"Sea" - what is it, definition of the term
A marine basin is a continuous, extensive body of saltwater, partially enclosed by continental landforms yet linked to the global oceanic system; it exhibits characteristic salinity, depth gradients, and distinct ecological zones, sustains a wide variety of marine organisms, and plays a significant role in climate regulation through heat exchange.
Detailed information
The ocean constitutes the planet’s largest continuous body of saltwater, covering roughly 71 % of the surface and containing about 97 % of all water. Its average depth exceeds 3,600 meters, while the deepest trench reaches more than 11,000 meters. This vast reservoir stores heat, carbon, and nutrients, influencing global climate and weather patterns.
Physical characteristics include a mean salinity of 35 ‰, a temperature gradient that declines with depth, and a network of currents driven by wind, Earth’s rotation, and density differences. Surface currents redistribute thermal energy, whereas deep‑water circulation transports dissolved gases and nutrients across basins.
Marine ecosystems host unparalleled biodiversity. Primary production is dominated by phytoplankton, which convert sunlight into organic matter and support a food web that extends to fish, marine mammals, and seabirds. Coral reefs, kelp forests, and pelagic zones each sustain distinct assemblages of organisms, many of which are endemic to specific habitats.
Economic activities depend heavily on this environment. Commercial fishing harvests billions of tons of protein annually; offshore oil and gas extraction supplies a significant portion of global energy; and maritime transport moves the majority of international trade. Coastal tourism generates substantial revenue in regions with attractive shorelines and marine attractions.
Environmental pressures threaten the stability of the oceanic system. Excessive nutrient runoff fuels harmful algal blooms, while plastic debris accumulates in gyres and on seabeds. Acidification, driven by increased atmospheric CO₂, reduces carbonate availability, impairing calcifying organisms. Rising temperatures alter species distributions and exacerbate coral bleaching.
Parasites associated with marine life include organisms commonly referred to as sea lice, which are copepod crustaceans that attach to fish and cause tissue damage. While ticks, bugs, lice, and fleas are primarily terrestrial arthropods, analogous ectoparasites exist in marine settings, adapting to saline conditions and host physiology. Their life cycles often involve free‑living larval stages that locate hosts through chemical cues in the water column. Control measures in aquaculture focus on environmental management and targeted treatments to reduce infestations and preserve animal health.