marine pelagic ecology - solas int
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SOLAS SUMMER SCHOOL 2011
Cargèse, Corsica, France (August 29th to Septembre 7th 2011)
MARINE PELAGIC ECOLOGY
Maurice LevasseurUniversité
Laval (Québec‐Océan), Québec, CanadaMaurice.levasseur@bio.ulaval.ca
2
Objective of the lectures
To provide a general understanding of the diversity of
pelagic marine life forms, their functions within
ecosystems, and of their contributions to the
biogeochemical cycling of SOLAS‐relevant
elements/compounds.
3
CO2
DMSN2
O
halogens
VOCs
CH4
SOLAS‐RELEVANT COMPOUNDS:
4
Oceans are huge…They contain 97% of all available water at the surface of the Earth.
Large volume…Their volume is ca. 1.3‐1.5 billions Km3.This is an immense heat reservoir (1200 times more than the atmosphere)
A vast environment for living organisms and biogeochemistry
Large surface…They cover 70% of the surface of the globe. They thus represent an
important interface for heat, particle and gas exchanges with the
atmosphere.
5
OUTLINE
1. A brief introduction on the origin of the oceans and evolution of life
2. Phytoplankton diversity and ecology
3. Phytoplankton growth and species succession
4. Photosynthesis and Primary Production
***
5. Phytoplankton elemental composition and nutrient requirements
6. The marine pelagic food web
7. The microbial loop
8. Future challenges
6
‐1‐
A brief introduction on the origin of the oceans and
evolution of life
7
A 4.5 billion years story
Mars Earth
8
Life on Earth(since
its
formation 4.5 Gyr
ago)
(Archaea)
Humans
(<1 Myr)
First Archeae
(3.5‐2.7 Gyr)
Cyanobacteria
(2.8 Gyr)Photosynthesis
Eukaryote
(1.4 Gyr)
Dinosaures
(230‐66 Myr)Ocean
formation (4.2‐4.5 Gyr)
9
Wikipedia
2011
The three domains of life
The recognition of Archaea
as a distinct domain of life is recent (Woese
et al, 1990).
Archeae
present a distinct sequence of ribosomal ARN.
10
The former reducing environment changed for an oxidative environment.Development of the ozone layer (protects the Earth from harmful UV).Life becomes possible on continents – increase of biodiversity.Organisms sensitive to O2
are now restricted to anoxic environments.
Photosynthesis changes the Earth in a definitive way
11
‐2‐
Phytoplankton diversity and ecology
12
The marine pelagic food web
Autotrophs
Heterotrophs
D. Pauly
http://cordis.europa.eu/inco/fp5/acprep8_en.html
13
Autotrophic organismsThe basis of the marine food web
14
PHYTOPLANKTON
Autotrophic component of the plankton community.
They use CO2
and solar energy to synthesize organic compounds (photosynthesis).
Possess pigments, mostly chlorophyll a, to capture light energy.
About 4,000 described species.
Can be classified into biochemically important ‘functional groups’
based on size:
Microplankton
(20‐200µm): ex. diatoms, dinoflagellatesNanoplankton
(2‐20 µm): ex. coccolithophores, flagellatesPicoplankton
(0.2‐2 µm ): ex.cyanobacteria
and/or functions:
Calcifiers: ex. coccolithophores, foraminifersN‐fixers: ex. cyanobacteriaSi‐users: ex. diatoms, silicoflagellates
15Lalli
and Parsons 1997
Taxonomic survey of the marine phytoplankton
16
Bacillariophyceae
(diatoms)
One of the largest group of microscopic algae.
Relatively large cells (2‐1000 µm).
Form large blooms in nutrient‐rich environments.
Responsible for spring blooms at mid and high latitudes.
Responsible for most of the ‘new production
‘ and carbon sequestration.
They support the ‘classical’
marine food web.
Use mostly nitrate as a nitrogen source.
Also require silicate
for their frustules.
r‐selected species adapted to unstable environments.
Two main groups: centric and pennates.
17
Example of diatoms
Silica valves (frustules)
Filaments(↑
floatability, ↓
grazing)
Several chain forming species
18
Diatoms are responsible for most oceanic blooms at mid and high latitudes
19
Dinophyceae
(dinoflagellates)
The second most abundant phytoplankton group.
Organisms of widely different forms and sizes.
They possess two flagella (transverse & longitudinal flagellum).
Can perform diel
vertical migrations.
Some species are naked (sensitive to sampling procedures).
Other species are covered with a theca made of cellulosic plates.
Some species are toxic or harmful.
They can form ‘red tides’
in coastal waters.
K‐selected species with complex life cycle (temporary and/or dormant cysts).
20
Dinoflagellates
Alexandrium
tamaremse
Epitheca
Hypotheca
Cingulum
Sulcus
Plates in cellulose
21
Noctiluca
bloom
22
Prymnesiophyceae
Small cells (4‐6 µm).
Cells with two flagella and a third different one called
haptonema.
Covered with organic scales.
Scales may be calcified
(e.g. Coccolithophores).
Blooms may cover vast oceanic areas.
Some species are toxic (ex. gender Chrysochromulina
and
Prymnesium).
Strong DMSP and DMS producers.
K‐selected species adapted to stable, resource‐limited
conditions.
23
Prymnesium
parvum Chrysochromulina
spp.
Examples of Prymnesiophyceae
http://aquaplant.tamu.edu/plant‐
identification/alphabetical‐index/golden‐alga/
Heidi Hällfors, FIMR
24
Example of calcified Prymnesiophyceae
Emiliania
huxleyi
(coccolithophore)
Scales
(CaCO2
)
25
Bloom of coccolithophores
as seen from space
Britain
Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC
NORTHATLANTIC
26
Phaeocystis
spp.
A special case of Prymnesiophyceae
Single cell form (4‐6 µm) Colonial form (> 250 µm)
Very
strong DMS producer
Image from The mystery of the foam on the sea shore
by Wim
van Egmondhttp://www.jochemnet.de/fiu/OCB3043_21.html
27
Cyanophyceae
Very small cell size (0.2 – 2.0 μm).
Unicellular or chain forming.
Thrive in warm, vertically stable nitrogen‐poor environments.
May be responsible for 50% of the PP.
Some species can fix atmospheric molecular N2
(contribution to
the oceanic new production).
Include the cyanobacteria
Trichodesmium, Synechococcus, and
Prochlorococcus.
28
Picophytoplankton
Picophytoplankton
as seen by epifluorescence
microscopy.
http://www.mreckermann.de/flow/index‐e.htm
29
Picophytoplankton
as revealed by flow cytometry
http://en.wikipedia.org/wiki/Flow_cytometry
30
Cox P A et al. PNAS 2005;102:5074-5078
©2005 by National Academy of Sciences
Cyanobacteria
Trichodesmium Synechococcus
Heterocysts
31
Figure 1. Percent of time Trichodesmium blooms are present (persistence) as estimated from SeaWiFS. The percentage of time is calculated at each pixel as the fraction of clear-sky observations which are identified as Trichodesmium blooms between January 1998 and December 2003, scaled to the frequency of clear-sky occurrences during that period. Bloom fields calculated at a spatial resolution of 1/4° (~27 km) using 8-day SeaWiFS reflectance data.
Westberry
and Siegel 2006
Global distribution of Trichodesmium
32
‐3‐
Phytoplankton growth and species succession
33
Phytoplankton growth phases
Cell numbers(cell l‐1)
Time (day)
Latentphase
Exponential
phase
Senescence phase
34
Time (day)
Diatoms (cell l‐1)
Nitrate or silicate (μmol L‐1)
0 10
Variations in cell number and macronutrient
concentrations during a typical diatom bloom
(in vitro)
Cell or nutrientconcentrations(rel. units)
35See
Tsuda et al. 2003
Variations in cell number and macronutrient concentrations during
the iron addition experiment SEEDS I
(µmol L‐1)
(µmol L‐1) (µg L‐1)
36
Calculation of phytoplankton growth rate
Increase in cells number:
N = N0
eµt
Growth rate:
μ
= ln
N – ln N0
/t
(units = day‐1)
Doubling time:
Td = 0.69/ μ
(units = day)
Phytoplankton doubling times vary between 0.5 and 2.0 days.
In the lab and in nutrient‐replete conditions, doubling time vary with water
temperature.
37Eppley, 1972
Influence of water temperature on phytoplankton growth rate
38
Time (day)
Diatoms
Nitrate or silicate (μmol L‐1)
0 10
Sinking/aggregation/
grazing
Variations in cell number and macronutrient
concentrations during a typical diatom bloom
(in situ)
(cell l‐1)
39
Evolution of the spring bloom and development of the deep chlorophyll
maximum
NO3
NO3
Chl
a
(µg L‐1) or NO3
(µmol L‐1)
Chl
a
Z(m)
Time (days)
40
WHAT IS LIMITING PP IN THE OCEAN?
The dilemma of aquatic autotrophs
Light is rapidly absorbed in the water column (first 100‐150 m) while the large
nutrient reservoir is located deeper in the water column.
How to access both resources?
Turbulence plays a key role in replenishing the upper part of the water column
with nutrients.
41
Phytoplankton succession
Ramon Margalef
(1919‐2004)
42
Margalef's matrix summarizing the sequence of phytoplankton (the
main
sequence) as a function of diminishing ‘turbulence’
and nutrient availability.
Margalef
1978
43
Margalef's Mandala developed from Figure 1, and including a ‘red tide’
or HAB
trajectory.
From Smayda
and Reynolds 2001
44
‐4‐
Photosynthesis and Primary Production
45
PHOTOSYNTHESIS6CO2
+ 6H2
O + light →
C6
H12
O6
+ 6O2
46
Capturing the light
Photosystem
II Photosystem
I
Pigments Pigments
Reaction center
Photons
Energy of excitation
The antenna are composed of:Chlorophyll a (most commonly used phyto‐biomass index) Accessory pigments (carotenoid, Chl‐b and ‐c, others)
Accessory pigments spread the light absorption spectra (use in ‘HPLC’
taxonomy).
Fluorescence
used as biomass
index.
47400‐700 nm band = Photosynthetically
available radiation (PAR)
http://12knights.pbworks.com/w/page/37702220/827‐‐Explain‐the‐relationship‐between‐the‐action‐spectrum
48
Light absorption spectra
Chl‐a
chlorophyll b
chlorophyll acarotenoids
phycoerythrin (a phycobilin)
(combined absorption efficiency across entire visible spectrum)
chlorophyll achlorophyll b
phycoerythrin (a phycobilin)
Accessory pigments fill the gaps
49
Global distribution of chlorophyll a in the first cm of the water column(false colors composite image)
MID‐HIGH LAT SPRING BLOOM
COASTAL UPWELLING BLOOM
LOW LAT OLIGOTROPHIC CONDITIONS
EQUATORIAL UPWELLING BLOOM
50
Longhurst
Biogeographic
Provinces
A. Longhurst, Ecological Geography of the Sea, second edition, 2007, Academic Press
51
Photosynthesis or PP can be measured in terms of carbon fixation
per unit of
volume per unit of time (mg C m‐3
h‐1) by using the 14C or 13C methods.
Addition of 14CO2
or 13CO2
as bicarbonate to bottles of seawater and measure of the
increase in activity over time.
Depending on the objective, the incubations may take different forms:
1. In situ
2. In situ simulated
3. Photosynthetic/light curve
The 14C or 13C incorporated in the cells is measured with either a scintillation
spectrometer or a mass spectrometer.
PP may also be determined by measuring the oxygen produced or CO2
consumed
during photosynthesis.
Measuring primary production
52
Primary production14C and 13C methods
Depth
Light
Samples
On‐deck incubator
1. in situ incubations
2. In situ simulated incubations
+ 14CO32‐
53
Photosynthesis/light curves
Depth
Light
20 min to h
Light
(Photosynthesis/chl
a)
Biomass‐normalised photosynthesis
54
Depth
Light
Light
P/B
Reconstruction of the PP profile from the vertical distribution
of phytoplankton biomass (Chl
a) and light.
Photosynthesis/light curves
55
P/B
Light
Pm
Ik
α
respiration0 Compensation point
Net production
Ik
= ca. 100 μE m‐2
s‐1
Ik
< 50 μE m‐2
s‐1
is
generally limiting for photosynthesis
ß
Pm
= assimilation number
α
= Initial slope = photosynthetic
efficiency
ß
= photo-inhibition parameter –
dark reaction rate (enzymatic reactions)
Ik
= photo‐adaptation parameter
Photosynthesis/light curves
56
Biomass
Primary
production
Exportproduction
Falkowski
et al.(in Fasham 2003)
57
Global oceanic PP: ~51 x 1015
g C/year
Oceans are responsible for 80% of marine PP.Coastal zones are responsible for 20%.
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