Kinds of Organisms Found in a Marine Ecosystem

Marine ecosystems are among the most biodiverse on the planet. This isn't surprising when you consider the fact that salt-water environments constitute more than 70 percent of Earth's surface. Contrary to popular perceptions, marine ecosystems encompass more than the world's oceans. Salt marshes, coral reefs and intertidal zones, with their flora and fauna, are parts of this dynamic biological interaction.

  1. Microfauna -- The Planktons

    • All sea creatures rely on plankton for their survival and sustenance.

      The oceans of the world teem with tiny creatures, called plankton, unseen and unnoticed by most humans, but crucial to the survival of marine life. Plankton can be divided into three major categories: phytoplankton, which rely on sunlight and photosynthesis for their survival; zooplankton, which feed on phytoplankton and are usually the larval phase of creatures like starfish, sea urchins, marine worms and fish; and bacterioplankton which are, as the name suggests, bacterial in nature. Plankton are consumed by practically all ocean dwellers, from other plankton all the way up to the great whales. Without plankton, life in the oceans would not exist. Rather than thinking of "food chains," the roles of plankton and other denizens of the deep are best conceived as being part of a "food web." The sustenance of life in the oceans relies on an interdependent dynamic that begins with phytoplankton and spreads out in a non-linear fashion to encompass all other animal life forms in the sea, in a continual dance of eating and being eaten.

    Corals and Coral Reefs

    • Corals are tiny animals, related to jellyfish. In their adult forms they spend their lives in one place. Most of us are familiar with the hard exoskeletons of dead corals, which are composed of calcium carbonate and form the base material of coral reefs among these colony animals. In their living state these reef colonies often resemble fantastical flower gardens. Most corals harbor symbiotic algae from whom they derive sustenance and energy, although many also consume small fish and plankton unfortunate enough to come within range of their tentacles. Coral reefs provide food and shelter to numerous creatures. The U.S. Environmental Protection Agency states that coral reefs are ". . .second only to tropical rain forests in plant and animal diversity."

    Forests of the Sea

    • Dolphins and Gray Whales often use kelp forests to hide from Orca predators.

      You might think it strange to think of forests growing beneath the ocean's waves, but they exist. Kelp is a large seaweed or macro-algae, usually brown in color, that grows in nutrient-rich waters in several of the world's oceans. The largest of these kelp forests grow in the waters of the Pacific. Individual plants can grow to more than 90 feet in length. Like their terrestrial counterparts, kelp forests have a canopy, a mid-range and a floor. And like their land-based cousins they are host to a great variety of of oceanic life. Birds, sea mammals and fish use the upper reaches for food and shelter. Snails and abalone can often be found in the mid-range. And their root analogs, called holdfasts, play host to creatures like starfish and sea urchins.