HABITAT SPECIALIZATION AND THE DISTRIBUTION AND ABUNDANCE OF CORAL-DWELLING GOBIES

Many fishes on coral reefs are known to associate with particular micr ohabitats. If these associations help determine population dynamics th en we would expect (1) a close association between the abundances of t hese fishes and the abundances of the most frequently used microhabita ts, and (2) changes in the abundance of microhabitats would result in a corresponding change in fish population sizes. We examined habitat a ssociations among obligate coral-dwelling gobies (genus Gobiodon) and then investigated relationships between the spatial and temporal avail ability of habitats and the abundances of Gobiodon species among locat ions and among zones on the reef at Lizard Island (Great Barrier Reef) . Out of a total of 11 Acropora species found to be used by Gobiodon, each species of Gobiodon occupied 1 or 2 species of Acropora significa ntly more often than expected from the availability of these corals on the reef. Across reef zones, the abundance of most species of Gobiodo n was closely correlated with the abundance of coral species most freq uently inhabited. However, the abundance of 1 species, G. axillaris, w as not correlated with the availability of most frequently used corals across reef zones or among locations. For G, axillaris, therefore, fa ctors other than habitat availability were more important in determini ng differences in abundance among zones and locations. Also, correlati ons between the abundance of 2 species, G. histrio and G, quinquestrig atus, and the coral species they most frequently used was less consist ent among locations than among zones. This suggests that the relative importance of habitat availability in determining the abundance of the se species of Gobiodon is reduced at the spatial scale of locations ar ound Lizard Island. The population dynamics of Gobiodon during this st udy were closely Linked to the population dynamics of host corals. Bec ause of a crown of thorns starfish (Acanthaster planci) outbreak the a bundance of corals declined in particular reef zones. Corresponding wi th this loss of habitat was a decline in Gobiodon abundance. This stud y demonstrated that the abundance of habitat specialised fishes can be closely correlated with the spatial and temporal availability of suit able habitats among and within reefs.