VERTICAL-DISTRIBUTION OF FISH LARVAE IN THE GREAT-BARRIER-REEF-LAGOON, AUSTRALIA

The vertical distribution of shorefish - primarily reef fish - larvae in the upper 20 m in relatively shallow (< 30 m) waters of the Great Barrier Reef Lagoon near Lizard Island was investigated from 27 February to 7 March 1983 during both day and night. Four strata were sampled by neuston net and opening/closing bongo net: neuston (0 to 0.1 m), upper (0 to 6 m), middle (6 to 13 m), and deep (13 to 20 m). Taxon-specific patterns of vertical distribution which changed little ontogenetically, were found for the 50 taxa (in 24 families) analysed. Vertical distribution was highly structured during the day, and with few exceptions was nearly unstructured at night. Most taxa had highest concentrations deep in the water column during the day, but in any given stratum some taxa had highest concentrations. Day/night changes in pattern apparently were due to randomization or spread, rather than active migration. Related taxa had similar patterns. Similarity analysis including 211 taxa produced three groupings of samples: day neuston; day upper/middle; and day deep plus all night samples. The sampling strategy of using drogues to tag water parcels for subsequent resampling was compared with one of sampling at a fixed point. The drogue strategy was not superior to the fixed-point strategy as measured by dissimilarity indices, but this may differ among strata.