Group Members: _____________________________________________________
Coral Recruitment Lab
February 2011
Background
Most corals reproduce sexually by broadcast spawning their gametes into the water column.
These gametes (eggs and sperm) fuse into a single cell in a process called fertilization. This
fertilized cell, called a zygote, quickly develops into a planktonic coral larva, called a planula.
Some species of corals can produce planulae asexually.
The planula larva will remain in the plankton for at least 2-4 days. It may remain there longer
depending upon environmental conditions and the particular species of coral. After this
planktonic period, the planula actively seeks a suitable substratum to recruit1. Coral
recruitment can be defined as a measure of new coral individuals arriving in a population
(Nzali). To successfully recruit, a coral planula must attach itself to the substratum and
metamorphose into a polyp. Hard substratum such as limestone from previously living corals or
rocks is preferred by the planula over soft bottoms. A planula larva can chemically detect the
suitability of the substrate that it settles upon.
Many factors influence recruitment on a coral reef. First biological factors such as spawning,
fertilization, larval development, settling, metamorphosis, and predation by other species can
influence recruitment levels. Also chemical factors such as substratum composition, salinity,
and available nutrients can affect whether planula survive in the water column or attach to a
particular substratum. Lastly, physical factors such as temperature, wave energy, currents, and
sedimentation will affect where planktonic larvae are carried and whether they determine a
particular reef to be suitable.
Objective
In this laboratory you will simulate coral recruitment. You will first investigate the success of
recruitment on a single reef. Then you will examine coral planulae that are able to populate
different reefs from the one where they were spawned. You will determine patterns of growth
in these reefs and what factors affect this type of recruitment. Finally, you will investigate how
natural and anthropogenic factors can affect coral recruitment on reefs.
Materials
Laboratory packet
Reef mat
Bag of single color LegosTM
Bag of “planulae confetti” – colored pieces of construction paper
meter stick
1
from the Latin recroitre meaning “to grow again”
Part I: Recruitment on a single reef
Procedure
1. Place your reef mat on the floor or on a lab table in a space free of obstructions (you will be
dropping objects onto the mat.)
2. Place a single Lego brick in the center of your reef. This brick represents a coral. It is
spawning time and this coral will produce many planulae. You will represent all of the
planulae that this coral produces with five (5) “planulae confetti.”
3. Use the meter stick to measure one meter above the reef. Have
planulae
one student hold the five planulae confetti in his hand one meter
confetti
above the reef as in Figure 1.
4. Drop the planulae confetti over the reef.
a. If a planula lands entirely on the reef, it has successfully
recruited. Replace the planula with a Lego brick to
represent a new colony.
b. If a planula lands off the reef or is partially off the reef, it
has not successfully recruited. Pick it up and add it to your
reef mat
bag of planulae confetti.
c. If a planula lands on the reef, but is touching a Lego brick,
it has not successfully recruited. Growing corals will not
allow planulae to recruit on top of them. Pick up the
planula and place it in your bag of planulae confetti.
5. Add a Lego brick to all old coral colonies. This represents a year of
Figure 1
growth. Do not add Lego bricks to new recruits.
6. Complete Table I.
a. Record how many new colonies recruited and the total number of colonies on the
reef.
b. Calculate the recruitment rate and reef growth rate.
c. Count the number of Lego bricks (not colonies) on your reef. Multiply the number of
bricks by five to determine the number of planulae confetti you will drop in the next
“year.” This represents the reproductive output for the following year. Larger corals
have more polyps; therefore, their reproductive output increases.
7. Repeat steps 4-6 using the number of planulae confetti you calculated in step 6c. After five
“years” complete Analysis questions for Part I.
Table I: Recruitment on a single reef
A
Year
1
B
# of
original
colonies
# of
planulae
produced
1
5
C
# of new
coral
colonies
D
recruitment
rate
(C/B)*100
E
reef growth
rate
(C/A)*100
F
G
coral
biomass
Next year’s
reproductive
output
(total # of
bricks on
reef after
step 5)
(F * 5)
Place this value
in column B of
the next row.
2
3
4
5
Analysis
1. What happens to “planulae confetti” when you drop them over the simulated reef? How is
this similar to what happens to planulae in nature?
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2. How does the recruitment rate change over time? Provide an explanation for your
observations.
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3. How does the reef growth rate change over time? Provide an explanation for your
observations.
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Part II: Recruitment on Multiple Reefs
Procedure
1. Work with two other groups. Place your reef mats on the floor or lab table near one
another. Leave at least one reef mat of distance between each.
2. Each reef mat is a different color. Place a single Lego brick of matching color in the center of
each reef. This brick represents a coral. It is spawning time and this coral will produce many
planulae. You will represent all of the planulae that this coral produces with five (5)
“planulae confetti” of a matching color.
3. Use the meter stick to measure one meter above each reef. Select a student to hold the
planulae confetti one meter above each reef as in Figure 1. Make sure that the color of the
planulae confetti matches the color of the reef mat they are above.
4. Drop the planulae confetti over the reefs at the same time.
a. If a planula lands entirely on any reef, it has successfully recruited. Replace the
planula with a Lego brick of matching color to represent a new colony.
b. If a planula lands off a reef or is partially off a reef, it has not successfully recruited.
Pick it up and add it to your bag of planulae confetti.
c. If a planula lands on a reef, but is touching a Lego brick, it has not successfully
recruited. Growing corals will not allow planulae to recruit on top of them. Pick up
the planula and place it in your bag of planulae confetti.
5. Add a Lego brick to all old coral colonies. This represents a year of growth. Do not add Lego
bricks to new recruits. Keep all colonies the same color. Do not mix Lego brick colors on a
single colony.
6. Each group should complete Table II for their reef.
a. Record how many new colonies of each color recruited and the total number of
colonies on the reef.
b. Calculate the recruitment rates and reef growth rate.
c. Count the number of Lego bricks (not colonies) on your reef. Multiply the number of
bricks by five to determine the number of planulae confetti you will drop in the next
“year.” Make sure that the colors of the planulae match the colors of the Lego bricks
(coral colonies) on each reef. For example: If a reef has 1 red brick, 2 yellow bricks,
and 3 blue bricks, then you would drop 5 red planulae, 10 yellow planulae, and 15
blue planulae.
7. Repeat steps 4-6 using the number of planulae confetti you calculated in step 6c. After five
“years” complete Analysis questions for Part II.
Table II: Recruitment on Multiple Reefs
Reef Color ____________________________________
1
2
3
4
5
0
(E/C)*100
I
J
reef
growth
rate
coral
biomass
(F/B)*100
(total # of
bricks on
reef)
K
L
Next year’s
reproductive
output
(J * 5)
Place this value
in column C of
the next row.
M
Total reproductive output
5
0
recruitment
rate
H
(Place in column D of next row)
5
G
Total biomass
1
Reef
Color
# of
new
coral
colonies
F
(F/D)* 100
# of
planulae
produced
E
Total recruitment rate
D
Total new coral colonies
1 0 0
C
Total planulae produced
Year
# of
original
colonie
s
B
Total original colonies
A
Analysis
1. At the start of this simulation each reef produces a certain “color” of coral. How does the
color of coral that each reef produces change over the course of the simulation?
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2. Why does the color composition of corals on each reef change? Is there a pattern in your
observations?
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3. What do your observations from #1 and #2 above suggest about coral recruitment on
natural reefs? Make three inferences.
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4. In this simulation, how does the recruitment rate change over time? Compare your
recruitment rate in this simulation with your recruitment rate from Part I. Explain any
differences.
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5. How do you think this recruitment rate compares with the natural recruitment rate of
corals? Is it realistic? Why or why not?
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6. In this simulation, how does the reef growth rate change over time? Compare your result in
this part with your result from Part I. Explain any differences.
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7. What factors might affect the recruitment of coral species on a reef? Which of these did you
simulate in this laboratory?
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8. How could you change this simulation to make it more accurate?
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Extension
Run Part II of the simulation with one of these modifications. Collect your results Table III.
Compare your results with those from Parts I and II. Answer the analysis questions that follow.
A. One reef experiences temperature increases that cause intermittent bleaching. As a result,
each coral colony only obtains enough energy to produce two larvae per “coral brick” rather
than the usual five.
B. Each reef is dominated by a different species of coral. Species from reef 1 are fast growing
and quadruple in size each year (1 brick becomes 4 bricks). Species from reef 2 are medium
growing and triple in size each year. Species from reef 3 are slow growing and only double
in size each year.
C. Nutrient pollution is high on a particular reef. This leads to eutrophication. Rampant algae
growth covers much of the substrate. Finding a good place to recruit is difficult for coral
larvae. As a result only 1 out of every 3 larvae that land on this reef will successfully recruit.
D. The distance between reefs is two reef mat lengths apart.
Table III: Recruitment on Multiple Reefs w Variable
Reef
Color/
Variable
1
2
3
4
5
1 0 0 1
recruitment
rate
(E/C)*100
H
I
J
reef
growth
rate
coral
biomass
(F/B)*100
(total # of
bricks on
reef)
K
L
Next year’s
reproductive
output
(J * 5)
Place this value
in column C of
the next row.
M
Total reproductive output
G
(Place in column D of next row)
# of
new
coral
colonies
F
Total biomass
E
(F/D)* 100
# of
planulae
produced
D
Total new coral colonies
C
Total planulae produced
Year
# of
original
colonies
B
Total original colonies
A
Variable _________________________________________________
Total recruitment rate
Reef Color____________________________________
Extension Analysis
What is the effect of the introduced variable on recruitment rate and reef growth rate in this
simulation?
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How might what you learned in this simulation be of use in creating regulations, policies, or
legislation that protect coral reefs?
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Works Cited
Nzali, L. M., Johnstone, R. W. & Mgaya, Y.D. "Factors Affecting Scleractinian Coral Recruitment on a
Nearshore Reef in Tanzania." Ambio (2008): 717.