Coral Reefs Lecture Notes (Topic 10D) – page 1
Coral Reefs Lecture Notes
Corals Polyps & Zooxanthellae
Coral Polyps
Are coral polyps algae or animals?
Description (What do coral polyps look like? Make a sketch of a coral polyp.)
Food (How do coral polyps get their food? What is their main source of food?)
Zooxanthellate
Are zooxanthellae algae or animals?
Where do they live?
Symbiotic Relationship between Corals and Zooxanthellae
How do zooxanthellae help their coral polyp?
How do coral polyps help their zooxanthellate?
How do coral polyps get or obtain the nutrients that they give to their zooxanthellae?
Coral Reefs Lecture Notes (Topic 10D) – page 2
Corals & Physical Conditions in the Ocean
Sunlight (Do corals like getting lots of sunlight or very little sunlight? Why? Explain.)
Sediments suspended in the water
(Do corals like lots of sediments in the water or few sediments in the water? Why? Explain.)
Temperature (Do coral reefs grow best in warm water or cold water? Why? Explain.)
Hints:
What do corals build their reef out of?
What happens to this material
in cold, carbon-dioxide-rich water?
How do corals get closer to the Sun?
Coral Bleaching
What is a “bleached” coral reef?
In other words, what has happened to the coral
on the reef? Why does bleached coral look “white”?
Hints:
What color is calcium carbonate?
What color are coral polyps?
Coral Reefs Lecture Notes (Topic 10D) – page 3
What can cause corals to “bleach”?
Why do bleached corals often die?
Nutrients (Do corals like water with lots of nutrients or few nutrients? Why? Explain.)
Coral and the Abundance of Life on the Reef
Corals help algae like phytoplankton and seaweed survive in the tropical ocean. Corals eat the
few plankton that drift into the reef environment from the open ocean. The more they eat, the
more they concentrate nutrients in their bodies – and ultimately in the reef environment when
they die of old age and decompose. Phytoplankton and seaweed grow well in coral reefs thanks
to these nutrients and because the shallow reef helps keep them near the Sun (phytoplankton
cannot sink to deep, seaweeds have a surface to grow on in the sunlight).
What do most animals who live in a coral reef eat,
(i) coral polyps or (ii) algae like phytoplankton and seaweed?
Does overfishing (removing lots of fish) help or harm the coral polyps of a coral reef?
Why or why not? Explain your reasoning.
Coral Reefs Lecture Notes (Topic 10D) – page 4
Kinds of Coral Reefs
Courtesy of
Dr. Charles
Herzig
Fringing Reef
Barrier Reef
Atoll
How or why does one kind of reef
become another kind of reef?
Beaches on Coral Islands
(Where does the sand on the beaches of a coral atoll come from? What is it made out of?)
Benefits of Coral Reefs (How do humans benefit from coral reefs?)
Coral Reefs Lecture Notes (Topic 10D) – page 5
Coral Reefs Review Questions
1. What are zooxanthellae?
a. algae
c. bacteria
b. animals
d. plankton
2. How do coral polyps get new nutrients?
a. from their zooxanthellae
b. filter nutrients out of the water with their tentacles
c. grabbing plankton with their tentacles
3. Why does a “bleached” coral look white?
a. corals grow more calcium carbonate
b. corals lose their zooxanthellae
c. marine snow falls all over the corals
d. toxins in the water stick to the coral
What can cause corals to bleach?
Why is “bleaching” bad for corals?
Coral Reefs Lecture Notes (Topic 10D) – page 6
4. Where are there more corals, on the west sides of oceans or the east sides of oceans?
a. west side of oceans
b. east side of oceans
Why? ____________________________________________________________
5. Are El Niño conditions good or bad for West Pacific coral reefs?
a. good for them
b. bad for them
Why? ____________________________________________________________
6. Some species of corals do not build large reefs and live in the deep ocean.
How do deep-sea corals get most of their food?
a. catch dead matter sinking from the surface
b. grab deep-sea zooplankton drifting or swimming by
c. their zooxanthellae carry out photosynthesis and give them some of the food they make
7. Do coral reefs like or dislike rivers?
a. like rivers
Why?
b. dislike rivers
(This is also why fringing reefs become barrier reefs.)
(1) ______________________________________________________________
(2) ______________________________________________________________
(2) ______________________________________________________________
8. “Removing lots of fish from a coral reef benefits coral polyps;
the coral polyps will be able to reproduce and grow more easily and safely.”
a. True
b. False
Coral Reefs Lecture Notes (Topic 10D) – page 7
Coral Reefs Practice:
Why is there so much more life in coral reefs than elsewhere in the tropical ocean?
If you can answer this question, then you have a pretty deep understanding of the coral reef
material. To answer this question, complete the sentences below.
First, explain why there is little life in warm tropical water (away from the coast):
The tropical open ocean is an ocean “desert.” In other words, there is very little life in the tropical
ocean far from land compared to other parts of the ocean. There are fewer zooplankton in the
tropical open ocean, because there are fewer ______________________________ for them to eat,
and there are fewer fish in the tropical open ocean, because there are fewer
________________________ for them to eat.
In the tropics, the phytoplankton population is low
because (A)________________ is (are)(B)_____________________________________
at the surface of the ocean.
Few nutrients are brought up by (C) ______________________________
because the surface water is too warm: The water brought up from below sinks back down almost
immediately after it is brought up, because the cool, nutrient-rich water which is brought up has
a (D)_________________ density than the warm surface water.
It also can be hard for phytoplankton to get enough sunlight
because the warm surface water has a (E)______________ density,
so it provides little support (it is hard to float), so they sink down away from the Sun.
A: carbon dioxide, nutrients, oxygen, sunlight, water
B: always abundant, rare (difficult to find)
C: upwelling, waves
D: higher, lower
E: high, low
CONTINUED ON THE NEXT PAGE
Coral Reefs Lecture Notes (Topic 10D) – page 8
Next, explain how and why corals are able to overcome the problems of surviving in warm tropical
water, and how they help produce the abundance of life in coral reefs:
Unlike elsewhere in the tropical open ocean, life is abundant in tropical coral reefs.
Corals are abundant, because they have “solved” the problem of the lack of food in the tropical
ocean: corals get most of their food from the algae who live inside them ()the zooxanthellae, not by
filter feeding phytoplankton or zooplankton. The corals make sure the corals get lots of food by
helping the zooxanthellae get sunlight and nutrients. The corals grow upwards towards the Sun by
putting layers of ____________________________ below them. (This is how they create the hard
“reef”.) The corals gather nutrients by ________________________________________________,
and then give the nutrients to their zooxanthellae. Unlike zooplankton, corals do not “waste”
precious nutrients by excreting them in fecal pellets which can sink deep down into the ocean and
cannot be used to grow the next generation of algae.
All the other living things in the reef are there because of the corals. During their lifetimes, corals
build up nutrients in their bodies by eating more and more of the rare plankton that drift into the
reef. When corals die of old age, their remains decompose and these nutrients are available for
algae like phytoplankton and seaweed to use for __________________________. (Thanks to the
corals, there are more nutrients in reef environment than elsewhere in the tropical open ocean.)
In addition, the shallow reef gives seaweed a place to attach to and grow in the Sun, and
the shallow waters keep phytoplankton from sinking too deep away from the Sun.
Thus, corals help phytoplankton and seaweed grow.
Animals are attracted to the reef to eat ______________________________________________.