It All Starts with the Humble Plankton

Plankton, those tiny, drifting organisms that form the foundation of the marine food web, are a vital source of nutrition for a wide range of sea creatures. From small fish and crustaceans to massive whales, these fascinating organisms provide sustenance for numerous marine animals.

Let’s start with the smallest of the bunch – phytoplankton and zooplankton. These microscopic organisms float near the ocean’s surface, harnessing the power of sunlight to produce energy through photosynthesis. Many larval crab species rely on phytoplankton and zooplankton as their primary food source, fueling their growth and development.

Moving up the food chain, small fish and crustaceans feed on plankton. These include species such as anchovies, sardines, and krill, which consume vast quantities of phytoplankton and zooplankton to sustain themselves. These small marine creatures serve as a crucial link, transferring energy from plankton up to larger predators.

Speaking of larger predators, many marine animals rely on consuming those small fish and crustaceans to satisfy their dietary needs. Seabirds like auklets and shearwaters swoop down from the skies, diving into the water to catch small fish and crustaceans that feed on plankton. These birds have adapted to this specific feeding strategy, enabling them to thrive in oceanic environments.

But perhaps the most impressive plankton eaters in the ocean are the giant blue whales. These majestic creatures can consume up to 4.5 tons of krill, a type of large zooplankton, every day. Blue whales are filter feeders, using baleen plates in their mouths to filter out water while keeping the krill trapped inside. This feeding strategy allows them to efficiently obtain the massive amounts of energy they need to sustain their enormous bodies.

It’s not just marine animals that rely on plankton for sustenance; humans also benefit from the nutritional value of these tiny organisms. Commercially valuable fish species like salmon, rockfish, flatfish, sardines, and squid all thrive on a diet rich in krill. These fish accumulate the energy and nutrients from consuming plankton, making them a valuable food source for humans as well.

The marine food web is intricately interconnected, with plankton playing a crucial role as the primary food source for a wide range of marine animals. From larval crabs to massive blue whales, these organisms sustain countless species and contribute to the overall health and balance of the ocean ecosystem. Understanding the importance of plankton and the diverse array of species that depend on them is essential for the conservation and management of our oceans.

What Mainly Eats Plankton?

Plankton, which consists of small organisms that float or drift in water bodies, serves as a crucial food source for numerous marine creatures. Various organisms, ranging from tiny zooplankton to larger marine mammals, rely on plankton as their primary source of nutrition. Here is a detailed list of organisms that feed on plankton:

1. Zooplankton: These microscopic animals primarily feed on phytoplankton, the plant-like component of plankton. Zooplankton includes small crustaceans like copepods, krill, and shrimp, as well as larval stages of many marine animals such as fish and invertebrates.

2. Baleen whales: These magnificent marine mammals, including blue whales, humpback whales, and fin whales, possess baleen plates in their mouths instead of teeth. They filter large volumes of water, trapping plankton with their baleen and consuming vast quantities of these tiny organisms.

3. Small fish: Many small fish species, such as anchovies, herrings, and sardines, have adapted to feeding on plankton. They possess specialized structures, such as gill rakers, that help them filter out planktonic organisms from the water column.

4. Jellyfish: Although gelatinous zooplankton like jellyfish and comb jellies are often considered as plankton themselves, they also consume other planktonic organisms. They capture prey by using their tentacles, which are armed with stinging cells that immobilize their prey.

5. Manta rays and whale sharks: These gentle giants are filter feeders that consume plankton by swimming with their huge mouths open. They rely on filter pads or gill rakers to sieve out plankton and small fish from the water as they swim.

6. Sea turtles: Some species of sea turtles, such as the green turtle and the loggerhead turtle, are known to feed on jellyfish, which often make up a significant portion of their diet. Since jellyfish are part of the planktonic community, turtles can be considered as indirect consumers of plankton.

7. Some birds: Certain seabirds, such as gulls, terns, and pelicans, have adapted to feed on planktonic organisms. They either catch floating plankton directly from the water surface or dive into the water to catch small fish and invertebrates that rely on plankton.

8. Filter-feeding invertebrates: Various invertebrates, including mussels, clams, and barnacles, are filter feeders that extract organic particles, including plankton, from the water. They use specialized body parts, such as gills or specialized appendages, to filter out the food particles from the surrounding water.

It is important to note that the specific diet of each organism can vary depending on factors such as location, availability of other food sources, and life stage. Nonetheless, plankton remains a vital food source for a wide range of marine organisms, forming the foundation of the oceanic food web.

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What Do Planktons Get Eaten By?

Plankton, being microscopic organisms that float in the water, serve as a vital food source for various organisms in the marine ecosystem. They are consumed by a wide range of organisms, including small fish and crustaceans, as well as larger predators.

Here is a breakdown of the different organisms that feed on plankton:

1. Small Fish: Many small fish species rely on plankton as their primary source of food. These fish, such as herring, anchovies, and sardines, have specialized feeding mechanisms that allow them to filter and consume tiny planktonic organisms.

2. Crustaceans: Crustaceans like krill, copepods, and shrimp also feed on plankton. They have various feeding strategies, including filter-feeding and actively hunting for plankton in the water column.

3. Larval Stage Organisms: Numerous marine animals have a larval stage that heavily depends on plankton for sustenance. Larval stages of fish, crabs, lobsters, and many other species rely on plankton as their primary source of nutrition until they develop into adults.

4. Larger Predators: Larger predators in the ocean prey on the smaller organisms that feed on plankton. These predators include larger fish, marine mammals like seals and sea lions, seabirds, and even some species of turtles. They consume the smaller fish and crustaceans that have fed on plankton, indirectly obtaining their energy from these microscopic organisms.

5. Filter-feeding Animals: Some species, such as baleen whales, filter-feed directly on vast quantities of plankton. For example, the blue whale, the largest animal on Earth, primarily feeds on krill, a large zooplankton. It can consume up to 4.5 tons of krill per day, sustaining its massive size.

It is important to note that the consumption of plankton creates a vital link in the marine food chain, transferring energy from microscopic organisms to larger predators. This intricate interdependence highlights the essential role plankton plays in sustaining diverse marine ecosystems.

Do Crabs Eat Plankton?

Crabs do eat plankton. However, it is important to note that the type of plankton consumed by crabs varies depending on their life stage. Larval or baby crabs primarily feed on phytoplankton and zooplankton. These microscopic organisms serve as a crucial food source for the developing crabs.

On the other hand, adult crabs have different dietary preferences. They live on the seafloor and their diet mainly consists of small crustaceans, clams, and fish. While adult crabs may not rely solely on plankton for sustenance, they do play a role in the overall marine food web. Plankton serves as a primary food source for many other marine organisms, which in turn can become prey for crabs as they move up the food chain.

To summarize, while crabs do eat plankton during their larval stage, their diet shifts to include a wider variety of prey items as they mature into adults. The consumption of plankton by crabs is an integral part of the marine ecosystem, contributing to the overall balance of the food web.

What Eats Plankton And Krill?

Plankton and krill serve as a vital food source for various marine organisms. Here is a list of organisms that consume plankton and krill:

1. Baleen Whales: Baleen whales, including the giant blue whale, primarily feed on krill. They have baleen plates in their mouths that act as filters to strain the water and trap the tiny krill, which they then consume.

2. Seabirds: Many seabirds, such as auklets and shearwaters, rely on krill as a significant part of their diet. They dive into the water to catch the krill and feed on them.

3. Commercially Valuable Fish: Several commercially valuable fish species depend on plankton and krill for sustenance. Salmon, rockfish, flatfish, sardines, and squid are some examples. These fish directly or indirectly consume plankton and krill, which provides them with essential nutrients.

4. Jellyfish: Some species of jellyfish also feed on plankton and krill. They use their tentacles to capture and consume these tiny organisms.

5. Small Fish: Various small fish species, such as anchovies and herring, feed on plankton and krill. They often form large schools and rely on these organisms as their primary food source.

6. Squid: Squid are opportunistic predators and feed on a wide range of prey, including plankton and krill. They have tentacles equipped with suction cups to capture and consume these small organisms.

7. Filter-Feeding Invertebrates: Filter-feeding invertebrates like barnacles, mussels, and certain species of shrimp also consume plankton and krill. They use specialized structures, such as feathery appendages or filtering mechanisms, to extract the tiny organisms from the water.

It is important to note that this list is not exhaustive, as there are numerous other marine organisms that rely on plankton and krill as a food source. The delicate balance and availability of these organisms play a crucial role in maintaining the overall health and productivity of marine ecosystems.


Plankton serves as a vital food source for a wide range of marine organisms, from small sea creatures like fish and crustaceans to larger predators such as whales and seabirds. These tiny organisms, including both phytoplankton and zooplankton, form the foundation of the marine food web. Larval crabs rely on plankton for their survival, while adult crabs feed on small crustaceans, clams, and fish. Krill, a large zooplankton, is a near-exclusive food for giant blue whales and also supports commercially valuable species like salmon, rockfish, flatfish, sardines, and squid. Even seabirds like auklets and shearwaters depend on plankton, particularly krill, for their sustenance. The intricate interconnections within the marine ecosystem highlight the significance of plankton in supporting the diverse array of life in our oceans.

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William Armstrong

William Armstrong is a senior editor with, where he writes on a wide variety of topics. He has also worked as a radio reporter and holds a degree from Moody College of Communication. William was born in Denton, TX and currently resides in Austin.