Ecology of Marine Phytoplankton LECTURE NOTES WILL BE POSTED AT hVp://ocean.mit.edu/~mick/ENS-­‐S06-­‐2013 Mick Follows: [email protected] •  Tuesday 5 Nov 2013 –  Introduc@on to marine phytoplankton –  Type II func@onal response: •  Encounter-­‐handling processes •  Wednesday 6 Nov 2013 –  Seasonal blooms –  Cell size and equilibrium resource compe@@on •  Thursday 7 Nov 2013 –  Equilibrium: Top down control and co-­‐existence –  Resource supply ra@os and co-­‐existence •  Nitrogen fixers Surface ocean chlorophyll from space NASA MODIS The ocean’s physical structure and circula@on The ocean’s physical structure and circula@on Equator Pole Why do they live there? Dashed line indicates light at 1% of surface incident flux Figure: Anna Hickman in Williams and Follows (2011) Diverse types of phytoplankton Biogeography on Atlan@c Meridional Transect – pico-­‐cyanobacteria -­‐ Prochlorococcus -­‐ diatoms -­‐ coccolithophores Aiken et al (2000) -­‐ Synechococcus Pico-­‐cyanobacteria •  Key traits: –  Smallest photo-­‐autotrophs •  Smallest is Prochlorococcus <1μm radius –  Small genome •  ~1.7-­‐9 Mbp •  (c.f. 12-­‐57 Mbp eukaryo@c phyto) –  Dominate popula@on in low-­‐
nutrient subtropical waters 0.1 micron Prochlorococcus: image C. Ting Prochlorococcus abundant in very low nutrient subtropical gyres Nitrate
Prochlorococcus
Synechococcus
AMT 15 Phytoplankton: log(cells ml-­‐1) Nitrate (micromoles kg-­‐1) Johnson et al, Science (2006) Distribu@on of Prochlorococcus from a sta@s@cal model Flohman et al, PNAS (2013) AMT phytoplankton popula@on Data: Maranon et al (2000) Redrawn in Williams and Follows (2011) Compe@@on for nitrogen in the REVIEW
ARTICLE Atlan@c tropical and subtropical a
b
80°
Nutrient amendments: Green dot = N limited 40°
Shading – surface nitrate 0°
-40°
-80°
50° E
150° E
110° W
10° W
t al, Nature Geo (indicate
2013) Figure 3 | PatternsMoore of nutrientelimitation.
Backgrounds
annual average surf
assist comparison, nitrate is scaled by the mean N:P ratio of organic matter (that is,
and secondary (outer circles) limiting nutrients as inferred from chlorophyll and/or p
Compe@@on for inorganic nitrogen dP
dt
R
= µo
P − mP
R + KR
growth loss •  P = phyto biomass •  μo = max growth rate •  R = external concentra@on of substrate •  KR = half-­‐satura@on •  m = loss rate 1 R -­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐ R+KR 0.5 KR R Equilibrium resource compe@@on: (K-­‐strategists, gleaners) R
0 ~ µo
P − mP
R + KR
Equilibrium mK R
R* =
µo − m
•  R* = subsistence concentra@on •  Organism with lowest R* excludes others •  Ambient concentra@on of R set to lowest R* •  e.g. Stewart and Levin (1974) Example from laboratory: Compe@ng bacteria Hansen and Hubbell, Science, (1980) Low R* phenotype High R* phenotype Is an equilibrium view appropriate anywhere? Is equilibrium limit relevant in a dynamic ocean? GB4017
GB
DUTKIEWICZ ET AL.: COUPLING OF ECOLOGY AND BIOGEOCHEMISTRY
Figure 5. Single resource case: Ratio of difference to actual nutrient concentration (N ! R* )/(N ).
(R -­‐ R*minat)/R Contours are
(!0.5, 0.5), green/yellow shading indicate R* close to ambient nutrient, red indicates
1
min
1
min
nutrients exceed R*min, and blue indicates that nutrients are less than the R*min. No shading indicates where
Simula@ons suggest seful limit n tropical and sline
ubtropical waters found. Transect
and circle indicate
locations for
no reasonable value
for theudiagnosed
R*min iwas
Figures 3 and 4.
Dutkiewicz et al (2009) down in the highly seasonal, subpolar oceans but may still
be achieved during the summer period of the seasonal
theory appears to hold is a subset of the domain whe
strategy types dominate. Unshaded regions are thos
How does R* scale with cell size? V = Vmax
R
R + KR
(From yesterdays lecture) Vmax = A {ET } K H
Area density of Handling Surface in rate (s-­‐1) area of cell transporters cell wall (m-­‐2) 2 2
α r (m )
KH
KR =
KE
Handling rate (s-­‐1) Encounter rate (s mol m-­‐3)-­‐1 How does R* scale with cell size? V = Vmax
R
R + KR
Vmax 0.5 Vmax Vmax ~ r 2
If V controlled by molecular diffusion at low R V = 4π Dr(R∞ − Ro ) ≈ 4π DrR∞
KR R How does R* scale with cell size? V
≈ 4π DrR∞
KR defined as R∞ when V = 0.5 Vmax 0.5Vmax
≈ 4π DrK R
2
r
1/3
K R ~ ~ r ~ Vol
r
Cell size and compe@@on for fixed nitrogen •  Litchman et al (2007) –  Empirical evidence –  KN ≈ 0.17 Vcell0.27 •  Smallest cell, lowest KN –  Lowest R* mK R
R* =
µo − m
Prochlorococcus: smallest cells, smallest effec@ve KN, lowest R* (?) Nitrate
Prochlorococcus
Synechococcus
AMT 15 Phytoplankton: log(cells ml-­‐1) Nitrate (micromoles kg-­‐1) Johnson et al, Science (2006) Gene@c and func@onal diversity of Prochlorococcus AMT 15 Johnson et al (2006)‫ ‏‬ Prochlorococcus growth rate vs T and R* mK R
R* =
µo (T ) − m
Johnson et al (2006) Gene@c and func@onal diversity of Prochlorococcus Many strains have lost ability to use nitrate Moore et al (2002) Prochlorococcus: smallest cells, lowest R* Nitrate
Prochlorococcus
Synechococcus
AMT 15 Phytoplankton: log(cells ml-­‐1) Nitrate (micromoles kg-­‐1) Johnson et al, Science (2006) Why are larger cells not excluded? picophytoplankton (<2 μm) nanophytoplankton (2-­‐20 μm) microphytoplankton (>20 μm) Size on AMT: Ward et al. J. Plankton Res. (2013) total chl a (mg chl m-­‐3) total chl a (mg chl m-­‐3)