Diversity of Aquatic Diversity of Aquatic OrganismsOrganisms

PhytoplanktonPhytoplankton&&

Phytoplankton Ecology Phytoplankton Ecology

Part 3Part 3

DesmidsDesmids Form rigid Semi-cells often Form rigid Semi-cells often

arranged like a snowflakearranged like a snowflake

Green Algae (Chlorophyta)Green Algae (Chlorophyta)

Filamentous green algae can often be Filamentous green algae can often be identified by the shape of the identified by the shape of the chloroplastchloroplast

SpirogyraSpirogyra • spiral chloroplastspiral chloroplast

MougeotiaMougeotia• ribbon chlorplastribbon chlorplast

ZygnemaZygnema • star chloroplaststar chloroplast

Characteristics of filamentous greensCharacteristics of filamentous greens• Form slimy masses on ponds, river Form slimy masses on ponds, river

poolspools• Store starch in the chloroplastStore starch in the chloroplast• Cell walls contain celluloseCell walls contain cellulose

Green Algae (Chlorophyta)Green Algae (Chlorophyta)

CharacteristicsCharacteristics• Large cells Large cells (10-30 um)(10-30 um)

• 2 flagellae of unequal lengths2 flagellae of unequal lengths• EukaryoticEukaryotic• Chlorophyll a, b, and cChlorophyll a, b, and c• May contain phycobilinsMay contain phycobilins• Always unicellularAlways unicellular• Often motileOften motile• Common in Laurentian Great Common in Laurentian Great

LakesLakes

Cryptophytes (Cryptophyta)Cryptophytes (Cryptophyta)

www.biol.tsukuba.ac.jp/~inouye/ino/cr/Cryptomonas2.GIF

CharacteristicsCharacteristics• Large cellsLarge cells• EukaryoticEukaryotic• Usually flagellatedUsually flagellated• Chlorophyll a and cChlorophyll a and c• Cells may be armoredCells may be armored• May be heterotrophicMay be heterotrophic

Can cause ‘Red Tides’ Can cause ‘Red Tides’ on ocean coastson ocean coasts

May exhibit May exhibit cyclomorphosiscyclomorphosis

Dinoflagellates (Pyrrophyta)Dinoflagellates (Pyrrophyta)

www.bio.mtu.edu/the_wall/phycodisc/DINOPHYTA/gfx/CERATIUM.jpg

CharacteristicsCharacteristics EukaryoticEukaryotic Chlorophyll Chlorophyll aa and and b, b, High concentration of High concentration of

carotenoids carotenoids Tolerant of low P Tolerant of low P

concentrationsconcentrations May compensate for low P by May compensate for low P by

switching to heterotrophyswitching to heterotrophy

Golden-Brown Algae (Chrysophyta)Golden-Brown Algae (Chrysophyta)

DinobryonMallomonas

CharacteristicsCharacteristics• EukaryoticEukaryotic• Unicellular or colonialUnicellular or colonial• Chlorophyll a and cChlorophyll a and c• Contain beta-carotene and Contain beta-carotene and

fucoxanthin pigmentsfucoxanthin pigments• External covering of SiOExternal covering of SiO22

Large requirement for SLarge requirement for S

• Usually require vitamin BUsually require vitamin B1212

Two major groupsTwo major groups Centrics – radial symmetryCentrics – radial symmetry Pennates – bilateral Pennates – bilateral

symmetrysymmetry

Diatoms (Bacillariophyta)Diatoms (Bacillariophyta)

Asterionella

Tabellaria

Diatoms (Bacillariophyta)Diatoms (Bacillariophyta)

protist.i.hosei.ac.jp/pdb/Images/Heterokontophyta/Centrales/Cyclotella/Cyclotella.jpg

microbes.limnology.wisc.edu/outreach/images

dr-ralf-wagner.de/Bilder/Surirella plantphys.info/organismal/lechtml/images/navicula.jpg www.ansp.org/research/pcer/images/Eucocconeis

Centric Diatoms

Pennate Diatoms

www.nature.ca/research/images/diatom_art.jpgthalassa.gso.uri.edu/flora/imagesfl/ansp4.jpg

Diatom ArtDiatom Art

CharacteristicsCharacteristics• EukaryoticEukaryotic• No sexual reproductionNo sexual reproduction• Chlorophyll Chlorophyll aa and and bb• Require vitamins BRequire vitamins B1212

• Flagellated and very motileFlagellated and very motile• May be heterotrophicMay be heterotrophic• Thrive in polluted waterThrive in polluted water• Respond to light with red eye-spotRespond to light with red eye-spot

Euglenoids (Euglenophyta)Euglenoids (Euglenophyta)

http://tbn0.google.com/images?q=tbn:fI400rN1fWCHSM:http://www.infovisual.info/02/img_en/001%2520Structure%2520of%2520a%2520euglena.jpg

Red algae (Rhodophyta)Red algae (Rhodophyta)

•Bangia•Invading littoral zones of Great Lakes

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

Phytoplankton EcologyPhytoplankton Ecology To survive, phytoplankton must maintain To survive, phytoplankton must maintain

photosynthesis to sustain carbon-fixation at rates photosynthesis to sustain carbon-fixation at rates greater than respiratory costs. (P>R) greater than respiratory costs. (P>R)

Below a certain depth, there will be insufficient light for Below a certain depth, there will be insufficient light for growth (P<R)growth (P<R)

• Compensation depth, where P=R (about 1% surface light)Compensation depth, where P=R (about 1% surface light) Phytoplankton are heavier than water, so they Phytoplankton are heavier than water, so they sinksink..

• Density of cellular componentsDensity of cellular components Proteins ~1.3 g cmProteins ~1.3 g cm-3-3 Carbohydrates ~1.5 g cmCarbohydrates ~1.5 g cm-3-3

Nucleic acids ~1.7 g cmNucleic acids ~1.7 g cm-3-3 SiOSiO22 (diatom walls) ~2.6 (diatom walls) ~2.6 Lipids ~0.86Lipids ~0.86 Phytoplankton density 0.999 - 1.26 g cmPhytoplankton density 0.999 - 1.26 g cm-3-3

Therefore, one of the greatest challenges for Therefore, one of the greatest challenges for phytoplankton is to remain in suspensionphytoplankton is to remain in suspension

Mechanisms to Reduce SinkingMechanisms to Reduce Sinking Small particles in water follow Small particles in water follow Stoke’s LawStoke’s Law

VVss = 2 gr= 2 gr22 ( (11--) / [9) / [9 (Ø (Ørr)])] VVss = terminal sinking velocity of a sphere = terminal sinking velocity of a sphere

g = acceleration of gravityg = acceleration of gravityr = radius r = radius = viscosity= viscosity((11--) = excess density (density of ) = excess density (density of

cell - density cell - density of water)of water)

(Ø(Ørr) = coefficient of form resistance ) = coefficient of form resistance

How can phytoplankton reduce their sinking velocity?How can phytoplankton reduce their sinking velocity?• Reduce radius (but this reduces cell volume)Reduce radius (but this reduces cell volume)• Increase form resistance (elongation, spines, colony formation)Increase form resistance (elongation, spines, colony formation)

How can phytoplankton reduce their sinking velocity?How can phytoplankton reduce their sinking velocity?• Reduce radius (but this reduces cell volume)Reduce radius (but this reduces cell volume)• Increase form resistance (elongation, spines, colony formation)Increase form resistance (elongation, spines, colony formation)• Reduce density Reduce density

Accumulate lipids (2-20% algal dry weight)Accumulate lipids (2-20% algal dry weight) Mucilage secretion (decreases density, but increases radius)Mucilage secretion (decreases density, but increases radius) Gas vacuoles (in cyanobacteria)Gas vacuoles (in cyanobacteria)

Patterns in Phytoplankton Community Patterns in Phytoplankton Community Composition and AbundanceComposition and Abundance

It is very difficult to predict which species of phytoplankton will be It is very difficult to predict which species of phytoplankton will be dominant in any given lake at any given time, but certain patterns dominant in any given lake at any given time, but certain patterns are common.are common.

As algal biomass increases (or TP), cyanobacteria become more As algal biomass increases (or TP), cyanobacteria become more dominantdominant

• Mesotrophic conditions favor diatomsMesotrophic conditions favor diatoms• Oligotrophic conditions favor diatoms, chrysophytes and CryptophytesOligotrophic conditions favor diatoms, chrysophytes and Cryptophytes

In dimictic temperate zone lakes, phytoplankton community and biomass In dimictic temperate zone lakes, phytoplankton community and biomass typically follow a seasonal pattern.typically follow a seasonal pattern.

1.1. Mid-winterMid-winter Low biomass because: very low light (snow-covered ice, short days)Low biomass because: very low light (snow-covered ice, short days)

2.2. Late-winterLate-winter Increasing biomass of dinoflagellates: (increasing light, calm water)Increasing biomass of dinoflagellates: (increasing light, calm water)

3.3. Spring circulationSpring circulation Increasing light, high nutrients, cold temperature, continuous mixing, low grazingIncreasing light, high nutrients, cold temperature, continuous mixing, low grazing

4.4. Early summer stratificationEarly summer stratification Increasing temperature in epilimnion, some grazing, Silica limitationIncreasing temperature in epilimnion, some grazing, Silica limitation

5.5. ““Clearwater” phaseClearwater” phase High sinking rate, low nutrients, high grazingHigh sinking rate, low nutrients, high grazing

6.6. Late summer stratificationLate summer stratificationØ Decreased grazing, low but increasing nutrients, sometimes low nitrogenDecreased grazing, low but increasing nutrients, sometimes low nitrogen

7.7. Fall CirculationFall CirculationØ Conditions similar to spring circulationConditions similar to spring circulation

Commonly observed patterns in reservoirs related to a gradient of environmental conditions from riverine to lacustrine (lake).

Spatial Patterns in Phytoplankton production

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)

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.

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?

Plot P and Si concentration on the x and y axis and note the equilibrium concentrations for both speciesThen, draw lines extending from the Si* and P* concentrations and fill in the boxes with the species that

can exist under those nutrient conditions

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