coral/algal reefs ii what forces maintain reef diversity?

Coral/algal Reefs IICoral/algal Reefs II

What forces maintain reef What forces maintain reef diversity?diversity?

Planet Earth videoPlanet Earth video

Ecological functional groupsEcological functional groups

A larger scale view: reef building A larger scale view: reef building processprocess

Atoll structureAtoll structure

Habitat diversity within an atollHabitat diversity within an atoll

Niche dimensions enhancing reef Niche dimensions enhancing reef fish diversityfish diversity

• Defensive tacticsDefensive tactics

• FeedingFeeding– Food typeFood type– Food locationFood location– Timing of foragingTiming of foraging

• Life-history and social structureLife-history and social structure

Physical defenses: Spines of Porcupine Physical defenses: Spines of Porcupine fishfish

Physical defenses: misdirection, Physical defenses: misdirection, Butterfly fishButterfly fish

Territoriality: Territoriality: PomacentrusPomacentrus

Poisons: Purple trunk fish, lionfishPoisons: Purple trunk fish, lionfish

Feeding: >50% feed on other fishFeeding: >50% feed on other fish

• Variation by size, location, timingVariation by size, location, timing

Feeding: coral (Triggerfish)Feeding: coral (Triggerfish)

Feeding: “inverts” by probing (file Feeding: “inverts” by probing (file fish)fish)

Feeding: marine worms (butterfly Feeding: marine worms (butterfly fish)fish)

Feeding: plankton (purple queen)Feeding: plankton (purple queen)

Feeding: algae (surgeon fish)Feeding: algae (surgeon fish)

Feeding: other fish/ cleaning Feeding: other fish/ cleaning symbiosissymbiosis

–Pacific Cleaner Pacific Cleaner WrasseWrasse

–Moray EelMoray Eel

–Saber Tooth Saber Tooth BlennyBlenny

External factors influencing External factors influencing diversitydiversity• Proximity to mangrove nurseriesProximity to mangrove nurseries

– Mumby et al. 2004, Nature 427:533Mumby et al. 2004, Nature 427:533– Compare fish biomass from reefs near mangroves Compare fish biomass from reefs near mangroves

and where mangroves scarceand where mangroves scarce

SpeciesSpecies Scarce Scarce mangrovemangrove

Rich Rich mangrovemangrove

H. sciurusH. sciurus 1,2051,205 33,34933,349

H. pumieriH. pumieri 5,1745,174 16,28016,280

HaemulidaHaemulidaee

11,63611,636 67,37067,370

L. apodusL. apodus 739739 6,1926,192

How can coral/algal reefs support so How can coral/algal reefs support so many species?many species?

• ““Bottom-up” hypothesesBottom-up” hypotheses– High degree of nutrient recycling (symbiotic High degree of nutrient recycling (symbiotic

mutualism) promotes coralsmutualism) promotes corals– Coral diversity promotes associated speciesCoral diversity promotes associated species– ““Biotic multiplier effectBiotic multiplier effect””

• ““Top-down” hypothesesTop-down” hypotheses– Predation rates/disturbance reduce Predation rates/disturbance reduce

competitioncompetition– Patchy environments with variable colonizationPatchy environments with variable colonization– Priority advantage (inhibition model)Priority advantage (inhibition model)

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?• Symbiosis (and dissolution of Symbiosis (and dissolution of

associations)associations)

• CompetitionCompetition

• Predation and grazingPredation and grazing

• Disturbance & recoveryDisturbance & recovery

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