Tropical Reefs: Coral/AlgalTropical Reefs: Coral/Algal

Diversity and ChallengesDiversity and Challenges

Questions:Questions:

• Why are tropical reefs comparable to Why are tropical reefs comparable to rain forests in diversity?rain forests in diversity?– Dissolved nutrients are scarceDissolved nutrients are scarce– Productivity & diversity normally go Productivity & diversity normally go

togethertogether

• Why are tropical reefs disappearing?Why are tropical reefs disappearing?

Increasing threats to coralIncreasing threats to coral

Current bleaching threatsCurrent bleaching threats

What are the challenges?What are the challenges?

• Low nutrients dissolved in waterLow nutrients dissolved in water

• Shallow habitats mean more intense Shallow habitats mean more intense wave actionwave action

• Long-term: sea level changesLong-term: sea level changes

Tropical reefs are geologically Tropical reefs are geologically importantimportant

Reef ecology has long challenged Reef ecology has long challenged biologistsbiologists

Dominant reef-building organismsDominant reef-building organisms

• Small individuals, magnified in effect Small individuals, magnified in effect by large numbersby large numbers

• Phylum CnidariaPhylum Cnidaria– Class AnthozoaClass Anthozoa

•Subclass ZoantheriaSubclass Zoantheria

• Diverse algae, depositing CaCODiverse algae, depositing CaCO33

Cnidaria polyps: radial symmetryCnidaria polyps: radial symmetry

Cnidaria: tentacles for feedingCnidaria: tentacles for feeding

Cnidaria: stinging cells on Cnidaria: stinging cells on tentaclestentacles

Not all corals deposit CaCONot all corals deposit CaCO33

““HermatypicHermatypic” corals create reefs ” corals create reefs in symbiosis with in symbiosis with SymbiodiniumSymbiodinium

Growth forms of colonies reflect Growth forms of colonies reflect tradeoffstradeoffs

• Access to light for symbiotic algaeAccess to light for symbiotic algae– Issues of depth (growth upward)Issues of depth (growth upward)– Issues of competition (shading)Issues of competition (shading)

• Risk of damage from turbulence in Risk of damage from turbulence in shallow seasshallow seas

• Diverse growth forms reflect different Diverse growth forms reflect different balancesbalances

Fast extension: linear growth formFast extension: linear growth form

Extension + more surface area: Extension + more surface area: branchingbranching

Lattice: a subset of “branching” Lattice: a subset of “branching” formform

Plate form: more resistant to Plate form: more resistant to turbulenceturbulence

Massive form: very wave-resistantMassive form: very wave-resistant

Independent algae build reefs: Independent algae build reefs: crustosecrustose

Algae can contribute a large fraction of reef Algae can contribute a large fraction of reef massmass

Independent algae: Green Independent algae: Green ((HalimedaHalimeda))

Reefs: a matrix of solid coral and Reefs: a matrix of solid coral and sandsand

Reef diversity – some examplesReef diversity – some examples

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