Aquatic

Aquatic is an adjective describing anything connected with water. It is used in biology to refer to organisms that spend all or part of their life in water, as well as to the habitats and processes occurring in water. The term covers a wide range of environments from freshwater lakes, rivers, and wetlands to marine seas and oceans, as well as brackish or estuarine zones where fresh and saltwater mix.

Aquatic habitats are often classified by salinity: freshwater (<0.5 ppt), brackish water (0.5–30 ppt), and marine water (>30 ppt). Many organisms are specialized for life in water, including aquatic plants (hydrophytes) such as water lilies, and aquatic animals such as fish, crustaceans, mollusks, amphibious, and invertebrates. Adaptations include gills or other respiration methods, fins or streamlined bodies for swimming, buoyancy control, and osmoregulatory mechanisms to cope with salinity and water balance.

Ecology: Aquatic systems support primary production largely through algae and aquatic plants, underpin food webs, and play key roles in nutrient cycling, sediment dynamics, and climate regulation.

Human activities rely heavily on aquatic environments for food, transportation, recreation, and water supply. Related disciplines include limnology (freshwater science) and marine biology.

Threats and management: Pollution, eutrophication, overfishing, habitat destruction, invasive species, and climate change threaten aquatic ecosystems. Conservation measures include water quality protection, habitat restoration, sustainable fishing, and watershed management; monitoring and research help guide policy.