A biome is a large community of plants and animals defined by its climate and habitat. Aquatic biomes are water-based environments that play a fundamental role in Earth’s ecosystems. This article explores aquatic biomes, focusing on the marine biome and its unparalleled scale.
Understanding Aquatic Biomes
Aquatic biomes are communities of organisms within bodies of water, categorized as marine or freshwater. Their defining difference is salinity, the concentration of dissolved salts: marine biomes have a high salt concentration (typically 35 parts per thousand (ppt) or 3.5%), while freshwater biomes have a very low salt concentration (generally less than 1 ppt). This distinction dictates the types of organisms that can inhabit each environment. Freshwater environments encompass habitats like ponds, lakes, rivers, streams, and wetlands, while marine environments include oceans, coral reefs, and estuaries where fresh and saltwater mix.
The Unrivaled Scale of the Marine Biome
The marine biome is the largest aquatic biome on Earth, surpassing all freshwater biomes in both area and volume. It covers approximately 70% to 75% of the Earth’s surface, making it the most expansive habitat. This immense expanse includes five main oceans—the Pacific, Atlantic, Indian, Arctic, and Southern—along with smaller seas, gulfs, and bays. Its sheer volume is equally remarkable, accounting for over 97% of all water on Earth. The average ocean depth is about 3,682 meters (12,080 feet). Oceanic trenches, like the Challenger Deep in the Mariana Trench, which plunges to about 10,935 meters (35,876 feet), contribute to this vastness.
Distinctive Features of Marine Environments
Marine environments are shaped by unique physical and chemical characteristics supporting a wide array of life. Salinity is relatively constant across much of the open ocean, influencing marine organisms’ adaptations. Marine biomes also have distinct zones based on light penetration, depth, and distance from shore.
Vertical Zones
Light penetration defines vertical zones:
The euphotic (or photic) zone: where sunlight allows photosynthesis, typically extending to 200 meters.
The dysphotic zone (twilight zone): where light is faint but insufficient for photosynthesis.
The aphotic zone: the perpetually dark region below approximately 1,000 meters.
Horizontal Zones
Horizontally, zones include:
The intertidal zone: where land meets sea and experiences tidal fluctuations.
The neritic zone: shallow waters over the continental shelf.
The pelagic zone: the open ocean water column.
The benthic zone: the ocean floor.
The hadal zone: the deepest parts, including oceanic trenches.
These diverse conditions support a variety of life, from microscopic phytoplankton to large marine mammals, fish, and invertebrates.