Dept of Biology, Lewis and Clark College | Dr Kenneth Clifton
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Biology
221 Lecture Outline
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An introduction to life in the sea: one important set of "little stuff": microbes, phytoplankton and zooplankton
Why are microorganisms important?
Very abundant
Primary producers
Nitrogen fixation
Who are we talking about? Among the "Monera" or Prokaryotes:
In the Eukaryotes: Protista (phytoplankton and protozoans)
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Five Kingdoms Three Kingdoms |
Recent attempts to census the diversity of microbial populations in the oceans reveals an amazing diversity and abundance of life
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 webs:
Thus, their location in time and space determines the distribution and abundance of many other creatures.
Defining "plankton" in terms of:
Energy sourcePhytoplankton are photosynthetic protists and plantsZooplankton 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 surfacePleuston are plankton that are at (some cyanobacterial mats), or even extend above (like some siphonophores), the water's surface
Size
Picoplankton (< 2 µm)Ultraplankton (2 - 5 µm)
Nanoplankton (5 - 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.
Phytoplankton require the sun's energy for photosynthesisZooplankton 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 organic compounds like lipids (note: 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 (be sure to check out the cool images in your text)
Diatoms: (Phylum Bacillariophyta)
Dominant in temperate and polar watersSilica 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 areasthey 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 commonCalcium 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:
CopepodsKrill
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)
An indicator species for acidification effects
Factors that bring plankton together or spread them apart
Physical properties that plankton detect (e.g. light, temperature, salinity)
Water currents and turbulence
Langmuir circulationEddies
Other currents
Consumption by predators
Reproduction
Aggregating behaviors
Vertical migration by zooplankton
Hypotheses
Light
Feeding on phytoplankton
Predator avoidance
Energy conservation
Surface mixing