What is Plankton?
The term "plankton" refers to a wide range of organisms found in both marine and freshwater environments that are non-motile and cannot swim against water currents. These organisms are carried along by water currents and include various life forms such as bacteria, algae, protozoa, crustaceans, coelenterates, mollusks, and others from different phyla.
Size and Ecological Role of Plankton
Plankton vary in size, ranging from tiny microorganisms of 0.2 micrometers (µm) to large organisms like jellyfish, which can grow over 20 cm in size.
Their distribution in water bodies is primarily influenced by the availability of light and nutrients. Large aquatic animals, including fish and whales, depend on plankton as their primary food source.
In addition, plankton play a crucial role in maintaining ecological balance, with phytoplankton accounting for approximately 50% of the oxygen produced through photosynthesis.
Difference Between Plankton and Other Aquatic Groups
Plankton are distinct from other aquatic life forms such as nekton, pleuston, neuston, and benthos based on their mobility and habitat-
Pleuston
Pleuston refers to organisms that float on or near the surface of water, typically at the interface of air and water. These organisms are usually macroscopic and buoyant.
Examples- Some cyanobacteria, Salvinia (floating fern).
Nekton
Nekton includes animals that are capable of actively swimming against water currents. Unlike plankton, nekton are strong swimmers and can navigate freely in the water.
Examples- Fish (both bony and cartilaginous like sharks), marine mammals (whales, seals), and certain reptiles (saltwater crocodiles, sea snakes).
Neuston
Neuston refers to organisms that live at or near the surface of the water. They are typically found in the surface layer of oceans, lakes, and slow-moving rivers.
Subtypes-
Epineuston- Organisms living just above the water’s surface but partially submerged.
Hyponeuston- Organisms living just beneath the water surface.
Examples- The alga Ochromonas.
Benthos
Benthos are organisms found at the bottom of aquatic environments, such as the sea floor, riverbeds, or lake beds. They can be sessile (stationary), burrow into the sediment, or move freely along the bottom.
Examples- Sea urchins, crabs, worms, corals, sponges, sea stars, and other bottom-dwelling invertebrates.
Key Distinctions in Aquatic Terminology
Pleuston- Floating organisms at the water-air interface, such as Salvinia and certain cyanobacteria.
Nekton- Actively swimming animals like fish, whales, and squids, capable of independent movement.
Neuston- Organisms that live on or near the water surface, with epineustons above and hyponeustons just below.
Benthos- Bottom-dwelling organisms, including those that attach to surfaces like rocks or burrow in sediment.
These distinctions help categorise aquatic life based on their behavior, habitat, and ability to move within their environments, each group playing a unique role in the ecosystem.
Types of Plankton
Plankton can be classified based on their life cycle, size, and role in the food web (trophic levels).
1. Lifecycle-Based Classification
Holoplankton- These organisms remain in the planktonic form throughout their entire life. Examples include algae and jellyfish.
Meroplankton- Organisms that only live as plankton during certain stages of their life cycle, such as the larvae of starfish, sea urchins, fish, and worms.
2. Size-Based Classification
Megaplankton: These are the largest plankton, typically over 20 cm in size, such as jellyfish, tunicates, and pyrosomes.
Macroplankton: These plankton range from 2 to 20 cm in size.
Mesoplankton: Plankton in this category range from 0.2 to 20 mm in size.
Microplankton: These plankton are between 20 and 200 micrometers (µm) and include most phytoplankton, protozoans, and larger protists.
Nanoplankton: These are smaller plankton ranging from 2 to 20 µm, such as protists, diatoms, and small algae.
Picoplankton: Very small plankton, ranging from 0.2 to 2 µm, including bacteria and certain types of algae like chrysophytes.
Femtoplankton: These plankton are the smallest, with a size of less than 0.2 µm, and primarily consist of marine viruses.
3. Trophic Level-Based Classification
Phytoplankton: These are primary producers (autotrophs), such as cyanobacteria, diatoms, algae, and dinoflagellates, that generate their own food through photosynthesis.
Zooplankton: These are primary consumers that feed on other plankton, including small protozoans and larvae of fish and other marine animals.
Mycoplankton: These are planktonic fungi that contribute to the decomposition of organic matter in aquatic ecosystems.
Bacterioplankton: Consisting of bacteria, bacterioplankton play an essential role in nutrient recycling and breaking down organic material in aquatic environments.
Virioplankton: Composed of viruses that influence microbial communities and contribute to nutrient cycles in aquatic ecosystems.
Mixotrophs: These organisms can function as both producers and consumers, depending on environmental conditions. In nutrient-rich environments, they perform photosynthesis, but when resources are limited, they feed on other plankton to meet their nutrient needs.
Ecological Significance of Plankton
Plankton play a crucial role in maintaining the balance of aquatic ecosystems-
Oxygen Production: As primary producers, phytoplankton are responsible for generating approximately half of the oxygen produced through photosynthesis on Earth.
Food Source for Fisheries: Plankton form the basis of the aquatic food chain, providing essential nutrients for fish and other marine organisms that are crucial for the fishing industry.
Applications in Space and Nutrient Fixation: Phytoplankton, particularly Chlorella, are used as food sources in space travel due to their ability to perform photosynthesis and provide oxygen. They also aid in carbon dioxide fixation, contributing to a balanced atmosphere.
Nutrient Recycling: Plankton play a vital role in recycling nutrients, turning dead organic matter into inorganic nutrients that plants and other organisms can use. This process supports the health and productivity of ecosystems.
Nitrogen Fixation: Certain planktonic species can fix atmospheric nitrogen into usable forms like ammonia and nitrates, which are essential for phytoplankton growth.
Carbon Dioxide and Oxygen Balance: Phytoplankton and zooplankton help regulate the levels of CO₂ and O₂ in the ocean. Phytoplankton contribute to CO₂ uptake, particularly when nutrient availability triggers growth.
Bioluminescence and Harmful Algal Blooms: Some plankton, such as certain dinoflagellates, are bioluminescent and can cause a blue glow in the water. In nutrient-rich environments, these organisms may multiply rapidly, causing blooms that can produce toxins harmful to fish and other marine life. These blooms are responsible for phenomena like red tides, which can disrupt marine ecosystems.
Essential Study Materials for NEET UG Success
FAQs on Plankton: Types, Meaning, Ecological Role, and Importance for NEET Exam
1. What is plankton, and why is it important?
Plankton are tiny organisms that drift in aquatic environments, and they play a crucial role in the food chain, oxygen production, and nutrient cycling.
2. How do plankton contribute to the oxygen cycle?
Phytoplankton produce oxygen through photosynthesis, accounting for around 50% of the oxygen in Earth’s atmosphere.
3. What is the difference between plankton and nekton?
Plankton are drifting organisms that cannot swim against currents, whereas nekton are strong swimmers that can navigate freely in the water.
4. Why are harmful algal blooms (red tides) a concern?
Certain plankton species can cause harmful algal blooms that produce toxins, which can disrupt marine ecosystems and harm fish and other animals.
5. How do plankton affect the global carbon cycle?
Phytoplankton absorb carbon dioxide (CO₂) through photosynthesis, helping regulate the levels of CO₂ in the ocean and the atmosphere.
6. What are the different types of plankton?
Plankton are classified based on their lifecycle (holoplankton and meroplankton), size (ranging from femtoplankton to megaplankton), and trophic levels (such as phytoplankton, zooplankton, and bacterioplankton). Each group plays a unique role in the aquatic ecosystem.
7. What are phytoplankton, and how do they contribute to the environment?
Phytoplankton are primary producers in the aquatic food chain. Through photosynthesis, they convert carbon dioxide into oxygen, contributing significantly to the oxygen supply on Earth.
8. Can plankton be harmful to marine life?
Yes, some types of plankton, such as dinoflagellates, can cause harmful algal blooms, including red tides, which produce toxins that can poison marine life, including fish, shellfish, and other organisms.
9. How do plankton affect the food chain?
Plankton form the foundation of most aquatic food chains. Zooplankton feed on phytoplankton, and in turn, they are eaten by larger animals such as fish and whales. The entire marine food web depends on the existence and health of plankton populations.
10. Why are plankton considered indicators of environmental health?
Plankton populations are highly sensitive to changes in water temperature, pollution, and nutrient levels. Monitoring plankton can help scientists assess the health of aquatic ecosystems and detect environmental changes or disturbances.
11. How do plankton contribute to nitrogen fixation?
Certain plankton species, including some types of cyanobacteria, can fix nitrogen from the atmosphere and convert it into usable forms like ammonia and nitrates, which support the growth of other organisms like phytoplankton.
12. Are plankton used for anything beyond the food chain?
Yes, plankton, particularly certain algae like Chlorella, are used in various applications, such as providing food for astronauts during space travel due to their high nutritional value and ability to perform photosynthesis. They are also researched for carbon dioxide fixation and as protein supplements.
13. How do plankton vary in size?
Plankton range in size from the smallest femtoplankton, which are less than 0.2 micrometers (µm) and primarily consist of viruses, to megaplankton, which can be over 20 cm in size, like large jellyfish.
14. What are the environmental factors that affect plankton distribution?
Plankton distribution is largely influenced by factors such as light availability, water temperature, nutrient levels, and water currents. These factors determine where plankton are found in the water column and how they thrive.
