coral reefs (exam 3)

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

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