Phytoplankton – Definition, Types, and Example

Phytoplankton are microscopic organisms found in aquatic environments, ranging from oceans to freshwater bodies. They are primary producers and lie at the bottom of aquatic food chains. Phytoplankton include algae, cyanobacteria, and protists. Phytoplankton play crucial ecological roles by influencing nutrient cycling, carbon sequestration, and global climate regulation. In this article, we will explore phytoplankton, its examples, types and much more.

What are Phytoplanktons?

Definition of Phytoplankton: Phytoplankton are microscopic plant-like organisms that live in water and are the primary producers of the aquatic food web.

The word Phytoplankton is derived from the combination of two Greek Words – python (plant) and planktons (drifter). They are microscopic, single-celled organisms that live in aquatic ecosystems. Phytoplanktons can be cyanobacteria, protists, or algae. They are photosynthetic organisms and act as producers in aquatic ecosystems.

Phytoplanktons are present at the base of an aquatic food web and play a crucial role in maintaining oxygen balance in water bodies and carbon cycling. Monitoring phytoplankton populations is essential for understanding and managing marine ecosystems and addressing environmental concerns such as eutrophication and harmful algal blooms.

Examples of Phytoplankton

Examples of phytoplankton organisms includes bacteria, algae, and some archaebacteria prokaryotes. There are approximately 500 known species of phytoplankton. Some examples are-

• Blue-green algae: Synechococcus, Prochlorococcus, Spirulina
• Green algae: Chlorella vulgaris, Dunaliella salina
• Diatom: Odonetella aurita, Phaeodactylum tricornutum
• Dinoflagellate

Types of Phytoplankton

Phytoplankton can be classified based on cell wall arrangement, and cell structure. We can also classify them based on their habitat.

• Diatoms: Diatoms are mainly known as microalgae with shell-like structures made of translucent silica. Now, we can classify them into a different group
  • Centric: These are diatoms that have a cylindrical or solenoid cell.
  • Pennate: They are elongated or roughly circular.
• Dinoflagellates: They are motile unicellular algae mainly found in freshwater. They have a eukaryotic cell and can be of different colors such as red, blue, or yellow depending on the pigment present in the cell. Some Dinoflagellates perform photosynthesis or can be heterotrophic, they are known as mixotrophic.
• Green Algae: They are green in color due to the presence of chloroplast in their leaves. They are mostly found in the coastal waters of the tropics and subtropics.
• Blue-Green Algae: Blue-Green Algae are mainly unicellular and they are mostly seen growing in colonies. They are blue due to the presence of a pigment called phycocyanin.
• Coccolithophores: They are known as the smallest phytoplanktons that are commonly seen in the open sea. They have a soft body with a tiny, circular shield.

Types of Phytoplankton

Classification of Plankton Based on their Size:

Phytoplanktons are classified on the basis of size as follows:

1. Ultraplankton (<2 µm): Microscopic plankton with sizes smaller than 2 micrometers
2. Nanoplankton (2 to 20 µm): Plankton falling within the size range of 2 to 20 micrometers.
3. Microplankton (2 to 200 µm): Intermediate-sized plankton ranging from 2 to 200 micrometers.
4. Macroplankton (200 to 2000 µm): Larger plankton with sizes ranging from 200 to 2000 micrometers.
5. Megaplankton (2000 µm): The largest category of plankton, with sizes equal to or exceeding 2000 micrometers

Classification Based on their Habitat

Phytoplankton are classified based on their habitat classification as:

• Neritic: Phytoplankton which are inhabiting waters overlying continental shelves.
• Oceanic: They commonly inhabit waters beyond continental shelves.
• Brackish water: They inhabit brackish water for example mangroves and lagoons.

What Affects Phytoplankton Growth?

Phytoplankton’s primary requirements is light for photosynthesis. The growth of phytoplankton depends on a variety of factors:

• Biotic factors: Among biotic factors, the availability of food is the most important. The availability of food and nutrients is a critical biotic factor that affects the abundance and growth of Phytoplankton.
• Abiotic factors: Light Intensity, Temperature, Water Quality, and Nutrient availability are among abiotic factors. Phytoplankton require light for photosynthesis. Some species of phytoplankton require equal distribution of sunlight, while some adapt to low-light conditions. Also, temperature and water quality, including pH and salinity affect the Phytoplankton growth.

Importance of Phytoplankton in Aquatic Ecosystem

Phytoplanktons are extremely important components of the aquatic ecosystem. Their ecological role of Phytoplanktons are given below:

• Phytoplankton are primary producers in aquatic ecosystems, forming the base of the food chain.
• They generate a significant portion of Earth’s oxygen through photosynthesis.
• Phytoplankton sequester carbon dioxide, helping regulate atmospheric carbon levels.
• These organisms play a crucial role in nutrient cycling within aquatic environments.
• Changes in phytoplankton populations serve as indicators of environmental health and climate change impacts.
• They support commercial fisheries and contribute to various industries, including aquaculture and pharmaceuticals.

Role of Planktons in Carbon Sequestration

Planktons play a crucial role in the oceanic carbon cycle by removing carbon dioxide from surface waters and transporting it to the deep ocean, where it can be stored for extended periods.

• Phytoplankton Photosynthesis: Phytoplankton are primary producers that utilize photosynthesis to convert carbon dioxide from the atmosphere into organic carbon compounds. This process removes carbon dioxide from the water, effectively sequestering carbon in the form of organic matter.
• Export of Organic Carbon: When phytoplankton die or are consumed by zooplankton, a portion of the organic carbon they’ve produced sinks to the ocean floor. This process, known as the biological pump. It transfers carbon from the surface ocean to deeper layers, where it can be stored for long periods, potentially for thousands of years.
• Calcifying Plankton: Some plankton, such as coccolithophores and foraminifera, incorporate carbon into their shells or skeletons made of calcium carbonate. When these organisms die, their calcium carbonate shells sink to the ocean floor, contributing to carbonate sedimentation and long-term carbon storage in marine sediments.

Conclusion: Phytoplankton – Definition, Types, and Example

Phytoplankton, comprised of microscopic photosynthetic organisms, play a vital role in aquatic ecosystems. These primary producers contribute significantly to oxygen production and serve as the foundation of marine food chains. The two main types, diatoms and dinoflagellates, exhibit diverse ecological functions, influence nutrient cycling and carbon sequestration. Understanding phytoplankton is important for assessing aquatic ecosystem health and responding to environmental changes.

FAQs on Phytoplankton

Is Phytoplankton a Plant or Bacteria?

Some phytoplankton are bacteria, some are protists, and most are single-celled plants.

Is Phytoplankton Unicellular or Multicellular?

Phytoplankton includes varieties of chemo-organotrophic unicellular and multicellular organisms which are as per capacity of photosynthesis.

What are the Three Main Types of Phytoplankton?

Dinoflagellates, diatoms, and cyanobacteria are the three main types of phytoplankton.

Is Phytoplankton Autotroph or Heterotroph?

Phytoplankton are tiny organisms that live in oceans and are autotrophs because they make their food through photosynthesis.

What Kingdom is Phytoplankton?

Phytoplankton are in the kingdom of Protista while most of the plants are in the kingdom Plantae.

What is Plankton Class 10?

Plankton refers to microscopic organisms that drift or float in aquatic environments, unable to swim against currents. These organisms can be found in oceans, seas, lakes, rivers, and other bodies of water.

What is the Difference Between Phytoplankton and Zooplankton?

Phytoplankton are microscopic, plant-like organisms that perform photosynthesis, while zooplankton are small animals that feed on phytoplankton and other zooplankton for energy.

What is a Photic Zone?

The photic zone is the upper layer of a water body, such as an ocean or lake, where sunlight penetrates sufficiently to support photosynthesis. Within the photic zone, phytoplankton and other photosynthetic organisms can thrive.

How are Plankton Classified?

Plankton are classified based on their size and behavior, categorized into three main groups: phytoplankton (plant-like), zooplankton (animal-like), and bacterioplankton (bacteria and archaea).