1. CORAL REEF: 2
Oscar Belloso, Alexandra Urdaneta, Ana Elena Sanchez and Claudia Martino

2. Variation in fish density, assemblage
composition and relative rates of predation
among mangrove, seagrass and coral reef
habitats.

3. INTRODUCTION
Introduction to the investigation: Key vocabulary, the purpose and some
background information.

4. KEY WORDS
• Assemblage: A collection of gathering things.
• Nursery: A place or habitat that breeds or supports animals.
• Mangrove/Seagrass Beds: Mangroves and seagrass beds are shallow-water
habitats that often have greater abundance of juvenile fishes to coral reefs.
They have been referred to as nursery habitats because of the apparent
increase in the survival of young individuals that these abundance patterns
suggest.

5. BACKGROUND
INFORMATION
• Null Hypothesis: There is no significant difference in nursery function among mangrove, seagrass
and shallow reef habitat as measured by: (a) patterns of juvenile and adult density, (b) assemblage
composition, and (c) relative predation rates.
• The results in this research suggested, that although both mangrove and seagrass showed
characteristics of nursery habitats, this pattern was weak.
• Very few species showed patterns that were significant. They were half of the mangrove and
seagrass sites which appeared to hold higher numbers of juvenile fish.
• Only four of the six most abundant and commercially important species (on research paper)
showed higher numbers of juvenile fish in mangrove and/or seagrass habitats relative to coral reefs.
• Although mangrove and seagrass had very low predation risk, this was not the case for all of them.
• The results caution against generalization that all mangrove and seagrass have nursery function.

6. PURPOSE OF
INVESTIGATION
• Coastal habitats such as coral reefs, mangroves and seagrasses beds are amongst the most diverse.
• Coastal habitats have very important scientific and economic reasons in vital ecosystem services:
✓ Nutrient cycling
✓ Waste treatment
✓ Disturbance regulation
• This study was to decide whether mangrove and seagrass beds of the Caribbean are more important for reef fish
species by testing the null hypothesis that there was no difference in nursery value among mangrove, seagrasses and
coral reef habitats.
• It is important to understand that there are many factors that affect the distribution and abundance of organisms among
coastal habitats.
• This investigation informs how these factors affect the distribution of species.

8. INTRODUCTION OF
INVESTIGATION
• Mangrove and seagrass are characterized in having shallow habitats that are often to observe to have
greater abundance of juvenile fishes compared to coral reefs.
• These habitats that are referred as nurseries have the following characteristics:
• They have an increase in juvenile survival.
• There are several factors that need to be considered in evaluating the value of a nursery:
✓ Growth
✓ Survival
✓ Density
✓ Movement

9. • There are factors that affect organism survival that is mention numerously in
this investigation:
• Competition
• Predation
• This factors will vary to which the organism settles.
• These factors increases the probability of an organism’s survival due to the
supply of food and shelter as well as the supplement of nearby populations.

10. SITES OF
EXPERIMENTATION
• They conducted this study in
three locations:
• Lee Stocking Island,
Great Exuma
• Bahamas
• Mahahual, Mexico
• Turneffe Atoll, Belize

11. EXPERIMENTAL DESIGN
Experimental design, materials, procedure and variables of the experiment.

12. PROCEDURE
1. One site from each habitat type was visually censused to find the abundances of juvenile and adult fishes.
✓ The juvenile and adult status was determined from a combination of size range and color patterns based on
published life history data.
✓ Fishes that were within 30 m2 of the transects were recorded.
1. The proportional abundance of juveniles among habitats was compared to test the null hypothesis of no differences among
habitats in terms of nursery potential.
✓ The proportional abundance of juveniles among habitats at the assemblage level was compared and then, the
proportional abundance of juveniles among habitats for each of the most abundant and commercially important
species were compared.
1. The null hypothesis of no difference in relative predation rates between habitats was tested by examining the removal times
of tethered fish.
✓ A live , juvenile smallmouth grunt (ranging in sizes from 3 to 6 cm total length) was used as baitfish in timed
experiments within mangrove and seagrass beds.
✓ A fish was tethered to active the stopwatch tethered timers to assess the relative rates of predation: a) between
habitats b) between morning and afternoon c) between sites
✓ 8 tethered baitfish were placed in an area of devoid predators

13. PROCEDURE
1. DENSITY
• The proportional abundance of juveniles among habitats was compared using:
✓ Univariate ANOVA was used to compare proportional abundance of juveniles among all three habitats at
each site.
✓ If necessary, this was followed up by Bonferroni post-hoct tests.
• Two levels of biological resolution were investigated:
1. Proportional abundance of juveniles among habitats at the assemblage level
2. Comparisons of the proportional abundance of juveniles among habitats for each of the most abundant and
commercially important species

14. 2. ASSEMBLAGE COMPOSITION
• Using Jaccard’s coefficient of similarity, the null hypothesis that species are not shared
among habitats was tested.

15. 3. RELATIVE PREDATION RATES
• The null hypothesis of no difference in relative predation rates between habitats was examined by
analyzing the removal times of tethered fish:
✓ A smallmouth grunt: used as baitfish in timed experiments within
mangrove/seagrass beds and coral reefs at each of two sites.
➡ Several smallmouth grunt were collected using a gill net, monitored for stress for 20 minutes and then attached to a tether
timer by placing a hook through the dorsal musculature.
➡ The length for each fish was recorded.
3. The tether timer was started and the timer with the batifish was placed in a given habitat.
➡ A stopwatch with a chronometer was fixed inside a 30 ml nalgene container and a magnetic switch was attached
to the start/stop function of the watch.
➡ Fish were tethered with a monofilament line, which in turn was connected to the start/stop switch.
➡ If a fish was taken the switch would open, causing the watch to stop.
➡ At the end of 90 minutes, experiments were concluded and the tether timers were collected.

16. Control - Relative Predation Rates Preliminary
Exam
Conducted to ensure that the movement
of the baitfish would not accidentally stop
the clock.
✓ Eight tethers, each with baitfish that were 6 cm in total length, were placed in
an area devoid of predators.
✓ The baitfish were visually monitored for 10 minutes with an observer 3 m
away.
✓ Observations confirmed that batfish removals or clock stoppages
were not the result of fish behavior.
Independant Variable - Amount of time (90
Minutes)
Dependant Variable - The survival of the fish

17. MATERIALS
• Univariate ANOVA (computer program)
• Tethered fish (Haemulon chrysargyreum or smallmouth grunt)
• Gill net
• Hook
• Stopwatches tethered timers
• Container
• Statistical software package

18. DATA PROCESSING & COLLECTION
The collection of data, how to process the data and the analysis.

19. ASSEMBLAGE
COMPOSITION
• If mangrove and seagrass habitats are
nurseries, then they are expected to
share species
• Tested null hypothesis:
‣ species not shared between
habitats ≈ lack of nursery potential

20. W THEY DID IT:
1. Used transect sampling to record all the
fishes if observed within 30 cm 2
2. Tested the null hypothesis by examining
similarity in assemblage structure among
habitats (censuses)

21. JACCARD’S COEFFICIENT OF
SIMILARITY
number of species that are in both
C habitats
c number of species present in habitat
Sj = A A
(a+b+c) number of species present in habitat
B B

22. • 7,200 fishes - 82 species
• Few species in common
• Between reef and mangrove:
• Sj = 0.22 +/- 0.18
• Between reef and seagrass:
• Sj = 0.23 +/- 0.20

24. RELATIVE PREDATION RATES
• If tethered fish was taken = switch would open, watch would stop
• Timers were started and placed in a given habitat
• Placed 3-8 replicate tether timers
• Experiments concluded at end of 90 min.
• Tethering experiments constrain behavior of the baitfish = can only assess
relative risk of predation

25. RELATIVE
PREDATION RATES

26. CONCLUSION AND EVALUATION
Population density, discussion and final comments.

27. DENSITY
Null hypothesis was rejected:
There is a difference in nursery function among mangrove, seagrass
and coral reef habitat
BUT it doesn’t mean that mangroves & seagrass provide nursery function.
Turneffe Atoll Site #6 higher abundance of juveniles in
mangroves
Turneffe Atoll Site #3 higher abundance of juveniles in reef
and seagrass
Analysis says: only 7/54 occasions demonstrated that there
was a higher abundance of juveniles in mangroves and/or
seagrass than coral reefs

28. ASSEMBLAGE
COMPOSITION
Null hypothesis was rejected:
Only 11 of the most abundant species were considered
Jaccard’s Coefficient of Similarity
→ few species were in common between:
Reef and Mangrove (0.22) Reef and seagrass (0.23)
Then, only the most abundant AND commercially important species were
considered
Jaccard’s Coefficient of Similarity
→ few species were in common between:
Reef and Mangrove (0.25) Reef and seagrass (0.20)

29. RELATIVE PREDATION
RATES
Null hypothesis was rejected:
Average survival rate of baitfish in mangrove/seagrass beds: 42%
Average survival rate of baitfish in coral reefs: 15%
(after 90 minutes of being tethered)
SITE 3
Morning Afternoon
Mangrove/Seagrass - 33% morality within 90 minutes Mangrove/Seagrass - 100% within 78 minutes
Coral reefs - 100% mortality within 80 minutes Coral reefs - no significant change between morning
and afternoon results
Evaluation: Tethering experiments contain behavior of baitfish

30. DISCUSSION
Juvenile survivorship =
2.7 times greater in mangrove/seagrass habitats than coral reefs
Mortality of individuals varied
between sites and time of the day.
Evaluation:
Conclusion identifies the need of similar studies to be conducted that
replicate habitats and thus better assesses nursery function
Results:
Population density, assemblage composition and relative rates of predation show that not
all mangrove and seagrass offer nursery function (generalization must be avoided)
Evaluation:
A more cautious and explicit analysis of ecological roles of such
habitats is required

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