Zooplankton laboratory

Learn what zooplankton we commonly find in the northeast Pacific Ocean, off the British Columbia coast.

On this page

• Crustaceans
• Molluscs
• Chordata
• Arrow worm
• Polychaete
• Sea gooseberry
• Cnidarium

Crustaceans

Zooplankton crustaceans common in the northeast Pacific Ocean include:

• krill
• copepods
• crab larvae
• shrimp
• mysids
• ostracods
• amphipods

Krill

We've found north Pacific krill and Arctic krill in:

• Puget Sound
• the Georgia Strait
• San Juan Archipelago

The most common krill off the west coast of Vancouver Island are north Pacific krill and thysanoessa spiniferaa.

Learn more about Euphausiids (krill).

Copepod

The largest number of individual crustacean zooplankton in the ocean are from the copepod class. Because most of these are small (less than 8 millimetres), they form a large part of the diet of larval fish. Many are parasites, and therefore carnivores, but most are herbivores.

Copepods have an exoskeleton (external skeleton). Their body is made up of several jointed segments, which each have a pair of legs. They also have a pair of short antennae and a pair of very long antennae. They use their legs to propel themselves through the water in short rapid jerks.

Crab larvae

Crabs have 2 juvenile (young) stages: the first is the zoea and the second is the megalops. We find these larvae in shallow coastal waters. 

The larvae need to find benthic (bottom) environments where they can settle and mature.

Larvae have displayed special movement responses to changing environments (such as salinity and tides). This may help them from getting scattered into the open ocean.

The reptania (crabs and lobster) in our samples include:

• aoea
• megalops
• munida squat lobster
• pelagic galatheid crab

Shrimp

There are 85 recorded species of shrimp found in British Columbia's waters, of which only 6 are commercially harvested.

These 6 species belong to the family of shrimp known as pandalidae, which is found worldwide. These 6 species are:

1. prawn
2. sidestripe
3. coonstripe
4. humpback
5. smooth pink
6. pink northern shrimp

Learn more about shrimp and prawn biology.

Mysids

Mysids look similar to shrimps and can be up to 3 centimetres (1.2 inches) in length. They can be found throughout the oceanic water column as well as in freshwater environments.

Mysids feed by:

• preying on other zooplankton
• scavenging (searching for and collecting discarded waste)
• grooming their body surface to collect small particles to eat

Marine mysids often are found in large swarms and are an important part of many fish diets. Mysids are also called 'opossum shrimp' because of the egg pouch on all mature females.

Ostracods

Ostracods are small crustaceans that are widely distributed in the sea and in fresh water. They look like bivalves (oysters or clams), but are only a few millimetres in length. They are sometimes called mussel or seed shrimps.

Their body is completely enclosed in a bivalve carapace (compressed body enclosed with a hinged shell). Most ostracods are bottom dwelling, but some are pelagic (living neither on the top nor bottom of the body of water).

Ostracods can be:

• carnivores (meat eaters)
• herbivores (non-meat eaters)
• scavengers (gathering waste)
• filter feeders (straining suspended matter and food particles from water)

We don't know much about the bivalve crustaceans in our area. Papers in 1930 and 1952 reported 35 species, mainly near Nanaimo, and 7 species from Puget Sound.

Amphipod

Amphipods are mostly marine (living in the ocean). They can be either benthic (living in low levels of the ocean) or pelagic (living in neither the top nor bottom of the ocean). However, there are some freshwater and land species.

Amphipods range in size from under 1 millimetre to 14 centimetres, with most of the ones we catch in the 10 to 15 millimetre length range.

Amphipods feed by:

• scavenging
• filtering water or sediment through their appendages
• consuming detritus (decomposing plant and animal parts as well as feces)

Some amphipods many supplement their diet by catching small animals, but strictly meat-eating feeding is uncommon.

Molluscs

Zooplankton molluscs common in the northeast Pacific Ocean include:

• pteropods
• squid and octopus larvae

Pteropod

Pteropods are known as:

• clione
• sea angel
• sea butterfly
• winged snails

They can reach a length of 12 millimetres (0.5 inches).

Pteropods are sea slugs, related to snails. We've found 2 members of this family in surface layers of the ocean. The limacina helicina have shells and feed on phytoplankton. Cleone limacina don't have shells and eat other sea butterflies.

Squid and octopus larvae

Cephalopods include squid and octopus. We only catch their larval forms in our nets. Larval forms range up to 4 centimetres (1.5 inches).

Squid have an internal shell or 'pen,' and octopi have no shell.

Octopi are usually found living on the bottom of the ocean, often in caves or between rocks. In British Columbia, there are 3 species of octopus, including:

• smoothskin octopus
• east Pacific red octopus
• giant Pacific octopus, which is commercially exploited (caught often for selling)

Octopus spawn (deposit eggs) in the fall, and the eggs hatch in the spring. Octopus larvae are planktonic (drifting free in the water) for about 2 months in the spring before settling on the bottom of the seafloor.

In British Columbia, we have 17 species of squid, 4 of which are commercially harvested. These include the:

1. red squid
2. nail squid
3. opal squid
4. flying squid

Squid live throughout the water column, actively feeding on other fish and invertebrates.

Mating occurs in February through August, and baby squid appear 3 months later. The babies remain near the surface of the ocean and feed on zooplankton until they reach a length of about 4 centimetres (1.5 inches). Then they move closer to the bottom.

Chordata

In the northeast Pacific Ocean, common zooplankton chordata include salp chain and fish larvae.

Salp chain

Individual salps are about 10 centimetres (4 inches) long. Salp chains can be up to 5 metres (15 feet) long.

Thaliaceans (salps) are a class of tunicates (marine invertebrate animals) that are specialized for a free-swimming, planktonic (drifting) existence. They pump water through their body for:

• feeding
• moving
• breathing

There are only 6 genera of salps and all are transparent (see-through).

Salps make a mucous film that runs along their body to their esophagus (mouth). This lets them feed on particles that the mucous film collects. Chains of salps feed near the surface.

A common salp predator is the sunfish, which is often seen in local waters and can be as long as 4 metres (13 inches).

Fish larvae

We catch various species of larval fish in our nets, but usually no bigger than about 4 centimetres (1.5 inches) long.

At different life stages, many animals pass through a planktonic (free-floating) form in their development. Icthyoplankton are larval fish that can be up to a few centimetres in length.

Arrow worm

Chaetognaths (arrow worms) are in a separate phylum by themselves. They're a totally carnivorous zooplankton and are known as:

• arrow worms
• glass worms
• tigers of the zooplankton

These meat-eaters catch large numbers of copepods, swallowing them whole. They're characterized by:

• bodies that are:
  • slender
  • transparent
  • torpedo-like in shape
• relatively large caudal fins
• anterior spines on either side of the mouth that help them grab and restrain prey

They're also reported to prey on early larval stages of fish, often attacking and consuming prey larger than themselves.

Chaetognaths alternate between swimming and floating. The fins along their body aren't used for swimming, but rather to help them float. They use the muscles that run the length of their body to dart forward.

Only 2 species are common in British Columbia waters, but some deep-water species may be collected in surface tows on occasion.

Polychaete

Polychaete worms, known as 'many bristles' worms, may reach more than 4 centimetres (1.5 inches) in length. They're a class of Annelids that are generally benthic (living at the bottom of the sea). However, species of 2 pelagic (free swimming) families occur in British Columbia coastal waters: tomopteridae and the typhloscolecidae.

Polychaetes have paddle-like appendages called parapodia on either side of their body that they use for swimming and burrowing. Polycheates vary in shape from sedentary tube worms to free-moving planktonic or benthic forms. They can feed either passively or actively.

Pelagic (free swimming) polycheates tend to be transparent to minimize the risk of being prey.

Sea gooseberry

Pleurobrachia bachei with a bell diameter of 20 millimetres and tentacle length of 160 millimetres.

Ctenophores are commonly called sea gooseberries or comb jellies. They're carnivorous ovoids (egg-shaped creatures) with 8 rows of cilia (comb-like swimming appendages around their circumference).

Their 2 contractile (able to become shorter) tentacles contain colloblasts that secrete a sticky substance which entangles the prey. However, they don't have stinging cells.

The tentacles then contract and pass food up to their mouth. Ctenophores may emit a bright green bioluminescence (glow) when disturbed.

Cnidarium

There are 4 different classes within the Cnidarium phylum:

1. Anthozoa (sea anemones and corals)
2. Hydrozoa(hydroids)
3. Scyphoza (jellyfish)
4. Cubozoa (box jellyfish)

Cnidarians have 2 different phases of life: the medusa stage (the 'jellyfish' form, with separate sexes) and the polyp stage (like sea anemones, with combined sexes).

Different classes of cnidarians spend different proportions of their lives in the medusa and/or polyp stages. But sexual reproduction can only occur in the medusa stage. Asexual reproduction can occur by 'budding' or 'dividing' of the polyp stage.

Scyphozans and Cubozoans commonly exist in the medusa phase, whereas Hydrozoans spend about half their time in the medusa phase. Anthozoans don't have a medusa stage. Ctenophones are similar to jellyfish, except that they don't have nematocysts.

A sea anemone found in British Columbia, Anthopleura xanthogrammica.

Nematocysts

All cnidarians have nematocysts (stinging cells) located on their tentacles. When something, such as prey, touches a tentacle, thousands of nematocysts 'fire' towards the object in an attempt to stun and retain it.

There are 3 types of nematocysts:

1. a coiled thread that can entangle prey
2. a barb that can inject toxins into prey
3. a sticky thread that will hold onto prey

Most species of jellyfish and anemones have nematocysts that won't harm humans. If you touch the tentacles of a sea anemone with your finger you'll feel a sticky sensation, which is the nematocysts attempting to hold onto you.

A few species of jellyfish are highly toxic to humans, such as the local cyanea capillata and the well-known Portuguese man-of-war.