Diversity of Aquatic Organisms Phytoplankton & Phytoplankton Ecology Part 3

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Diversity of Aquatic OrganismsPhytoplanktonPh
ytoplankton Ecology Part 3
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Green Algae (Chlorophyta)

• Desmids
• Form rigid Semi-cells often arranged like a
  snowflake

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Green Algae (Chlorophyta)

• Filamentous green algae can often be identified
  by the shape of the chloroplast
• Spirogyra
• spiral chloroplast
• Mougeotia
• ribbon chlorplast
• Zygnema
• star chloroplast
• Characteristics of filamentous greens
• Form slimy masses on ponds, river pools
• Store starch in the chloroplast
• Cell walls contain cellulose

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Cryptophytes (Cryptophyta)

• Characteristics
• Large cells (10-30 um)
• 2 flagellae of unequal lengths
• Eukaryotic
• Chlorophyll a, b, and c
• May contain phycobilins
• Always unicellular
• Often motile
• Common in Laurentian Great Lakes

www.biol.tsukuba.ac.jp/inouye/ino/cr/Cryptomonas2
.GIF
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Dinoflagellates (Pyrrophyta)

• Characteristics
• Large cells
• Eukaryotic
• Usually flagellated
• Chlorophyll a and c
• Cells may be armored
• May be heterotrophic
• Can cause Red Tides on ocean coasts
• May exhibit cyclomorphosis

www.bio.mtu.edu/the_wall/phycodisc/DINOPHYTA/gfx/C
ERATIUM.jpg
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Golden-Brown Algae (Chrysophyta)

• Characteristics
• Eukaryotic
• Chlorophyll a and b,
• High concentration of carotenoids
• Tolerant of low P concentrations
• May compensate for low P by switching to
  heterotrophy

Dinobryon
Mallomonas
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Diatoms (Bacillariophyta)

• Characteristics
• Eukaryotic
• Unicellular or colonial
• Chlorophyll a and c
• Contain beta-carotene and fucoxanthin pigments
• External covering of SiO2
• Large requirement for S
• Usually require vitamin B12
• Two major groups
• Centrics radial symmetry
• Pennates bilateral symmetry

Asterionella
Tabellaria
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Diatoms (Bacillariophyta)
Centric Diatoms
microbes.limnology.wisc.edu/outreach/images
protist.i.hosei.ac.jp/pdb/Images/Heterokontophyta/
Centrales/Cyclotella/Cyclotella.jpg
Pennate Diatoms
www.ansp.org/research/pcer/images/Eucocconeis
dr-ralf-wagner.de/Bilder/Surirella
plantphys.info/organismal/lechtml/images/navicula.
jpg
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Diatom Art
www.nature.ca/research/images/diatom_art.jpg thala
ssa.gso.uri.edu/flora/imagesfl/ansp4.jpg
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Euglenoids (Euglenophyta)

• Characteristics
• Eukaryotic
• No sexual reproduction
• Chlorophyll a and b
• Require vitamins B12
• Flagellated and very motile
• May be heterotrophic
• Thrive in polluted water
• Respond to light with red eye-spot

http//tbn0.google.com/images?qtbnfI400rN1fWCHSM
http//www.infovisual.info/02/img_en/0012520Stru
cture2520of2520a2520euglena.jpg
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Red algae (Rhodophyta)

• Bangia
• Invading littoral zones of Great Lakes

www.marietta.edu/biol/biomes/images/competition/2
algae.jpg
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Phytoplankton Ecology

• To survive, phytoplankton must maintain
  photosynthesis to sustain carbon-fixation at
  rates greater than respiratory costs. (PgtR)
• Below a certain depth, there will be insufficient
  light for growth (PltR)
• Compensation depth, where PR (about 1 surface
  light)
• Phytoplankton are heavier than water, so they
  sink.
• Density of cellular components
• Proteins 1.3 g cm-3 Carbohydrates 1.5 g cm-3
• Nucleic acids 1.7 g cm-3 SiO2 (diatom walls)
  2.6
• Lipids 0.86
• Phytoplankton density 0.999 - 1.26 g cm-3
• Therefore, one of the greatest challenges for
  phytoplankton is to remain in suspension

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Mechanisms to Reduce Sinking

• Small particles in water follow Stokes Law
• Vs 2 gr2 (?1-?) / 9? (Ør) Vs terminal
  sinking velocity of a sphere
• g acceleration of gravity
• r radius
• ? viscosity
• (?1-?) excess density (density of cell -
  density of water)
• (Ør) coefficient of form resistance
• How can phytoplankton reduce their sinking
  velocity?
• Reduce radius (but this reduces cell volume)
• Increase form resistance (elongation, spines,
  colony formation)

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• How can phytoplankton reduce their sinking
  velocity?
• Reduce radius (but this reduces cell volume)
• Increase form resistance (elongation, spines,
  colony formation)
• Reduce density
• Accumulate lipids (2-20 algal dry weight)
• Mucilage secretion (decreases density, but
  increases radius)
• Gas vacuoles (in cyanobacteria)

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Patterns in Phytoplankton Community Composition
and Abundance

• It is very difficult to predict which species of
  phytoplankton will be dominant in any given lake
  at any given time, but certain patterns are
  common.
• As algal biomass increases (or TP), cyanobacteria
  become more dominant
• Mesotrophic conditions favor diatoms
• Oligotrophic conditions favor diatoms,
  chrysophytes and Cryptophytes

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• In dimictic temperate zone lakes, phytoplankton
  community and biomass typically follow a seasonal
  pattern.
• Mid-winter
• Low biomass because very low light (snow-covered
  ice, short days)
• Late-winter
• Increasing biomass of dinoflagellates
  (increasing light, calm water)
• Spring circulation
• Increasing light, high nutrients, cold
  temperature, continuous mixing, low grazing
• Early summer stratification
• Increasing temperature in epilimnion, some
  grazing, Silica limitation
• Clearwater phase
• High sinking rate, low nutrients, high grazing

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• Late summer stratification
• Decreased grazing, low but increasing nutrients,
  sometimes low nitrogen
• Fall Circulation
• Conditions similar to spring circulation

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Spatial Patterns in Phytoplankton production
Commonly observed patterns in reservoirs related
to a gradient of environmental conditions from
riverine to lacustrine (lake).
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Resource Competition

• Laboratory cultures can be used to determine
  rates of nutrient uptake among phytoplankton
  species.
• Uptake rates can be used to predict winners and
  losers in competition for a specific resource.

Growth curves for species A and B in competition
for resource R
D Death rate Population growth rate growth
rate - D RA Equilibrium resource
concentration for Species A RB Equilibrium
resource concentration for Species B
R concentration of resource (e.g. P, Si, N, etc)
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In this culture, species A will grow faster and
dominate if the nutrient is continually
replenished. If the concentration of nutrient is
allowed to drop to low levels, Species A will
disappear and eventually only species B will
remain.
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What happens if two species of phytoplantkon are
competing for two nutrients?
Example Two diatom species (Asterionella and
Cyclotella) compete for both phosphorus and Silica
Asterionella is the superior competitor for P
But Cyclotella is the superior competitor for Si
How will this competition play out?
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• Plot P and Si concentration on the x and y axis
  and note the equilibrium concentrations for both
  species
• Then, draw lines extending from the Si and P
  concentrations and fill in the boxes with the
  species that can exist under those nutrient
  conditions

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If both nutrients are continually supplied at the
proper ratio, both diatoms can coexist. If Si
and P concentrations are allowed to decline, one
of the species is likely to disappear. Who wins
depends on the Initial nutrient ratio. Who wins
in nature will depend on the supply ratio of the
nutrients