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THE COMMUNITY ECOLOGY OF TABULATE ACROPORA COLONIES 

Introduction

Tabulate Acropora coral colonies are a very important component of coral reef systems as they often dominate shallow reefs due to their rapid growth rates and high competitive ability.  They are also a habitat for many reef fishes and invertebrates, providing shelter from predation and food.  The species assemblages, abundance of individuals present and the size of the fish inhabiting the colonies may be influenced by morphological attributes.  Other influences may include depth and reef health.  This project hopes to assess the community ecology of these colonies and determine the factors affecting this.

Aims and objectives: 

1. To understand the effect of depth and reef health on tabulate coral morphology and fish assemblages utilizing the colonies by assessing species richness and abundance on tabulate colonies at differing depths and on reefs of varying health.
2. To understand the effect of coral morphology on the species richness, abundance and size of organisms living within the colonies by measuring the size, inter-branch volume and the number of branches of the colonies and relate it to size and abundance of reef fishes present.
3. To understand the temporal stabilities of the reef fish communities within the tabulate colonies by measuring the species richness and abundance of fishes on the same colonies over several days.
4. To understand any changes in community composition over the diurnal period by comparing the fish assemblages present during the day with those present during the night.

Method

40 colonies from each of three reefs, Kaledupa, Sampela and Hoga, were studied.  The diameter, height and inter-branch space of each table was measured.  Degree of branching and the depth of each colony were also recorded.

The fish present at each colony were identified and counted and their sizes were estimated.

To assess the temporal stability of the communities, 20 colonies were tagged and the fish assemblages recorded.  These colonies were then revisited over 3 days and during the night; the fish assemblages were recorded on each visit. 

Preliminary results 

• Smaller colonies with smaller inter-branch volume have lower species richness than larger colonies although size of the colony does not appear to have any effect on overall abundance
• The inter-branch volume controls the size of the fishes present within colonies.
• Colonies at depth have lower richness than colonies at the reef crest.  Depth does not affect overall abundance.
• Fish assemblages remained relatively stable over the study period apart from a few species which passed through the sample sites e.g. Labroides dimidiatus 
• All species present during the day were absent at night.
• Species richness and abundance of fishes inhabiting the colonies is lower at Sampela than at Hoga and Kaledupa. 

Dissemination of results

A final year dissertation report entitled The community ecology of tabulate Acropora colonies will be completed by Laura Corrigan, University of Essex by May 2003.