Coral Biology & Ecology

Coral Questions

• What is a coral?

• What do they eat?

• How do they spread or reproduce?

• How do they get their color?

• How old are they?

• What kinds of coral do we have on the Big Island?

• What eats coral?

• What is coral disease and bleaching?

Coral Reefs Worldwide

• 284,300 square kilometers (110,000 square miles )• 0.7% of the ocean floor, support over 25% of all known marine

species

Coral Reef Facts

• Corals are over 500 million years old

• Cover over 600,000 sq kilometers of earth’s surface Estimated 88% of coral reefs are in Southeast Asia

• Since 1975, over 90% of live coral cover lost in Florida Keys

• Colonies may be 1,000 years old and attain a height of 25ft

• Atolls and barrier reefs can consist of coral limestone deposits up to 5,000 ft thick

Biogeography: Larval Dispersal

Number of species highest in “Cradle of Diversity”, with speciation declining with distance. - Viable larvae in plankton, - Rafting

Endemism

• Endemic: unique to a defined place or region and not naturally found anywhere else.

• Hawai‘i has some of the highest endemism: overall 30% of shallow water species are endemic

What is Coral?

Coral Family Tree

AnthozoaHard, soft, and precious corals, sea fans, zooanthids, anemones, sea

pens

Cubozoabox jellies

Hydrozoahydroids, medusae

Scyphozoa

true jellies

Phylum

CnidariaDefining characteristic: cnidae (nematocyst)

Polyp and Medusa stages

Polyp only

Polyp Cross Section

• Upright hollow cylinders of tissue

- Tentacles- Mouth- Stomach- Mesenterial filaments

• 2 tissue layers- Epidermis- Gastrodermis- Mesogloea (matrix

between layers

• Hard corals:- Calcium carbonate

skeleton

Coral Tissue

• 2 tissue layers

Epidermis

Gastrodermis

Nematocyst

Mucous Cells

Zooxanthellae

Stinging Cells: Cnidocytes and Nematocysts

• Cnidocytes: stinging cells on tentacles• Nematocysts: Thread with venomous

barb

The Coral/Algal Symbiosis

• Highly efficient nutrient cycling- Coral fertilizes the zooxanthellae- zooxanthellae “feeds” the coral

• Evolved to thrive in nutrient poor waters

• Very little “outside” energy needed

Symbiosis: Who benefits?

• Coral benefits:- Removes coral waste products - Provides nutrients from photosynthesis

(up to 95% of photosynthesis product)- Enhances coral’s rate of calcification

• Zooxanthellae benefits:- Gains nutrients from coral waste- Protected in tissues- Harmful UV light filtered by coral tissue

• Mutualistic symbiosis: both benefit

Hard or Stony Corals

Coral Colony: the Wall of Mouths

Coensarc

Polyp

Skeleton

Calyx

Septa

Coral Diet

• Zooxanthellae provide as much as 98% of colony’s nutrients

• Carnivorous Animals

- Zooplankton

- Tentacles and nematocysts catch prey

• Mucus Membranes

- Trap organisms, cilia pass along to mouth

- Transfer nutrients between polyps

• Absorption through cell walls

- DOM (dissolved organic matter)

Sexual Reproduction

Mature Colony

Primary Polyp

Budding & Fission

(cloning)

Settlement

BroodersInternal

fertilization

Planulae released

Sperm

Sperm

BroadcastersExternal fertilization

Synchronous releaseEgg

s

Planulae

Zygote

Asexual Reproduction

Mature Colony

Polyp Bail-out

Attachment

Budding & Fission

(cloning)

Fragmentation

Attachment

Coral Reefs of the World

Why are corals only in the tropics?

Coral Limiting Factors

Limiting factor: controls a process, such as an organism’s growth, a species population size, or distribution.

• Light Intensity

• Depth 0 – 150m

• Hard Substrate

• Low Nutrients

• Salinity: 32-35 ppt

• Sediments

Darwin’s Point

• Point where subsistence and erosion is greater than coral growth

29o N

What eats coral?

Coral Predators: Invertebrates

Coral Predators: Fish

What are coral disease and bleaching?

Coral Bleaching

• Coral Bleaching 

• Response to stress - Temperature - UV - Oxygen - Darkness - Sedimentation

• Who initiates bleaching? • Can corals recover? • Where do zooxanthellae go? 

• “Free” zooxanthellae are rarely found in plankton samples - May become benthic, sessile - May go into dormant stage

Coral Disease

• Montipora tissue loss

• Porites Trematodiasis

• Band Disease

• Tumors: Hyperplasia

Hawaiian Corals

Hawaiian Coral Facts

• In Hawai‘i: approximately 150 species - Approximately 45 species are reef building - Others includes

- Octocorals and soft corals- zooanthids- black and wire coral

- Hawaiian names: ‘āko‘ako‘a, ko‘a, puna kea

• The Hawaiian Islands have 410,000 acres of living reef in the main islands alone, more than the landmass of O‘ahu

Coral Growth Forms

Coral Zonation

Zonation driven by physical parameters:

• Encrusting- Very high wave energy or very

low light intensity• Branching Corals:

- Low wave energy- High light intensity- Exception: Cauliflower coral

• Massive:- Moderate wave energy- Moderate light intensity

• Columnar:- Low wave energy- Low light intensity

• Plate:- No wave energy- Very low light levels

The fight for space

• Nematocysts/Tentacles• Mesenterial filaments• Overgrowing• Shading

Branching Corals

Cauliflower Coral (Pocillopora meandrina)Most common in shallow, high

energySpawning April – May at full moon

Antler Coral (Pocillopora eydouxi)

Largest branching coralPredators: Blue-eye damselfish and butterflyfish

• Provides protection for small organisms• Reproduction: Separate sexes, broadcast spawning April–May at

full moon• Predators: Acanthaster planci, butterflyfish

Rice Corals

Blue Rice Coral (Montipora flabellata)

- Endemic- Fluorescent pigments

Rice Coral (Montipora capitata)

- encrusting, branching and plate forms

• Reproduction: Hermaphroditic, broadcast spawning April-May, full moon

• Predators: Acanthaster planci and butterflyfish

Acropora sp.

• Most common pacific coral, over 350 species

• In Hawai‘i, only 5 species in Northwest Hawaiian Islands

• Why?

Lobe Coral pōhaku puna

Green Lobe Coral (Porites lobata)EndemicMassive and encrusting growth

formsMajor reef builderReproduction: July – August

Predators: Shortbodied blenny, butterflyfish

• Massive forms, major reef builders 10 – 50 ft depth• Colonies up to 10ft high, growth 1cm/yr• Up to 400 years old

Brown Lobe Coral (Porites lutea)Polyps not fully retracted –

“fuzzy looking”Reproduction: August –

September

Predators: butterflyfish

Finger Coral

Porites compressa• Endemic• Most common species in wave-

protected areas• Complex growth form provides

protection to many organisms

• Reproduction: - Separate sexes- Syncronized broadcast

spawning, June – August full moon

• Predators: Nudibranchs and butterflyfish

Plate and Pillar Coral

• Porites rus • Common on Kona

coast• Thick columns in

shallow water and stacked plates deeper down

• Fragile plates

• Reproduction: - Broadcast spawning –

Unknown

• Predators: Butterflyfish

Mushroom Coral

Fungia scutaria • Free living polyp• Prefer calm or deep

areas

• Reproduction: - Separate sexes- Broadcast spawning- Summer, full moon- Juveniles grow on

stalk attached to parent

• Predators: Nudibranchs and butterflyfish

Other Encrusting Corals

• Corrugated Coral (Pavona varians)- Meandering ridges and valleys- Often overgrows bases of Finger coral- Separate sexes

• Crust Coral (Leptastrea purpurea)- Large calyces- Widely dispersed: High energy to deep reef- Hermaphroditic

Non-Reef Building Corals

Orange Cup Coral (Tubastraea coccinea)

Black coral (antipathes sp.) Snowflake Coral(Carijoa riisei)

Zoanthid (Zoanthus sp.)

Wire Coral (cirrhipathes sp.)

Soft corals (Sinularia sp.)

Describe this environment…

Describe this environment…

Describe this environment…