Coral/algal Reefs IIICoral/algal Reefs III

The future?The future?

Utilitarian justification for reef Utilitarian justification for reef conservationconservation

• Therapeutic compounds from marine Therapeutic compounds from marine speciesspecies– Anti-virals from sponges, seagrassAnti-virals from sponges, seagrass– Anti-tumor compounds from tunicate, dogfish, Anti-tumor compounds from tunicate, dogfish,

bryozoan, sea hares, cyanobacteria, spongebryozoan, sea hares, cyanobacteria, sponge– Compounds to promote bone grafts from stony Compounds to promote bone grafts from stony

coralscorals

• TourismTourism• FoodFood• Impact on global climate, carbon Impact on global climate, carbon

exchangeexchange• Models for scientific studyModels for scientific study

Processes important in reef Processes important in reef dynamics – what maintains the dynamics – what maintains the reef structure?reef structure?• Symbiotic mutualism (and dissolution Symbiotic mutualism (and dissolution

of associations)of associations)

• CompetitionCompetition

• Predation and grazingPredation and grazing

• Disturbance & recoveryDisturbance & recovery

Questions:Questions:

• Are symbiotic Are symbiotic relationships relationships increasingly disrupted?increasingly disrupted?

• What are the What are the consequences?consequences?

• How are organisms How are organisms linked through linked through symbiosis?symbiosis?

• Are changes reversible?Are changes reversible?

Coral bleaching (Hoegh-Guldberg)Coral bleaching (Hoegh-Guldberg)

Coral bleaching – dissolution of Coral bleaching – dissolution of symbiosissymbiosis

• zooxanthellae zooxanthellae expelled from expelled from tissuetissue

• polyp can persist – polyp can persist – for a whilefor a while

• new associations new associations can be formedcan be formed

• responses to responses to stressesstresses

A general introduction to A general introduction to “symbiosis”“symbiosis”

• De Bary (1850’s) – “The living De Bary (1850’s) – “The living together of different species for an together of different species for an extended period of time.”extended period of time.”

• Proximity, not outcomes, define Proximity, not outcomes, define symbiosissymbiosis

• Variation in characterizing some Variation in characterizing some associations, e.g., pollinationassociations, e.g., pollination

Symbiosis has many dimensionsSymbiosis has many dimensions

• Form of physical associationForm of physical association

• Types of organisms involvedTypes of organisms involved

• Nature of the exchange or influenceNature of the exchange or influence

• Outcomes of the interaction (+, 0, -)Outcomes of the interaction (+, 0, -)

• Degree of dependenceDegree of dependence

• Evolutionary derivation of the Evolutionary derivation of the associationassociation

Physical nature of the associationPhysical nature of the association

• Close proximity, Close proximity, but physically but physically independentindependent

• External contactExternal contact

• InternalInternal

What taxa are associated?What taxa are associated?

• Algae-invertebrateAlgae-invertebrate

• Among animalsAmong animals

• Bacteria/archaea - Bacteria/archaea - animalsanimals

What is exchanged?What is exchanged?

CapabilityCapability DonorDonor RecipientRecipientphotosynthesisphotosynthesis algae, bacteriaalgae, bacteria protists, invertsprotists, inverts

chemosynthesischemosynthesis bacteriabacteria invertebratesinvertebrates

added nutrientsadded nutrients bacteriabacteria many animalsmany animals

methanogenesismethanogenesis bacteria, bacteria, protistsprotists

anaerobic anaerobic protistsprotists

cellulose digestioncellulose digestion bacteria, bacteria, protistsprotists

herbivores herbivores (terrest.)(terrest.)

luminescenceluminescence Vibrio, Vibrio, Photobact.Photobact.

molluscs, fishmolluscs, fish

protectionprotection cnidariacnidaria fishfish

What are the outcomes of symbiotic What are the outcomes of symbiotic associations?associations?

-- 00 ++--

00 amensalisamensalismm

commensacommensall

++ parasitismparasitism mutualismmutualism

–RecipientRecipient

Outcomes: nutrient exchangeOutcomes: nutrient exchange

• What is the evidence for exchange What is the evidence for exchange with endosymbiotic dinoflagellates?with endosymbiotic dinoflagellates?

• Experiment: remove zooxanthellaeExperiment: remove zooxanthellae– ammonium content of polyp risesammonium content of polyp rises

• For For TridacnaTridacna clams clams– experimentally enrich with ammoniumexperimentally enrich with ammonium– algal symbiont increases in densityalgal symbiont increases in density

What is the degree of What is the degree of dependence?dependence?

• FacultativeFacultative

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

• Symmetry is not necessarily foundSymmetry is not necessarily found

What is the evolutionary origin of What is the evolutionary origin of the association?the association?

• Parasite-host may evolve to be Parasite-host may evolve to be mutualisticmutualistic

• Predator-prey (coral/dinoflagellate)Predator-prey (coral/dinoflagellate)

• Close proximity may lead to Close proximity may lead to coevolved relationshipcoevolved relationship

How can we evaluate importance?How can we evaluate importance?

• Removal Removal experiments, experiments, e.g., cleaner fishe.g., cleaner fish

• Alter Alter background background conditions – conditions – Chlorella/HydraChlorella/Hydra experimentexperiment

Bleaching occurs with high SSTBleaching occurs with high SST

How does heat (& light) disrupt How does heat (& light) disrupt mutualism?mutualism?

• SymbiodiniumSymbiodinium is damaged by is damaged by oxidative stressoxidative stress

Coral ResponsesCoral Responses

• Polyp responds immunologicallyPolyp responds immunologically– Apoptosis & autophagyApoptosis & autophagy

• Zooxanthellae can be expelledZooxanthellae can be expelled

• Polyp switches to heterotrophyPolyp switches to heterotrophy– This is a short-term strategyThis is a short-term strategy

Sensitivity to SST varies Sensitivity to SST varies

• Among genotypes of Among genotypes of SymbiodiniumSymbiodinium

• Among colonies within coral species Among colonies within coral species

• Between different coral species Between different coral species

• Geographically for the same coral speciesGeographically for the same coral species

Variation in Florida Keys corals, Variation in Florida Keys corals, 20052005

Brandt, M. E. 2009. The effect of species and colony Brandt, M. E. 2009. The effect of species and colony size on the bleaching response of reef-building size on the bleaching response of reef-building corals in the Florida Keys during the 2005 mass corals in the Florida Keys during the 2005 mass bleaching event. Coral Reefs 28:911-924.bleaching event. Coral Reefs 28:911-924.

• BackgroundBackground– Summer & fall, 2005 – high SST in ne Summer & fall, 2005 – high SST in ne

CaribbeanCaribbean– Mass bleaching documentedMass bleaching documented

• MethodsMethods– Monitor corals for 191 colonies in Monitor corals for 191 colonies in

permanent quadratspermanent quadrats

Bleaching was correlated with Bleaching was correlated with heatingheating

Bleaching prevalence varied Bleaching prevalence varied among sppamong spp

Bleaching incidence varied with Bleaching incidence varied with colony sizecolony size

Why and what’s next?Why and what’s next?

• Symbiont “clades” vary geneticallySymbiont “clades” vary genetically– Corals can switchCorals can switch– SymbiodiniumSymbiodinium communities can vary communities can vary

across environmental gradientsacross environmental gradients– Degree of flexibility is debatedDegree of flexibility is debated

• Hosts (corals) also varyHosts (corals) also vary– Different fluorescent proteins for protectionDifferent fluorescent proteins for protection– Different abilities in heterotrophyDifferent abilities in heterotrophy– Coral structure affects the light Coral structure affects the light

environmentenvironment

Competitive dynamicsCompetitive dynamics

• Exploitation competition (for light)Exploitation competition (for light)– Upright, branching corals can shade Upright, branching corals can shade

massive coralsmassive corals– Encrusting algae can spread over coralsEncrusting algae can spread over corals

• Interference competition (for space)Interference competition (for space)– External digestion by some coralsExternal digestion by some corals– ““Sweeper” tentacles for some speciesSweeper” tentacles for some species

• Hierarchy of competitive dominanceHierarchy of competitive dominance– Algae easily overgrow most coralsAlgae easily overgrow most corals– Among corals Among corals PocilloporaPocillopora is nastiest is nastiest

Dynamics of predation on coral reef Dynamics of predation on coral reef speciesspecies

• Coral-feeding fish are present but Coral-feeding fish are present but usually not devastatingusually not devastating– Territorial damselfish create safe zones Territorial damselfish create safe zones

(up to 60% of surface area)(up to 60% of surface area)– Coral-feeders have their own predatorsCoral-feeders have their own predators

• Starfish, such as “Crown-of-Thorns” Starfish, such as “Crown-of-Thorns” can be problematiccan be problematic– Population “outbreaks” can damage Population “outbreaks” can damage

living coralsliving corals

Dynamics of grazing on algal reef Dynamics of grazing on algal reef speciesspecies• Urchins are major Urchins are major

consumers (e.g., consumers (e.g., Diadema antillarumDiadema antillarum))

• Grazing by herbivorous Grazing by herbivorous fish can be specialized fish can be specialized on algae (more impact on algae (more impact than fish feeding on than fish feeding on corals)corals)

• Grazing can suppress Grazing can suppress competitively dominant competitively dominant algaealgae

• Indirect effects can Indirect effects can become importantbecome important