Coral Reefs Scleractinian corals Phyllum Cnidaria Class Anthozoa

Coral Reefs

Scleractinian corals • Phyllum Cnidaria – Class Anthozoa • Subclass Zoantharia – Order Scleractinia Only polyp phase (no medusae) Colonial organisms Ca. CO 3 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 (CO 2 + 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 24 o. N – 24 o. S latitude

Coral Reefs environmental requirements • Temperature (18 – 30 o. C) – Low Solubility of Ca. CO 3 at high temp. • Depth (0 -150 m) – Within photic zone – Below tide • Sedimentation – Low tolerance (prefer clear waters) • Salinity (33‰ and up) – Low tolerance of fresh water • Wave action – (high O 2, clear water and pelagic food supply)

Coral reef distribution and Diversity Indo. Pacific 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 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: – – Hurricanes and Storms Coral Bleaching Predation of Corals Coral Diseases • Human Indirect Disturbances – – 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 -20 cm

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 o. C) (enhanced by high UV exposure) • El Niño – Mass Bleaching • Global Warming • +2 o. C / 100 years

Zooxanthella

Coral Bleaching www. ogp. noaa. gov