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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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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

    • Compounds to promote bone grafts from stony corals

  • Tourism

  • Food

  • Impact on global climate, carbon exchange

  • Models for scientific study


Processes important in reef dynamics – what maintains the reef structure?

  • Symbiotic mutualism (and dissolution of associations)

  • Competition

  • Predation and grazing

  • Disturbance & recovery


Questions:

  • Are symbiotic relationships increasingly disrupted?

  • What are the consequences?

  • How are organisms linked through symbiosis?

  • Are changes reversible?


Coral bleaching (Hoegh-Guldberg)


Coral bleaching – dissolution of symbiosis

  • zooxanthellae expelled from tissue

  • polyp can persist – for a while

  • new associations can be formed

  • responses to stresses


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


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


Physical nature of the association

  • Close proximity, but physically independent

  • External contact

  • Internal


What taxa are associated?

  • Algae-invertebrate

  • Among animals

  • Bacteria/archaea - animals


What is exchanged?


What are the outcomes of symbiotic associations?

  • Recipient


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


What is the degree of dependence?

  • Facultative

  • Obligate (often has very specialized morphology and life history)

  • Symmetry is not necessarily found


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


How can we evaluate importance?

  • Removal experiments, e.g., cleaner fish

  • Alter background conditions – Chlorella/Hydra experiment


Bleaching occurs with high SST


How does heat (& light) disrupt mutualism?

  • Symbiodinium is damaged by oxidative stress


Coral Responses

  • Polyp responds immunologically

    • Apoptosis & autophagy

  • Zooxanthellae can be expelled

  • Polyp switches to heterotrophy

    • This is a short-term strategy


Sensitivity to SST varies

  • Among genotypes of Symbiodinium

  • Among colonies within coral species

  • Between different coral species

  • Geographically for the same coral species


Variation in Florida Keys corals, 2005


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


Bleaching was correlated with heating


Bleaching prevalence varied among spp


Bleaching incidence varied with colony size


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


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


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


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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