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Coral/algal Reefs III

Coral/algal Reefs III. The future?. Utilitarian justification for reef conservation. Therapeutic compounds from marine species Anti- virals from sponges, seagrass Anti-tumor compounds from tunicate, dogfish, bryozoan , sea hares, cyanobacteria , sponge

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Coral/algal Reefs III

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  1. Coral/algal Reefs III The future?

  2. Utilitarian justification for reef conservation • Therapeutic compounds from marine species • Anti-virals from sponges, seagrass • Anti-tumor compounds from tunicate, dogfish, bryozoan, sea hares, cyanobacteria, sponge • Compounds to promote bone grafts from stony corals • Tourism • Food • Impact on global climate, carbon exchange • Models for scientific study

  3. Processes important in reef dynamics – what maintains the reef structure? • Symbiotic mutualism (and dissolution of associations) • Competition • Predation and grazing • Disturbance & recovery

  4. Questions: • Are symbiotic relationships increasingly disrupted? • What are the consequences? • How are organisms linked through symbiosis? • Are changes reversible?

  5. Coral bleaching (Hoegh-Guldberg)

  6. Coral bleaching – dissolution of symbiosis • zooxanthellae expelled from tissue • polyp can persist – for a while • new associations can be formed • responses to stresses

  7. A general introduction to “symbiosis” • De Bary (1850’s) – “The living together of different species for an extended period of time.” • Proximity, not outcomes, define symbiosis • Variation in characterizing some associations, e.g., pollination

  8. Symbiosis has many dimensions • Form of physical association • Types of organisms involved • Nature of the exchange or influence • Outcomes of the interaction (+, 0, -) • Degree of dependence • Evolutionary derivation of the association

  9. Physical nature of the association • Close proximity, but physically independent • External contact • Internal

  10. What taxa are associated? • Algae-invertebrate • Among animals • Bacteria/archaea - animals

  11. What is exchanged?

  12. What are the outcomes of symbiotic associations? • Recipient

  13. Outcomes: nutrient exchange • What is the evidence for exchange with endosymbioticdinoflagellates? • Experiment: remove zooxanthellae • ammonium content of polyp rises • For Tridacna clams • experimentally enrich with ammonium • algal symbiont increases in density

  14. What is the degree of dependence? • Facultative • Obligate (often has very specialized morphology and life history) • Symmetry is not necessarily found

  15. What is the evolutionary origin of the association? • Parasite-host may evolve to be mutualistic • Predator-prey (coral/dinoflagellate) • Close proximity may lead to coevolved relationship

  16. How can we evaluate importance? • Removal experiments, e.g., cleaner fish • Alter background conditions – Chlorella/Hydra experiment

  17. Bleaching occurs with high SST

  18. How does heat (& light) disrupt mutualism? • Symbiodinium is damaged by oxidative stress

  19. Coral Responses • Polyp responds immunologically • Apoptosis & autophagy • Zooxanthellae can be expelled • Polyp switches to heterotrophy • This is a short-term strategy

  20. Sensitivity to SST varies • Among genotypes of Symbiodinium • Among colonies within coral species • Between different coral species • Geographically for the same coral species

  21. Variation in Florida Keys corals, 2005

  22. Brandt, M. E. 2009. The effect of species and colony size on the bleaching response of reef-building corals in the Florida Keys during the 2005 mass bleaching event. Coral Reefs 28:911-924. • Background • Summer & fall, 2005 – high SST in ne Caribbean • Mass bleaching documented • Methods • Monitor corals for 191 colonies in permanent quadrats

  23. Bleaching was correlated with heating

  24. Bleaching prevalence varied among spp

  25. Bleaching incidence varied with colony size

  26. Why and what’s next? • Symbiont “clades” vary genetically • Corals can switch • Symbiodinium communities can vary across environmental gradients • Degree of flexibility is debated • Hosts (corals) also vary • Different fluorescent proteins for protection • Different abilities in heterotrophy • Coral structure affects the light environment

  27. Competitive dynamics • Exploitation competition (for light) • Upright, branching corals can shade massive corals • Encrusting algae can spread over corals • Interference competition (for space) • External digestion by some corals • “Sweeper” tentacles for some species • Hierarchy of competitive dominance • Algae easily overgrow most corals • Among corals Pocillopora is nastiest

  28. Dynamics of predation on coral reef species • Coral-feeding fish are present but usually not devastating • Territorial damselfish create safe zones (up to 60% of surface area) • Coral-feeders have their own predators • Starfish, such as “Crown-of-Thorns” can be problematic • Population “outbreaks” can damage living corals

  29. Dynamics of grazing on algal reef species • Urchins are major consumers (e.g., Diadema antillarum) • Grazing by herbivorous fish can be specialized on algae (more impact than fish feeding on corals) • Grazing can suppress competitively dominant algae • Indirect effects can become important

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