Coral reefs

Chapter 9

Coral ReefsCoral Reefs

Coral reefs are living structures that provide homes and attachment sites for countless marine organisms in shallow tropical oceans.

Coral Reefs

Anatomy and Growth

Coral reefs are created by many species of colonial cnidarians.

These anemone-like polyps produce a CaCO3 skeleton in a great variety of sizes and shapes.

Coral Reefs

Anatomy and Growth

Fig. 9.1 Extended polyps of a coral colony. The numerous light-colored spots on the tentacles are

batteries of cnidocytes.

Fig. 9.2 Cross-section of a coral polyp and a calcareous corallite skeleton. The living coral tissue forms a thin interconnection, the cenosarc, over the

surface of the reef.

© Photos.com

Coral Reefs

Anatomy and Growth

Fig. 9.3 Coral exhibit a large variety of growth forms.

Coral Reefs

Anatomy

and Growth

Fig. 9.4 Parrotfishes, major grazers of coral skeletal

material, use their powerful jaws to produce large

amounts of carbonate sand on the reef.

© Wolfgang Amri/ShutterStock, Inc.

Coral Reefs

Coral Distribution Living coral reefs usually are located:

• within 30º latitude of the equator

• in water that averages at least 20ºC

• on the eastern sides of most continents

• within the photic zone at depths of 0-50 meters

Coral ReefsCoral Distribution

Fig. 9.5 Distribution of reef-forming corals, by number of genera. Heavy black lines indicate continental barrier reefs.

Light blue: <20 generaMedium blue: 20-40 genera

Dark blue: > 40 genera

Coral Reefs

Coral Ecology

Reef-building corals maintain a mutualistic relationship with a dinoflagellate called zooxanthellae

The alga provides photosynthetic products to the coral to aid in its survival and growth

The alga receives unlimited carbon dioxide and nitrogenous wastes from the coral polyp in a competition-free setting

Coral Reefs

Coral Ecology

Fig. 9.6 Exchange of materials between zooxanthellae and their coral host.

Coral Reefs

Coral Reef Formation Charles Darwin was the first to suggest that

coral reefs are sequential developmental stages in the life cycle of a single reef:

• fringing reefs

• barrier reefs

• atolls

Coral Reefs

Fig. 9.7 A satellite view of a portion of the hundreds of atolls

that make up the nation of Maldives.

Courtesy of NASA Earth Observatory

Coral Reefs

Fig. 9.8 The developmental sequence of coral reefs, from young fringing reefs (left), to barrier reefs (center), and finally to atolls (right).

Coral Reefs

Coral Reef Formation and Hot SpotsFig. 9.9 Chains of

volcanoes along the Hawaiian Island-

Emperor Seamount are carried, in a conveyer-belt

fashion, north into deeper water by the

movement of the Pacific Plate. Each volcano was formed over the “hot spot,” a continuous source of new molten material

presently under Hawaii, and is carried

to its eventual destruction in the Aleutian Trench.

Courtesy of NGDC/NESDIS/NOAA

Coral Reefs

Reproduction in Corals

Corals reproduce in a great variety of ways, both asexually and sexually

Most sexually reproducing corals are hermaphroditic spawners

Coral Reefs

Fig. 9.10 Spawning corals. (a) Female brain coral releasing eggs; (b) male mushroom coral releasing sperm.

b

a

© Gary Bell/OceanwideImages.com

© Marty Snyderman/Visuals Unlimited

Coral Reefs

Fig. 9.11 Micrograph of a planula larva of

the coral Pocillopora.

© Valerie Hodgson/Visuals Unlimited

Coral Reefs

Zonation on Coral Reefs

Wave force, water depth, temperature, salinity, and a host of biological factors vary greatly across a reef

Together they result in both horizontal and vertical zonation of the species that form the reef

Coral Reefs


Fig. 9.12 Cross-sectional

zonation of a barrier reef.

Coral Reefs

Fig. 9.13 Echinometra, a

common tropical sea urchin.

© Ewen Cameron/ShutterStock, Inc.

Coral Reefs

Fig. 9.14 A giant clam, Tridacna, amid mixed corals. Note the blue mantle

tissue that is brightly colored due to the presence of innumerable mutualistic

zooxanthellae.

© Andy Lim/ShutterStock, Inc.

Coral Reefs


Fig. 9.15 Variations in coral growth forms: (a) table coral,

Acropora; (b) brain coral, Diploria; and (c) staghorn

coral, Acropora.

a

b

c© Andy Lim/ShutterStock, Inc.

© Lawrence Cruciana/ShutterStock, Inc.

© Andy Lim/ShutterStock, Inc.

Coral Reefs

Coral Diversity and Catastrophic Mortality

Reefs worldwide are threatened by human activities, succumbing to:

• pollution

• destructive fishing practices

• bleaching

• a host of diseases

Coral Reefs

Fig. 9.16 The predatory sea star, Acanthaster, and (b) its major predator, the Pacific triton, Charonia.

a

b

Courtesy of David Burdick/NOAA

Courtesy of AIMS/NOAA

Coral Reefs

Coral Diversity and Catastrophic Mortality.

Fig. 9.17 Black band disease overgrowing a coral head. This star coral, Montastrea, which could be as much as 500 years old, will probably be dead within

one year.

Fig. 9.18 Wide-spread bleaching on a Pacific coral reef.

Courtesy of David Burdick/NOAA

Courtesy of Dr. Phillip Dustan, College of Charleston

Coral Reef Fishes

Fig. 9.19 Some common reef fishes on a tropical Caribbean reef:

1. nurse shark (Ginglymostoma),

2. reef shark (Carcharhinus),

3. barracuda (Sphyraena),

4. surgeonfish (Acanthurus),

5. butterflyfish (Chaetodon),

6. angelfish (Pomacanthus),

7. hawkfish (Amblycirrhitus),

8. grouper (Mycteroperca),

9. moray eel (Gymnothorax),

10. stingray (Dasyatis),

11. grunt (Haemulon),

12. soldierfish (Myripristis),

13. porcupinefish (Diodon).Angelfish photo from Joyce and Frank Burek/NOAA; all other photos from John Morrissey

Coral Reef Fishes

Coral Reef Sharks and Rays Reefs worldwide are dominated by:

• benthic orectolobid sharks (nurses, wobbegongs, and bamboosharks)

• and more typical pelagic carcharhinid sharks (blacktips, whitetips, tigers, and reef sharks)

Coral Reef Fishes

Coral Reef Sharks and Rays

Fig. 9.20 Dermal flaps around the mouth of a wobbegong, a benthic reef shark.

Coral Reef Fishes

Coral Reef Teleosts About 50% of all

living vertebrates are teleost fishes, and many of these fishes inhabit coral reefs.

Fig. 9.21 Numerous species of teleost fishes are associated with coral reefs.

Courtesy of NOAA

Coral Reef Fishes

Coral Reef Teleosts

The great diversity of teleost fishes have evolved numerous symbiotic relationships such as inquilinism and cleaning behaviors.

Coral Reef Fishes

Fig. 9.22 Two remoras, Echeneis, with modified

dorsal fins accompanying a nurse shark,

Ginglymostoma.

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.23 Shrimpfish, Aeoliscus, seeking shelter amid the spines of a sea urchin.

Fig. 9.24 A clownfish, Amphiprion, nestled within the protective tentacles of its host anemone.

© Russell Swain/ShutterStock, Inc.

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.25 A nearly transparent cleaner shrimp, Periclimenes, on a Caribbean sponge. Fig. 9.26 Neon gobies, Elacatinus, clean the head of a

large green moray, Gymnothorax.

Courtesy of Dr. Anthony R. Picciolo, NOAA NODC© Kelpfish/ShutterStock, Inc.

Coral Reef Fishes

Coral Reef Teleosts

The brightly colored patterns of coral reef fishes illustrate the advertisement, disguise, and concealment roles of brilliant coloration in a coral reef environment.

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.27 A well-camouflaged scorpionfish, Scorpaena (left),

with magnified chromatophores from a section of skin (right).

© Frank Boellmann/ShutterStock, Inc. © Rene Frederic/age fotostock

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.28 Disruptive coloration patterns of two species of butterflyfishes, Chaetodon.

© Lawrence Cruciana/ShutterStock, Inc. © cbpix/ShutterStock, Inc.

Coral Reef Fishes

Fig. 9.29 A cleaner wrasse, Labroides

(above), and its mimic, Aspidontus (below).

Coral Reef Fishes

Coral Reef Teleosts

About one fourth of all reef-fish species place sticky benthic eggs in a guarded nest on the reef.

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.30 Two bicolor damselfish mate inside a discarded PVC pipe on a Caribbean reef.

Fig. 9.31 A sergeant major (Abudefduf) guards its purple egg mass in the Caribbean Sea.

Courtesy of Dr. Michael P. Robinson

© David Fleetham/Alamy Images

Coral Reef Fishes

Coral Reef Teleosts

Most reef teleosts are pelagic spawners.

As many as 30 or more species at any given time will assemble around a coral promontory to broadcast as many as 50,000 eggs apiece into the water column.

After fertilization, these pelagic eggs drift away from the reef and disperse for one day to a year or more.

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.32 Dog snappers, Lutjanus jocu, return to the reef after a spawning run in

the water column off Belize.

© Doug Perrine/Seapics.com

Coral Reef Fishes

Fig. 9.33 Locations of U.S. National Marine Sanctuaries

and National Estuarine Research Reserves.

Coral Reef Fishes

Coral Reef Teleosts The great diversity of

reef fishes results in sexual systems that range from species with separate sexes to simultaneous and sequential hermaphrodites.

Fig. 9.34 Clasping hamlets above a reef.

© WaterFrame/Alamy Images

Coral Reef Fishes

Coral Reef Teleosts

Fig. 9.35 Male and female “bluehead” wrasses in their initial yellow phase.

Fig. 9.36 Terminal-phase bluehead male surveying his territory.



Coral Reef Fishes

Fig. 9.37 Relative reproductive success experienced by males and females of protandrous clownfishes (left) and protogynous wrasses (right).

Coral reefs

Technology

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