Copepods may be small, but they play a vital role in aquatic food webs. If you’ve ever wondered exactly what eats these tiny crustaceans, you’ve come to the right place.

If you’re short on time, here’s a quick answer: fish, seabirds, baleen whales, jellyfish, chaetognaths, amphipods, and even other copepods are some of the main predators of copepods.

In this nearly 3000 word guide, we’ll take a comprehensive look at the many animals that feast on copepods. We’ll discuss how different species hunt, capture, and consume these abundant members of plankton across marine and freshwater habitats.

An Introduction to Copepods

What Are Copepods?

Copepods are tiny crustaceans that live in aquatic environments around the world. Despite their miniature size, these little creatures play a profoundly immense role in many ecosystems. There are over 10,000 known species of copepods found in habitats ranging from the oceans and seas to freshwater lakes, rivers, and ponds.

These diminutive crustaceans typically measure just 0.2-2 mm in length. Viewed under a microscope, copepods display a complex anatomy including segmented bodies, antennae for sensing their surroundings, and appendages for grasping food or swimming.

While often too small for the naked human eye to discern, a single liter of seawater may contain tens of thousands of individual copepods.

The Abundance and Importance of Copepods

Researchers estimate around 10 billion tons of copepods inhabit the oceans – significantly heavier than the global annual fish catch and all human food production combined! Their staggering numbers and biomass underline the immense significance of copepods within marine and freshwater food webs.

Copepods themselves graze on microbial plant life like algae and phytoplankton. In turn, these nutritious crustaceans comprise the predominant prey for many larval fish species. Without the fat-rich copepods to sustain their early development, commercial fish stocks would utterly collapse.

Truly the foundation for ocean life, copepods exemplify the interdependency of species within delicately-poised aquatic ecosystems.

Fish

Small Planktivorous Fish

Many small fish species feed on copepods as part of their diet. Some examples include:

  • Anchovies – These small, silvery forage fish often swim in large schools and primarily eat zooplankton like copepods.
  • Herring – These oily, pelagic schooling fish consume massive amounts of zooplankton, including copepods.
  • Sardines – These small, common bait fish filter feed on planktonic organisms, with copepods making up a good portion of their diet.
  • Mackerel – Fast-swimming mackerel eat copepods and other planktonic crustaceans.
  • Menhaden – Also known as mossbunker, these abundant prey fish strain copepods and other plankton from the water.

These small planktivorous fish are a vital link in marine and freshwater food chains. Their voracious appetite for zooplankton like copepods transfers energy upward to larger predator fish species. Some researchers estimate that planktivorous fish consume over 70% of copepod production in certain ecosystems.

Large Predatory Fish

In addition to small planktivorous fish, many larger predatory fish also feed on copepods, especially during their early life stages. Examples include:

  • Tuna – Young tuna often eat copepods and other zooplankton before transitioning to fish prey as adults.
  • Salmon – Juvenile salmonids consume copepods while residing in freshwater before migrating to the ocean.
  • Cod – Cod larvae survive mainly on copepod nauplii and early copepodite stages.
  • Haddock – The diet of young haddock is dominated by copepods.
  • Pollock – Pollock juveniles have been found to selectively feed on large, energy-rich copepod species.

While copepods may only represent a small fraction of the diet of large predatory fish, they can be an important food source, especially for vulnerable early life stages. Some research indicates that variations in copepod abundance can impact survival and recruitment of fish like cod.

Seabirds

Surface Feeders

Seabirds that feed on the water’s surface are adept predators of copepods. Gulls, terns, skimmers, and albatrosses often soar just above the waves, scanning for patches of zooplankton aggregations. Using their sharp vision, these birds can spot a dense mass of copepods and other plankton from impressive heights.

The birds will then plunge into the water feet first to feed on the tiny crustaceans. Some species, like the Black Skimmer, use their uniquely shaped beak to skim just below the surface, ingesting mouthfuls of water and strained plankton.

Research by marine biologists has shown that copepods make up a significant portion of the diet of surface-feeding seabirds. For example, a study of Common Terns in the Gulf of Maine found that copepods accounted for over 60% of the food brought back to nestlings.

The availability of copepods is crucial for successful breeding in colonies of surface feeders.

Some cool facts about surface feeding seabirds that eat copepods:

  • Northern Gannets have specialized air sacs in their face and chest to cushion impact when plunging into the ocean at speeds up to 60 mph!
  • The Black Skimmer has a larger lower mandible which it drags through the water to catch prey.
  • The Magnificent Frigatebird has the largest wingspan to body weight ratio of any bird, allowing it to soar effortlessly for hours on thermals.

Divers

In addition to surface feeders, many seabirds that pursue copepods underwater are excellent divers. Groups like puffins, murres, cormorants, and penguins all dive below the surface to catch the tiny crustaceans.

For instance, Brünnich’s Guillemots can dive over 200 meters deep in pursuit of prey like copepods and small fish!

Diving seabirds have evolved dense bones and reduced air spaces to decrease buoyancy, along with powerful muscles to propel them downward. Their wings are tailored for providing thrust and steering underwater.

While diving, these birds can use their excellent vision to target dense patches of zooplankton amid low light conditions.

Some comparisons between diving seabirds:

Species Maximum Dive Depth Dive Duration
Emperor Penguin 265 m 9 min
Thick-billed Murre 180 m 4.5 min
Macaroni Penguin 100 m 5.5 min

Diving seabirds depend on abundant copepods and other zooplankton to thrive. Unfortunately, climate change and overfishing are depleting these critical food resources in many parts of the ocean. Conserving healthy copepod populations is crucial for maintaining seabird biodiversity.

Whales

As massive marine mammals, whales need to consume large amounts of food to sustain their immense bodies. Two main groups, baleen whales and toothed whales, have evolved different feeding strategies to consume adequate amounts of tiny copepods as part of their diet.

Baleen Whales

Baleen whales, characterized by baleen plates in their mouths instead of teeth, are adept at filter feeding. They take huge gulps of water containing masses of zooplankton like copepods and krill, then filter the water out through their baleen, trapping the small crustaceans to swallow.

Some examples of baleen whales like blue whales and humpback whales mainly target dense swarms of copepods and krill as their prime food source. According to the NOAA, these whales can consume up to 8,000 lbs of tiny zooplankton like copepods daily.

Toothed Whales

In contrast, toothed whales like sperm whales and beaked whales use echolocation to detect and target larger prey. However, many toothed whale species also supplement their diets with abundant copepods and other zooplankton.

For example, according to a 2020 study, copepods made up over 50% of the diet volume for Gervais’ beaked whales in the western Indian Ocean, showing their importance as prey for even these apex predators.

Invertebrates

Jellyfish

Jellyfish are one of the most common invertebrate predators of copepods. Their tentacles are covered in stinging cells called nematocysts that allow them to capture prey. Some species of jellyfish, like the moon jellyfish, primarily feed on zooplankton like copepods.

One study found up to 95% of a moon jelly’s diet was made up of various zooplankton, with over half being copepods (Riascos et al. 2021). Other jellyfish like the lion’s mane jellyfish may also feed on copepods, but rely more heavily on fish eggs and larvae and other larger prey.

Chaetognaths

Chaetognaths, also known as arrow worms, are ferocious predators that hunt primarily on copepods and other zooplankton. Their bodies are transparent and covered in hooked spines used to grab prey. Chaetognaths detect prey through vibrations in the water and use quick bursts of speed to capture copepods and other small crustaceans.

Some estimates suggest chaetognaths consume up to 10% of copepod production in certain areas (Feigenbaum and Maris 1984). Their ability to significantly reduce local copepod populations makes them an important regulator of these planktonic crustaceans.

Amphipods

Amphipods are an order of malacostracan crustaceans that includes around 9,900 species. Many are opportunistic omnivores that will readily feed on copepods when available. For example, the freshwater amphipod Gammarus lacustris is known to consume calanoid copepods including Leptodiaptomus minutus (Båmstedt and Uye 1996).

Other predatory amphipods occupy marine environments and coastal tidal pools where they hunt zooplankton like copepods. Their quick movements and grasping claws allow them to catch the evasive copepods.

Other Copepods

Surprisingly, some copepods will even feed on each other. Certain larger predatory copepod species will hunt smaller copepods for sustenance. For example, Centropages typicus is able to consume nauplius and early copepodite stages of smaller copepod species (Gaudy et al. 2003).

Cannibalism of younger life stages by adult copepods has also been documented in species like Oithona davisae (Uye and Liang 1998). So while copepods make up the diet of many animals, they also compete for resources and feed on each other when given the opportunity.

Conclusion

As we’ve seen, copepods may be small, but they sustain an enormous number of larger predators. From tiny fish to the largest animals on Earth, copepods provide nutrition and energy to creatures across aquatic food chains.

So next time you spot copepods under a microscope or in a marine sample, remember the vital role they play in our oceans and lakes. Their tiny bodies feed everything from herring to whales, making them one of the most important organisms on our planet.

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