Wonders of Plankton: Tiny Organisms, Huge Impact

Wonders of plankton: tiny organisms, huge impact

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The ocean is filled with weird and wonderful creatures but most of us are familiar with the ones that are easy to spot. Plankton are a group of tiny organisms but they’re vital to the health of our oceans and to the ecosystem. Let’s get to know these minute creatures a little better.

What is Plankton?

What is plankton?
Plankton are Drifting Microorganisms that Form the Foundation of Marine Life’s Intricate Web

Plankton refers to a variety of microorganisms found in the ocean. They’re incredibly important as they form the base of the food chain in their marine environments. Unlike other marine creatures, plankton are not free-moving but instead drift on the ocean current.

Plankton are found in both marine and brackish environments and can be anything from bacteria to algae, and protozoa.

Crucial Role of Plankton in Ecosystem Dynamics

Importance of plankton in the ecosystem
Manta Ray Filter-Feeding on Plankton

While they may be tiny, the world’s oceans would be a very different place without plankton, as they play an essential role in the ecosystem.

Primary Producers

A primary producer is an organism that doesn’t require food in the traditional sense but converts things like light into energy. The photosynthesis of plants is one of the best examples of this, but plankton are primary producers too.

But why is this important?

Well, without primary producers like plankton, there would be no base of the food chain, and these organisms provide food for a whole host of marine species.

Phytoplankton are considered to be the most important producers because they make their own energy and even serve as a food source for zooplankton.

Food Web

As I discussed, plankton forms the very base of the food web. Amazingly, life in the ocean is made up of around 95% plankton, so you can already get an idea of just how important they are in the food chain.

Certain species of whales feed primarily on plankton despite their huge size, as well as fish like sardines and even the manta ray.

If plankton were to no longer exist, then the rest of the food chain would likely collapse and that could seriously affect the biodiversity of the ocean.

Carbon Cycling

Climate change is a serious global problem, and one of the main greenhouse gasses responsible for this is carbon. With humans creating millions of tons of carbon emissions every year, it’s vital that we find ways to store it.

Carbon sinks are areas that absorb and retain carbon, and did you know that one of the largest and most efficient carbon sinks is the ocean?

But it cannot work alone, and plankton are responsible for soaking up enormous amounts of carbon. It’s thought that these tiny creatures alone absorb as much as 50% of the earth’s carbon production. And the more carbon they absorb and convert to energy, the more plankton masses grow

Oxygen Production

Not only do plankton absorb millions of tons of carbon every year, but in doing so they’re also creating fresh oxygen.

This is a very similar process to trees, which most of us know ‘breathe out’ oxygen. When plankton absorb carbon, their tissues convert it into energy, and the by-product of that process is oxygen, which allows humans to breathe clean air!

Types of Plankton

While we usually refer to these tiny organisms as just plankton, it’s important to remember that there is more than one type. In fact, there are three different types of plankton, each with its own important role in the ocean.


Phytoplankton can be found in both fresh and marine waters and are sometimes referred to as microalgae.
Volvox Phytoplankton Under a Microscope

Phytoplankton can be found in both fresh and marine waters and are sometimes referred to as microalgae. These are the types of plankton that perform photosynthesis by using energy from the sun to convert into food. As a result of this, they are available for zooplankton to feed on and so the food web continues.

There are several different types of phytoplankton, including coccolithophores, cyanobacteria, dinoflagellates, and diatoms. And what’s special about these organisms is their ability to absorb carbon. As I mentioned earlier, plankton is responsible for removing up to 50% of the world’s carbon, and it’s phytoplankton that plays this essential role.


Instead of being a plant-like organism, zooplankton are more like microscopic animals.
Close-Up of Copepod Zooplankton

Zooplankton are one step up in the food chain after phytoplankton, on which they feed. Instead of being a plant-like organism, zooplankton are more like microscopic animals. However, they’re often too weak and small to be able to move around, so they drift along with the ocean current and serve as food for larger marine creatures.

You’re probably more familiar with some of the types of zooplankton which include krill. Just like phytoplankton, they play a critical role in maintaining a healthy ocean biogeochemical cycle by recycling important nutrients and organic matter.

What’s really amazing about zooplankton is that, while they’re unable to swim, they hold the title of having the longest migration on earth. That’s because while they spend the day floating on deeper ocean currents, at night, they float to the surface where they feed on phytoplankton. That may not seem like a huge distance to you and I, but when you consider how small they are, it’s a mammoth journey.


While bacteria sometimes fall under the umbrella of phytoplankton, they also have their very own grouping called bacterioplankton. These are microscopic bacteria but they still play an essential role in the marine ecosystem.

The reason for this is that bacterioplankton help to break down organic matter and recycle nutrients, both of which are important for the carbon and nitrogen cycles in the ocean. Without these cycles, the pH balance of the ocean would be out of whack, and the oxygen levels would decrease.

The main type of bacterioplankton is known as prokaryotes, and many of these organisms are primary producers, converting energy from the sun into sustenance that allows them to survive.

Characteristics of Plankton

Characteristics of plankton
Various Types of Plankton, Including Dinoflagellates, Exhibit Bioluminescence

If you really want to get to know plankton well then it’s important to understand their characteristics. Yes, we know that they’re super small but what else defines plankton?

Size & Shape

The size of various types of plankton can vary quite dramatically. For example, according to the BBC, some larger zooplankton could measure up to 20 cm while their microscopic counterparts may be no bigger than 2 micrometers. These smaller types of phytoplankton are often single-celled organisms but they can come in a range of shapes.

Some of them are spiral-shaped, while others are spherical, and there are many types of diatoms that have such distinct shapes, they’re very easy to identify to the trained eye.

While there is some variation in the size and shape of phytoplankton, this variation is much greater between zooplankton. There are many types of zooplankton that have a size and shape very similar to shrimp; krill is a good example of this.

However, there are some jellyfish that are considerably large and many people may not have classed them as plankton until they are told otherwise. Some of these jellyfish species have a globe-like shape while others are more elongated.

It’s also worth noting that plankton are separated into different groups according to their size.

  • Megaplankton are those that are larger than 20 cm
  • Macroplankton are those that range in size between 2 cm and 20 cm
  • Mesoplankton are those that range between 200 micrometers and 2 cm
  • Microplankton are those that range between 20 and 200 micrometers
  • Nanoplankton range in size between 2 and 20 micrometers
  • Picoplankton can measure between 0.2 and 2 micrometers
  • Femtoplankton are any types of plankton smaller than 0.2 micrometers

The size and shape of plankton can affect the organism’s ability to move, position itself to gain energy from the sun, and even its reproductive rate. For example, some of the smaller phytoplankton can reproduce extremely quickly, which means they dominate the later column. On the other hand, larger plankton species are better able to compete for resources owing to their ability to resist sinking.


One of the most remarkable characteristics of plankton is how quickly it can reproduce. There are some species that produce offspring so rapidly that their populations can more than double in the space of a couple of hours. But that doesn’t mean that they’re not complex and in fact have very interesting life cycles.

For example, there are many species of plankton that are able to switch between reproduction methods (sexual and asexual) according to the current environmental conditions. Although the methods of reproduction do vary between zooplankton and phytoplankton species.

However, asexual reproduction is more common in phytoplankton. Dinoflagellates, for example, use a process called binary fission where a parent cell splits into two new organisms and this process continues over and over. But that doesn’t mean they aren’t capable of sexual reproduction, and they do this by releasing sex cells into the water, which connect to other sex cells and form a zygote. This is what then grows into a new individual plankton.

Just like phytoplankton, zooplankton are able to reproduce both sexually and asexually. The main difference with their method of asexual reproduction compared to zooplankton is that, rather than releasing a parent cell, they’ll do something known as budding. The offspring actually forms and grows off of the parent before breaking away at the right time.

Again, zooplankton are perfectly capable of sexual reproduction, and this is very similar to the process used by phytoplankton, with egg and sperm cells being released into the water where they’re then able to combine. For example, colonies of green algae are either male or female, and each colony will release one type of cell. Once these cells are released, they’ll fuse with the sperm cells of another colony to form a zygote and so the process continues.

There are certain environmental factors that affect the reproductive cycles of plankton, including the time of year. Some are more sensitive to seasonal changes and will therefore only reproduce at certain times of the year, whereas others follow a continuous cycle of reproduction.


One of the most obvious adaptations of plankton is its ability to produce its own food through a process of photosynthesis. This applies only to phytoplankton, but without this ability, these species would be unable to survive and that would impact the entire marine food web.

But this isn’t the only adaptation of these amazing organisms; some of them are even able to produce their own light through something known as bioluminescence. There are many creatures, particularly in the marine environment that are capable of this, and it’s a phenomenon that occurs for several reasons, including communication, attracting predators, and as a self-defense mechanism. This is seen in certain species of dinoflagellates that glow in the water to prevent them from being eaten by copepods.

What’s more, there are other species of plankton that are easily able to adapt to poor conditions by entering a state of dormancy known as diapause. This is not the same as hibernation, where animals enter a long state of sleep without the need to eat. Instead, diapause occurs as and when necessary, such as when there is a low availability of nutrients or the water temperature is not favorable.

The benefit of this is that the plankton is able to conserve important energy, which helps it to survive and it will remain in this state until conditions return to a viable state. In studies, it was noticed that certain species of zooplankton would enter diapause in low light conditions or when the temperature was too cold, only coming back out of this state when temperatures increased to between 20 and 30 degrees Celsius.

Threats Facing Plankton

Threats facing plankton
Microplastics Impacting Plankton can Trigger Cascading Effects Throughout the Entire Ecosystem

As is the case with many species, plankton don’t have it easy, and they face a number of threats that are causing their numbers to plummet. For example, it’s thought that, since the 1940s, our oceans hold 90% less plankton purely as a result of climate change.

Climate Change

I’ve talked about climate change a lot, and it’s something that’s really important to be aware of, not just because of how it directly affects humans but because of the impact on our wildlife and oceans. Plankton are not exempt from the effects of climate change, and studies are ongoing to better understand how they’re reacting to this. 

One Canadian study suggested that the number of phytoplankton in the ocean has decreased by as much as 40% since the 1950s. When it comes to zooplankton, research suggests that there are some species that are easily able to adapt to changing temperatures and conditions while others are not so flexible and could face potential extinction if rapid warming was to occur. Further research demonstrated that plankton found in warm water regions was more likely to be able to adapt to change compared to those found in polar areas.

Where plankton are unable to survive in certain areas because of rising temperatures, it’s reported that they may begin to migrate. While this might sound good for their survival, the problem is that introducing new species to new areas will upset the balance of the ecosystem.

What’s more, the enormous amount of carbon that’s being sequestered in our oceans is causing the pH to be thrown off and oceans are suffering from acidification. Worryingly, this could mean the total wipe out of certain plankton species that are unable to adapt to these new conditions. With the pH of the oceans expected to drop even more by the year 2100, scientists are concerned that, while some species will die out, others will thrive which will drastically upset the biodiversity and balance of our oceans. 

Moreover, this acidification could affect the calcification rates of plankton, which would mean another shift in the biological balance. Although, right now, we aren’t entirely sure whether phytoplankton rates will increase or decrease over the coming few decades. 


Plastic pollution in the oceans is a significant problem, and it’s estimated that around 15 billion kilograms of plastic are being thrown into the ocean every year. I cannot overstate enough what a devastating impact this has on marine life, including plankton.

What’s worrying is that the pollutants from these plastics may be transferred to phytoplankton. Since they’re the base of the food web, any animals that consume them and the zooplankton on which they feed, could also suffer the effects.

What’s more, there are concerns that when phytoplankton ingest small amounts of plastic pollution, this hinders their ability to contain carbon. The reason for this is that usually, when these types of plankton feed on algae, they produce carbon which is stored in their fecal matter. When this is released, it sinks to the bottom of the ocean, where the carbon is stored. However, when this fecal matter contains microplastics, it becomes more buoyant and therefore cannot sink, along with the carbon, to the ocean floor.


Humans have been overfishing for decades and this is having a dramatic impact on the marine ecosystem of which plankton are a part. One of the major problems is that when humans fish larger predatory species, the number of plankton on which they feed grows significantly. While you might not initially think that this would be a problem, you have to consider that this boom in smaller, less nutritious plankton species might not be suitable to support the creatures higher up in the food web.

Not only this, but as plankton populations grow, individuals are going to suffer because of a lack of resources. The greater the number of plankton, the more they have to compete over food and nutrients, which in turn puts their numbers at risk.

While removing large predators can affect the available resources for plankton, it can also affect their ability to efficiently play their role in cycling carbon and nitrogen. This is because they will feed on the feces of larger creatures like whales and will also take nutrients from their carcasses. Where there are fewer of these items available, it has a direct impact on plankton.

What’s more, as larger dominant species are overfished, studies have shown that smaller, plankton species, such as the sprat, become dominant which affects the entire ecosystem and the trophic levels.

Plankton Blooms

Plankton bloom
NASA’s Satellite View of a Phytoplankton Bloom Off Iceland

Plankton blooms, often referred to as harmful algae blooms or red tide, are large masses of plankton that accumulate, often around the surface of the ocean where light sources are most accessible. One of the biggest examples of this occurs around the Gulf Coast of Florida on an annual basis and this is extremely harmful to the environment.

These algae blooms can be made up of both phytoplankton and zooplankton, but it’s more common to see phytoplankton blooms. The reason they’re sometimes called red tides is that these masses of plankton can actually cause the surrounding water to change color.

However, we have to keep in mind that not all algae blooms are harmful, in fact many are considered to be beneficial since they’re producing resources for the food web. But there are some that often occur around coastal areas that release toxins into the water, and this can affect the health of other marine creatures, in some cases, killing them and upsetting the biodiversity of the area.

Not only this, but these toxins often make fish unsafe for human consumption, which means that algae blooms impact fisheries and therefore, the economy. In some cases, the presence of algae blooms has even affected the water quality, making it unsafe for humans to drink. Doing so may cause a range of symptoms, such as vomiting and diarrhea or even liver problems. But what’s most concerning is that the occurrence of red tides appears to be increasing, according to studies. But the good news is that scientists are continuing their studies in the hope that they’ll be able to predict when algae blooms are going to happen and provide warnings to local residents so they’re able to adequately prepare.

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