coral reefs (exam 3)

identify & describe environmental factors that allow for coral formation/growth

* only on continental shelves/surrounding islands/seamounts
* Require high PAR: shallow/clear water
* sensitive to decrease in salinity
* sensitive to high nutrient/pollution: like oligotrophic waters (nutrient poor)
* warm water for growth/reproduction

Ahermatypic corals

* non-reef building


* soft corals/black corals/gorgonians
* worldwide in deep/cold water
* often lack zooxanthelleae

hermatypic corals

* reef-building corals
* stony/blue/fire/organ-pipe corals
* Coral polyps produce CaCO3 skeletons that produce large limestone reefs overtime

global distribution of coral reefs

* 30 degrees N/S of equator: Caribbean, Indo-west Pacific
* Not in areas w/ cool water upwelling: Tropical coasts of americas, west Africa

how are coral reefs formed?

large amounts of calcium carbonate deposits

reef building organisms

* hermatypic corals
* encrusting coralline algae
* foams
* snails
* clams/mollusks
* bacteria

two major groups that deposit limestone that form coral reefs?

* hermatypic coral polyps and skeletons
* encrusting coralline algae

encrusting coralline algae

* rock hard sheets that deposit CaCO3
* build reef/keep it from washing away
* glue that holds reef together/cements sediment in place

Coral Polyps

* cylinder tissue w/ ring of tentacles surrounding mouth that opens to simple gut on top
* continually lay down CaCO3 to build Skeleton
* catch zooplankton and detritus
* connected digestive system and shared nervous system

mesenterial filaments within coral

secrete digestive enzymes

planula

* coral polyp larvae

coral growth forms

* plate-like
* foliaceous (leaf-like)
* columnar
* massive
* branching
* encrusting
* free-living (can move)

fringing reef

* simplest/most common
* grow along hard bottom in narrow band along shore
* closest to land
* reef flat, reef slope, reef crest

reef flat (fringing reef)

* wide/shallow
* can be exposed at low tides
* some living corals
* soft corals, seagrasses, seaweeds

reef slope (fringing reef)

* steep/vertical
* more gradual slope = more diversity
* densest coral cover/high species richness

reef crest (fringing reef)

* upper/outer ridge of reef flat
* intense wave action
* algal ridge absorbs wave energy: formed by encrusting coralline algae

Barrier reefs

* miles from shore & separated by deep lagoon
* GBR is largest
* Back-reef slope, fore-reef slope, reef crest, reef flat

lagoon

* separates barrier reef from shore
* soft-bottom sediment with seagrasses
* patch reefs, coral knolls, coral pinnacles can be found back

back-reef slope (barrier reefs)

* gentle sloping or steep


* no direct wave action but waves sweep sediment down slope so less abundant coral growth
* higher diversity/abundance on gentle slopes

fore-reef slope (barrier reefs)

* may have spur and groove formations due to wave/wind action

Atolls

* ring of reefs/islands or sand cays
* surround central lagoon
* active volcano/fringing reef/barrier reef/atoll
* < 1 mile- 30 miles across
* tropical Indian Ocean/west Pacific Ocean
* no FW or sediment runoff

tropic structure of coral reefs

* high PP due to production & efficient use of nutrients
* zooxanthellae & coral polyp mutualism: support vast communities in nutrient poor waters
* turf algae grow in thick mats on reef flats: consumed by fishes, sea urchins, snails

zooxanthellae and coral polyp mutualism

* efficient nutrient cycling occurs
* coral polyps benefit through: increased growth/reproduction/calcification/conservation of nutrients
* zooxanthellae benefit through: supply of CO2/nutrients, protection from UV radiation

reef growth is a balance between?

accretion and erosion

reef growth and bioemersion

* bio erosion done by organisms mainly boring into coral skeletons
* influenced by dominance of fishes & inverts
* herbivorous fish: clear places for coral to settle
* sea urchins/parrot fish good bioeroders

competition on reefs

* high competition for space and light access
* hard/soft corals, sponges, seaweeds, sessile species compete for space

examples of coral competition

* digest tissues of neighbors encroaching on their space
* sweeping tentacles w/ nematocysts sting neighbors

more aggressive vs less aggressive corals

* more aggressive: massive, slow growing forms
* less aggressive: faster-growing, upright/branching forms

competition on reef for encrusting algae

* grows slow
* grows where corals can’t due to waves, sedimentation, predation

soft vs hard coral competition

* soft corals grow faster than hard corals
* hard corals more efficient in photosynthesis
* soft corals can detach and move/blown by current or wave

larval settlement on reefs?

determines species abundance and composition

threats to coral reefs

* direct/social drivers
* disease
* storms
* crown of thorn starfish
* **pollution**
* **fishing**
* **climate change**
* tourism
* invasive species
* El nino events

El nino events

* decrease upwelling in central & eastern pacific


* decrease productivity
* increase mass mortality of fishes in costal areas/cold water adapted species
* mass coral bleaching

bleaching of coral in in Indo west pacific and along GBR

* >95% mass coral mortality in IWP
* 67% coral loss overall in GBR
* 85-95% coral loss in northern GBR