Marine biology is the study of plants and animals in the ocean. Marine biologists also seek to understand the ecological relationships between these plants and animals.
Around 70% of the Earth is covered by water, and most of that is saltwater. The average depth of the ocean is 2.4 miles, over 12,000 feet. Plants and animals live through out the ocean, making it a rich source of life.
Until recently, our understanding of underwater life forms was restricted to what we could bring to the surface. With improvements in science and technology, we are now able to study the organisms of the ocean.
There are approximately a half a million known marine species. Each are classified according to their way of life. Nektonic organisms like fish, whales, and squid swim freely around the ocean. Tiny planktonic organisms drift through the water at the mercy of the tides. Benthic organisms live on the bottom of the sea. Some benthic organisms are capable of movement, like snails, crabs, clams, and worms. Others, like corals, sponges, and oysters, stay in one place. In recent years, hydrothermal vents have been discovered, along with strange lifeforms never before encountered.
Finding creatures in the ocean can be as challenging as finding a needle in a haystack. Their distribution depends on many factors. The warmth of the sea water, the amount of nutrients available, and the salinity affect which animals live in the area. Ocean currents mix oxygen and nutrients through the water, while carrying plankton, larvae, spores and eggs.
Creatures that rely on photosynthesis (algae, plants, and cyanobacteria) live near the surface where sunlight is plentiful. Plankton also live near the surface, relying on the Sun for food and the currents for transportation.
Below 300 feet, the ocean is a cold and dark place. Only 2% of the ocean floor lies under water shallow enough to allow sunlight to penetrate. In these areas, benthic creatures which rely on photosynthesis can thrive. In deeper areas where no light can penetrate, photosynthetic organisms cannot survive.
The deepest reaches of the ocean seem to be a barren wasteland. However, bacteria thrive here, as they do in the upper reaches. Hydrothermal vents have been discovered, along with incredible life forms not found anywhere else. Modern technology makes it possible for us now to study the creatures thousands of feet under the ocean surface. And yet, much remains a mystery.