Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Coral Structure and Function II – Primary Production – Benthic – Cnidaria – Atoll analysis 1. Calcareous red algae 2. Calcareous green algae (Halimeda) 3. Foraminifera (20-40m protists, porous CaCO3 shell) 4. Corals – Coral polyp – predacious • Endosymbiont – zooxanthellae • 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 • 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 • 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 mucus nematocysts • 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 • 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 • 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 Usually a single Symbiodinium clone in a coral colony. Sometimes two. Adjacent colonies have same or similar Symbiodinium populations. Symbiodinium Diversity Patterns 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 • 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 Davy et al: Microbiol. Mol. Biol. Rev. June 2012 vol. 76 no. 2 229-261 • 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 • 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 • 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 • 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 • 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 • 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” • 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 • “host release factor” HRF • Various suggestions: – 10kDa protein – Free amino acid suite – Mycosporine-like amino acids – Taurine • Tension between HRF and PIF – photosynthesis-inhibiting factor Davy et al: Microbiol. Mol. Biol. Rev. June 2012 vol. 76 no. 2 229-261 • 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 FOOD Polyp Protein CHO Lipid AAs Sugars Fatty acids Growth & metabolism ATP NH3 CO2 NH3 CO2 O2 O2 glycerol AAs AAs Sugars Fatty acids LIGHT ATP NADPH Protein PO4- PO4- SO4- SO4- CHO Growth & metabolism H2O Alga H2O Mar Drugs. 2010; 8(10): 2546–2568. Calcification - growth of the reef Alga stores CHO – starch • • Polyp stores lipid – fat bodies • • • Broken down at night Energy reserve Algal Photosynthesis • base of reef productivity • energy source for reef building • Huge ATP demand • 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 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) • 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 Calcification Calcite Aragonite Magnesian calcite (Mg carbonate) • Examples: organism Molluscs Corals Some green algae Red algae Sponges Some bryozoans CaCO3 calcite & aragonite just aragonite just aragonite magnesian calcite aragonite (with silica) all 3 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 Calcification