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Benthic animals live on the ocean floor at all depths. Benthos species are extremely diverse. Some marine biologists classify benthos by size, but classifying them by what and how they feed provides a more accurate picture of their role in marine ecosystems.
The largely immobile suspension feeders attach themselves to rocks, coral or the ocean floor. They consume suspended particles in the water through appendages covered in mucus. Algae, sea weed and kelp are common suspension feeders. They provide most of the world’s oxygen and serve as the base of the marine food chain. Many suspension feeders can grow quite large; some species of kelp, for example, can grow to over 100 feet long.
Like suspension feeders, filter feeders consume bacteria and other microscopic organisms in the water. However, filter feeders create their own water current using siphon-like appendages that suction the water through the animal. Sponges are a common example of filter feeders. Sponges cannot move and are the most primitive of multi-celled animal species.
Grazers and Detritus Feeders
Well-known grazers and detritus feeders include sea urchins and sea cucumbers. These mobile, sometimes venomous creatures live on hard rock and coral surfaces on the ocean’s floor, and feed primarily on algae. Sea urchins and sea cucumbers are harvested in some waters including off the coast of Iceland.
Scavengers vary widely in size and are found at all depths. They primarily feed on dead bodies and remnants found on the ocean’s floor or floating in the water. Many crustaceans, including shrimp and crab, are scavengers, with true crab and lobster being the largest of these. Smaller crustaceans roles in the marine ecosystem are similar to those of insects on land.
Often the largest benthic animals, predators live at all ocean depths. While many are highly mobile, some, such as coral, are stationary predators that consume whatever marine life passes within their reach. Squids and octopuses are prime examples of large, active predators. The less mobile starfish is also a voracious predator. The 1800 species of starfish vary widely and exist in all the world’s oceans.
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