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Coral Structure and Function II. Primary Production Benthic Cnidaria Atoll analysis 1. Calcareous red algae 2. Calcareous green algae ( Halimeda ) 3. Foraminifera ( 20-40  m protists, porous CaCO 3 shell ) 4. Corals Coral polyp – predacious Endosymbiont – zooxanthellae.

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slide2
Primary Production
  • Benthic
  • Cnidaria
  • Atoll analysis

1. Calcareousred algae

2. Calcareousgreen algae (Halimeda)

3. Foraminifera (20-40m protists, porous CaCO3 shell)

4. Corals

  • Coral polyp – predacious
    • Endosymbiont – zooxanthellae
slide3
Much of the productivity from corals
  • Cnidaria - from the Latin “nettle” – a plant
  • have often been mistaken for plants
    • attached to a substrate
    • do not wander about
    • same colour as many

marine plants

    • same branched nature

and growth habit

slide4
Much of the food needed by the polyp comes from the SYMBIONT
  • Many corals have different growth forms - can vary with local environment - light, depth etc.
  • Local environment affects distribution of the zooxanthellae
slide5
Zooxanthellae:
    • ZOO - animal
    • XANTHE - gold-coloured
  • single-celled alga, with 2 flagellae
    • a dinoflagellate
  • spherical, 8 - 12um dia
  • Most dinoflagellates are free-living
    • unusual group of algae
    • feeding modes ranging from photosynthetic autotrophy to heterotroph
slide6

mucus

nematocysts

slide7
Zooxanthellae can live outside their host
    • essential in some species for finding a host
  • Dinomastigotesstage
    • motile free-living state, have two flagellae
  • Coccoid stage
    • living in animal cells, lack flagellae
  • In culture, zooxanthellae alternate between coccoid and dinomastigote stages
slide8
Almost all zooxanthellae are in the dinflagellate genus Symbiodinium (1959)
  • taxonomy of Symbiodinium in a state of flux
  • 1980 - Symbiodinium microadriaticumassumed to be the one species found in almost all corals
slide9
Recent work
    • great genetic diversity in zooxanthellae
    • clearly more than one species
    • now dozens of different algal taxa
    • zooxanthellae found in closely related coral species not necessarily closely related themselves
    • zooxanthellae found in distantly related coral species may, in fact, be closely related
    • may have multiple species in same coral
slide11

Usually a single Symbiodinium clone in a coral colony.

Sometimes two.

Adjacent colonies have same or similar Symbiodinium populations.

slide13
Acquisition of Zooxanthellae by Corals

either

1. open (or indirect) transmission or acquisition

  • from the environment

or

2. closed (or direct) transmission or acquisition

- via gametes or

- during asexual reproduction

slide14
Indirectacquisition
    • provides potential for host to establish a symbiosis with a different strain or species of zooxanthellae than was in symbiosis with the host’s parents
  • Coral bleaching
    • may also allow establishment of new symbiosis with different zooxanthellae strain,
    • has been proposed as a possible adaptive mechanism to environmental change
  • Shifting symbioses
    • controversial topic
slide16
In all hermatypic corals endosymbiotic algae provide an important source of nutrients
  • can demonstrate mutualistic relationship
  • feed 14CO2 to the coral
    • quickly taken up by alga and ends up in the polyp
  • feed zooplankton raised on 15N to coral
    • quickly taken up by polyp and ends up in the alga
slide17
clear they exchange a lot of material
    • benefit each other
  • reef-shading experiments
    • 3 months in the dark
      • algae expelled from the polyps
      • later the polyps died
  • Most coral polyps have absolute requirement for alga - but not vice-versa
slide18
MUTUALISM - benefits for algae?
    • shelter
    • protection from nematocysts, & other predation
    • receive waste products of polyp - CO2 & N
  • N is v.limiting in marine environment
    • the major limitation to plant growth
    • algal blooms occur in response to

small changes in N

    • pressure exists to optimize N scavenging
    • favours such a mutualistic relationship
  • Disadvantage
    • algae restricted to shallow tropical waters
slide19
MUTUALISM - benefits for polyp?
    • food (CHO)
    • O2
    • greatly increased ability to precipitate CaCO3
    • without the alga, coral could not have such a high rate of metabolism
      • could not build such extensive reef structures
slide20
Polyp can survive extended periods with no external food source
  • Tight internal N-cycling and algal PS
  • Polyp lays down extensive lipid reserves to be drawn on in times of starvation
  • High light and high food availability
    • ejection of pellets containing viable algal cells
      • Control of algal cell number ?
  • Algae divide within host polyp
slide21
Analyze algal cell
    • C,H,O from PS
    • N,P,S, from host (normally limiting)
  • Symbiosis controlled by host
  • Polyp controls permeability of algal membrane
  • “signal molecules”
slide22
Freshly isolated zooxanthellae
  • Incubate in light with 14CO2
  • Release very little organic C into medium
  • Add some polyp extract - releases lots of organic carbon into medium
  • Other cnidarian extracts work
slide23
“host release factor”HRF
  • Various suggestions:
    • 10kDa protein
    • Free amino acid suite
    • Mycosporine-like amino acids
    • Taurine
  • Tension between HRFand PIF
    • photosynthesis-inhibiting factor

Davy et al: Microbiol. Mol. Biol. Rev. June 2012 vol. 76 no. 2 229-261

slide24
Alga donates most of it’s fixed C to polyp
    • used for resp, growth, etc.
  • Polyp respires
    • releases CO2 to alga
  • Polyp excretes N waste - NH3
    • used by alga
  • Polyp also releases PO4-, SO4-, NO3- to alga
    • 1000x more conc. than in seawater
    • Algae grow faster - helps polyp
slide25

FOOD

Polyp

Protein

CHO

Lipid

Growth &

metabolism

AAs

Sugars

Fatty acids

ATP

NH3

CO2

O2

NH3

CO2

O2

glycerol

AAs

AAs

Sugars

Fatty acids

LIGHT

ATP

NADPH

Protein

CHO

PO4-

PO4-

H2O

H2O

Growth &

metabolism

SO4-

SO4-

Alga

slide28
Alga stores CHO – starch
    • Broken down at night
  • Polyp stores lipid – fat bodies
    • Energy reserve
  • Algal Photosynthesis
    • base of reef productivity
    • energy source for reef building
    • Huge ATP demand
slide29
Overall productivity of the reef:

4.1 - 14.6 gC/m2/d

  • this is organic carbon production
  • must also consider carbonate production (deposition of physical structure of the reef)
    • Get about half of this from the coral symbiosis
    • the rest from the calcareous green & reds algae
slide30
CALCAREOUS ALGAE (greens & reds) are major contributors to reef calcification
    • the more flexible magnesian calcite
  • last 30 years - role of these algae receive more attention
    • play a much bigger role in calcium deposition than previously thought
  • 10% of all algae CALCIFY (about 100 genera)
slide31
In ocean, mostly find 3 forms of CaC03
  • Calcite
    • Mostly of mineral origin
  • Aragonite
    • Fibrous, crystalline form, mostly from corals
  • Magnesian calcite
    • Smaller crystals, mostly plant origin
slide32
Calcification

Calcite

Aragonite

Magnesian calcite

(Mg carbonate)

slide34
Corals
  • remove Ca++ & CO3-- from seawater
  • Combines them to CaCO3
  • transports them to base of polyp
    • Calcicoblastic epidermis
  • minute crystals secreted from base of polyp
  • Energy expensive
    • Energy from metabolism of algal PS products