Skip to Content

Do Crabs Eat Plankton?

Have you ever wondered what crabs eat? With their big claws and armoured shells, they might seem like ferocious predators. But in reality, many crab species have diverse diets that include plant matter and decaying organisms. One food source that sustains crabs in coastal ecosystems is plankton. Keep reading to learn all about the crabs that eat plankton and why this tiny food is so important.

Do Crabs Eat Plankton?

Do crabs eat plankton?

Yes, many crab species do eat plankton! plankton refers to the tiny plants, animals and bacteria that drift in the water. While invisible to the naked eye, plankton are found in oceans, seas, lakes and ponds across the globe. 

For crabs that live in coastal habitats, plankton are a vital food source. Plankton floats right into their habitats, providing a convenient feast. Crabs will eat phytoplankton (the plant kind) and zooplankton (the animal kind). Here are some of the most common plankton-eating crab species:

  • Fiddler crabs: These small crabs live in burrows along the beach. When the tide comes in, they venture out to filter feed on plankton.
  • Blue crabs: The juveniles of this commercially important crab eat plankton before graduating to larger prey. 
  • Spider crabs: These spindly crabs don’t have big claws for hunting. Instead, they catch plankton with feather-like appendages. 
  • Mangrove tree crabs: Living among mangrove roots, these crabs sift plankton from the coastal waters.
  • Pea crabs: These tiny crabs often reside inside mussels and oysters, eating the plankton filtered by their hosts.

So, in short, yes – a wide array of crab species chow down on plankton daily! Their small size and abundance make plankton the perfect staple.

Why Do Crabs Eat Plankton?

For crabs, plankton offers an abundant, nutrient-dense food source. Here’s why these tiny drifters are an important part of many crabs’ diets:

  • Energy: Plankton provides energy for crabs. Since they drift right into crab habitats with tides and currents, plankton are easy to access. Crabs don’t have to waste energy hunting down this food.
  • Nutrition: Plankton supply essential fatty acids, vitamins and minerals. Diatoms and dinoflagellates (two major types of phytoplankton) are packed with nutrients. 
  • Availability: Plankton are found in massive numbers. A single drop of seawater can hold tens of thousands of plankton. There’s plenty to go around, even for many crabs feeding at once.
  • Digestibility: Plankton are soft-bodied and lack hard shells or indigestible parts (excluding diatoms). This makes it easy for crabs to digest and absorb nutrients efficiently.
  • Size: Plankton are tiny, ranging from microscopic to a couple of millimetres long. For small juvenile crabs or species with small mouthparts, plankton are perfectly bite-sized. 
  • Adaptability: Plankton comes in many diverse forms. Based on availability, crabs can switch between phytoplankton, zooplankton, fish eggs, and other types.

With their strong nutritional value, abundance and ease of eating, plankton is one of the most reliable food sources crabs can find in their coastal ecosystems. It makes good evolutionary sense for crabs to take advantage of these tiny ocean drifters.

How Do Crabs Eat Plankton?  

Crabs have adapted a few different techniques to consume these teeny plankton effectively. Here are some of the main strategies:

  • Filter feeding: Crabs like fiddler crabs use feathery appendages to filter plankton out of the water. As waves wash over their feeding structures, plankton get trapped.
  • Straining: Mangrove tree crabs and some swimming crabs have mouthparts specialized for straining. They sieve water to remove all the tasty plankton inside.
  • Ambush predation: Many small juvenile crabs wait in vegetation and ambush plankton as they drift by. Their pincers and quick movements let them snatch up unsuspecting plankton. 
  • Surface grazing: Some specialized crabs can actually graze on surface films teeming with plankton. Using unique leg adaptations, they skim the surface, eating whatever sticks.
  • Symbiotic relationships: Pea crabs get plankton second-hand by living inside bivalves like mussels and oysters that filter seawater. The crabs eat any excess plankton their host doesn’t digest. 
  • Scavenging: Crabs will happily scavenge dead or decaying plankton that sink to the seafloor. This carrion snow provides an easy meal.

While tiny, plankton are packed with nutrients crabs need. With good filtering skills and diverse feeding styles, crabs are well-equipped to reap this bountiful food source.

What Plankton Do Crabs Eat?

Crabs will eat both major types of plankton – phytoplankton (plant) and zooplankton (animal). Here are some of the most commonly consumed plankton:


  • Diatoms: Single-celled algae encased in glass-like cell walls made of silica. Abundant food source with key fatty acids. 
  • Dinoflagellates: Armored plankton also contain oils. Some species glow bioluminescent at night!
  • Green algae: Provides protein, vitamins, minerals and omega-3s.
  • Blue-green algae: Rich source of nutrients like B-vitamins, iron, magnesium and potassium. 


  • Copepods: One of the most common zooplankton. Their small size and high numbers make them a plankton staple.
  • Krill: Shrimp-like crustaceans packed with nutrition. An important food higher up the food chain.
  • Rotifers: Tiny animals with a ring of cilia around their mouth. Simpler nutrients than copepods. 
  • Fish eggs and larvae: Nutritious packets of proteins and fats. An abundant seasonal food source.
  • Barnacle larvae: Young barnacles drift as plankton before settling on rocks. Rich in carbs.

Crabs aren’t too picky – they will eat a wide variety of phyto and zooplankton based on availability in their habitat. This variety balances their nutritional needs.

Do All Crabs Eat Plankton?

While many coastal and small crab species eat plankton, not all crabs include plankton in their main diets. Here are a few examples of crabs that don’t rely on these tiny drifters:

  • King crabs: These large crabs live in deep, cold Alaskan waters far from plankton-rich surfaces. Instead, they hunt worms, clams, sea stars and other meat.
  • Coconut crabs: The world’s largest land crab lives on islands in the Indian Ocean. Without access to ocean plankton, they climb trees to eat coconuts and other vegetation. 
  • Yeti crabs: These blind albino crabs live by deep-sea vents where no plants grow, and plankton don’t drift. Their food source is mysterious. 
  • Hermit crabs: Living in abandoned shells, they scrape algae and detritus off rocks with mouthparts adapted for grazing. They don’t filter feed or hunt plankton.
  • Stone crabs: These sizable crabs live in rock beds and coral crevices. Their massive claws grab and crush large prey like snails, clams and oysters.

The crabs that don’t eat plankton tend to be larger species living in specialized habitats away from plankton-filled shallows. Their habitat and adaptations allow them to hunt larger prey instead.