Chapter 14Part 2

Coral Reefs

Other Reef BuildersConditions for Reef Growth

Coral ReproductionKinds of Reefs

Reef Builders

• Hermatypic corals• Coralline algae (Porolithon sp., Lithothamnion

sp.)• Halimeda sp.• Sponges• Foraminifera • Stromatolites

Coralline Algae• Porolithon sp., Lithothamnion sp.• Red algae that deposit CaCO3

• Hold reef together – keep it from washing away

• Algal ridge on outer edge of many reefs – protects reef from wave action

• Grow over and cement sediment that settle on corals

Halimeda sp.• Calcareous green alga• Deposits CaCO3 in tissues for support and to

deter predators• Remnants of Halimeda accumulate on reefs

and can be bound by encrusting organisms• Microcosm of diversity

www.turtles.org www.nceas.ucsb.edu

More Halimeda

Sponges• Bind sediments into place

www.johneasley.com

Foraminifera• Eukaryotic protists• CaCO3 shells

• Benthic, but a few are planktonic• Some have endosymbiotic algae• Bioindicator

www.proprofs.com

www.wikipedia.com

Stromatolites• Cycling of microbial communities (cyanobacteria)

and sediment• 3.5 billion years old (Earth is 4.5 billion yrs old!)• Not common today – Exuma, Bahamas• Rich source of fossil information

www.flickriver.com www.stromatolite.info

Highbourne CayExumas, Bahamas

Conditions for Reef Growth

• Hard bottom • Shallow water (< 50 m) with bright sunlight• Clear water• Warm water (> 20°C)

Coral Reproduction• Sexually– Egg + Sperm = Planula– Mostly hermaphroditic– Self fertilization (egg fertilized before released)– Broadcast spawners– What are advantages to mass spawning?

Coral Planula

G.Spencer

Coral Spawning

NOAA video BBC video

Coral Reproduction• Asexually– Fragmentation– Budding– Fission (esp. Fungiidae)

www.wikipedia.com

Budding

The distribution of coral reef communities p. 304

Bioerosion

• Erosion caused by living organisms• Who causes bioerosion?

fw.dpnr.gov.vi

www.coral.org

Bioerosion

• Epilithic organisms– Remain at surface of the calcareous substrate, where they

rasp, scrape, and/or etch the surface. – The majority of damage occurs during algal grazing. – Browsers consume plant material above the substrate – Grazers consume plant material down to, and sometimes

below, the surface of the substrate.• Grazers often consume quantities of coral skeleton as well as the

invertebrates associated with it and inflict much more damage than browsers. Neither grazers nor browsers usually have a great influence on strength of the greater coral structure (Kleemann 2001)

Bioerosion

Bioerosion• Endolithic organisms– Beneath the surface of the coral skeleton. – Bore for food or shelter. – Majority are suspension feeders

• Large borers, in particular polychaetes, are important in oxygenating the interior of coral structures to support smaller organisms.

• Internal bioeroding species degrade calcareous materials to fine textures

• External bioeroders generally erode to much coarser textures (Kleemann 2001)

Reef GrazersGrey angelfish and Blue tangs

Coral Reefs and Zonation3 main categories of reefs

1. Fringing – close to shore, high nutrients, high turbidity

2. Barrier – farther from shore, usually a lagoon between the reef and the shore

3. Atoll - Circular reef with central lagoon and possibly small islands formed on the reef.

Types of Coral Reefs: Fringing Reefs

• Simplest and most common• Rocky shorelines provide the best conditions for

fringing reefs

Upward growth of reef flats is limited by the tides. Figure 14.16

Barrier Reefs• Distinction between barrier and fringing reefs

sometimes unclear• Occur farther offshore• Presence of lagoons

Lady Musgrave Island Great Barrier Reef

Australia-trips.info

Spur and Groove formations• Debate about what causes it• Wind, waves, or both involved• Develop primarily on reef slopes that are

exposed to strong winds

Atolls

• Occur mostly in the Indo-West Pacific region• Practically no land around (no silt, little FW

runoff)• Spectacular coral growth and great water clarity

Atoll in Fiji

Atoll Formation

Typical Atoll Structure