can all do their best to defend themselves, as will your domestic cat.
What about the really big stuff? Seeing a whale shark, at around 18m long the biggest fish in the sea, can be an awe-inspiring moment and that awe won't diminish if you see one again.
A whale shark has a mouth that could easily engulf a man, but it doesn't. Why? Because it's a plankton-feeder, hoovering up the smallest life-forms in the water and filtering them with baleen-like plates in its throat, just like a whale. So this leviathan is one of the most passive and gentle animals in the sea.
The same goes for manta rays, which also eat plankton and are similarly gentle giants. Your only worry is whether you can get close enough to one without alarming it so that it beats a hasty retreat.
You may be surprised to learn that dolphins can be a little daunting to a diver. Yes, that cuddly animal with the friendly smile! That's because they are quick-thinking, fast-moving, warm-blooded mammals.
However, encounters with wild dolphin are invariably fleeting. They are there one moment and gone the next.
Pods of dolphin are often accompanied by schools of silky sharks. They pick up the injured and dying fish the dolphin may drop. Dolphins are such messy eaters!
If you swim on the surface in the open ocean with a pod of dolphins you may well be investigated by silky sharks wondering why you are splashing around so much, doing an impression of a dying fish. What's the answer? Scuba-dive!
Moray and conger eels can look impressive. Morays gulp water to extract the oxygen from it and can look as if they are snapping their jaws at you. In fact they are frightened of you but, being poor swimmers, prefer to stay in the protection of their hole in a wreck or rock rather than risk being picked off by a predator in open water. Just don't put your hand in their mouths.
Sting rays have an impressive barb which they might use against a shark that attacks them and tries to eat them. But the only danger to a human from a sting ray is that it might sting you if you stand on one by accident while wading in the shallows.
You can take it as read that very few creatures are going to chase after you to try to harm you. It's the sedentary animals that pose a possible danger to divers.
Many animals lie passively in wait for their prey to pass, and some are armed with poison. So if you see an animal being particularly brave about your presence, ask yourself why. Nothing is going to try to sting or poison you, but if you touch some animals such as stonefish or scorpionfish, which may be well-camouflaged, they can defend themselves in a nasty way. The same goes for certain shellfish.
So the golden rule is, don't touch anything if you don't know what it is. That goes for some of the rocks! Fire-coral ruins more divers' holidays than anything else. It got its name because it packs a burning sting.
This all sounds pretty hazardous. Poisonous rocks. Animals with teeth. It might well be if you encountered such things on terra firma, but the rules are different in the weightlessness of the undersea environment.
In this three-dimensional world, your buoyancy under control, you can hover above the coral reef in a leisurely manner.
You can approach the most venomous creature as closely as you like without falling on it. You aren't limited to standing on a surface. Remember that diving is a visual experience, and use you eyes rather than your hands.
And if you see a shark, count yourself lucky, before it turns and flees from you.
So what is dangerous? The water, and there's tons of it! You can't breathe under water without technological assistance.
As for the wildlife, enjoy!
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千与.千寻
2011-05-13 06:21:48谢谢走马！是reply给我的还是林贝卡的还是两个人的？