Diversity of Aquatic Organisms Phytoplankton & Phytoplankton Ecology Part 3

1. Diversity of Aquatic OrganismsPhytoplankton&Phytoplankton Ecology Part 3

2. Green Algae (Chlorophyta) • Desmids • Form rigid Semi-cells often arranged like a snowflake

3. 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

4. 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

5. 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/CERATIUM.jpg

6. 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

7. Diatoms (Bacillariophyta) Asterionella • 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 Tabellaria

8. 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

9. Diatom Art www.nature.ca/research/images/diatom_art.jpg thalassa.gso.uri.edu/flora/imagesfl/ansp4.jpg

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

11. Red algae (Rhodophyta) • Bangia • Invading littoral zones of Great Lakes www.marietta.edu/~biol/biomes/images/competition/2algae.jpg

12. Phytoplankton Ecology • To survive, phytoplankton must maintain photosynthesis to sustain carbon-fixation at rates greater than respiratory costs. (P>R) • Below a certain depth, there will be insufficient light for growth (P<R) • Compensation depth, where P=R (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

13. Mechanisms to Reduce Sinking • Small particles in water follow Stoke’s 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)

15. 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)

17. 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

18. 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

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

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

21. 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)

22. 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.

23. 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?

24. 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

25. 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