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1. Today’s Class Outline
I. Coastal Ecosystems – why they are awesome
II. Coral reefs
I. Basic biology
II. Threats

2. An abundance of life in coastal ecosystems!
What do I mean by this?
Lots of primary production! Lots of species
diversity
Why?
Dynamic spatial ‘gradients’ (rapid changes over
space) of important controls on ocean life:
• Salinity
• Temperature
• Light
• Nutrients
• Sediment types (sandy vs. muddy)
• Water levels (tides)
All of the factors foster
extreme productivity and
biodiversity – coastal systems
are dynamic ecosystems!

3. Many different types of coastal ecosystems,
depending on climate, type of coastline (rocky vs.
gradual slope)
Underwater (sub-tidal) habitat type examples
• Coral reefs
• Seagrass meadows
• Kelp forests
Inter-tidal habitat types examples
• Mangrove forests (tropics/sub-tropics)
• Salt marshes (temperate/boreal/polar latitudes)
Estuaries – larger regions of where ocean
meets rivers (‘Bays’)

4. A plant An animal A type of rock
structure
An algae
25% 25% 25% 25%
What is a coral?
A. A plant
B. An animal
C. A type of rock structure
D. An algae

5. What is a coral?
A coral is an animal – a type of Cnidarian (yes, like a jellyfish)
Colonial organisms - clonal colonies composed of many physically connected,
interdependent individuals
Individual animals known as “polyps”. Few mm in diameter
Polyps grow together to produce
calcium carbonate, which form
the hard stony coral ‘reefs’ over
time

6. Coral reefs – where do these proliferate?
• Warm water (>18°C, ideally 23-25°C) so 30°N to 30°S
• Shallow (<70 m depth, usually<25m)
• Fully saline (marine, near 33 ppt)
• Low sediment supplies because need clear water
• Very limited exposure to air (<1 hr per day)

7. Coral anatomy
• Each polyp has a stomach that opens at only one end - the mouth,
which is surrounded by a circle of tentacles
• Tentacles for defense, capture small animals for food, clear away debris
• Food goes into polyp through mouth, waste also comes out mouth!
• Most corals feed at night
• Corals have nematocysts (stinging cells, similar to jellyfish), located in
tentacles and outer tissues - delivering powerful toxins to capture prey
• Coral eat tiny zooplankton and even small fish (depends on size). Can
also collect organic particles in mucous film and strands

8. Why are corals so colorful?
Zooxanthellae!!

9. Mutualistic relationship with phytoplankton
Corals contain photosynthetic algae, called zooxanthellae.
Both corals and algae benefit from this relationship.
Zooxanthellae live in coral’s tissues – coral provides algae with
protected environment and compounds needed for photosynthesis
Algae produces oxygen and organic carbon (glucose, glycerol, and
amino acids) that coral needs, and remove wastes
Tight recycling of nutrients in nutrient-poor tropical waters!
Driving force behind growth & productivity of corals
>90% of organic material photosynthetically produced by
zooxanthellae transferred to the host coral

10. Individual polyps combine to form stony reefs
Over the course of many years, stony coral polyps create
massive reef structures
Reefs form b/c polyps secrete calcium carbonate (CaCO3)
Polyps will lift off its base and secrete a new basal plate
above the old one, creating a small chamber in the skeleton.
While the colony is alive, CaCO3 is deposited, adding
partitions and elevating the coral.
Polyps are small (1 to 3 mm in diameter) but entire colonies
can grow large & weigh several tons
Growth rate: 2 mm to 10 cm per year

11. Coral overview

12. Coral Reproduction
Corals do both sexual and asexual reproduction -
Asexual reproduction important for increasing size of
colony. Sexual reproduction increases genetic diversity
Asexual reproduction – fragmentation (pieces broken
off and attach elsewhere to develop new colonies).
Done early on and throughout life.
Sexual reproduction –Takes 7-10 yrs to sexually
reproduce
Two types of sexual reproduction:
1) Broadcast spawning - external fertilization. By far
most common
2) brooding – internal fertilization.
https://oceanservice.noaa.gov/education/kits/corals/media/supp_coral03h.html

13. Broadcast spawning – a “blizzard” of gametes!
Most corals (~75%) are hermaphroditic (polyps produce both male
and female gametes)
Once a year (based on cues from moon, sun, and water
temp) entire colonies of coral reefs simultaneously
release eggs and sperm (gametes) at the same time –
mass synchronized spawning
Gametes are visible to naked eye - billions of colorful
flakes
Bundles of gametes rise to surface for fertilization, break
open and release egg and sperm to join together to form
larva (“planula”).
Creates sheen on water with distinct odor
Planulae float for days or weeks before settling on floor.
Then zooxanthellae settle

14. Coral spawning

15. The other type of sexual reproduction: brooding
Internal fertilization
Far less common (~1/4 of sexual
reproduction)
Coral release larvae (not eggs or
sperm)
Extended reproductive season (few
months to sometimes continuous)
http://coral.aims.gov.au/info/reproduction-sexual.jsp

16. Many types of corals
(Don’t memorize these for the exam)
• Branching
• Pillar (no secondary branches)
• Table
• Elkhorn – thick, fast growing,
high wave action
• Folaise – great habitat
• Encrusting – slow growing
• Massive – slow growing
• Mushroom - solidary

17. Deep Sea Coral

18. What types of organisms live on coral reefs?
Mobile invertebrates (crustaceans, echinoderms,
polychaetes, mollusks) and sessile (non-moving)
invertebrates (corals themselves, sponges)
Algae
Fish! So many fish!
Organisms at every stage on tropic cascade, from
primary producers to higher order consumers
As a result, corals have highest biodiversity in world. ~1/4 all ocean species
depend on coral reefs for survival

19. Animals that live on Coal Reefs