Plankton 101: Their Role in Nature and Your Aquarium

What is Plankton?

Plankton refers to the diverse collection of small, often microscopic, organisms that drift or float in the oceans, seas, and freshwater bodies. They play a foundational role in aquatic ecosystems and serve as the base for most aquatic food webs. The term “plankton” is derived from the Greek word “planktos,” meaning wanderer or drifter, signifying their largely passive movement with the currents.

There are two primary categories of plankton based on their functional role in the ecosystem:

  1. Phytoplankton: These are the photosynthetic plankton, primarily consisting of single-celled algae and cyanobacteria. They harness sunlight to convert carbon dioxide and nutrients into organic matter through photosynthesis. This process not only produces the oxygen we breathe but also forms the base of the marine food web. Examples include diatoms, dinoflagellates, and blue-green algae.
  2. Zooplankton: These are the tiny animals that feed on phytoplankton or other zooplankton. They, in turn, are consumed by larger animals. Zooplankton can range from microscopic organisms, like copepods or rotifers, to larger organisms, like krill or jellyfish larvae.

Plankton can also be classified based on size:

  • Picoplankton (less than 2 μm)
  • Nanoplankton (2-20 μm)
  • Microplankton (20-200 μm)
  • Mesoplankton (200 μm to 2 mm)
  • Macroplankton (2-20 mm)
  • Megaplankton (over 20 mm)

Plankton’s ecological significance is immense:

  • They contribute significantly to primary production in aquatic systems.
  • They serve as the principal food source for many marine organisms, including whales, fish larvae, and certain fish species.
  • The carbon they sequester through photosynthesis plays a role in regulating global climate.

With climate change and other environmental stresses, the distribution, abundance, and seasonal dynamics of plankton communities can undergo changes, which can have cascading effects on larger marine ecosystems.


Background on Plankton

Plankton are largely at the mercy of the ocean’s currents, winds and waves and don’t have much (if any) mobility. Zooplankton are either too small to compete against the ocean currents or large (like many jellyfish) but have relatively weak propulsion systems. The word plankton comes from the Greek word planktos meaning “wanderer” or “driter.” The word zooplankton incorporates the Greek word zoion, for “animal.

Species of Zooplankton

There are thought to be over 30,000 species of zooplankton. Zooplankton can live in fresh or salt water, but this article focuses on marine zooplankton.

Types of Zooplankton

Zooplankton may be classified according to their size or by the length of time they are planktonic (largely immobile).  Some terms that are used to refer to plankton include:

  • Microplankton: organisms that are 2-20 µm in size, including some copepods and other zooplankton.
  • Mesoplankton: organisms that are 200 µm-2 mm in size, which includes larval crustaceans.
  • Macroplankton: organisms 2-20 mm in size, which includes euphausiids (e.g., krill) – an important food source for many organisms, including baleen whales.
  • Micronekton: organisms 20-200 mm in size. Examples include some euphausiids and cephalopods.
  • Megaloplankton: planktonic organisms greater than 200 mm, including jellyfish and salps.
  • Holoplankton: organisms that are planktonic throughout life, such as copepods.
  • Meroplankton: organisms that have a planktonic stage but grow out of it at some point, like fish and crustaceans.

You can see a list of marine zooplankton groups with examples on the Census of Marine Zooplankton website.

Varieties of Plankton

varieties of plankton

Amphipod: Small, laterally compressed crustaceans, amphipods thrive in both marine and freshwater habitats. While they might resemble shrimp, they lack a carapace.
Zooplankton: These are tiny animals drifting in aquatic environments. As primary consumers, they feed on phytoplankton and are consumed by larger marine creatures.
Moina: A relative of Daphnia, Moina are small freshwater crustaceans, often used in aquaculture and aquariums as food due to their high nutritional value.
Artemia: Often referred to as brine shrimp, Artemia thrive in salt lakes and serves as a popular live feed in aquaculture, especially for larvae.
Copepod: Vital to the aquatic food web, copepods are tiny crustaceans in marine and freshwater settings. They feed on phytoplankton and become prey for larger organisms.
Daphnia: Often referred to as “water fleas” due to their jerky movements, Daphnia are freshwater crustaceans and are important in aquatic food chains, serving as food for many small fishes.
Brachionus: A genus of rotifers, Brachionus thrives in aquaculture settings. They actively feed on phytoplankton and serve as a primary food source for fish larvae.
Krill: Small shrimp-like crustaceans found in cold ocean waters. Krill are a major food source for many marine animals, including whales, seals, and penguins.
Atlanta: A genus of small, planktonic marine snails, Atlanta is part of the larger mollusc family and is known for their transparent, spiral shells.
Phyllosoma: The larval stages of spiny and slipper lobsters are transparent with long, spindly legs and predominantly found in oceanic waters.
Rotifer: Microscopic aquatic animals, rotifers are essential to freshwater food webs. They consume detritus and phytoplankton and serve as food for larger zooplankton and small fish.
Phytoplankton: These microscopic plants and algae float in the water column. As the base of the aquatic food web, they perform photosynthesis, producing a significant amount of the world’s oxygen and serving as primary producers in the food chain.

What do plankton eat?

Plankton consists of a vast array of tiny organisms, and their diets can be diverse. Here’s a general breakdown of what plankton eat based on their classification:

  1. Phytoplankton:
    • Phytoplankton are primary producers, which means they produce their own food through photosynthesis. They use sunlight, carbon dioxide, and nutrients (such as nitrogen and phosphorus) from the water to produce organic compounds.
    • Some phytoplankton, like dinoflagellates, can also be mixotrophic, meaning they can both photosynthesize and consume other organisms.
  2. Zooplankton:
    • Herbivorous zooplankton: These consume phytoplankton. Examples include many types of copepods and cladocerans.
    • Carnivorous zooplankton: These feed on other zooplankton. For instance, larger copepods and certain types of jellyfish can consume smaller zooplankton.
    • Omnivorous zooplankton: These feed on both phytoplankton and other zooplankton.
    • Detritivorous zooplankton: These consume detritus or organic matter that falls from the upper layers of the water column.
  3. Bacterioplankton:
    • These are the bacterial components of the plankton and typically feed on organic molecules dissolved in water, breaking them down and recycling nutrients.

Given plankton’s vast diversity, their diets can be quite varied, ranging from photosynthesis to consumption of other plankton and organic matter.

What eats zooplankton?

In the intricate web of aquatic life, zooplankton is a crucial link in the food chain. While abundant and diverse, these tiny organisms are a primary source of nutrition for various aquatic creatures. Numerous species rely on zooplankton as a vital component of their diet.

  1. Fish: Many species of fish, both marine and freshwater, depend on zooplankton as a primary food source during their larval stages. Fish like herring, anchovies, and juvenile cod are known to feed on copepods and other plankton, ensuring their growth and survival.
  2. Invertebrates: Various invertebrates, such as jellyfish and comb jellies, are filter feeders that actively consume plankton. These gelatinous creatures extend their tentacles or cilia to capture zooplankton drifting in the water.
  3. Whales and Baleen Sharks: Some of the largest animals in the ocean, including baleen whales like humpbacks and fin whales, rely on plankton as a significant part of their diet. These massive filter feeders use their baleen plates to strain zooplankton from the water.
  4. Birds: Many seabirds, such as puffins and shearwaters, forage for zooplankton on the ocean’s surface. They employ various feeding strategies to capture these tiny organisms, including surface skimming and plunge-diving.
  5. Cnidarians: Corals and sea anemones often extend their stinging tentacles to capture plankton drifting nearby. These organisms supplement their diet with the nutrients provided by zooplankton.
  6. Other Zooplankton: Some larger plankton species are cannibalistic and feed on smaller plankton. This intra-plankton predation is common among copepods, for instance.

Understanding the predators of plankton is essential to comprehending the dynamics of marine and freshwater ecosystems. Plankton availability can influence the distribution and abundance of numerous species, highlighting the interconnectedness of life in aquatic environments.

How Does Plankton Reproduce?

Phytoplankton may reproduce sexually or asexually, depending upon the species.  Asexual reproduction occurs more often and can be accomplished through cell division, in which one cell divides in half to produce two cells.


  • Harris, R., Wiebe, P., enz, J., Skjoldal, H-R., and M. Huntley.  ICES Zooplankton Methodology Manual. Accessed May 30, 2014.
  • Marine Education Society of Australasia. Zooplankton. Accessed May 30, 2014.
  • Morrissey, J.F. and J.L. Sumich. 2012. Introduction to the Biology of Marine Life, Tenth Edition. Jones & Bartlett Learning, LLC.  467pp.

Woods Hole Oceanographic Institution.  Jellyfish and Other plankton.  Accessed May 30, 2014

The Essential Role of Plankton in Your Aquarium

Diversity in Size and Form

These minute entities, invisible to the naked eye or sometimes noticeably larger, represent various microorganisms drifting along with water currents. From minuscule copepods to significantly larger species like certain jellyfish, plankton exhibits an incredible diversity in size and form.

The Nutritional Powerhouse

Plankton is indispensable in aquariums for a multitude of reasons. As a primary and vital food source for various aquatic lives, plankton is particularly crucial for fish during their larval stages. Furthermore, it offers essential nourishment for corals, supplementing their dietary needs besides the nutrients they derive from photosynthesis via zooxanthellae (a type of algae).

Beyond Nutrition: Ecological Contributions

However, the importance of plankton’s extends beyond being merely a dietary staple. These microorganisms actively participate in the aquarium’s ecological processes, contributing substantially to the decomposition of organic waste and detritus. Plankton, particularly amphipods, are integral in maintaining a clean and healthy environment within your aquarium, actively participating in its carbon cycle and ensuring its stability and vitality.

Understanding Plankton

A Broad Category: Free-Floating Organisms

The term ‘plankton’ encompasses a broad category of free-floating organisms thriving in oceans, seas, and bodies of fresh water. Rather than denoting a specific species, plankton is an umbrella term for myriad microscopic entities drifting with the currents, often unable to swim against them.

Not a Single Species

It’s crucial to understand that “plankton” does not refer to a single species or type of organism. Instead, it’s a collective term for a diverse assembly of life forms, ranging from bacteria and algae to animal larvae and tiny crustaceans, each playing a unique role in the aquatic food web.

Diversity in Size and Visibility

Plankton exhibits a remarkable range in sizes. While many are microscopic and invisible to the naked eye, others are large enough to be observed directly. For instance, copepods are tiny but visible, whereas certain jellyfish species, also classified as plankton, can grow considerably larger. This diversity makes plankton a fascinating group, revealing the wonders and complexities of life within water bodies, including your home aquarium.

From Microscopic to Macroscopic

The sizes of plankton vary greatly. While many are microscopic, others can grow to be quite large. For example, some jellyfish species, classified as plankton, can be observed without a microscope. On the smaller end, copepods, despite being visible to the naked eye, are often just about the size of a rice grain. This variance in size reflects the immense diversity within the plankton community, making each member’s role crucial and distinct in maintaining a balanced and thriving aquatic ecosystem.

Why Plankton is Essential in Aquariums

Natural Food Source: A Nutritional Powerhouse

Plankton is a fundamental component in the dietary spectrum of various aquatic creatures, serving as a robust natural food source. These tiny organisms are densely packed with nutrients, providing essential vitamins, minerals, and fatty acids crucial for the healthy growth and development of fish and other marine life housed in your aquarium.

Crucial for Fish Larvae

Fish, particularly during their delicate larval stages, rely heavily on plankton. At this point in their life cycle, fish larvae require a diet rich in proteins and other nutrients that plankton abundantly offers, supporting their rapid growth and fortifying their immune systems. A steady supply of plankton in your aquarium ensures that the fish pass through their larval stage healthily, laying a solid foundation for their adult lives.

Supporting Coral Nutrition

Corals, while often relying on photosynthesis for their nutritional needs, also capture and consume various forms of plankton. Zooplankton and bacterioplankton, in particular, are significant in the diets of many coral species. Despite having zooxanthellae (a type of dinoflagellate algae) living within their tissues to aid in photosynthesis, corals benefit tremendously from the additional nutrients obtained through plankton consumption. This dual nutritional strategy enhances their growth, colouration, and overall health, making plankton indispensable for coral-containing aquariums.

Contributing to Organic Matter Breakdown

Beyond serving as a dietary staple, plankton plays an active role in breaking down and recycling organic matter within the aquarium. Various plankton forms, such as amphipods, act as efficient scavengers, feeding on detritus and waste materials. This keeps the tank cleaner and actively participates in the crucial carbon cycling processes within your aquarium’s ecosystem, fostering a healthy and dynamic environment for all inhabitants.

Plankton’s Contribution to Aquarium Health

Organic Matter Decomposition: Nature’s Little Cleaners

Plankton in aquariums is integral for maintaining a clean and balanced environment. Their role in breaking organic matter is vital, as they consume detritus and waste materials. This natural scavenging process helps in minimising the accumulation of waste, providing a cleaner habitat for your aquarium’s residents and preventing the development of harmful algae blooms and other unwanted conditions.

Active Participants in the Carbon Cycle

Plankton contributes to the dietary needs of aquarium inhabitants and plays a pivotal role in the aquarium’s carbon cycle. Through their feeding and metabolic activities, plankton’s help in carbon cycling, a fundamental process in all aquatic environments. By consuming waste and then being consumed by larger organisms, plankton’s facilitates the continuous flow of energy and matter within the aquarium’s miniature ecosystem, helping maintain its overall health and vitality.

Duality of Phytoplankton and Zooplankton: A Harmonious Balance

For a thriving aquarium, having a mix of phytoplankton and zooplankton is beneficial. Phytoplankton, the microscopic plants or algae, are primary producers that convert light energy into chemical energy through photosynthesis, providing a valuable food source for various organisms. They also contribute to maintaining stable pH levels and increasing dissolved oxygen in the water, creating an optimal environment for aquarium inhabitants.

On the other hand, zooplankton, the tiny animal plankton, feed on phytoplankton and other small organisms, serving as a crucial link in the food chain by transferring the energy to larger animals. The harmonious presence of phytoplankton and zooplankton creates a dynamic, self-sustaining food web within your aquarium, supporting the life and vibrancy of the delicate underwater world you nurture at home.

In fostering an environment where plankton can thrive, you’re investing in the health and vibrancy of your aquarium, providing a dynamic, balanced habitat for all its dwellers. Whether you’re an avid aquarist or a beginner, understanding and leveraging the power of plankton is key to a flourishing aquatic ecosystem.

Supporting and Controlling Plankton Growth

Navigating Plankton Growth: Encourage or Discourage?

Aquarium enthusiasts have various methods at their disposal to either support or control the growth of plankton within their aquatic environments. The choice depends on the specific needs and balance of each aquarium.

Filtration’s Double-Edged Sword

Traditional filtration processes, like skimmers and filters, might inadvertently remove plankton from the aquarium environment. While these filters are essential for keeping the water clean, they may also extract the plankton or eliminate their food sources, depriving your aquarium’s inhabitants of this crucial nutritional resource. Careful management and understanding of filtration systems are necessary to provide a nourishing environment without compromising the water quality.

The Refugium Advantage: Sumps as Safe Havens

Sumps used as refugium offer a significant advantage for fostering plankton’s growth. Serving as separate, protected spaces, the refugium provides a haven where plankton’s can thrive without the threat of over-harvesting by fish and other invertebrates residing in the main display tank. These specially designed compartments allow a continuous supply of plankton to be washed back into the main tank, serving as a steady food source.

Refugiums also benefit from the inflow of waste and detritus, which serves as fodder for plankton’s, aiding their growth and activity. Many aquarium keepers intentionally introduce macroalgae into these sumps. These larger algae absorb excess nutrients, reducing algae blooms and offering shelter and protection to the zooplankton, creating a more stable and nurturing microenvironment for plankton populations.

Implementing a thoughtful approach to support and control plankton growth will contribute significantly to the health and balance of your aquarium ecosystem, creating a thriving, vibrant underwater world for you and your aquatic pets to enjoy.

Benefits of Plankton for Various Aquarium Inhabitants

A Vital Food Source for Diverse Aquatic Life

Plankton’s serves as a fundamental food source for many aquarium inhabitants. Its importance cannot be overstated, as it’s nutritious and easily accessible for different life forms within the tank. Plankton’s availability and nutritional value make it indispensable for maintaining a vibrant and healthy aquarium.

Supporting Filter Feeders

Aquariums often house various filter feeders that rely on plankton’s for their dietary needs. These include the Australian freshwater mussels (with over 50 varieties), marine mussels, clams, cockles, scallops, rock oysters, and pipis. All these organisms actively filter plankton from the water, absorbing the necessary nutrients for their growth and vitality.

Nourishing Corals and Anemones

Corals and anemones, while often relying on photosynthesis for their energy needs, also capture and consume plankton to supplement their diet. This additional nutrition is crucial for their health and colour vibrancy, making plankton essential in tanks that house these beautiful and delicate life forms.

Essential for Larval Fish and Zooplankton

Larval fish and various forms of zooplankton in the aquarium significantly depend on plankton. During the early stages of life, many fish species predominantly feed on plankton, making it imperative to have a steady supply for the proper development and growth of young aquatic life within your tank.

Aiding in the Thriving of Tube Worms and Other Invertebrates

Tube worms, among other invertebrates, also benefit significantly from the presence of plankton in the water. These organisms feed directly on plankton, absorbing nutrients for survival and growth.

Through these various roles, plankton is an irreplaceable part of the dietary cycle within the aquarium, supporting life and health across different species and life stages. Ensuring a steady and abundant supply of plankton within the aquarium environment is pivotal for the thriving and well-being of its diverse inhabitants.

Practical Tips for Managing Plankton in Your Aquarium

Balancing Plankton Amounts

Managing the amount of plankton’s within your aquarium is a delicate balancing act. Too many plankton’s might lead to water quality issues, while too little could starve your filter feeders and other plankton-dependent inhabitants. Regularly monitor plankton levels, adjusting to maintain a healthy, thriving aquatic environment.

Using Sumps Effectively

Sumps can be invaluable in fostering plankton’s growth. They provide an isolated space where plankton’s can thrive without being consumed immediately. By strategically placing sumps, you create refugiums that allow plankton’s populations to grow, eventually circulating back into the main tank, providing a consistent food source for your aquarium inhabitants.

Refugiums: A Safe Haven for Plankton

Refugiums are specific sections of your aquarium system designed to provide a safe space for smaller, vulnerable organisms like plankton. Within the refugium, plankton can reproduce and grow without the immediate threat of predation, later introduced into the main tank, where they serve as essential food sources.

Intentional Macroalgae Placement

Many aquarists intentionally incorporate macroalgae within their sumps or refugium. Macroalgae aid in water filtration and offer shelter and protection to plankton. This practice creates microenvironments where plankton can safely reproduce and grow, enhancing the overall plankton population within your aquarium system.

Monitoring and Adjusting

Regularly observe the conditions within your aquarium, paying close attention to the visibility and water quality. Sometimes, an overabundance of plankton’s might cloud the water. If this occurs, consider adjusting your filtration system or temporarily reducing the introduction of additional plankton’s until balance is restored.

Through careful and considered management practices, plankton’s can become a sustained, invaluable resource within your aquarium, supporting a diverse and vibrant aquatic life community. These practical tips guide maintaining the ideal plankton balance, promoting a healthy, thriving ecosystem within your tank.


Summing Up Plankton’s Role

Plankton’s plays an indispensable role in sustaining a healthy and dynamic aquarium ecosystem. From serving as a fundamental food source for a myriad of aquatic life to actively participating in the breakdown of organic matter, the presence of plankton’s is crucial. Different sizes and types of plankton’s collectively contribute to nourishing various aquarium inhabitants, supporting their growth and vitality.

Effective Plankton Management

Effectively managing plankton’s within your aquarium is not just about maintaining adequate amounts; it’s also about fostering an environment where plankton’s can thrive and support the dietary needs of different species in your tank. With the right balance, plankton’s becomes a driving force that underpins the health and well-being of your aquatic pets and plants.

Foster a Thriving Aquarium

In conclusion, understanding and appreciating the importance of plankton’s in your aquarium is key to cultivating a lively and resilient aquatic habitat. By implementing the practical tips and insights shared in this article, you can effectively manage plankton levels, ensuring their survival and the thriving life of various aquarium dwellers that depend on them. Whether you are a novice aquarist or an experienced hobbyist, being mindful of the plankton’s in your aquarium will set the stage for a vibrant and harmonious underwater world.