Phytoplankton and primary production 4

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1 Aquatic ecology BIO 4400 Phytoplankton and primary production 4 k a Bente Edvardsen 2009

2 Aims of learning - marine botany Give an understanding and knowledge on: Ecological role of phytoplankton Primary production, photosynthesis and growth Effects of ecological factors: light, nutrients, temperature, salinity Phytoplankton diversity Distribution in time and space Ecological strategies

3 Content Methods to measure primary production phytoplankton biomass 2. Phytoplankton distribution in space globally vertically horisontally 3. Phytoplankton distribution over time seasonal cycles succession 4. Phytoplankton ecological strategies

4 How can we measure primary Photosynthesis: production in the sea? light 6CO 2 + 6H 2 O + -> C 6 H 12 O 6 + 6O 2 14 C-method (Steemann Nielsen 1950) Isotope 14 C in bicarbonate-form (tracer) added to flasks with water that are incubated 14 C-uptake measured as β-radiation from photosynthesis products (scintillator)

5 Paasche C-method in situ

6 14 C-method in situ Water samples are incubated at the depth they come from In dark flasks only respiration occur From Garrison

7 14 C-method: calculations 14 C uptake Assimilated C L -1 t -1 = 1,05 ΣCO 2 -C 14 C added ΣCO 2 -C = (CO 2 +HCO CO 3- ) 2 mmol 24 mg C in 35 PSU sea water

8 Figur 9. Relative distribution of dissolved CO 2, bicarbonate and carbonate as a function of ph and at 35 PSU and 20 C.

9 14 C-method Errors resulting in an underestimate: 14 C-labeled organic compounds can be respired 14 C-labeled organic compounds can leak out of the cell (10-50% extracellular production) Algae containing 14 C-labeled organic compounds can be eaten

10 Other methods for measuring primary production O 2 -method: development of oxygen Winkler-titration before and after incubation nco 2 +2nH 2 O ->(CH 2 O)n+nO 2 +nh 2 O Change in algal biomass during incubation These methods are less sensitive than the 14 C- method PAM (Pulse Amplitude Modulated) fluorometry

11 High- and low productive areas of the seas

12 Primary production pr m 2 sea surface

13 Chlorophyll a is an estimate for algal biomass

14 Methods for estimating phytoplankton biomass chlorofyll a - in vitro fluorescence chlorofyll a - in vivo fluorescence Remote sensing (Fjernmåling) of chl a Particulate C or N Cell number and estimate biovolume

15 Relationship between photosynthesis and chlorophyll Fotosynteseprofil sammen med en klorofyllprofil fra Barentshavet om sommeren.

16 Phytoplankton distribution neritic: coastal oseanic: open ocean meroplanktonic: benthic life cycle stage holoplanktonic: whole life in the plankton geographical distribution determined mainly by the temperature: polar, temperate, tropical, bipolar, cosmopolitic

18 Sinking and buoyancy (synking og oppdrift) Sinking velocity (synkehastighet) (H)= g r 2 (density of alga density of water) viscosity of water form resistance (modified Stokes lov) Sinking velocity increases with water temperature due to reduced viscosity Large cells sink faster than small, but large diatoms have reduced surface to volume ratio and have relatively less frustule material But Stokes law is not always valid. Live cells may sink slower that dead particles

vacuole in diatoms gives buoyancy, exchange heavy

19 Horns and spines increase the form resistance, but can cause flocculation (flokkulering) Cell vacuole in diatoms gives buoyancy, exchange heavy ions (K +, Ca 2+ ) with lighter (Na +, Mg 2+, NH 4+ ) JT

20 Swimming capasity in planktonic microalgae Depth Cell diameter JT

21 Vertical distribution of some microalgae in stratified waters C.f.= Ceratium E.h.= Emiliania S.c.= Skeletonema Paasche Fig. 27

22 Patchy distribution of phytoplankton Langmuir cells (=Konveksjonsceller): Sinking cells accumulate in divergences (D) and upwards swimming cells in convergences (K).

23 Phytoplankton distribution (Planteplanktonets fordeling) Plankton is unevenly (ujevnt) distributed both vertically and horisontally: Because Vertical stratification and pycnocline prohibit full circulation Vertical migration and sinking Wind and currents cause Langmuir circulation Marine snow cause patchy distribution of nutrients, phytoplankton and zooplankton

24 The spring bloom (våroppblomstringen) Decreasing chl a level from orange, yellow, green to blue

25 The beginning of the spring bloom (våroppblomstringen)

26 Light inhibition Critical depth (kritisk dyp) Depth Light saturated photosynthesis Compensation depth from Paasche 05 Critical depth

27 Critical depth and pycnocline Relation between change in radiation, critical depth, pycnocline and vertical mixing

28 Stability (stabilitet) Stability is increase in density with depth expressed as σ t (sigma-t) per meter High value stable water masses Low stability water is easily mixed by wind σ t (sigma-t); describes the density of the water σ t = (specific weight (kg/l) 1 ) x 1000

29 Stability diagram unstable water column stable surface layer

30 Norwegian sea (Norskehavet) from Eggvin 1963 and Skjoldal 2004

31 Weather Ship M

32 original by Sverdrup 1953

33 Stratification, critical depth and phytoplankton biomass in Norwegian Sea

34 Phases of phytoplankton biomass and critical depth in Norwegian Sea

35 Seasonal variation of nitrate levels and phytoplankton biomass (chl a)

36 Chlorophyll a and nitrate from Rey 2004 Primary production mg C. m -2. day -1 winter < 20 prebloom bloom > > 1.5 g postbloom < 500 summer < 250 autumn < 250 autumn blooms > 500 late autumn < 100 from Rey 2004

37 Winter mixing Seasonal cycle Surface water sinks due to cooling Water masses are unstable and are easily mixed Nutrient-rich deep water is mixed inn High compensation depth and critical depth Photosynthesis < respiration, phytoplankton spend too short time in the light to give net production

38 Seasonal cycle - 2 Spring increased stability and stratification due to fresh and brackish water influence (coastal waters) and increased radiation (coastal and oceanic waters) decreased depth of the mixed layer larger compensation depth and critical depth, thicker euphotic zone photosynthesis > respiration Vernal (spring) bloom can start when critical depth is larger than the upper mixed layer (UML, øvre blandingslag)...and decline when nutrients are consumed

39 Spring bloom in non-stratified water In fjords the mixing is low and the spring bloom can start before the water is stratified Photosynthesis near the surface results in some heating and shading of deeper waters that may contribute to some stability

40 Changes in species composition over time Species composition in the phytoplankton community is steadily changing over time Diatoms dominate the vernal bloom based on nitrate (and silicate) Flagellates dominate during summer based on ammonium Change within water mass: succession (suksesjon) Change of water mass: sequence (sekvens)

41 Phytoplankton seasonal cycle in the Oslofjord (1976) From Paasche 2005

42 Ecological strategies: r- and K

43 Succession in the phytoplankton community Margalef s mandela:

44 Influence of nutrients and grazing on the phytoplankton composition Low nutrient levels result in low phytoplankton biomass and a larger part of pico- and nanoplankton Microphytoplankton grow faster than their grazors (mesozooplankton). Blooms decline due to nutrient limitation ( bottom up control ) Pico- and nanoplankton is grazed by microzooplankton that grow at a similar rate. The populations are regulated by the grazors ( top down control )

45 Seasonal production in the Norwegian Sea from Rey 2004

Biological Oceanography

Biological Oceanography What controls production in the sea? The BIG 2: 1) Light (energy) 2) Nutrients (matter) Secondarily 3) Temperature 4) Stratification (coupled to 2 & 3) 5) Grazing/predation The