MARINE PELAGIC ECOLOGY

Transcription

1 SOLAS SUMMER SCHOOL 2011 Cargèse, Corsica, France (August 29th to Septembre 7th 2011) MARINE PELAGIC ECOLOGY Maurice Levasseur Université Laval (Québec Océan), Québec, Canada

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. 2

3 SOLAS RELEVANT COMPOUNDS: CH 4 CO 2 DMS N 2 O halogens VOCs 3

4 Oceans are huge They contain 97% of all available water at the surface of the Earth. Large volume Their volume is ca billions Km 3. 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. 4

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 5

6 1 A brief introduction on the origin of the oceans and evolution of life 6

7 A 4.5 billion years story Mars Earth 7

8 Life on Earth (since its formation 4.5 Gyr ago) Dinosaures ( Myr) Humans (<1 Myr) Ocean formation ( Gyr) First Archeae ( (Archaea) Gyr) Eukaryote (1.4 Gyr) Cyanobacteria (2.8 Gyr) Photosynthesis 8

9 The three domains of life Wikipedia 2011 The recognition of Archaea as a distinct domain of life is recent (Woese et al, 1990). Archeae present a distinct sequence of ribosomal ARN. 9

10 Photosynthesis changes the Earth in a definitive way 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 O 2 are now restricted to anoxic environments. 10

11 2 Phytoplankton diversity and ecology 11

12 The marine pelagic food web Heterotrophs Autotrophs D. Pauly 12

13 Autotrophic organisms The basis of the marine food web 13

14 PHYTOPLANKTON Autotrophic component of the plankton community. They use CO 2 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: and/or functions: Microplankton (20 200µm): ex. diatoms, dinoflagellates Nanoplankton (2 20 µm): ex. coccolithophores, flagellates Picoplankton (0.2 2 µm ): ex.cyanobacteria Calcifiers: ex. coccolithophores, foraminifers N fixers: ex. cyanobacteria Si users: ex. diatoms, silicoflagellates 14

15 Taxonomic survey of the marine phytoplankton Lalli and Parsons

16 Bacillariophyceae (diatoms) One of the largest group of microscopic algae. Relatively large cells ( 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. 16

17 Example of diatoms Silica valves (frustules) Filaments ( floatability, grazing) Several chain forming species 17

18 Diatoms are responsible for most oceanic blooms at mid and high latitudes 18

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). 19

20 Dinoflagellates Plates in cellulose Epitheca Cingulum Hypotheca Sulcus Alexandrium tamaremse 20

21 Noctiluca bloom 21

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. 22

23 Examples of Prymnesiophyceae Prymnesium parvum index/golden alga/ Chrysochromulina spp. Heidi Hällfors, FIMR 23

24 Example of calcified Prymnesiophyceae Emiliania huxleyi (coccolithophore) Scales (CaCO 2 ) 24

25 Bloom of coccolithophores as seen from space NORTH ATLANTIC Britain Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC 25

26 Phaeocystis spp. A special case of Prymnesiophyceae Single cell form (4 6 µm) Colonial form (> 250 µm) Image from The mystery of the foam on the sea shore by Wim van Egmond Very strong DMS producer 26

27 Cyanophyceae Very small cell size ( 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 N 2 (contribution to the oceanic new production). Include the cyanobacteria Trichodesmium, Synechococcus, and Prochlorococcus. 27

28 Picophytoplankton Picophytoplankton as seen by epifluorescence microscopy e.htm

29 Picophytoplankton as revealed by flow cytometry 29

30 Cyanobacteria Trichodesmium Synechococcus Heterocysts Cox P A et al. PNAS 2005;102: by National Academy of Sciences

31 Global distribution of Trichodesmium 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

32 3 Phytoplankton growth and species succession 32

33 Phytoplankton growth phases Cell numbers (cell l 1 ) Senescence phase Exponential phase Latent phase Time (day) 33

34 Variations in cell number and macronutrient concentrations during a typical diatom bloom (in vitro) Cell or nutrient concentrations (rel. units) Diatoms (cell l 1 ) Nitrate or silicate (μmol L 1 ) 0 10 Time (day) 34

35 Variations in cell number and macronutrient concentrations during the iron addition experiment SEEDS I (µmol L 1 ) (µmol L 1 ) (µg L 1 ) See Tsuda et al

36 Calculation of phytoplankton growth rate Increase in cells number: N = N 0 e µt Growth rate: μ = ln N lnn 0 /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. 36

37 Influence of water temperature on phytoplankton growth rate Eppley,

38 Variations in cell number and macronutrient concentrations during a typical diatom bloom (in situ) Diatoms (cell l 1 ) Sinking/aggregation/ grazing Nitrate or silicate (μmol L 1 ) 0 10 Time (day) 38

39 Evolution of the spring bloom and development of the deep chlorophyll maximum Chl a (µg L 1 ) or NO 3 (µmol L 1 ) Chl a Z (m) NO 3 NO 3 Time (days) 39

40 WHAT IS LIMITING PP IN THE OCEAN? The dilemma of aquatic autotrophs Light is rapidly absorbed in the water column (first 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. 40

41 Phytoplankton succession Ramon Margalef ( ) 41

42 Margalef's matrix summarizing the sequence of phytoplankton (the main sequence) as a function of diminishing turbulence and nutrient availability. Margalef

43 Margalef's Mandala developed from Figure 1, and including a red tide or HAB trajectory. From Smayda and Reynolds

44 4 Photosynthesis and Primary Production 44

45 PHOTOSYNTHESIS 6CO 2 + 6H 2 O + light C 6 H 12 O 6 + 6O 2 45

46 Capturing the light Photons Fluorescence used as biomass index. Pigments Pigments Energy of excitation Reaction center Photosystem II Photosystem I The antenna are composed of: Chlorophyll a (most commonly used phyto biomass index) Accessory pigments (carotenoid, Chl band c, others) Accessory pigments spread the light absorption spectra (use in HPLC taxonomy). 46

47 nm band = Photosynthetically available radiation (PAR) 47 Explain the relationship between the action spectrum

48 Accessory Light absorption pigments spectra fill the gaps chlorophyll b (combined absorption efficiency across entire visible spectrum) chlorophyll a Chl a carotenoids phycoerythrin (a phycobilin) chlorophyll b phycoerythrin (a phycobilin) chlorophyll a 48

49 Global distribution of chlorophyll a in the first cm of the water column (false colors composite image) MID HIGH LAT SPRING BLOOM EQUATORIAL UPWELLING BLOOM LOW LAT OLIGOTROPHIC CONDITIONS COASTAL UPWELLING BLOOM 49

50 Longhurst Biogeographic Provinces A. Longhurst, Ecological Geography of the Sea, second edition, 2007, Academic Press 50

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 14 C or 13 C methods. Addition of 14 CO 2 or 13 CO 2 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 Measuring primary production The 14 C or 13 C 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 CO 2 consumed during photosynthesis. 51

52 Primary production 14 C and 13 C methods Light 1. in situ incubations Samples + 14 CO 3 2 Depth 2. In situ simulated incubations On deck incubator 52

53 Photosynthesis/light curves Light Depth 20 min to h Biomass normalised photosynthesis (Photosynthesis/chl a) Light 53

54 Photosynthesis/light curves Light P/B Depth Light Reconstruction of the PP profile from the vertical distribution of phytoplankton biomass (Chl a) and light. 54

55 Photosynthesis/light curves P/B P m P m = assimilation number α = Initial slope = photosynthetic efficiency ß ß = photo-inhibition parameter dark reaction rate (enzymatic reactions) α Net production I k = photo adaptation parameter 0 Compensation point respiration I k Light Ik = ca. 100 μe m 2 s 1 Ik < 50 μe m 2 s 1 is generally limiting for photosynthesis 55

56 Biomass Primary production Export production Falkowski et al. (in Fasham 2003) 56

57 Global oceanic PP: ~51 x g C/year Oceans are responsible for 80% of marine PP. Coastal zones are responsible for 20%. 57