marine biology, study of ocean plants and animals and their
ecological relationships. Marine organisms may be classified
(according to their mode of life) as nektonic, planktonic, or
benthic. Nektonic animals are those that swim and migrate
freely, e.g., adult fishes, whales, and squid. Planktonic
organisms, usually very small or microscopic, have little or no
power of locomotion and merely drift or float in the water.
Benthic organisms live on the sea bottom and include sessile
forms (e.g., sponges, oysters, and corals), creeping organisms
(e.g., crabs and snails), and burrowing animals (e.g., many
clams and worms). Seafloor areas called hydrothermal vents, with
giant tube worms and many other unusual life forms, have been
intensively studied by marine biologists in recent years. The
distribution of marine organisms depends on the chemical and
physical properties of seawater (temperature, salinity, and
dissolved nutrients), on ocean currents (which carry oxygen to
subsurface waters and disperse nutrients, wa