Transcript Phytoplankton 9 Oct 2001

Phytoplankton
• Announcements:
– Exam: next Wednesday
– Review Tuesday pm at Olin O4 (here?!)
Two nearby lakes are similar in area and
productivity, but one experiences winterkills, and
the other does not. Why?
• Concentrations same,
volume different
• Same productivity ~~ same
decomposition (O2 demand)
• Little to no photosynthesis
(why?)
• Not really strong stratification
under ice (why?)
Explain why Lake Washington's watershed, morphology and
flushing rate influenced recovery from nutrient loading. WHY are
these characteristics important?
Under what conditions (lake characteristics) would simply reducing
P-inputs not work? Why not?
Lake Washington
Doesn’t work when…
Deep basin that never went anoxic so little
to know internal loading (P buried in
sediments; how?)
Forested and urban water (little non-point
sources of P; why?)
Low WRT (after sewage was diverted, Pladen water quickly washed out)
Hypolimnion goes anoxic, resulting in lots
of internal loading of P (how does this
work?)
Non-point sources of P persist (like what?)
Organisms
• Plankton: organisms that weakly swim or go where the
water takes them
• Phytoplankton
• Periphyton: benthic algae
• Epiphyton: algae growing on macrophytes
Phytoplankton taxonomy
• Was once based on morphology or pigments, now more
molecular. See Graham and Wilcox 2000 Algae for more information.
• Usually grouped in Divisions (VARIABLE!)
• Also often grouped by
– Size
– Mobility (motility)
• Flagella: movable filament that can be used to propel organism through the
water
• Gas vacuoles
Phytoplankton groupings, con't
– Origin:
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Periphyton (benthic)
Tychoplankton (detach from benthos)
Meroplankton (part of life on sediments)
Euplankton/holoplankton (entire life in water column)
Potomoplankton (resuspended algae in lotic systems)
Phytoplankton Taxonomy (Divisions)
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Cyanophyta - cyanobacteria
Chlorophyta - green algae
Euglenophyta - single flagella
Bacillariophyta - diatoms
Chrysophyta - golden brown algae
Cryptophyta - flagellated
Pyrophyta - dinoflagellates
Cyanobacteria
~1,350 species
• Prokaryotes: lack plastids and distinct membrane
bound nucleus
• Photosynthesize functionally like plants
• Chloroplasts of other algae and plants originated from
cyanobacteria through endosymbiosis
Cyanobacteria, con't
Often dominant, esp. eutrophic
lakes
– Some species fix N
(heterocysts)
– Large cyanobacteria often
dominate due to
disproportionate losses of
other species
– Allelopathy (toxic or inhibitory
effects on other species)
Anabaena 400x
• Buoyant (gas vacuoles)
heterocysts
Cyanobacteria, con't
• Resting stages:
• thick-walled resting cells (cysts)
called akinetes (Anabaena &
Aphanizomenon)
• Vegetative resting stage
(Mycrocystis)
• linkage between benthos and
pelagic
Chlorophyta: Green algae
~2,400 species
• Eukaryotes
• Includes unicellular flagellated and nonflagellated cells,
colonies and filaments and macroalgae (Chara)
• Represent 40-60% species with high biomass
contribution in eutrophic and hypereutrophic lakes
• Often dominate benthic algae
Spirogyra 200x
Volvox
Cladophora 40x
Chlorophyta
Chlamydomonas 400x
Hydrodictyon 40x
Chlorophyta
Scenedesmus 600x
Assorted desmids
Euglenophyta
~1,020 species
• Small to medium sized
flagellated species
• Often abundant in well-mixed
eutrophic ponds and littoral
areas
Euglena
www.mib.uga.edu/.../mibo3000/ eukaryotic/01232001.html
bio.rutgers.edu/euglena/ mainpage.htm
Bacillariophyta - diatoms
~5,000 species
• Wide range in size: 2um - 2mm
• Require silica (Si) to build frustules
• abundant during mixing when Si abundant
• when lake stratifies, diatoms sink to bottom & remove Si from epilimnion
• Heavy & no flagella: sink after stratification & form
resting stage on sediments: viable after 100's years
• Two groups:
– pennate: bilaterally symmetrical
– centric: radially symmetrical
Diatoms
www.mib.uga.edu/.../mibo3000/ eukaryotic/diatoms.jpg
www.cnas.smsu.edu/labimages/ Biology/Bio122/week1.htm
Chrysophyta
• Small single-celled
flagellates and flagellated
colonies
• Common in oligotrophic clear
lakes and humic lakes
• Often codominate with
cryptophytes
• Diatoms are often grouped
under chrysophyta
~450 species
Synura, http://microbes.limnology.wisc.edu/outreach/majorgroups.php
Cryptophyta
• Small or medium-sized
flagellates
• Common in oligotrophic
lakes
• Single-cell cryptophytes,
chrysophytes, dinoflagellates
main food of rotifers and
crustacean zooplankton (next
week!)
• Mixotrophic (more than one
more of nutrition): eat
bacteria & smallest algae
~100 species
http://protist.i.hosei.ac.jp/taxonomy/Phytomastigophora/Cryptophyta/Cryptomonadaceae.html
Pyrophyta - dinoflagellates ~ 220 species
• Motile (flagellates)
• Have resting cysts
• Some do not have
chlorophyll
• Red tide in the ocean Peridinium
Ceratium
www.cnas.smsu.edu/labimages/ Biology/Bio122/week1.htm
Size
influences
- growth rate
- energy paths (consumption)
- sinking time
Size
E Daphnia head
(e - eye) (large zooplankton)
A bacterium
• Picoplankton (0.2-2 m dia)
• Nanoplankton (2-30 m dia)
• Microplankton (30-200 m
dia)
• < 30 m = edible algae
C Scenedesmus (green)
B Cryptomonas (Cryptomonad)
D Keratella (small zooplankton)
Influences of size
• Pico- and nanoplankton: high rates of production
• Large surface to volume ratio (exchange of nutrients)
• Very slow sinking rates
• Nanoplankton are tasty
• Microplankton
• Sink faster
• Grow slower
• Not tasty
Extracellular release of organic compounds
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Represent a significant loss of fixed C (<20%)
Multiple functions:
– modify growth & behavior
– e.g., fischerellin released by cyanobacteria; inhibits photosynthesis by
algae
Release of metabolic intermediates of low molecular weight by diffusion
(glycolic acid, organic acids, organic phosphates, peptides…)
Release of metabolic end products of high molecular weight more deliberate
(?)
(carbohydrates, peptides, volitile compounds, growth-promoting and
growth-inhibiting compounds)
Bacteria rapidly utilize LMW compounds
Photosynthesis
• Photosynthesis= fixing carbon
nCO2 + nH2O ------> (CH2O)n + nO2
(n=# molecules)
• Change in population biomass = growth - consumption sinking
• Growth=photosynthesis
Compensation point
• Compensation point:
photosynthesis = respiration
• Maximize the amount of time spent above the
compensation point (in the light)
Ways to stay in light
• Mixing
• sink slow enough to stay in mixed epilimnion
• Mobility
• flagella
• gas vacuoles
• Change sinking rate
• change shape or density
modifications
Muscilaginous cover around Staurastrum species (green)
- reduce sinking (to a point)
- reduce consumption (or digestion)
Photosynthesis rate (mg C)
Effects of light & temperature on
photosynthesis
Light
Limited
(photochemical
rxns)
Light
Saturated
(enzymatic
rxns limited
by temp)
Available light
Maximum
photosynthesis
Photoinhibited
Biomass
Photosynthesis
Photosynthesis distribution=
specific primary production * light
climate * algae biomass
Mesotrophic epilimnion (well mixed)
Depth
Eutrophic with surface bloom
Oligotrophic with max. biomass at
metalimnion
Shallow transparent lakes with max.
biomass on bottom
Depth distribution of photosynthesis
Trophogenic zone ~
euphotic zone
Note that phytoplankton on the surface of
hypereutrophic lakes shade out the
water column
Horizontal distribution
• Wind & currents
Langmuir spirals
Foam, buoyant algae
surface algae
deep
algae
Neg. buoyant
algae
Lake Mendota cyanobacteria blooms
Horizontal distribution
Proximity to littoral zone often
results in less phytoplankton
– Must compete for nutrients
with periphytic algae and other
microorganisms attached to
macrophytes and sediments
– Macrophytes are refuge for
herbivorous zooplankton
Factors influencing seasonal
distribution
Physical
• Temperature
• Light
Limiting nutrients
• silica
• nitrogen
• phosphorus
Biological
• competition
• resources, sinking
Biological
• grazing
• parasitism
Seasonal distribution in a temperate, dimictic lake
(green)
(diatoms)
1. Light limited: small, often motile (but productive)
2. Light increasing,still ice cover, no mixing (dynoflagellates can
swim up towards light)
3. Spring mixing: high nutrients, low grazing, increasing
light, diatoms dominate
4. Initial stratification: diatoms settle & die, loss of Si to <
0.5 mg/L
5. Clearwater phase: high light availability, warm
temperatures, but many herbivores and reduction of
nutrients leads to population crashes
6. Mid-summer stratification: Cyanobacteria dominate (fix
N, migrate between nutrient-rich lower depths &
epilimnion)
7. Fall mixing: high nutrients, less light, diatoms dominate
again with increases in Si
8. Late autumn decline
The plankton