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THE BEHAVIOUR OF CHAETODONT TRIFASCIATUS IN RESPONSE TO DEGRADED CORAL REEF HABITAT

Introduction

The health of coral reefs throughout the world can be measured/monitored by using several different methods. By monitoring certain representative species, known as indicator species, it is possible to ascertain certain aspects of the health of the coral reef.

These species should be conspicuous inhabitants of the reef, such as corallivores. The butterflyfish indicator method (Crosby, M.P and E.S Reese 1996) method is considered to be a simple and inexpensive way of monitoring the health of coral reefs.  Observing the behaviour of certain butterflyfish species, eg Chaetodont trifasciatus, enables one to begin to understand not only the health of the focal coral reef, but also how it compares to coral reefs throughout the world. 

The establishment of a no fishing zone (NFZ) around the home reefs of Hoga island has enabled studies to be carried out whereby sites protected by the NFZ can be compared and contrasted to those sites that are left unprotected. This study will utilize the butterflyfish indicator method, using the behavioural patterns of Chaetodont trifasciatus, to investigate whether there is a difference in coral reef health between the protected coral reefs, and those open to exploitation by the local fishing community.

Aims 

1.      To understand how Chaetodont trifasciatus behaviour, both feeding and agonistic, changes with differing types of coral reef health.(degraded/protected/unprotected) 

2.     To understand the relationship between coral cover and feeding behaviour, within territories.

3.   To assess the value of Chaetodont trifasciatus as indicator species.

Methodology

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. 

Preliminary results

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.

Report

A dissertation entitled The Behaviour of Chaetodont fasciatus in Response to Degraded Reef Habitat will be produced by Sam Kent, University of Southampton by April 2003.