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Productivity and the Coral Symbiosis II

Productivity and the Coral Symbiosis II. dinoflagellates chlorophylls a and c lack chlorophyll b characteristic dinoflagellate pigments diadinoxanthin and peridinin ~ 3 x 10 6 cells/cm 2 coloured tinge to the coral brown to yellow brown.

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Productivity and the Coral Symbiosis II

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  1. Productivity and the Coral Symbiosis II

  2. dinoflagellates • chlorophylls a and c • lack chlorophyll b • characteristic dinoflagellate pigments diadinoxanthin and peridinin • ~ 3 x 106 cells/cm2 • coloured tinge to the coral • brown to yellow brown

  3. 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

  4. 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

  5. Recent work • great genetic diversity in zooxanthellae • clearly more than one species • at least 16 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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”

  14. 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

  15. 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

  16. 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

  17. Mar Drugs. 2010; 8(10): 2546–2568.

  18. Alga stores CHO – starch • Broken down at night • Polyp stores lipid – fat bodies • Energy reserve • Algal PS: 90% fixed C to coral host • Used for metabolic functions • Growth, reproduction & • Calcium deposition

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