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					Coral Reefs

 Chapter 14
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
Figure CO 14
Figure 14.1
Mushroom coral              Boulder coral
a single polyp
            Figure 14.2ab   colonies of polyps
Polyps are
interconnected
Figure 14.3
Removed piece shows a single polyp
               Figure 14.4
Figure 14.5
Coral shapes & Growth Forms Figure 14.6
Figure 14.8




           The
        process of
           reef
         building
Distribution of Coral Reef Communities Figure 14.10
Upper
Temperature
Limits of
Corals
Figure 14.11
Red alga, Kappaphycus striatum, introduced to Hawai’i
    from the Phillipines (See arrow below) Figure 14.13
Fringing Reef Figure 14.14
Fringing reef in Bismarck Islands of Southwest Pacific Figure 14.14 inset
Extreme low tide in Great Barrier Reef, keeps reef flats flat Figure 14.15
Structure of a Barrier Reef   Figure 14.17
Coral
Growth
on a
back-reef
slope in
the
Pacific
Figure 14.18
Spur-and –
Groove
Formations
Figure 14.19
Structure of an Atoll Figure 14.22a
1.Lagoon           2. Back-reef Slope   3. Fore-reef slope
 Figure 14.22bde
Formation
of an Atoll
Figure 14.23
Mutualism Symbiosis of Coral Polyps & Zooxanthellae
                      Figure 14.24
Ecosystem of the Coral Reef: Zooxanthellae are the
  Primary Producers & Basis of Food Web Figure 14.25
Generalized Coral Reef Food Web Figure 14.26
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
Soft corals lack skeleton but have spicules instead and
    toxic chemicals to discourage predation. Figure 14.28
Soft coral: gorgonian sea fan
Chevron butterflyfish is a coral predator, mouth adapted to nip off indiv. polyps.
Figure 14.30
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
          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
               Outbreaks
           of Crown of Thorns
1. Guam 1968-69: 90% of coral killed along 38 km
   of coastline
2. Australia: 28% of reefs affected along hundreds
   of km of GBR
   1. Previous outbreak strictly man-made due to ignorance
      about starfish’s asexual reproduction
3. Philippines: population boom on dynamited
   reefs, finishes corals off & prevents recovery
4. Okinawa, Japan: population remains high, very
   few large, fast-growing reef-building corals left
  Why is Acanthaster such a problem?

1. Natural cycle: there is evidence that the population
   will naturally increase and decrease over time
2. 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)
Hypotheses about
population control
1.   Nutrient runoff: higher
     levels increase larval
     survival
2.   Spawning coinciding with
     particular currents: more
     larvae transported to
     suitable sites
3.   Predation on larvae has
     decreased because we
     have overfished the
     predators
4.   Predation on juveniles has
     decreased
5.   Predation on adults has
     decreased
                                 Sources
Reef Check, http://www.reefcheck.org/methods/instructions.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/echi
  noderms/crown_of_thorns.html, Date Viewed: 3/13/05

Barrier Reef Australia,
  http://www.barrierreefaustralia.com/backgrounds/crown-of-
  thorns1024.jpg, Date Viewed: 3/13/05

MSN Encarta, http://encarta.msn.com/media_461529318_761562320_-
 1_1/Crown-of-Thorns_Starfish.html, Date Viewed: 3/13/05

				
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