Life In the Oceans
Water covers 75 per cent of the earth's surface. For every square mile of dry land there are two and a half square miles of ocean surface. The continents seem no more a reality than islands springing out of one single ocean, dividing it into various entities that we arbitrarily call oceans, seas, rivers gulfs and bays. There are so many mysteries hidden beneath that not even the most learned marine scientist can claim that he knows everything about marine life. I often wonder why our planet has been named Earth as "Oceanus" seems a more appropriate name, keeping the above facts in mind. You might have explored the ocean in the animated movie Finding Nemo, but now it is time for us to take a deep breath, and get ready for an expedition.There are hundreds of thousands of creatures that dwell in the sea, each superbly adapted to its environment. The basic functions of the aquatic creatures are similar to those on land, to reproduce in whatever manners they are capable of, feed - if necessary, by preying on other living creatures - and move about for self-defence.
Plants In The Ocean
Let us discuss plants first, as they are the basic element of the food chain. Plants serve three vital functions. They provide food, help to oxygenate the water, and provide refuge and habitat for much of the microfauna, which would otherwise be quickly consumed by the smaller fish and other predators.
The simplest example of the aquatic plant is the tiny plants that we buy for our fish tanks. To make it a bit easier, we can divide it into two categories: freshwater plants and saltwater or marine plants. Freshwater plants are found in streams, rivers, ponds and lakes while marine plants are found in oceans and seas.
Plankton can be tiny water plants, animals or bacteria. These organisms range in size from microscopic bacteria and plants to larger animals. Plankton generally has limited or no swimming ability and is transported through the water by currents and tides. The plankton plant species is also known as the oxygen factory as it produces more oxygen than any rain forest.
Seaweed is the most abundant aquatic plant; it grows in oceans and seas as well as freshwater areas. Seaweed is found at the depth of 100 to 200 metres. Giant seaweed's length can vary up to five metres. One amazing fact about it is that it has air bladders, which helps it in floating. They form a kind of underwater forest. Do you know what is the most important thing about it? It is used in ice cream!
Sea grass isn't involved in such important things as ice creams but as it is the most known aquatic plant so I think we should know a little about it. Sea grass is found in coastal waters and grows into extensive shallows sea grass beds.
Although its name is a bit odd, Elodea is something exotic. It seems to offer little attraction to the rotifers and epiphytic growth that encrust other water plants and its leaves and stems are always fairly clean.
The tiny aquatic plant lemna minor, more commonly known as duckweed, is frequently seen as a uniform carpet across the entire area of even quite large ponds. Many organisms (Hydra, rotifer) can be found attached to the fragile rootlets, which hang down from the underside of each leaf. A waxy secretion on the leaf surface produces a high surface tension, ensuring that the leaf always floats on the pond surface.
Nymphaea alba sounds very unfamiliar, right? It's the white water lily! Its leaves float on the water surface attached to the pond bottom by sloping stems.
Algae is a diverse group of non-vascular plants, meaning that they don't have roots, stems leaves or flowers, although they may have similar looking structures. Other aquatic plants are sea cabbage, and kelp. Rice is also an aquatic plant, and is the most important crop.
Animals In The Oceans
Our oceans and seas alike are filled with colourful and interesting animal species that interest us the most. Some of the marine animals are sponges, fish, crabs, dolphins, whales, etc.
Sponges are the simplest forms of multi-cellular animals. A sponge is a bottom-dwelling creature, which attaches itself to something solid in a place where it can find enough food to grow. The scientific name for sponge is "Porifera," which translates into "pore-bearing."
Fish are the most common and the most colourful aquatic animals. There are about 25,000 species of fish. Don't worry I won't describe them all, just a brief introduction of some of them.
Fish can be divided into three groups. The most abundant group is of bony fish, having skeleton. Second one is the cartilage fish, having cartilage instead of bones, e.g. sharks. The third group is the jawless ones; these have suction cups instead of jaws.
Let's start with the very peculiar kinds of fish, that have the ability to swell up twice or four times their actual size. This ability helps these fish to scare away their predator. Some of these are porcupine fish, which look much similar to a pincushion and puffer fish. Lionfish and scorpion fish are examples of the species that injects the poisonous material by means of its spike like outgrowth. These fish look colourful and beautiful but beware of them.
Sea Lamprey is a jawless fish, but it attaches its mouth to its prey by suction. The sandpaper-like tongue of the lamprey scratches the scales and skin off the fish so the lamprey can suck its blood.
While eels normally eat small fishes and a few invertebrates, the genus like Echide the chainlink, have teeth that are modified to crush the shells and carapaces of crustaceans and mollusks. Some morays even eat sea urchins, imagine eating a pincushion, ooch! There are about 20 other families of eels; the moray is the most commonly kept. However, electric eel is very different to the other family members; in its sausage-like body it paws a natural electric current generating system. The electric eel and the two bony fish - the stargazer and the African catfish - share their electric current generating ability.
Be very careful now, here comes the most feared and hated member of cartilaginous family - the sharks. Although only 39 of its 350 species attack human beings, I think they are quite enough. They mostly eat dolphins, seals, other sharks and fish. They have two remarkable plus points - a lifetime supply of teeth and five to seven pairs of gill slits. They hear, feel and smell everything in the water at a great distance.
Other Cartilaginous Fishes
Besides the sharks, some other noteworthy cartilaginous fish includes the ray, the skate and sawfish. Of these the ray is the most dangerous, although none of its 100 odd species has either the equipment or the inclination to prey on men, more people are injured by this curiously shaped creature than by any other fish.
The most dangerous species of ray is the venomous (poisonous) stingray. It varies in shape from round to kite, or diamond like and in size from five inches to seven feet across. On the other hand, manta ray, also known as "devilfish", is one of the gentlest creatures in the sea. Another member of this group, the non-venomous skate fish, so closely resembles the ray that fishermen and the scuba divers often get confused.
Sawfish, the third member of the group as the name implies, possesses a long saw-toothed snout with which it cuts and chops smaller fish to death for food.
Crabs, lobsters and shrimps all belong to a same group - exoskeleton. They have an outer skeleton that covers their soft body. However, they have evolved so that they can walk or run sideways, as well as burrow and swim. A chitinous shell called carapace covers the body. Their segmented body has several pairs of appendages, of which usually five pairs serve as walking legs and two as sensory antennae.
Oysters, in my opinion are the most precious sea creatures. Do you know why? Yes, because pearls are formed in it. Enclosed within a thick sturdy shell, it is also a member of the exoskeleton group. The soft body of an oyster is adapted for filtering minute planktonic organisms from the surrounding water.
The world of spineless sea creatures as jellyfish corals, hydroids, sea anemones, and octopus is very bright and beautiful. Jellyfish is a free-floating creature, and rightly named too, because it is jelly-like and almost transparent in its appearance. It is made of 90 per cent water and quickly disintegrates when taken out of water. It propels itself with a series of movements and is able to fish effectively and reproduce its kinds.
Octopus, are found in tropical and warm waters. Octopus has a soft body with a well-developed brain. They are known to be very intelligent and can dig their dens and even close the entrance after getting into it.
Marine mammals are those mammals that spend the majority of their time in or near the sea. Animals like dolphins, seals, sea otters (seal and sea otters are called pinnipeds - those that have flippers for movements, and commonly known as fin-footed) and even polar bear are considered marine mammals.
Dolphins are actually small toothed whales. It's a friendly natured animal and very playful too. It make sounds that bounce or echo off an object, letting them know exactly how far away something is. Dolphins eat octopus, squids and many kinds of fish. They are known to grow up to 20 feet in length.
Whales like dolphins spend their entire life in the ocean. Some feed on fish, squids, and small marine animals while others like baleen whale take tons of water in to filter plankton and other food. They make high-pitched sound that is how they communicate with each other.
The cutest marine animal is the penguin. They belong to the mammal family that lay eggs, and usually feed on small fishes.
After such a long list, there is one thing very important for all of us to understand. For centuries we have used the sea as our ultimate cesspool and garbage dump. In recent decades, we have added to the water the oil spillage from ships, tanks and underwater wells. As a result we have already disturbed the essential food chain that provides us with the basic necessities of life: breathable air, potable water, edible food and tolerable climate. Thus the most dangerous sea predator, is neither shark nor any sea monster, it's us. Think about it!