The aquatic biome includes the habitats around the world that are dominated by water—from tropical reefs, to brackish mangroves, to Arctic lakes. The aquatic biome is the largest of all the world's biomes—it occupies about 75 percent of the Earth's surface area. The aquatic biome provides a vast array of habitats that, in turn, support a staggering diversity of species.
The first life on our planet evolved in ancient waters about 3.5 billion years ago. Although the particular aquatic habitat in which life evolved remains unknown, scientists have suggested some possible locations—these include shallow tidal pools, hot springs, and deep-sea hydrothermal vents.
Aquatic habitats are three-dimensional environments that can be divided into distinct zones based on characteristics such as depth, tidal flow, temperature, and proximity to landmasses. Additionally, aquatic biomes can be divided into two main groups based on the salinity of their water—these include freshwater habitats and marine habitats.
Another factor that influences the composition of aquatic habitats is the degree to which light penetrates the water. The zone in which light penetrates sufficiently to support photosynthesis is known as the photic zone. The zone in which too little light penetrates to support photosynthesis is known as the aphotic (or profundal) zone.
The various aquatic habitats of the world support a diverse assortment of wildlife including virtually many different group of animals including fishes, invertebrates, amphibians, mammals, reptiles, and birds. Some groups—such as echinoderms, cnidarians, and fishes—are entirely aquatic, with no terrestrial members of these groups.
The following are the key characteristics of the aquatic biome:
- largest of all the world's biomes
- dominated by water
- life first evolved in the aquatic biome
- three-dimensional environment that exhibits distinct zones of communities
- ocean temperatures and currents play key role in world's climate
The aquatic biome is classified within the following habitat hierarchy:
Biomes of the World > Aquatic Biome
The aquatic biome is divided into the following habitats:
- Freshwater habitats - Freshwater habitats are aquatic habitats with low salt concentrations (below one percent). Freshwater habitats are further classified into moving (lotic) bodies of water and standing (lentic) bodies of water. Moving bodies of water include rivers and streams; standing bodies of water include lakes, ponds, and inland wetlands. Freshwater habitats are influenced by the soils of surrounding areas, the pattern and speed of water flow, and local climate.
- Marine habitats - Marine habitats are aquatic habitats with high salt concentrations (more than one percent). Marine habitats include seas, coral reefs, and oceans. There are also habitats where freshwater mixes with saltwater. In these places, you'll find mangroves, salt marshes, and mud flats. Marine habitats often consist of five zones including the intertidal, neritic, oceanic pelagic, abyssal, and benthic zones.
Animals of the Aquatic Biome
Some of the animals that inhabit the aquatic biome include:
- Anemonefish (Amphiprion) - Anemonefish are marine fish that live amongst the tentacles of anemones. Anemonefish have a layer of mucus that prevents them from getting stung by the anemones. But other fish (including those that are predators to anemonefish) are susceptable to the anemone stings. The anemonefish are thus protected by the anemones. In return, anemonefish chase away fishes that eat anemones.
- Pharaoh cuttlefish (Sepia pharaonis) - Pharaoh cuttlefish are cephalopods that inhabit coral reefs in the Indo-Pacific ocean and the Red Sea. Pharaoh cuttlefish have eight arms and two long tentacles. They have no external shell but do have an internal shell or cuttlebone.
- Staghorn coral (Acropora) - Staghorn corals are a group of corals that includes about 400 species. Members of this group inhabit coral reefs around the world. Staghorn corals are fast-growing reef-building corals that form a variety of colony shapes (including clumps, branches, antler-like, and plate-like structures).
- Dwarf seahorse (Hippocampus zosterae) - The dwarf seahorse is a tiny species of seahorse that measures less than an inch in length. Dwarf seahorses live in the seagrass beds in the Gulf of Mexico and in the waters around the Florida Keys, Bahamas, and Bermuda. They use their long tails to hold onto blades of seagrass as they graze on tiny plankton that drifts by in the current.
- Great white shark (Carcharodon carcharias) - Great white sharks are large predatory fishes that grow to about 15 feet in length. They are skilled hunters that have several hundred serrated, triangular teeth that grow in rows in their mouth. Great white sharks inhabit warm coastal waters throughout the world.
- Loggerhead sea turtle (Caretta caretta) - The loggerhead sea turtle is a marine turtle whose range includes the Atlantic Ocean, Pacific Ocean, Mediterranean Sea, and the Indian Ocean. Loggerhead turtles are an endangered species whose decline is largely attributed to their becoming entangled in fishing gear. Loggerhead sea turtles spend the majority of their life at sea, venturing on land only to lay their eggs.
- Blue whale (Balaenoptera musculus) - The blue whale is the largest living animal. Blue whales are baleen whales, a group of marine mammals that have a set of baleen plates in their mouth that enable them to filter tiny plankton prey from the water.