Plankton What is Plankton?

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What is Plankton?

  • Animals and plants that either float passively in the water, or possess such limited powers of swimming that they are carried from place to place by the currents.

Where does the word “plankton” come from?

  • The word plankton comes from the Greek word planktos, which means ‘wandering’ or ‘drifting’.

Where are plankton found?

  • Plankton dominates the well-lit surface layers of the world's oceans.

Types of Plankton

  • Phytoplankton- microscopic plants and bacteria.

  • Zooplankton- microscopic animals


  • Carry out photosynthesis.

  • Produce 80% of the Earth’s oxygen and 75-80% of the organic matter.

  • Why must they live in the photic zone?

  • Can undergo rapid population growth or “algae blooms” when water temperatures rise in the presence of excess nutrients.

  • During a bloom most phytoplankton dies, sinks to bottom and decomposes.

  • This depletes the bottom waters of dissolved oxygen which is necessary for the survival of other organisms.

Plankton Bloom


Impact of Ozone on Phytoplankton

  • Produce more oxygen than all plant life on earth and are vital in maintaining the earth’s atmosphere.

  • They are also the organisms most likely to be affected by global warming and climate change.

  • Scientists around the world are concerned that harmful rays from the sun could pass through the hole in the ozone layer and kill phytoplankton, which live mostly in the upper layers of the ocean.


  • Single-celled yellow green algae.

  • Have a cell wall.

  • Cell wall contains silica, a glass-like substance.

  • Come in lots of shapes and sizes

  • Intricate lines and etchings

  • Word “diatom” means cut in two because its cell wall is made of 2 parts one fitting over the other.


  • Probably the single most important food source in the ocean!!!!

  • YUMMMY!!!

  • Eaten by small plankton and by larger oysters and clams.


  • Propel themselves using 2 flagella

  • Can swim like simple animals

  • Photosynthesize like plants

2 Species: Gonyaulax & Gymnodinium responsible for Red tides

What is a Red Tide?

  • Plankton-rich water.

  • Responsible for fish mortality and paralytic shellfish poisoning.


  • Floating or weakly swimming animals that rely on water currents to move any great distance.

    • Microzooplankton (< 200 microns) in size
    • Mesozooplankton (200 microns- 2 mm)
    • Macrozooplankton (> 2 mm)

Classified according to size

  • Smallest  Largest

  • Nannoplankton (Ex. Protozoans)

  • Microplankton (Ex. Primarily eggs and larvae, usually of invertebrates).

  • Macroplankton (Ex. Copepods)

  • Megaplankton (Ex. Portuguese Man of War)


  • Zooplankton are the favorite food of a great many marine animals so camouflaging themselves is a very important survival strategy.

  • Developing effective camouflage when you live in clear, blue water is no easy matter.

  • The best solution and the one most often used by members of the zooplankton is to be as transparent as possible or, in the case of many surface floating jellyfishes, blue.

There are two major types of zooplankton:

  • 1) Those that spend their entire lives as part of the plankton (called HOLOPLANKTON)

  • 2)Those that only spend a larval or reproductive stage as part of the plankton (called MEROPLANKTON).


  • Blue Sea Slug

  • Adapted for life floating upside down in the sea and is often found with the beautiful blue jellyfish Porpita.

  • Blue Sea Slugs feed almost exclusively on the tentacles of 'Bluebottles'.

  • Interestingly, the nematocysts (stinging cells) on these tentacles pass through the Blue Sea Slug intact. The slug can then use these stinging cells in its own defense.


Polychaete Worm or bristle worm.

Portuguese Man of War


  • Meroplankton spend only the larval or early stages of their life as part of the plankton and spend their adult lives on the reef.


  • Many meroplankton bear little resemblance to the adults that they will become.


  • While living in the plankton, meroplankton either feed on other members of the plankton, or they live off the yolk they have retained from the egg they hatched from.


  • Larvae spend varying amounts of time in the plankton, from minutes to over a year.

  • However, just how long these tiny animals can be considered truly planktonic is under some debate.

Meroplankton- Examples

  • Lobster Larvae

Lobster Larvae

Anemone Larva & Adult

Sea Cucumber Larva & Adult

Brittle Star Larvae & Adult

Cone Shell Larvae & Adult

Octopus Larvae & Adult

Starfish Larvae & Adult


  • Meroplankton that sinks to the bottom of the ocean and lives there is called BENTHOS.

  • Nearly 16% of all animal species are benthic.

There are 3 types:

  • INFAUNA- animals that live in the bottom like clams and worms

  • EPIFAUNA- animals on the bottom surface like crabs, coral and starfish

  • EPIFLORA- plants that live on the bottom.


  • Not plankton

  • Swim

  • Ex. Invertebrates & vertebrates

  • (Squid) (Whales)

How long are they larvae?

  • Larvae spend varying amounts of time in the plankton, from minutes to over a year.

  • However, just how long these tiny animals can be considered truly planktonic is under some debate.

  • Scientists in recent years have discovered that many of these tiny animals in the plankton quickly become very good swimmers capable of incredible speed and endurance.

Marine Protozoa

  • Protozoan = one celled organism.

  • Usually microscopic

  • Most live in water

  • Some are plankton, others benthic

  • Three groups: Sarcodinians, ciliates, flagellates.


  • Word “sarcodina” means creeping flesh.

  • Describes how they move.

  • Contract and expand projections of their bodies called pseudopodia or “false feet.”

  • 2 groups: forams & radiolarians

Facts about Forams

  • Shell made of Calcium carbonate.

  • Pseudopodia project out through holes in shell.

  • Feed on diatoms & other protozoans.

  • Secrete digestive juices onto their food to dissolve it!!!

  • Waste expelled through body surface.


  • Planktonic

  • Large amount of

  • these shells have

  • been deposited

  • in sediment.

  • Studied to reveal information about climate in past geological eras.

Archaias angulatus

  • Turtle grass foram

Archaias compressus

  • Button foram


  • Mostly planktonic

  • Perforated outer skeleton of silica.

  • Pseudopodia extend through holes as long, sticky filaments.

  • Skeleton does NOT dissolve at great depths like the Forams.


Radiolarian Art


  • Covered with hair like cilia

  • Cilia used in eating, locomotion, respiration.

  • Most are solitary and free swimming.

  • Some are attached and colonial.

  • Common among sand grains (eat plant cells and bacteria!)



  • Bell animals

  • Planktonic ciliates

  • Common in open ocean

  • Ring of cilia surround mouth (locomotion & catching food).

  • Hard shell of protein.

Phylum Mastigophora

  • Flagellates

  • Propelled by a flagella

  • Whip like

  • The most abundant members of the zooplankton, both in species and total numbers are the crustaceans.

  • Crustaceans include lobsters, crabs, prawns, pill bugs, krill, barnacles, water fleas, brine shrimp (sea monkeys) and copepods.

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