Bio124
I.
Tropical Seas
Lecture #18 (10/27/16)
Tropics
A. Tropical oceanic environment
B. The exception: coral reefs – epicenters of biodiversity
Why?
C. Abiotic requirements for coral reefs
D. What is Coral?
E. Coral feeding
F. Symbiosis allows coral reef development
G. Abiotic requirements for coral reefs
H. Biotic factors for coral reefs
1. Tight nutrient cycling
2. Importance of CCA
I. Global coral diversity patterns
J. Threats to coral reefs: Bleaching
Corals &
Coral Reefs
A ‘desert’ due to limited vertical
water circulation –
• Year-round warmth
• Low nutrients
Coral reef ecosystems
Oases (1%) in nutrient-poor tropical
waters
Reefs provide habitat & food for millions
of other organisms
Extremely
high
biodiversity:
“Rainforests
of the sea”
http://marinebio.org/oceans/coral-reefs/
Coral reefs : epicenters of biodiversity
only 0.2% of ocean
but 25% of all known marine species
& 65% of all fish species!
Why?
1
Competition!
Strawberry anemone, Vancouver Isl 2006
Phylum Cnidaria
stinging animals
Cnidarian groups
Anthozoans (“flower animals”)
a) anemones
Cnidarian groups
Cnidarian groups
Anthozoans (“flower animals”)
b) gorgonians & soft corals
Coral anatomy
Anthozoans (“flower animals”)
c) stony corals
CaCO3 deposition by thin
layer of cells
(calicoblastic epithelium)
2
Sexual reproduction
-> coral larvae
(meroplankton)
Corallites – stony ‘cups’
for each polyp
Larva settles –
becomes polyp
Polyp asexually
reproduces
-> coral colony
What are stony corals?
“The Enchanted Braid”…
Symbiosis of coral & zooxanthellae
Mutualism (“win-win”)
Animal
+
Algae
= ‘Rock’
Reef
Symbiosis of other reef invertebrates &
photosynthetic algae/bacteria
coral feeding modes: Hetertophy
1.Suspension feed
- tentacles with nematocysts
(also used for defense)
Tridacna (Giant Clam)
Tunicates (Didemnidae)
Sponges
2. Absorb DOM (dissolved organic matter)
3
Class Anthozoa: coral feeding
3.Mucus sheets
Coral Feeding
5. Symbiosis: Mutualism
Mutually beneficial
relationship
Zooxanthellae
(dinoflagellates)
photosynthesize,
providing coral with
food & extra energy
4.Mesenterial filaments
Also used for defense!
Symbiosis between corals &
zooxanthellae allow corals to build reefs
Biogenic habitat:
ecosystem created by an organism
Coral Reefs
> biogenic structures
Habitat
Food
Photo: Matt Keiffer
Coral reef ecosystems
Abiotic Requirements
1. Sunlight
• Water clarity
2. Water quality:
Salinity, Pollution
Refuge
Tight nutrient cycling:
1.Zooxanthellae
2. Cyanobacteria
3. Algae -> Herbivores -> food web
3. Warm Temperature
within range: 20-30C (68-86F)
4. Hard substrate
4
Corals also dependent
upon another type of
algae Crustose coralline
2. CCA also provides a ‘landing pad’
for coral larvae
algae (CCA)
1. Cements reefs
together/ helps build
reefs up
The Coral Triangle
Threats to coral reefs
Bleaching (heat stress)
Disruption of
symbiosis with
zooxanthellae
Stress
Lecture 18 (10/27/16): Coral Reefs
1.
Explain in detail why tropical waters are a
‘desert’.
2.
Explain why coral reefs have such high
species diversity.
3.
Define: coral, polyp, soft coral, stony coral,
corallite, zooxanthellae, crustose coralline algae
4.
Describe the basic structure of a stony coral
5.
Describe 5 different ways stony corals feed as
heterotrophs.
6.
List the benefits that mutual symbiosis
provides to each of corals & zooxanthellae.
7.
What does the symbiosis between corals &
zooxanthellae allow corals to do?
5
Lecture 18 (10/27/16): Coral Reefs
8.
Define biogenic habitat.
9.
List 4 abiotic conditions necessary for growth
of coral reefs.
10. What is meant by tight nutrient cycling on
coral reefs? Describe how that occurs within corals
and how it occurs on the reef itself.
11. Crustose coralline algae (CCA) is important to
coral reefs for 2 reasons. Explain them.
12. Where is the Coral Triangle and what is
significant about it?
13. What is coral bleaching? Why does it
happen?
6