An introduction to life in the sea: one important set of "little stuff": the phytoplankton

Why are microorganisms important?

Very abundant

Primary producers

Nitrogen fixation

 

Who are we talking about?

Bacteria

Heterotrophs (mostly decomposers)

Autotrophs: photosynthesis and chemosynthesis

Cyanobacteria (formerly "blue-green algae)

 

Archaea

More decomposers: methane producers

Hydrothermal vent populations

Unicellular algae: an essential component of "the plankton"

Plankton are "drifters"

basically too small to swim against the ocean's currents (though local movements over shorter distances are possible.... many can swim).

"Plankton" it is a very general term that encompasses a wide variety of organisms... from microscopic plants and animals up to colonial siphonophores a third of a meter across.

Plankton are a central feature of life in the oceans, forming the base of virturally all food chains:

Thus, their location in time and space determines the distribution and abundance of many other creatures.

Defining "plankton" in terms of:

Energy source

Phytoplankton are photosynthetic protists and plants

Zooplankton are planktonic animals that consume phytoplankton or other zooplankton

Mixoplankton can photosynthesize and consume other plankton (some protists)

Life History

Holoplankton spend their entire lives drifting in the open sea.

Meroplankton: planktonic early life-history, then benthic as an adult (many multi-cellular organisms)

Location

Neuston are plankton associated with the surface

Pleuston are plankton that extend above the water's surface (like some siphonophores)

Size

Ultraplankton (< 2 µm)

Nanoplankton (2 - 20 µm)

Microplankton (20-200 µm)

Macroplankton (200-2,000 µm)

Megaplankton (> 2,000 µm)

Keeping close to the surface is critically important for plankton (see p. 77 in text).

Phytoplankton require the sun's energy for photosynthesis

Zooplankton need phytoplankton and other zooplankton to eat

 

Ways that plankton can avoid sinking below the surface

Active processes: (dead material typically sinks must faster than living)

Reduced density: gas, lighter ionic compound (lift from buoyancy diminishes with depth)

 

Swimming: very small plankton can't, but microplankton and larger can: have to know which way is up

 

High surface area to volume ratios (lots of drag): lots of elaborate structures that probably help

 

Water turbulence tends to re-suspend plankton

 

Some important types of phytoplankton

 

Diatoms: (Phylum Bacillariophyta)

Dominant in temperate and polar waters

Silica case or shell (frustule) looks like a "pill box"

Found singly or in chains

Planktonic forms are radially symmetrical

Can reproduce very quickly, up to 6x/day via asexual reproduction (also have sexual reproduction)

 

Dinoflagellates (Phylum Dinoflagellata or Pyrrhophyta)

Dominant in tropical and subtropical waters.... also summer in temperate areas

they have two flagella and a shell of cellulose plates (called theca)

Asexual reproduction and fast population growth can lead to "red tides"

They secrete a neurotoxin called saxitoxin: bioaccumulates in shell fish and other filter feeders... can be fatal

Zooxanthellae are dinoflagellates: more when we talk about cniderians (corals).

 

Coccolithophores (Haptophyta)

Tropical... often very common

Calcium carbonate shells or "tests"

Their skeletons make important depositional structures, but "naked" forms are not preserved

 

Silicoflagellates (Chrysophyta)

Biflagellated, silica internal skeleton... found world wide, particularly in Antarctic

 

Green Algae (Chlorophyta)

Not common except in lagoons and estuaries... often associated with coastal pollution

 

Cryptomonad Flagellates (Chryptophyta)

have chlorophyll a and c... adapted for turbid waters

Protozoans

Some important types of protistan plankton

Ciliates (Ciliophora)

Foraminifera (Foraminifera)

Radiolaria (Polycystina)

Plankton patches and "blooms"

Some important types of multicellular zooplankton

 

Crustaceans:

Copepods

Krill

Cladocera

Mysids

Ostracods

 

Jellies

Coelenterates (True jellies, Man-of-wars, By-the-wind-sailors)

Ctenophores (comb jellies)

Urochordates (salps and larvacea)

 

Worms (Arrow worms, polychaetes)

 

Pteropods (planktonic snails)

 

Factors that bring plankton together or spread them apart

Physical properties that plankton detect (e.g. light, temperature, salinity)

 

Water currents and turbulence

Langmuir circulation

Eddies

Other currents

Consumption by predators

Reproduction

Aggregating behaviors

Vertical migration by zooplankton

Hypotheses

Light

Feeding on phytoplankton

Predator avoidance

Energy conservation

Surface mixing