An aquatic biome is a large community of organisms living in water environments. These biomes support diverse life forms adapted to specific conditions. Aquatic biomes play a significant role in Earth’s ecosystems, covering approximately 75% of the planet’s surface.
Defining Characteristics of Aquatic Biomes
Aquatic biomes are shaped by fundamental water properties that influence life within them. Salinity, the amount of dissolved salt, is a primary distinguishing factor, separating freshwater from marine environments. Light penetration into the water column is another characteristic, determining where photosynthesis occurs, forming the base of many aquatic food webs. The photic zone, where sunlight allows photosynthesis, typically extends to 200 meters. Below this, the aphotic zone lacks sufficient light.
Temperature variations also influence aquatic life, affecting growth rates and dissolved oxygen availability. Warmer waters generally hold less dissolved oxygen, which can limit aquatic species diversity. Water movement is significant, impacting oxygen and nutrient distribution. Organisms must adapt to these conditions.
Freshwater Aquatic Biomes
Freshwater aquatic biomes have a low salt concentration, typically less than 1%. These environments include rivers, streams, lakes, ponds, and wetlands, each with distinct features. Rivers and streams are lotic systems, involving moving water that flows in one direction, often originating from springs or melting snow. Water speed depends on factors like slope, bed shape, and volume, and organisms must adapt to constant motion.
Lakes and ponds are lentic systems with standing or slow-moving water. Lakes are generally larger and deeper than ponds, with some areas potentially lacking sunlight (aphotic zones), while ponds are typically shallow enough for sunlight to reach the bottom. This difference in light influences plant growth, with ponds often supporting vegetation throughout their depth. Wetlands are areas where soil is saturated with water, permanently or periodically, distinct from lakes due to their shallow depth and emergent vegetation. These include marshes, swamps, and bogs, supporting a wide array of plants adapted to saturated soils, such as cattails and water lilies, along with amphibians, reptiles, and birds.
Saltwater Aquatic Biomes
Saltwater aquatic biomes, also known as marine biomes, have a high salt concentration and are Earth’s largest biomes. They encompass oceans, coral reefs, and estuaries, each presenting unique conditions and supporting diverse life. Oceans are vast, continuous bodies of saltwater divided into zones based on light and depth. The intertidal zone, where land and sea meet, experiences fluctuating conditions as it is alternately covered and exposed by tides, requiring organisms like crabs, starfish, and mussels to adapt to changes in moisture, temperature, and salinity.
Beyond the intertidal zone is the pelagic zone, the open water column, subdivided by depth. The epipelagic (sunlight) zone, extending to 200 meters, receives sufficient light for photosynthesis by phytoplankton, forming the base of the marine food web and supporting abundant marine life. Deeper zones, such as the mesopelagic (twilight) and bathypelagic (midnight) zones, have progressively less light, higher pressure, and colder temperatures, with organisms often relying on bioluminescence or marine snow for sustenance. The benthic zone refers to the ocean floor, where organisms, known as benthos, live on or in the sediment, often adapted to low light, high pressure, and limited food sources, relying on organic matter sinking from above.
Coral reefs are formed by colonies of marine invertebrates in warm, shallow waters, providing complex habitats for a vast diversity of fish, mollusks, and other organisms. Estuaries are transitional areas where freshwater rivers meet the ocean, resulting in brackish water with fluctuating salinity, creating unique breeding grounds for many species adapted to these variable conditions.