Life in the World's Oceans

No matter where you live, your climate, weather, and even available foods are determined to a great extent by ocean circulation. The uneven heating of the Earth by the Sun and the Coriolis effect result in vast circulation cells of air above the Earth, the movement of huge water masses in the oceans, and resultant "hot spots" of marine life.

How and where did life begin on Earth? The existence of both photosynthetic and chemosynthetic food chains points to the possibility that life could have originated through two different paths. While many questions remain unanswered, two things seem certain: Life began in the oceans, and bacteria are the most successful organisms on the planet.

Beach organisms exist with the constantly changing winds, waves, and tides (sometimes underwater, sometimes fully exposed to the air). Life in estuaries, where rivers meet the oceans, face constant fluctuations in environmental salinity. And hard corals are continually pummeled by wave action. Yet each of these physically challenging environments can be diverse and fecund ecosystems.

Phytoplankton form the base of almost all marine food chains, including that of the blue whale, the largest animal known to have ever existed. But far below the penetration of sunlight, a very different and only recently discovered food web relies solely on the chemosynthetic ability of bacteria.

When we think of healthy marine ecosystems, we should be thinking about phytoplankton. In many ways, we owe our existence to these diatoms, dinoflagellates, green algae, cyanobacteria, and others. Not only do scientists believe they are the ancestors of terrestrial plants, but phytoplankton continues to produce about half of all the oxygen available in our atmosphere today.