Diversity of Aquatic Organisms Phytoplankton & Phytoplankton Ecology Part 3

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

 Filamentous green algae can often be identified by the shape of the chloroplast Spirogyra Spirogyra spiral chloroplastspiral chloroplast Mougeotia Mougeotia ribbon chlorplastribbon chlorplast Zygnema Zygnema star chloroplaststar chloroplast  Characteristics of filamentous greens Form slimy masses on ponds, river poolsForm slimy masses on ponds, river pools Store starch in the chloroplastStore starch in the chloroplast Cell walls contain celluloseCell walls contain cellulose Green Algae (Chlorophyta)

 Characteristics Large cells (10-30 um)Large cells (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 LakesCommon in Laurentian Great Lakes Cryptophytes (Cryptophyta)

 Characteristics 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’ on ocean coasts Can cause ‘Red Tides’ on ocean coasts May exhibit cyclomorphosis May exhibit cyclomorphosis Dinoflagellates (Pyrrophyta)

 Characteristics Eukaryotic Eukaryotic Chlorophyll a and b, Chlorophyll a and b, High concentration of carotenoids High concentration of carotenoids Tolerant of low P concentrations Tolerant of low P concentrations May compensate for low P by switching to heterotrophy May compensate for low P by switching to heterotrophy Golden-Brown Algae (Chrysophyta) Dinobryon Mallomonas

 Characteristics EukaryoticEukaryotic Unicellular or colonialUnicellular or colonial Chlorophyll a and cChlorophyll a and c Contain beta-carotene and fucoxanthin pigmentsContain beta-carotene and fucoxanthin pigments External covering of SiO 2External covering of SiO 2 Large requirement for S Large requirement for S Usually require vitamin B 12Usually require vitamin B 12  Two major groups Centrics – radial symmetry Centrics – radial symmetry Pennates – bilateral symmetry Pennates – bilateral symmetry Diatoms (Bacillariophyta) Asterionella Tabellaria

Diatoms (Bacillariophyta) protist.i.hosei.ac.jp/pdb/Images/Heterok ontophyta/Centrales/Cyclotella/Cyclotell a.jpg microbes.limnology.wisc.edu/outreach/images dr-ralf-wagner.de/Bilder/Surirella plantphys.info/organismal/lechtml/images/navicula.jpg Centric Diatoms Pennate Diatoms

thalassa.gso.uri.edu/flora/imagesfl/ansp4.jpg Diatom Art

 Characteristics EukaryoticEukaryotic No sexual reproductionNo sexual reproduction Chlorophyll a and bChlorophyll a and b Require vitamins B 12Require vitamins B 12 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) =tbn:fI400rN1fWCHSM: w.infovisual.info/02/img_en/001% 2520Structure%2520of%2520a% 2520euglena.jpg

Red algae (Rhodophyta) Bangia Invading littoral zones of Great Lakes

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) Below a certain depth, there will be insufficient light for 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 sink. Phytoplankton are heavier than water, so they sink. Density of cellular componentsDensity of cellular components Proteins ~1.3 g cm -3 Carbohydrates ~1.5 g cm -3 Proteins ~1.3 g cm -3 Carbohydrates ~1.5 g cm -3 Nucleic acids ~1.7 g cm -3 SiO 2 (diatom walls) ~2.6 Nucleic acids ~1.7 g cm -3 SiO 2 (diatom walls) ~2.6 Lipids ~0.86 Lipids ~0.86 Phytoplankton density g cm -3 Phytoplankton density g cm -3  Therefore, one of the greatest challenges for phytoplankton is to remain in suspension

Mechanisms to Reduce Sinking  Small particles in water follow Stoke’s Law V s = 2 gr 2 (  1 -  ) / [9  (Ø r )]V s = terminal sinking velocity of a sphere g = acceleration of gravity r = radius  = viscosity (  1 -  ) = excess density (density of cell - density of water) (Ø r ) = 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 densityReduce 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 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 As algal biomass increases (or TP), cyanobacteria become more dominant 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 typically follow a seasonal pattern. 1.Mid-winter Low biomass because: very low light (snow-covered ice, short days) Low biomass because: very low light (snow-covered ice, short days) 2.Late-winter Increasing biomass of dinoflagellates: (increasing light, calm water) Increasing biomass of dinoflagellates: (increasing light, calm water) 3.Spring circulation Increasing light, high nutrients, cold temperature, continuous mixing, low grazing Increasing light, high nutrients, cold temperature, continuous mixing, low grazing 4.Early summer stratification Increasing temperature in epilimnion, some grazing, Silica limitation Increasing temperature in epilimnion, some grazing, Silica limitation 5.“Clearwater” phase High sinking rate, low nutrients, high grazing High sinking rate, low nutrients, high grazing

6. Late summer stratification Ø Decreased grazing, low but increasing nutrients, sometimes low nitrogen 7. Fall Circulation Ø Conditions 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 R A * = Equilibrium resource concentration for Species A R B * = 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 PBut 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 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

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