Download Coral Reefs & Global Warming

Coral Reefs
Scleractinian corals
• Phyllum Cnidaria
– Class Anthozoa
• Subclass Zoantharia
– Order Scleractinia
Only polyp phase (no medusae)
Colonial organisms
CaCO3 exoskeleton
Symbiosis with zooxanthellae
http://krupp.wcc.hawaii.edu/
Cnidarian Polyp
Antozoan corals form
Reefs by accumulation
of exoskeletons
Zooxanthellae
• Non-motile naked
dynoflagellates
• Embedded in
transparent polyps
• Use corals wastes (CO2
+ nutrients)
• Contribute 60% of
primary production to
polyp
• Corals get ~50% energy
from Zoox; ~50% from
heterotrophic feeding
Scleractinian corals stats
• Average Colony Age ~ 100 years
• Growth rates ~ 0.5 – 20 cm/year
– Boulder corals  slow growth (0.5-1)
– Branching corals  fast growth (10-20)
• Corals reefs
– Originated in Triassic (220 mya)
– Distributed between 24oN – 24oS latitude
Coral Reefs environmental requirements
• Temperature (18 – 30 oC)
– Low Solubility of CaCO3 at high temp.
• Depth (0-150 m)
– Within photic zone
– Below low tide
• Sedimentation
– Low tolerance (prefer clear waters)
• Salinity (33‰ and up)
– Low tolerance of fresh water
• Wave action
– (high O2, clear water and pelagic food supply)
Coral reef distribution and Diversity
IndoPacific Diversity
Eastern Ocean Dominance
Global Surface Currents
Chlorophyll Concentration
Ecosystem Productivity
(Annual net productivity)
Coral reef productivity
• Efficient Coral – Zooxanthellae simbiosis
– Little loss of nutrients to water
• Steep drop-offs promote increase
pelagic productivity
– Backreef eddies, local nutrient upwelling
• Partially closed systems
– high ammounts of benthic organic detritus
Fringe reefs
Evolution of
Coral Reefs
(Darwin)
Barrier reefs
Atolls
subsidence ~0.03 mm/yr =
1,200,000 mm/40,000,000 yr
1950 Enewetak
Cross-sections of various types of coral reefs
Turtle Grass Lagoon
Sandy Lagoon
Patch reef lagoon
Reef flat
Reef crest
Reef crest – high wave energy
Shallow seaward reef
Shallow seaward reef – Acropora corals
Reef outer slope
Buttress Zone with sand channels
Outer reef wall
Coral Reef Zonation
• Lagoon
– Filled with sediments, corals grow or not according to
sediment suspension & re-suspension rates
• Reef flat
– Protected, clear oceanic water, high growth rates
• Reef crest
– High wave turbulence, tidal exposure, calcareous algae
can dominate
• Outer or seaward reef slope
– High coral complexity, buttress formations
• Outer reef wall or drop-off
– Low light adapted species, Deep coral morphs,
heterotrophy
Present degradation of coral reefs
• Natural Disturbances:
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Hurricanes and Storms
Coral Bleaching
Predation of Corals
Coral Diseases
• Human Indirect Disturbances
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Land Sedimentation
Eutrophization (coral diseases)
Overfishing (trophic cascading)
Global Warming (bleaching)
Hurricanes, Typhoons & Cyclones
Hurricanes & Typhoons
• Destroy reefs by:
– Wave Action
– Sedimetation
• Hurricanes hit a specific reef every ~
20 years
• Coral growth rate ~1-20cm
Coral Diseases
• Black-Band Disease
• White-Band Disease
• Cyanobacteria infection
• Affects boulder corals
• Bacterial infection
• Affects Acropora spp.
• St. Croix ~95% kill
Aspergillosis
Bacterial Bleaching
Black Band
Dark Spots
White Band
White Plague
White Pox
Yellow Band
Future of Coral Reefs
Coral Bleaching
• Expulsion of Zooxanthellae symbionts
• Causes:
– Decrease in Salinity
• River runoff, heavy rains
– Decrease of Light
• Sedimentation – Turbidity
– Increase water Temperature (+30’s oC)
(enhanced by high UV exposure)
• El Niño – Mass Bleaching
• Global Warming
• +2 oC / 100 years
Zooxanthella
Coral Bleaching
www.ogp.noaa.gov