SPATIAL, TEMPORAL AND ONTOGENIC PATTERNS OF HABITAT USE BY CORAL-REEFFISHES (FAMILY LABRIDAE)

The continuous reef tract on the semi-exposed side of Lizard Island, n orthern Great Barrier Reef, can be divided into 6 habitat zones, which are distinctly different in terms of their physical (depth, slope and wave exposure) and biological characteristics (percentage of living c over, percentage cover of each substratum type, substratum diversity a nd complexity). Sixty-four labrid species were found to use these habi tat zones in 5 surveys conducted over 3 yr. Thirty-eight species (1804 individuals) were recorded in a single survey (area, 13500 m(2)), of which 8 were abundant (n > 5% of total number of individuals), 6 were common (1% < n < 5% of total) and 24 were rare (n < 1% of total). Seve n of the abundant species showed strong patterns of habitat use, such that the assemblages of these species differed significantly among hab itat zones (p < 0.0001). Only 1 abundant species, Labroides dimidiatus , occurred in similar densities in all habitat zones. Depth appeared t o be of overriding importance in determining habitat use, with most sp ecies occurring either in shallow or deep zones. Within depth ranges, the labrid assemblages differed among habitat zones in terms of the re lative abundance of species. In contrast, no clear relationship was de tected between labrid density or diversity and other habitat features such as percentage living substratum, substratum diversity or complexi ty. These patterns were consistent at each of 3 sites separated by > 1 km and over 3 yr and 2 seasons (summer and winter). Only 2 of the 8 a bundant species showed different patterns of habitat use by adults and recruits, suggesting ontogenetic shifts in habitat use by these speci es. In contrast, the others showed no evidence of ontogenetic shifts i n habitat use, inferring that recruitment patterns may be important in structuring patterns of habitat use by these species. Further studies are now required to test this hypothesis.