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THE DISTRIBUTION, ABUNDANCE AND FEEDING BEHAVIOUR OF Bohadschia graeffei, A NON-EXPLOITED HOLOTHUROIDEAN 

Introduction

Bohadschia graeffei is a large Holothuroidean which is common to the coral reefs of the Wakatobi Marine Park (see figure 1). It is unusual as it is not exploited by the local fisheries due to the difficulty in drying down this species and the low economic return. Consequently can often reflect potential exploited Holothuroidean densities .Despite its obvious importance there is only limited literature available concerning the biology and ecology of this species.

Aims:

• To understand factors effecting the distribution of B. graeffei on different reef systemsTo know general population densities on different reef systems and reef ecozones
• To understand the habitat preference of B. graeffei
• To know features related to the behaviour of B. graeffei in the field and under laboratory conditions

Methods

A variety of techniques were employed to determine the abundance of B. graeffei and the best technique was to use time restricted transects at determined depths using constant search effort. 

When an individual was located its size, and behaviour (feeding, moving, searching, swaying or motionless) was recorded as was the substratum type, depth and general reef characteristics. 

To determine behavioural responses and feeding behaviour individuals were transplanted from different surfaces (those deemed feeding surfaces compared to those which were not feeding surveys) and behavioural characteristics were observed.  

Feeding rates were estimated by examining the rate of buccal tentacle movement to the oral disk, and experiments were carried out in the field and in the laboratory. 

Tentacle ultra structure was observed under the microscope. 

Preliminary Results

Over 80 individuals were found (with inter-site and -zone differences) and lengths ranged between 18 – 45 cms. Average length was approximately 28 cms. No juveniles were found during the study. The majority of individuals were found feeding on coral rubble and when found on other substrata were not observed to be feeding but usually searching or moving and swaying. 

The swaying response has only previously been theoretically linked to spawning activity but might be a sensing technique. Results from other aspects  of the study will be fully analysed back in the UK. 

Dissemination of results

A final year dissertation report will be completed by May 2003 by Rosalind Day from the University of Essex.