Spatial, temporal and ontogenetic patterns of habitat use by coral reef fishes (Family Labridae)

The continuous reef tract on the semi-exposed side of Lizard Island, northern 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 cover, percentage cover of each substratum type, substratum diversity and complexity). Sixty-four labrid species were found to use these habitat 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). Seven of the abundant species showed strong patterns of habitat use, such that the assemblages of these species differed significantly among habitat zones (p < 0.0001). Only 1 abundant species, Labroides dimidiatus, occurred in similar densities in all habitat zones. Depth appeared to be of overriding importance in determining habitat use, with most species occurring either in shallow or deep zones. Within depth ranges, the labrid assemblages differed among habitat zones in terms of the relative abundance of species. In contrast, no clear relationship was detected between labrid density or diversity and other habitat features such as percentage living substratum, substratum diversity or complexity. 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 abundant species showed different patterns of habitat use by adults and recruits, suggesting ontogenetic shifts in habitat use by these species. In contrast, the others showed no evidence of ontogenetic shifts in 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.