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abyssal zone deepest part of the seafloor, below 2,000 meters.

anadromous fish that breed in freshwater but spend most of their adult life in the ocean, such as salmon.

aphotic depths of the ocean below which no light penetrates.

autotroph an organism that produces its own nutrients, usually through photosynthesis.

baleen fringed filter in the mouth of some whales that is used to strain food from seawater.

bathyal zone region of the seafloor from the shelf edge (200m) to the start of the abyssal zone (2,000m).

bends dangerous condition caused by gas bubbles in the blood stream, suffered by divers who ascend from pressurized depths too quickly.

benthic relating to the ocean bottom.

Biological Oxygen Demand (BOD) the amount of dissolved oxygen that will disappear from an enclosed water sample as aerobic bacteria decompose the organic material in the water.

bioluminescent organisms capable of generating light.

blue-green algae bacteria capable of performing aerobic photosynthesis.

continental shelf the shallow bottom just offshore of most continents between water's edge and a sharp dropoff where the bottom plunges steeply.

Coriolis effect drifting of a moving object to the right in the northern hemisphere and the left in the southern; or the direction in which it initially begins motion, due to the rotation of the Earth.

diadromous organism that spends part of its life cycle in freshwater and part in saltwater.

diatom a photosynthetic single celled organism enclosed by a shell of silica.

doldrums area along the meteorological equator where surface sea winds are weak and variable and rainfall is heavy.

food chain simplest ecological feeding relationship, in which one species eats only one species of prey and is eaten by only one species of predator.

intertidal shore between highest and lowest tides; also called the littoral zone.

kelp very large brown algae or seaweed, often growing in oceanic "forests."

littoral see intertidal.

neap tide interval when high tides are moderately high and low tides moderately low; neap tides, the opposite of spring tides, occur every other week when the sun and moon are at right angles.

neritic water and organisms over the continental shelves.

pelagic organism that lives in open water off the ocean's bottom.

pinniped fin-footed marine animal such as a walrus, seal, or sea lion.

plankton drifting organisms that lack the ability to swim against currents.

spreading center region of the seafloor where newly formed crustal material moves in opposite directions

swim bladder gas-filled pouch found in most bony fishes, used for buoyancy, sound production, and detection.

thermocline narrow range of depths at which temperature changes abruptly between surface warmth and deep cold.