MESOSCALE DISTRIBUTION PATTERNS OF LARVAL AND PELAGIC JUVENILE FISHESIN THE CENTRAL GREAT-BARRIER-REEF LAGOON

Larval and pelagic juvenile fish were collected along 2 transects with in the central Great Barrier Reef lagoon, Australia, using plankton ne ts and light traps in October, November and December 1989. Multivariat e analyses were used to examine spatio-temporal variability in the dis tributions of the fish collected with both techniques. Plankton nets r evealed a relatively stable cross-lagoon pattern, with (1) a distincti ve nearshore component characterized by gobiids, callionymids, leiogna thids and teraponids; (2) a cross-lagoon group including nemipterids, carangids, platycephalids and scorpaenids; and (3) an outer-lagoon ass emblage dominated by clupeids, lutjanids, pomacentrids, and scombrids. Significant temporal coherence in the abundance patterns of a number of families with cross-lagoon and offshore affinities was also detecte d. This coherence could have been generated by either a synchronous sp awning event, or by hydrographic phenomena acting over synoptic scales of al least 50 km in both alongshore and cross-shelf directions. Ligh t trap catches were much more ephemeral than those from the plankton n ets, and were dominated by collections at a single station in October. Numbers of principal taxa at this station were variable on each of th e 3 sampling occasions during the month. The most numerous taxa, Pomac entrus spp., were captured in high numbers on all of the 3 nights. Let hrinus spp. and Chromis sp. were abundant on the second night, but low numbers were taken on the first and third nights. Mullids were captur ed in progressively higher numbers through the sampling period. Compar ison of plankton net and light trap data suggested that multi-specific patches of reef fish larvae were characteristic only of late-larval a nd pelagic juvenile stages. Patch generation may, therefore, be due to active aggregation rather than passive accumulation of larvae. Althou gh the ultimate fate of late-stage larvae within this multi-specific p atch was unknown, the data are consistent with the hypothesis that maj or settlement events occur when occasional dense patches of larvae col lide with reef habitats.