Lakes, oceans, rivers and other bodies of water are brimming with wildlife. The animals that inhabit the water range in size, color and shape. There are two common types of aquatic organisms: plankton and nekton. Any living thing in the ocean will belong to one of these groups.
Plankton are viewed as the foundation for food webs in the oceanic ecosystem. The group are a collection of animals, plants, bacteria and single-celled organisms that drift in the pelagic zone (which is at or near the surface of ocean, seas and bodies of fresh water). The plankton provide a source of food for larger organisms such as fish, crustaceans and even whales.
Phytoplankton are a type of plankton that use photosynthesis to provide energy to the rest of the body. This energy is gathered by other animals upon consuming the phytoplankton. Many species of phytoplankton are single-celled and microscopic in size. Some phytoplanktom, such as diatoms, join together to form long chains. Other common forms of phytoplankton are dinoflagellates, phaephyta and cyanobacteria. The organisms, according to Nature Works, serves as the food source for zooplankton.
Zooplankton are oceanic animals that rarely swim. Instead, the organisms drift and move using currents and waves in the body of water. Most zooplankton are single-celled organisms as well. Jellyfish, however, are a type of zooplankton. There are two types of zooplankton. Holoplankton are zooplankton that will remain that way permanently. Meroplankton are temporary zooplankton that are the larvae of fish, crustaceans and other marine organisms. The meroplankton will grow into nekton.
Nekton are fish, crustaceans and other aquatic organisms that move freely in the body of water. The organisms comprise a variety of shapes, sizes and species. The nekton live in both shallow and deep waters. Nekton will eat zooplankton or other smaller nekton. There are three types of nekton groups. Chordate nekton are organisms (such as fish, whales, sharks, turtles, dolphins and seals) that have bones and/or cartilage. Molluscan nekton are are octopus, squid and similar organisms. Arthropod are organisms such as benthos that dwell at the bottom of the water.
Nekton in the ocean have advantageous physical adaptions to their body that other aquatic organisms do not possess. Gas-filled organs in the nekton's body allows the organism to control their buoyancy in the water. Certain species also use special adaptions such as sensory systems for echolocation, insulating layers of blubber, locomotion and surface resistance.
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