The floor of an aquatic biome, known as the benthos, was once thought to be a dead zone because of the lack of oxygen and light. However, the sediment in the benthos provides nutrients enough to support organisms such as worms, fish, and bacteria. The sea floor contains some unusual ecological niches called hydrothermal vents, where energy from the interior of Earth creates hot springs of water and communities of bacteria that can withstand high temperatures. These areas could have been key to the emergence of life.
There are freshwater and marine benthic ecosystems. In freshwater, the benthos may be only a few feet from the surface, but in the ocean it may be up to 7 mi (11 km) deep. The deeper the benthos is in a body of water, the less is known about its ecosystem, because of the difficulty of scientific exploration.
Historical Background and Scientific Foundations
The benthos is the floor of a body of water, whether it is a stream or an ocean. The shallower the water is, the more likely it is to have been explored for its ecology. Therefore, it is known that snails and burrowing worms live at the bottom of freshwater habitats such as lakes and rivers. They tolerate the relatively low oxygen concentrations and live off the nutrient-rich sediment that characterizes a freshwater benthos.
The sea and ocean, or marine, benthos is a cold, oxygen-poor environment where, it was argued, few species could survive. In fact, the sea floor is diverse, with over 200,000 species having been discovered already. Most of these are small, around 0.1 in (0.25 cm) long, living in the muddy sediments of the benthos. The revelation of the rich diversity of the benthos came as scientists became more able to study smaller species.
Research has also shown that the benthos is a dynamic environment, providing organisms with various niches. Larger animals, like fish, passing along the sea floor churn up fine mud sediment and create peaks and channels. There is also the deposition of detritus from above layers, called marine snow, which creates hot spots of nutrition.
The benthos is an environment for invertebrates, rather than larger animals. Experiments sending explorer vehicles to the sea floor have discovered crustaceans, starfish, snails, worms, and sea cucumbers. The latter represent a dominant group in the benthos worldwide. They range in size from a fraction of an inch in length to several inches and they feed by vacuuming the surface of the mud. The poverty of food supplies on the benthos means that most organisms are stationary. Besides sea cucumbers, they include sponges, sea anemones, and tube worms.
The majority of animals in the benthos are single-celled creatures such as the foraminiferans, which feed by engulfing bacteria. There are also radiolaria, which are single-celled organisms that have skeletons made of silica. The benthos is also home to various species of bacteria that are either free-living or found living on or in other animals.
In the 1970s, new species of bacteria were discovered in hydrothermal vents, which are hot springs on the benthos where water comes through heated by the core of Earth. Many new bacterial species have been discovered here, which are able to withstand temperatures far beyond that of boiling water.
WORDS TO KNOW
BIOME: A well-defined terrestrial environment (e.g., desert, tundra, or tropical forest) and the complex of living organisms found in that region.
DETRITUS: Matter produced by decay or disintegration of living material.
FORAMINIFERANS: Single-celled animals which feed on bacteria.
HYDROTHERMAL VENTS: Underground jets of mineral-rich hot water.
RADIOLARIA: Single-celled animals with silica skeletons.
Impacts and Issues
The benthos is difficult to explore because of its depth—at least in the marine environment. Modern technology is making it possible to explore these regions and revealing that they are a much richer ecosystem than previously suspected.
The existence of hydrothermal vents and newly discovered species associated with these ecological niches is especially interesting. The bacteria found here have been classified into a new kingdom called the Archaea. As the name suggests, these organisms have a very long history. Their existence suggests that life itself may have evolved in a hydrothermal vent environment.
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NOAA Coastal Services Center. “Benthic Habitat Mapping.” July 24, 2007. http://www.csc.noaa.gov/benthic/start/what.htm (accessed on April 7, 2008)