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Phytoplankton Announcements: –Exam: next Wednesday –Review Tuesday pm at Olin O4 (here?!)

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Presentation on theme: "Phytoplankton Announcements: –Exam: next Wednesday –Review Tuesday pm at Olin O4 (here?!)"— Presentation transcript:

1 Phytoplankton Announcements: –Exam: next Wednesday –Review Tuesday pm at Olin O4 (here?!)

2 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 (O 2 demand) Little to no photosynthesis (why?) Not really strong stratification under ice (why?)

3 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 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, P- laden water quickly washed out) Doesn’t work when… Hypolimnion goes anoxic, resulting in lots of internal loading of P (how does this work?) Non-point sources of P persist (like what?)


5 Organisms Plankton : organisms that weakly swim or go where the water takes them Phytoplankton Periphyton : benthic algae Epiphyton : algae growing on macrophytes

6 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

7 Phytoplankton groupings, con't –Origin: 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)

8 Phytoplankton Taxonomy (Divisions) Cyanophyta - cyanobacteria Chlorophyta - green algae Euglenophyta - single flagella Bacillariophyta - diatoms Chrysophyta - golden brown algae Cryptophyta - flagellated Pyrophyta - dinoflagellates

9 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

10 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) Buoyant (gas vacuoles) Anabaena 400x heterocysts

11 Cyanobacteria, con't Resting stages: thick-walled resting cells (cysts) called akinetes ( Anabaena & Aphanizomenon ) Vegetative resting stage ( Mycrocystis ) linkage between benthos and pelagic

12 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

13 Volvox Chlamydomonas 400x Cladophora 40x Spirogyra 200x Hydrodictyon 40x Chlorophyta

14 Scenedesmus 600x Assorted desmids

15 Euglenophyta ~1,020 species Small to medium sized flagellated species Often abundant in well-mixed eutrophic ponds and littoral areas eukaryotic/01232001.html Euglena mainpage.htm

16 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

17 Diatoms eukaryotic/diatoms.jpg Biology/Bio122/week1.htm

18 Chrysophyta ~450 species 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 Synura,

19 Cryptophyta ~100 species 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

20 Pyrophyta - dinoflagellates ~ 220 species Motile (flagellates) Have resting cysts Some do not have chlorophyll Red tide in the ocean Peridinium Ceratium Biology/Bio122/week1.htm

21 Size influences - growth rate - energy paths (consumption) - sinking time

22 Size Picoplankton (0.2-2  m dia) Nanoplankton (2-30  m dia) Microplankton (30-200  m dia) < 30  m = edible algae A bacterium E Daphnia head (e - eye) (large zooplankton) B Cryptomonas (Cryptomonad) D Keratella (small zooplankton) C Scenedesmus (green)

23 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

24 Extracellular release of organic compounds 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

25 Photosynthesis Photosynthesis= fixing carbon nCO 2 + nH 2 O ------> (CH 2 O)n + nO 2 (n=# molecules) Change in population biomass = growth - consumption - sinking Growth=photosynthesis

26 Compensation point Compensation point: photosynthesis = respiration Maximize the amount of time spent above the compensation point (in the light)

27 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

28 modifications Muscilaginous cover around Staurastrum species (green) - reduce sinking (to a point) - reduce consumption (or digestion)

29 Effects of light & temperature on photosynthesis Maximum photosynthesis Light Limited (photo- chemical rxns) Light Saturated (enzymatic rxns limited by temp) Photo- inhibited Photosynthesis rate (mg C) Available light

30 Photosynthesis distribution= specific primary production * light climate * algae biomass Mesotrophic epilimnion (well mixed) Eutrophic with surface bloom Oligotrophic with max. biomass at metalimnion Shallow transparent lakes with max. biomass on bottom Depth PhotosynthesisBiomass

31 Depth distribution of photosynthesis Trophogenic zone ~ euphotic zone Note that phytoplankton on the surface of hypereutrophic lakes shade out the water column

32 Horizontal distribution Wind & currents Langmuir spirals Foam, buoyant algae Neg. buoyant algae surface algae deep algae

33 Lake Mendota cyanobacteria blooms

34 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

35 Factors influencing seasonal distribution Physical Temperature Light Limiting nutrients silica nitrogen phosphorus Biological competition resources, sinking Biological grazing parasitism

36 Seasonal distribution in a temperate, dimictic lake (green) (diatoms)

37 1. Light limited: small, often motile (but productive) 2. Light increasing,still ice cover, no mixing (dynoflagellates can swim up towards light)

38 3. Spring mixing: high nutrients, low grazing, increasing light, diatoms dominate

39 4. Initial stratification: diatoms settle & die, loss of Si to < 0.5 mg/L

40 5. Clearwater phase : high light availability, warm temperatures, but many herbivores and reduction of nutrients leads to population crashes

41 6. Mid-summer stratification: Cyanobacteria dominate (fix N, migrate between nutrient-rich lower depths & epilimnion)

42 7. Fall mixing: high nutrients, less light, diatoms dominate again with increases in Si 8. Late autumn decline


44 The plankton

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