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THE FEEDING AND TERRITORIAL BEHAVIOUR OF CHAETODON TRIFASCIATUS: POSSIBLE INDICATORS OF REEF HEALTH
Monitoring
the health of coral reefs is an important task considering many of the world’s
coral reefs have been destroyed or severely degraded. Many different methods
have been employed to assess the benthic composition of coral reefs, such as
using line intercept transects. However, these methods are time consuming and
require trained scientists to carry them out. There may be, however, reliable
ways to indirectly assess the health of a coral reef and monitor it through
time: certain members of an easily identifiable conspicuous family of fish,
Chaetodontidae, have been posited to be reliable indicators of reef heath.
The
pair of divers descend to the reef crest of the selected reef area (Sampela, NFZ
or outside NFZ) and locate a pair of C.trifasciatus foraging on the reef.
In order to identify the territory of this pair so that they can be
located on successive dives, a brightly coloured water bottle, or flagging tape
is attached to the substrate to act as a marker.
The
pair is then followed for a 40 minute period. The observation period is divided
into 8x5 minute periods. Diver A
records general aspects of behaviour, such as: The zone of the reef being
foraged on (recording the time when the pair move to another zone), aggressive
and submissive interactions with other fish (if both exhibit the behaviour it is
counted as occurring twice). If
another individual Chaetondont passes within 50cm of the focal pair then it is
recorded as ‘tolerate spp. X’. In addition, other interesting foraging and
territorial behaviour and whether they are paired or separated (greater than 4m
apart) is recorded. Diver A also
marks out the boundary of the territory as the pair of divers follow the pair by
attaching bright flagging tape to the substrate at times when the fish are seen
to hesitate. This territory size is later assessed; the longest distance across
the territory is measured and the tape remains taught on the substrate.
At certain points along this line the distance at right angles to it is
measured. Benthic data, using the line intercept method, within the territory is
also collected. There will be three benthic data transects through each
territory, to give an accurate measure of the coral/substrate cover.
Diver
B follows the pair and focuses on one of the individuals for the entire 40
minute period, noting down the number of bites taken on each genus of coral
during each 5 minute period.
Any
distinct features of the butterfly fish will be noted to aid the identification
of a focal individual.
There
will be 3 focal pairs at each site, measuring the feeding behaviour and
territory size of each of these pairs on 3 occasions each. This will enable us
to make conclusions concerning territory size as we will have replication on
independent samples as well as repeat measurements of the same individual pairs.
Feeding
behaviour will be statistically analysed using ANOVA (2-way), and then trends
and correlations can be seen both within and between territories, and within and
between sites.
Territories
seem to be larger in degraded coral reefs than those territories in the
unprotected and protected sites. Possible explanations could be that inhabitants
of the degraded reefs have to travel further to forage for coral to feed upon
than those in the protected and unprotected sites. Territory data will be
analysed in accordance with the benthic data, as well as the feeding and
agonistic behaviour.
A
final year dissertation report entitled The feeding and territorial behaviour
of Chaetodon fasciatus: can it be used as an indicator of reef health will
be completed by John Griffin, University of Nottingham by May 2003