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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Benthic zone | 3/5 | https://en.wikipedia.org/wiki/Benthic_zone | reference | science, encyclopedia | 2026-05-05T07:34:28.462475+00:00 | kb-cron |
Both foraminifera and diatoms have planktonic and benthic forms, that is, they can drift in the water column or live on sediment at the bottom of the ocean. Regardless of form, their shells sink to the seafloor after they die. These shells are widely used as climate proxies. The chemical composition of the shells are a consequence of the chemical composition of the ocean at the time the shells were formed. Past water temperatures can be also be inferred from the ratios of stable oxygen isotopes in the shells, since lighter isotopes evaporate more readily in warmer water leaving the heavier isotopes in the shells. Information about past climates can be inferred further from the abundance of forams and diatoms, since they tend to be more abundant in warm water.The sudden extinction event which killed the dinosaurs 66 million years ago also rendered extinct three-quarters of all other animal and plant species. However, deep-sea benthic forams flourished in the aftermath. In 2020 it was reported that researchers have examined the chemical composition of thousands of samples of these benthic forams and used their findings to build the most detailed climate record of Earth ever. Some endoliths have extremely long lives. In 2013 researchers reported evidence of endoliths in the ocean floor, perhaps millions of years old, with a generation time of 10,000 years. These are slowly metabolizing and not in a dormant state. Some Actinomycetota found in Siberia are estimated to be half a million years old.
=== By trophic level ===
==== Zoobenthos ==== Zoobenthos, prefix from Ancient Greek zôion 'animal', animals belonging to the benthos. Examples include polychaete worms, starfish and anemones.
==== Phytobenthos ==== Phytobenthos, prefix from Ancient Greek phutón 'plant', plants belonging to the benthos, mainly benthic diatoms and macroalgae (seaweed).
=== By location ===
==== Endobenthos ==== Endobenthos (or endobenthic), prefix from Ancient Greek éndon 'inner, internal', lives buried, or burrowing in the sediment, often in the oxygenated top layer, e.g., a sea pen or a sand dollar.
==== Epibenthos ==== Epibenthos (or epibenthic), prefix from Ancient Greek epí 'on top of', lives on top of the sediments, e.g., sea cucumber or a sea snail.
==== Hyperbenthos ==== Hyperbenthos (or hyperbenthic), prefix from Ancient Greek hupér 'over', lives just above the sediment, e.g., a rock cod.
=== By habitat ===
Modern seafloor mapping technologies have revealed linkages between seafloor geomorphology and benthic habitats, in which suites of benthic communities are associated with specific geomorphic settings. Examples include cold-water coral communities associated with seamounts and submarine canyons, kelp forests associated with inner shelf rocky reefs and rockfish associated with rocky escarpments on continental slopes. In oceanic environments, habitats can also be zoned by depth. From the shallowest to the deepest are: the epipelagic (less than 200 meters), the mesopelagic (200–1,000 meters), the bathyal (1,000–4,000 meters), the abyssal (4,000–6,000 meters) and the deepest, the hadal (below 6,000 meters).
Human impacts have occurred at all ocean depths, but are most significant on shallow continental shelf and slope habitats. Many benthic organisms have retained their historic evolutionary characteristics. Some organisms are significantly larger than their relatives living in shallower zones, largely because of higher oxygen concentration in deep water. It is not easy to map or observe these organisms and their habitats, and most modern observations are made using remotely operated underwater vehicles (ROVs), and rarely crewed submersibles. Tide pools provide somewhat demanding benthic homes for organisms such as sea stars, mussels and clams. Inhabitants deal with a frequently changing environment: fluctuations in water temperature, salinity, and oxygen content. Hazards include waves, strong currents, exposure to midday sun and predators. Waves can dislodge mussels and draw them out to sea. Gulls pick up and drop sea urchins to break them open. Sea stars prey on mussels and are eaten by gulls themselves. Black bears are known to sometimes feast on intertidal creatures at low tide. Although tide pool organisms must avoid getting washed away into the ocean, drying up in the sun, or being eaten, they depend on the tide pool's constant changes for food. Tide pools contain complex food webs that can vary based on the climate.
== Ecological roles ==