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ABUNDANCE AND DIVERSITY OF CHAETONTIDAE IN RESPONSE TO VARIATION IN CORAL COVER
Butterflyfish (family Chaetodontidae)
are commonly used as an indicator species of coral health. Indicator species can
be used to detect low-level changes in the coral reef habitat, and act as a
warning system for stress within this ecosystem. Commonly used indicator species
of Chaetodont include those which are obligate corallivores e.g. C.trifasciatus.
Correlations have been found between the abundance and diversity of these
species and coral abundance and diversity.
Crosby and Reese (1996) stated “the butterflyfish indicator method is
sensitive to changing conditions on the reef and should provide an “early
warning” that a change is occurring. This may provide enough time for remedial
actions to be taken before entire coral reef habitats are lost.”
The distribution of Chaetodonts on
coral reefs has been linked to the amount of live coral cover (Bell &
Galzin,1984; Bouchon-Navaro,1985; Hourigan,1988).
Aswell as other factors including topographic complexity, food
availability, current flow and the availability of hiding places.
1.
Test for variation
in the abundance and diversity of Chaetodont species in response to variation in
coral cover.
2.
Test whether using
a restricted range of Chaetodont species e.g. strong corallivores gives a better
correlation with habitat variables than using total counts.
Objectives
1.
To identify the
species of butterflyfish present within the sampling area
2.
To identify the
numbers of each species present within the sampling area
3.
To record the level
of coral cover present along each transect line within the sampling area
Eight sites were selected both inside and
outside the No Fishing Zone:
Transect lines were set up along the reef
crest, each line being 50m in length and at a depth of 3m below the reef crest.
For each of these sites three transects were laid, and these replicates were
surveyed a total of three times, giving a total of three benthic surveys and
nine Chaetodont surveys for each site. There was a gap of at least 5m
between each of the replicates to ensure separation, with each 50m Chaetodont
survey taking approximately 15 to 20 minutes to complete, and each 50m benthic
survey taking approximately 40 minutes to complete. When each transect line was
laid on the reef, they were left for approximately 10 minutes to allow the fish
to resume normal behaviour. Surveys were completed between 9AM and 5PM to allow
for diurnal movement of Chaetodonts.
As yet, no analysis has been carried out on
the data that has been collected over the last eight weeks; however, some
interesting observations have been made. It has been noted, for example, that in
Sampela where the reef is exceptionally degraded there is still a very high
diversity of chaetodonts, although the abundance remains lower in these sites.
Multivariate Analysis e.g. PRIMER will be
used to correlate abundance and diversity of Chaetodonts with habitat variables
e.g. live coral cover. Tests such as the T-test and ANOVA (Analysis of Variance)
can be used to look at site differences.
Report
A
dissertation entitled Abundance and diversity of Chaetondontidae with
variations in coral cover will be produced by Louise Withecombe, University
of Plymouth by April 2003.