1. Productivity and the Coral Symbiosis II

4. 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

5. Zooxanthellae can live outside their host –essential in some species for finding a host Dinomastigotes stage –motile free-living state, have two flagellae Coccoid stage –living in animal cells, lack flagellae In culture, zooxanthellae alternate between coccoid and dinomastigote stages

6. Almost all zooxanthellae are in the dinflagellate genus Symbiodinium (1959) taxonomy of Symbiodinium in a state of flux 1980 - Symbiodinium microadriaticum assumed to be the one species found in almost all corals

7. 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

8. 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

9. Indirect acquisition –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

10. In all hermatypic corals endosymbiotic algae provide an important source of nutrients can demonstrate mutualistic relationship feed 14 CO 2 to the coral –quickly taken up by alga and ends up in the polyp feed zooplankton raised on 15 N to coral – quickly taken up by polyp and ends up in the alga

11. 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

12. MUTUALISM - benefits for algae? –shelter –protection from nematocysts, & other predation –receive waste products of polyp - CO 2 & 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

13. MUTUALISM - benefits for polyp? –food (CHO) –O 2 –greatly increased ability to precipitate CaCO 3 –without the alga, coral could not have such a high rate of metabolism could not build such extensive reef structures

14. 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

15. 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”

16. Freshly isolated zooxanthellae Incubate in light with 14 CO 2 Release very little organic C into medium Add some polyp extract - releases lots of organic carbon into medium Other cnidarian extracts work

17. Alga donates most of it’s fixed C to polyp –used for resp, growth, etc. Polyp respires –releases CO 2 to alga Polyp excretes N waste - NH 3 –used by alga Polyp also releases PO 4 -, SO 4 -, NO 3 - to alga –1000x more conc. than in seawater –Algae grow faster - helps polyp

18. FOOD CHOProtein AAsSugarsFatty acids Alga Polyp NH 3 CO 2 O2O2 O2O2 NH 3 AAs Protein AAsSugars CHO Lipid ATP NADPH Fatty acids Growth & metabolism Growth & metabolism glycerol H2OH2OH2OH2O LIGHT PO 4 - SO 4 - ATP

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

20. 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