Coral Reefs

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Coral Reefs

• Chapter 14

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Major Groups of Corals, Phylum Cnidaria

• 1. Anthozoans
• Lack medusa stage, live only as polyps, related
  to sea anemones
• Scleractinian corals main reef builders
• Soft corals not reef builders
• Organ-pipe corals (Tubipora) minor reef building
• Blue coral (Heliopora) reef building only in
  some places
• Gorgonians not reef builders
• Black corals not reef builders
• 2. Hydrozoans
• Have both medusa and polyp stages, related to
  cnidarian jellies
• Fire corals (Millepora) reef building only in
  some places
• Lace corals not reef builders

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Figure CO 14
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Figure 14.1
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Mushroom coral Boulder corala single polyp
Figure 14.2ab colonies of polyps
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Polyps are interconnectedFigure 14.3
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Removed piece shows a single polyp Figure 14.4
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Figure 14.5
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Coral shapes Growth Forms Figure 14.6
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Figure 14.8
The process of reef building
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Distribution of Coral Reef Communities Figure
14.10
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Upper Temperature Limits of CoralsFigure 14.11
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Red alga, Kappaphycus striatum, introduced to
Hawaii from the Phillipines (See arrow below)
Figure 14.13
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Fringing Reef Figure 14.14
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Fringing reef in Bismarck Islands of Southwest
Pacific Figure 14.14 inset
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Extreme low tide in Great Barrier Reef, keeps
reef flats flat Figure 14.15
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Structure of a Barrier Reef Figure 14.17
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Coral Growth on a back-reef slope in the Pacific
Figure 14.18
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Spur-and Groove FormationsFigure 14.19
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Structure of an Atoll Figure 14.22a
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Lagoon 2. Back-reef Slope 3. Fore-reef slope
Figure 14.22bde
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Formation of an AtollFigure 14.23
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Mutualism Symbiosis of Coral Polyps
ZooxanthellaeFigure 14.24
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Ecosystem of the Coral Reef Zooxanthellae are
the Primary Producers Basis of Food Web Figure
14.25
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Generalized Coral Reef Food Web Figure 14.26
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Figure 14.27
Competition for Space Pink band separates brown
Porites lutea and blue Mycedium elphantotus Pink
band is dead zone where blue has killed brown in
process of overgrowing it. Band width
corresponds to length of polyp tentacles. Figure
14.27
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Soft corals lack skeleton but have spicules
instead and toxic chemicals to discourage
predation. Figure 14.28
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Soft coral gorgonian sea fan
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Chevron butterflyfish is a coral predator, mouth
adapted to nip off indiv. polyps. Figure 14.30
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Acanthaster- Crown of Thorns Starfish Case History

• Indo-Pacific species
• Coral specialist
• Individuals consume 5-6 m2 coral/year
• Populations consume 0.5-0.6 km2 coral/yr

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Crown of Thorns Physiology

• Can grow to 80 cm in diameter
• Spines are 4-5 cm long
• Most echinoderms have 5 arms
• has as many as 21
• Spawning in summer, day or night, as long as
  water temperature is correct
• Prefers to eat fast-growing hard coral polyps
  like staghorn and plate corals
• This allows slower growing species to compete for
  space on the reef

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Outbreaksof Crown of Thorns

• Guam 1968-69 90 of coral killed along 38 km of
  coastline
• Australia 28 of reefs affected along hundreds
  of km of GBR
• Previous outbreak strictly man-made due to
  ignorance about starfishs asexual reproduction
• Philippines population boom on dynamited reefs,
  finishes corals off prevents recovery
• Okinawa, Japan population remains high, very few
  large, fast-growing reef-building corals left

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Why is Acanthaster such a problem?

• Natural cycle there is evidence that the
  population will naturally increase and decrease
  over time
• Anthropogenic (man-made) the outbreaks are
  larger in scale and more frequent now
• Remove the top predators whelks or larval
  predators
• Eutrophication increased nutrient runoff
  improves larval survival rate (65 mill/ season)

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Hypotheses about population control

• Nutrient runoff higher levels increase larval
  survival
• Spawning coinciding with particular currents
  more larvae transported to suitable sites
• Predation on larvae has decreased because we have
  overfished the predators
• Predation on juveniles has decreased
• Predation on adults has decreased

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Sources

• Reef Check, http//www.reefcheck.org/methods/instr
  uctions.asp,
• Date Viewed, 3/11/05.
• Castro, Peter, and Huber, Michael E. Marine
  Biology, 5th ed. McGraw Hill Higher Education,
  New York, NY, 2005.
• ReefED, http//www.reefed.edu.au/explorer/animals/
  marine_invertebrates/echinoderms/crown_of_thorns.h
  tml, Date Viewed 3/13/05
• Barrier Reef Australia, http//www.barrierreefaust
  ralia.com/backgrounds/crown-of-thorns1024.jpg,
  Date Viewed 3/13/05
• MSN Encarta, http//encarta.msn.com/media_46152931
  8_761562320_-1_1/Crown-of-Thorns_Starfish.html,
  Date Viewed 3/13/05