Coral Reefs
•Built entirely by biological activity
•CaCO3 solubility low above 20o isotherm
•Radioactively labeled Ca absorption low on cloudy
days
•Global distribution limited by temperature
•70 m is max depth (1-2% surface illumination)
•32-35 ppt salinity range
•Limited by sediment & exposure to air (subtidal)
•Enhanced by wave action to a point
Terminology/Taxonomy
Hermatypic: Reef building
Domain: Eucarya
Kingdom: Animalia
Phylum: Cnidaria (Coelenterata)
Class: Anthozoa
Prop/support
animal
Flower
Order:
•No medusa stage (only polyp)
•All marine
•Solitary or colonial
•Polar and tropical
•Some supported by skeleton
•Largest class of Cnidarians
Scleractinia
Hard
Ray or beam
Cnidarian body plan
Two-Way Digestive System
Dinoflagellates
Classification is changing:
•
Used to be in Kindom: Protista
•
Now some taxonomists put them in a Kingdom or Phylum : Alveolata
•
(Bauman 2007).
•
•
•
•
•
Both fresh water & marine
Many are bioluminescent
Cause Red Tide
Some produce neurotoxins
Pfiesteria has gotten a lot of press in NC
Zooxanthellae apparently loose (or they adhere to the cell wall)
their flagella when they live in corals.
Zooxanthallae is a genus among the
Dinoflagellata
It will loose its flagella and live in the tissue
of corals
Zooxanthallae exist as endosymbionts in
bivalves, other coelenterates & gastropods
Xenia sp. host with its Zooxanthallea sp.
endosymbiont
Zoanthus sociatus has zooanthallae as intracellular endosymbiont and uses photosynthate
and feeds on other zooplankton too. Uses autotrophy & heterotrophy (mixotrophic)
(Trench 1974)
Giant clam (Tridacna sp.) both digests and uses photosynthate from zooxanthallae
Coral reefs found in waters with notoriously low productivity.
Open Tropical Seas produce 18-50 gC/m2/yr (Nybakken 1988)
Vs.
Coral reefs :1500-5000 gC/m2/yr (Kohn & Helfrich (1957), Odum & Odum (1955),
Johannes et al. (1972)
How can this be?
Coral reefs, like tropical rain forests hold on to nutrients. Both exist in nutrient POOR
Regions.
Zooxanthellae live IN coral polyp tissue, thus their photosynthate (carbon compounds)
remains in the tissue and does not diffuse in the surrounding sea water.
Since polyps are predatory, they capture plankton that float in from the ocean and
HOLD the nutrients and support the zooxanthellea nutritionally.
Mutualistic Relationship (+/+)
How do the coral & and the
Zooxanthallae do this?
Mutualism: Host & tenant ?
both must benefit
Predation : Predator & prey ?
sometimes “host” digests “tenant’
Parasitism: Host and parasite?
Zooxanthallae use lipids captured by coral
for their uses
Corals may eject Zooxanthallae
Changes with species of coral, environmental conditions, and possibly with species
of Zooxanthallea
Lipids constitute 1/3 dry weight of corals (excluding skeleton)
Levinton 1982
Light
Food: Plankton
Photosynthesis by
Zooxanthallae sp.
Carnivory by the
coral polyp
Carbohydrates to generate
ATP
Lipids in prey
Acetyl -CoA
Saturated fatty acids most common in shallow reefs
Unsatured fatty acids increase with depth
Lipids
Large surface area, many zooxanthallae
Low SA,
Few
Zooxanthallae
Short tentacles, catch few plankters,
many Zooxanthallae
Long tentacles, catch many
plankters, few Zooxanthallea
Atoll formation
Sea level
Fringing Reef
Time
Barrier Reef: Larger geologic feature. Pierced by numerous channels
“large” lagoon between reef and continent. Ex: Australia, Bahamas
Rate of submergence= S
Rate of coral growth=CG
If S>CG; guyot is formed
Sedimentation
lagoon
WIND
High wave action
Little sedimentation
High plankton abundance (from ocean)
High light:
Low wave action: sediment settles
Diminished Coral Growth:
Lagoon formation
Rapid coral & coralline algae growth
Balanced by wave destruction
Darwin 1842
Wind & Waves
Leeward
Windward
No surge channels
Branching corals
Levinton 1982
Surge channels
Spur & Buttress Zone
Nybakken 1988
Atlantic vs. Pacific Reefs
Few atolls
Corals
36 Genera
62 Species
Many atolls
Corals
80 Genera
700 Species
Acropora sp.
Dominant reef builder
3 species
200 species
Same trends for molluscs, crustaceans, fish
Balance of Accretion & Subsidence
160-206 tons CaCO3/yr/ha
Acropora cervicornis
Staghorn coral
Can grow 10 cm/yr
Montastrea annularis
0.25-0.7 cm/yr
•Wave damage
•Rapid sea level rise
•Boring animals
•Sponges
•Bivalve molluscs
•Polychaetes
•Gnawing fish
•Echinoderms (Acanthaster sp.)
Defecation of CaCO3: “Sand”
Complex Species Interactions
•Direct effects
•Indirect effects
Acropora sp (fast growing)
Algae
-
Montastrea sp. (slow growing)
-
Corallivorous Fish
+
Damselfish (Pomacentridae)
Chaetodon capistratus
Foureye butterfly fish
Remove damselfish,
coral gets grazed down
Return damselfish
Acropora sp. grows back faster
than Montastrea sp.
Some Web Sites
Crustose coralline red algae (Rhodophyta)
http://www.mbari.org/staff/conn/botany/reds
/ian/default.htm
Zooxanthellae sp.
http://coralreef.noaa.gov/aboutcorals/coral10
1/symbioticalgae/
References
Bauman, R.W. 2007. Microbiology with diseases by taxonomy. 2nd Ed.
Pearson/Benjamin Cummings
Darwin, C. 1842. The structure and distribution of coral reefs. Being the first part
of the geology of the voyage of the Beagle. London: Smith, Elder.
Johannes, R. El, et al. 1972. The metabolism of some coral reef communities:
A team study of nutrient and energy flux at Eniwetok atoll. Bioscience. . 22:541-543.
Kohn, A., and P. Helfrich. 1957. Primary productivity of a Hawaiian coral reef.
Limnol. Oceanogr. 2(3):241-251
Nybakken, J.W. 1988. Marine Biology: An Ecological Approach, 2nd Ed. Harper Collins
NY, NY
Odum, H.T., and E.P. Odum. 1955. Trophic structure and productivity of a windward
coral reef community on Eniwetok Atoll. Ecol. Monogr. 25:291-320
Ogden, J.c., and P.s. Lobel. 1978. The role of herbivorous fishes and urchins in coral
reef communities. Envir. Biol. Fishes 3:49-63.
Trench RK (1974) Nutritional potentials in Zoanthus sociathus (Coelenterata,
Anthozoa). Helg wiss Merresu 26:174–216