Plankton, nekton, benthos - three groups into which all aquatic living things can be divided. Plankton form algae and small animals that swim near the surface of the water. Necton consists of animals that can actively swim and dive in the water, these are fish, turtles, whales, sharks and others. Benthos are organisms that live in the lowest layers of the aquatic environment. It includes animals ecologically related to the bottom, including many echinoderms, benthic fish, crustaceans, mollusks, annelids, and so on.
Types of marine life
Sea animals are divided into three groups: plankton, nekton, benthos. Zooplankton is represented by drifting animals, which are usually small in size, but can grow to fairly large sizes (for example, jellyfish). Zooplankton may also include temporary larval forms of organisms that can grow and leave planktonic communities and join groups such as nekton, benthos.
The nekton class makes up the largest part of the animals living in the ocean. A variety of fish, octopuses, whales, moray eels, dolphins and squids are all examples of nekton. This large-scale category includes a number of very diverse creatures that are very different from each other by many criteria.
What is benthos? The third type of marine animals that spend their whole life at the bottom of the ocean. This group includes lobsters, starfish, all kinds of worms, snails, oysters and many others. Some of these creatures, such as lobsters and snails, can independently move along the bottom, but their lifestyle is so tightly connected to the ocean floor that they could not survive far from this environment. Benthos are organisms that live on the bottom of the ocean and include plants, animals, and bacteria.
Plankton - the most common form of life in the aquatic environment
When you imagine life in the ocean, usually all associations are somehow connected with fish, although in fact fish is not the most common form of life in the ocean. The largest group is plankton. The other two groups are nekton (actively swimming animals) and benthos (these are living organisms that inhabit the bottom).
Most plankton species are too small to be seen with the naked eye.
There are two main types of plankton.
- Phytoplankton, which produces food through photosynthesis. Most of them are various algae.
- Zooplankton, which feeds on phytoplankton. It includes tiny animals and fish larvae.
Plankton: general information
Plankton are microscopic inhabitants of the pelagic environment. They are essential components of food chains in the aquatic environment, as they provide food for nekton (crustaceans, fish and squid) and benthos (sea sponges). They also have a global impact on the biosphere, since the balance of the components of the Earth’s atmosphere depends largely on their photosynthetic activity.
The term "plankton" is derived from the Greek planktos, which means "wandering" or "drifting". Most of the plankton spends its existence, swimming along with ocean currents. However, not all species go with the flow, many forms can control their movements, and their survival depends almost entirely on their independence.
Sizes and representatives of plankton
In size, plankton ranges from tiny microbes, whose length is 1 micrometer, to jellyfish, whose gelatinous bell can reach 2 meters in width, and tentacles can extend more than 15 meters. However, most planktonic organisms are animals less than 1 millimeter in length. They exist due to nutrients in sea water and due to photosynthesis.
Representatives of plankton are a wide variety of organisms, such as algae, bacteria, protozoa, the larvae of some animals and crustaceans. Most planktonic protists are eukaryotes, predominantly unicellular organisms. Plankton can be divided into phytoplankton, zooplankton and microbes (bacteria). Phytoplankton carries out photosynthesis, and zooplankton is represented by heterotrophic consumers.
Nekton
The representatives of nekton are active swimmers and often the most famous organisms in sea waters. These are the main predators in most marine food chains. The distinction between nekton and plankton is not always sharp. Many large animals (for example, tuna) spend their larval stage in the form of plankton, while in the adult stage it is quite large and active nekton.
The vast majority of nekton are vertebrates; these are fish, reptiles, mammals, mollusks and crustaceans. The largest group is made up of fish, with a total of approximately 16,000 species. Necton is found at all depths and latitudes of the sea. Whales, penguins, seals are typical representatives of nekton in polar waters. The greatest variety of nekton can be found in tropical waters.
The most diverse life form and its economic value
This also includes the largest mammal on planet Earth, the blue whale, which grows up to 25-30 meters in length. These giants, as well as other baleen whales, feed on plankton and micronecton. The largest representatives of nekton are whale sharks, which reach a length of 17 meters, as well as toothed whales (killer whales), great white sharks, tiger sharks, bluefin tuna and others.
Necton forms the basis of fisheries around the world. Anchovies, herring, sardines usually make up from one quarter to one third of the annual sea crop. Squids are also an economically valuable nekton. Halibut and cod are bottom fish, which have commercial value as food for humans. As a rule, they are mined in the waters of the continental shelf.
Benthos
What is the meaning of the word "benthos"? The term “bentos” comes from the Greek noun bentos and means “depths of the sea”. This concept is used in biology to denote the community of organisms at the bottom of the sea, as well as fresh water bodies such as lakes, rivers and streams.
Benthic organisms can be classified according to size. Organisms larger than 1 millimeter are referred to macrobenthos. These are various gastropods, bivalves, sea lilies, carnivorous starfish and gastropods. Organisms with sizes from 0.1 to 1 mm are large microbes that dominate the bottom food chains, acting as a biogenic utilizer, primary producer and predator. Microbenthos category includes organisms smaller than 1 millimeter in size, these are diatoms, bacteria and ciliates. Not all benthic organisms live in sedimentary rocks, some communities live on rocky substrates.
There are three different types of benthos.
- Infauna - organisms that live on the ocean floor, buried in the sand or hiding in shells. They have very limited mobility, live in sediment, are exposed to the environment and have a fairly long life span. These include sea shells and various mollusks.
- Epifauna can live and move along the surface of the seabed to which they are attached. They live by attaching to stones or moving along the surface of sediments. These are sponges, oysters, snails, starfish and crabs.
- Organisms that live on the bottom of the ocean, but can also swim in the water above it. This includes soft bottom fish - pufferfish, flounder, using crustaceans and worms as a food source.
The relationship between the pelagic environment and benthos
Benthos are organisms that play a critical role in the marine biological community. Benthic species are a heterogeneous group, which is the main link in the food chain. They filter water in search of food, remove deposits and organic matter, thus purifying the water. At the bottom of the seas and oceans, unused organic matter settles, which are then processed by benthic organisms and returned to the water column. This process of mineralization of organic matter is an important source of nutrients and is crucial to ensure high primary production.
The concepts of pelagic and benthic environments are interconnected according to many criteria. For example, pelagic plankton are an important source of food for animals living on soft or rocky ground. Anemones and sea ducks serve as a natural filter of the surrounding water. The formation of the pelagic environment at the bottom is also due to molting of crustaceans, metabolic products, and dead plankton. Over time, plankton forms marine deposits in the form of fossils, which are used to determine the age and origin of rocks.
Aquatic organisms are classified according to their habitat. Scientists believe that the habitat of these animals has a huge impact on their evolution. Moreover, most of them are well adapted to life in the specific environment that they inhabit. What is the main difference between the groups called plankton, benthos and nekton?
Plankton are microscopic or small animals compared to the other two types. Necton is a free-floating animal. What is benthos? It includes both freely moving, and those organisms that can not imagine their existence without the ocean floor. What about organisms that live mostly at the bottom, but can also swim - octopus, sawfish, flounder? Such life forms may well be called nectobenthos.