LIFE in the Oceans
According to current theories, life first evolved in the oceans, where organic chemicals became organized into primitive cells over a billion years ago. Today the complexity of life in the sea is like no other biome on earth. The variety of sea organisms that exist there range from jellyfish to coral to whales. All of these organisms form a delicate web that can easily be thrown off balance. Perhaps the best way to understand the life of the ocean is to approach it as a food chain, with tiny photosynthetic algae producing the primary food that all the other animals (including us humans) eat.
|At the bottom of this chain are the microscopic plankton. Plankton are the major source of food in the ocean. Phyto-plankton (at right) include photosynthetic algae that are the basic food source of all living things in the ocean, directly or indirectly. Most are microscopic, but some algal forms (seaweeds) grow to large size. Zooplankton (far right) are tiny animal organisms, commonly larval forms of larger animals like arthropods and molluscs. Plankton cannot be seen by the naked eye but there can be as many as 300,000 per cubic metre found in the open ocean|
Of course, there are also many different types of algae or "seaweed" found in the ocean. Brown, red, and green algae are the 3 types of multicellular "plants" that can stand the harsh conditions the oceans presents. Algae is actually a protist, although there has been much debate on the topic. There are also diatoms that look as though they are multicelllular but are actually a colony of thousands or millions of diatoms.
Many primitive invertebrate (without backbone) animals live only in ocean environments. The following list gives examples of the main groups of invertebrates that live in the oceans.
|Sponges, anemones, corals, and jellyfish are primitive animals that live in great numbers in the oceans of the world. The sponge at right is actually a collection of many single organisms that live together in a colony. Sponges trap plankton and other fine particles in collar cells around the top of the colony, digesting them like an amoeba. At far right is a Portugese man 'o war, a more advanced organism with a float bladder that traps small fish with its poisonous tentacles. Men 'o war washed up on beaches are a major hazard for swimmers, as those stinging tentacles can be painful.|
|Worms include many different groups-- flat, round, hook, segmented, and other specialized groups. Most live in the bottom sediments and eat detrital (dead) materials that drifts down from the water above. The giant tube worms shown at left occur in very deep ocean waters near vents that spew out heated, high-sulfur water from the mantle. Sulfur-oxidizing bateria inside the worms use the sulfur and live symbiotically with the worms.|
|Molluscs are diverse group of animals that includes clams, mussels, oysters, octopi, and squids. All have a mantle of muscle and soft tissue on the dorsal side, usually with a secreted calcareous shell. They have all the internal organs of higher animals, and thus are relatively advanced. Shell-bearing molluscs are mostly sedentary, filtering plankton from shallow seawater. The octopus (at right) is the most advanced mollusc, preying on a range of marine animals. The largest (and rarest) mollusc is the giant squid, which lives in the deep ocean and may weigh up to 1 ton with a length of 90 ft (!).|
|Crustaceans are arthropods, related to insects and spiders. They include crabs, lobsters, barnacles and shrimp. They have a hard exoskeleton made up of segments, each with a pair of legs. They range in size from less than an inch up to several feet. The tiny shrimp called krill make up the diet of the giant baleen whales. Larger lobsters (at left) eat a variety of small fish, and are themselves delicacies for us humans.|
Vertebrate animals are more evolved and complex, and more familiar to us. They include the large group of fishes, as well as oceanic birds, reptiles, and mammals.
|Fishes are familiar to everyone, but include a wide range of different organisms. Sharks (at left) are actually the more primitive fish, lacking both a swim bladder to stabilize them, and a true internal skeleton (they have cartilage instead of bones). They must swim constantly to stay afloat. They are, however, the fiercest predators of the seas, eating most kinds of fish and sea-going mammals. Sharks evolved from the more primitive lampreys and hagfish, which are bottom feeders.|
|Bony fishes include over 16,000 species, most of them adapted to salt water. Their swim bladders, filled with air, stabilizes them in the water, allowing them to float effortlessly and swim with great speed and agility. Many live in large schools (left) to aid in reproduction efficiency and for protection from predators. Most are themselves carnivorous, eating smaller fish and invertebrates. They are a major food source for humans as well. Since they are near the top of the ocean food web, however, pollution and overfishing may affect their ability to survive in large numbers in the future.|
|Birds and reptiles are only occasional or limited inhabitants of the ocean environment. Some birds such as the albatross (at right) may spend most of their lives over the open ocean, diving to catch fish swimming near the surface. They glide on thermal air currents coming off the water, and thus don't need to land to rest. Similarly, most reptiles are land dwellers, but several species of turtles and snakes are nearly completely ocean-dwelling, except for during reproduction when they come ashore to lay eggs. Several turtle species nest on the Georgia coast, and some are endangered due to over-use by humans of beach nesting grounds.|
|Mammals of the ocean are represented by seals, otters, walrus, whales, dolphins and porpoises. All are air-breathers, and must surface occasionally, although dolphins and whales may remain submerged for nearly an hour. The blue whale is the largest mamal that ever lived. All are predatory, some eating small shrimp (baleen whales) while others eat mostly fish or invertebrates.|
|Whale Songs: move your mouse over the blue whale at right to hear a US Navy recording of a blue whale song recorded in the deep ocean. Whale songs are believed to be a form of communication, but no one is sure what is being discussed down there! [NOTE: turn up your speaker volume a little for better listening]|
All these animals live together, and depend on each other, in the giant food web that makes up the oceanic biome. All also depend on the environmental conditions existing in the ocean for their survival. Humans threaten this delicate balance in many ways: as we use our technology to make life better for ourselves, sometimes we create problems that can have far-reaching effects on other ecosystems.