Aquatic ecology BIO 4400
Phytoplankton and primary
production 4
k
a
Bente Edvardsen 2009
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
Content - 4
1. Methods to measure
•
•
primary production
phytoplankton biomass
•
•
•
globally
vertically
horisontally
•
•
seasonal cycles
succession
2. Phytoplankton distribution in space
3. Phytoplankton distribution over time
4. Phytoplankton ecological strategies
How can we measure primary
production in the sea?
Photosynthesis:
•
light
6CO2 + 6H2O + -> C6H12O6 + 6O2
14C-method (Steemann Nielsen 1950)
• Isotope 14C in bicarbonate-form (tracer) added to
flasks with water that are incubated
•
measured as β-radiation from
photosynthesis products (scintillator)
14C-uptake
14C-method
Paasche 2005
– in situ
14C-method
– in situ
•Water samples
are incubated at
the depth they
come from
•In dark flasks
only respiration
occur
From Garrison
14C-method:
14C
calculations
uptake
Assimilated C•L-1 • t-1 = ————— • 1,05 • ΣCO2-C
14C
added
ΣCO2-C = (CO2 + HCO3 - + CO3- ) ≈ 2 mmol
≈ 24 mg C in 35 PSU sea water
Figur 9. Relative distribution of dissolved CO2, bicarbonate and
carbonate as a function of pH and at 35 PSU and 20 °C.
14C-method
Errors resulting in an underestimate:
•14C-labeled organic compounds can be respired
•14C-labeled organic compounds can leak out of the
cell (10-50% extracellular production)
•Algae containing 14C-labeled organic compounds
can be eaten
Other methods for measuring
primary production
• O2-method: development of oxygen
• Winkler-titration before and after incubation
nCO2+2nH2O ->(CH2O)n+nO2+nH2O
• Change in algal biomass during incubation
These methods are less sensitive than the
method
14C-
• PAM (Pulse Amplitude Modulated) fluorometry
High- and low productive areas of the
seas
Primary production pr m2 sea surface
Chlorophyll a is an estimate for algal biomass
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
Relationship
between
photosynthesis
and chlorophyll
Fotosynteseprofil sammen
med en klorofyllprofil fra
Barentshavet om sommeren.
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
Sinking and buoyancy
(synking og oppdrift)
Sinking velocity (synkehastighet) (H)=
g · r2 · (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
Horns and spines increase the form
resistance, but can cause flocculation
(flokkulering)
Cell vacuole in diatoms gives
buoyancy , exchange heavy ions
(K+, Ca2+) with lighter (Na+, Mg 2+,
NH4+)
JT
Swimming
capasity in
planktonic
microalgae
Depth
Cell
diameter
JT
Vertical distribution of some
microalgae in stratified waters
C.f.= Ceratium
E.h.= Emiliania
S.c.= Skeletonema
Paasche
Fig. 27
Patchy distribution of phytoplankton
Langmuir cells (=Konveksjonsceller): Sinking
cells accumulate in divergences (D) and upwards
swimming cells in convergences (K).
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
The spring bloom (våroppblomstringen)
Decreasing chl a level from orange, yellow, green to blue
The beginning of the
spring bloom
(våroppblomstringen)
Depth
Light inhibition
Critical depth
Light saturated
photosynthesis
Compensation depth
(kritisk dyp)
Critical depth
from Paasche 05
Critical depth and pycnocline
Relation between change in radiation, critical
depth, pycnocline and vertical mixing
Stability (stabilitet)
• Stability is increase in density with depth
expressed as σt (sigma-t) per meter
• High value – stable water masses
• Low stability – water is easily mixed by wind
• σt (sigma-t); describes the density of the water
σt = (specific weight (kg/L) – 1 ) x 1000
Stability diagram
unstable
water
column
stable
surface layer
Norwegian sea
(Norskehavet)
from Eggvin 1963 and Skjoldal 2004
Weather Ship
”M”
original by Sverdrup 1953
Stratification, critical depth and
phytoplankton biomass in Norwegian Sea
Phases of phytoplankton biomass and
critical depth in Norwegian Sea
Seasonal variation of nitrate levels and
phytoplankton biomass (chl a)
Chlorophyll a and nitrate
from Rey 2004
Primary production
mg C.m-2.day-1
winter
< 20
prebloom
200-400
bloom
> 300-500 >| 1.5 g
postbloom
< 500
summer
< 250
autumn
< 250
autumn blooms >| 500
late autumn
< 100
from Rey 2004
Seasonal cycle
Winter mixing
• 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
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
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
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)
Phytoplankton seasonal cycle in the Oslofjord
(1976)
From Paasche 2005
Ecological strategies: r- and K
Succession in the phytoplankton
community
Margalef’s mandela:
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’)
Seasonal production in the Norwegian Sea
from Rey 2004