An aquatic ecosystem is a community of living organisms interacting with their non-living environment within a body of water. These environments encompass a wide array of physical and chemical characteristics, such as water chemistry, light penetration, and temperature. Aquatic ecosystems are home to a diverse collection of life, with organisms relying on each other and their surroundings for survival.
Freshwater Ecosystems
Freshwater ecosystems are characterized by their low salt concentration, typically less than 0.5 parts per thousand (ppt). These systems include both standing water bodies, known as lentic systems, and flowing water bodies, or lotic systems. Lentic environments, such as lakes, ponds, and marshes, have still or slow-moving water, with movement primarily influenced by wind and thermal stratification. Lotic environments, including rivers, streams, and brooks, feature continuous water movement driven by gravity.
Temperature and oxygen levels vary significantly across freshwater habitats. Deeper lakes can experience thermal stratification, leading to reduced oxygen in lower layers. In contrast, flowing water in lotic systems often results in higher oxygen levels due to constant movement. Organisms in these diverse freshwater settings have developed specific adaptations to cope with varying conditions.
Marine Ecosystems
Marine ecosystems are defined by their high salt content, with average salinity around 35 parts per thousand (ppt), though this can vary. These are the largest aquatic ecosystems on Earth, covering over 70% of the planet’s surface and containing more than 97% of its water supply. Marine environments are vast, including diverse zones such as the open ocean, the deep sea, and coastal areas.
Coastal marine habitats feature ecosystems like coral reefs and intertidal zones. Coral reefs are complex underwater structures built by tiny animals, providing habitat for numerous marine species in shallow, nutrient-poor waters. Intertidal zones, where land meets sea, expose organisms to regular fluctuations in water, temperature, and salinity, requiring specialized adaptations like hard shells or the ability to seek shelter. Salinity is a key factor influencing water density and ocean currents, which are important for nutrient distribution and climate regulation.
Estuarine Ecosystems
Estuarine ecosystems represent transitional zones where freshwater from rivers and streams mixes with saltwater from the ocean. This mixing creates a unique environment characterized by fluctuating salinity levels, which can range from nearly freshwater to almost full seawater. These dynamic conditions make estuaries challenging habitats, but they are also among the most productive natural environments globally due to high nutrient levels from both fresh and marine inputs.
Estuaries encompass various habitats, including bays, sounds, and river mouths. They serve as important nurseries for many marine species, providing sheltered areas for breeding and the development of juvenile fish and shellfish. Organisms inhabiting estuaries often possess specialized physiological adaptations, allowing them to tolerate a wide range of salinity changes.
Wetland Ecosystems
Wetland ecosystems are areas where water saturates the soil, either permanently or seasonally, supporting specialized vegetation adapted to waterlogged conditions. These areas form a transition between dry land and water bodies, with their unique characteristics determined by water levels and plant types. Wetlands can be either freshwater, such as marshes, swamps, bogs, and fens, or saltwater/brackish, like salt marshes and mangrove swamps.
Marshes are often dominated by soft-stemmed plants, while swamps are characterized by woody trees or shrubs. Bogs are typically acidic and low in nutrients, contrasted with fens which receive more mineral-rich groundwater. Wetlands perform several ecological functions, including purifying water by trapping sediments and absorbing excess nutrients, controlling floods by storing water, and providing diverse habitats for wildlife.