IN-SITU SWIMMING SPEEDS OF THE LATE PELAGIC LARVAE OF SOME INDO-PACIFIC CORAL-REEF FISHES

Swimming speeds of the late-stage, pelagic larvae of coral-reef fishes were measured in situ near Lizard Island on Australia's Great Barrier Reef, and Rangiroa Atoll, Tuamotu Islands, French Polynesia during 19 95-96. Larvae were captured with light traps End crest nets, and relea sed individually in open water. They were then followed by SCUBA diver s, normally for 10 min, and their speed was measured with a modified p lankton-net flow meter and a stop watch. Swimming speeds of 260 larvae of 50 species in 15 families of mostly perciform reef fishes are pres ented. Most measurements were for pomacentrids (8 genera, 16 species, 127 individuals), apogonids (1 genus, similar to 5 species, 18 individ uals), chaetodontids (3 genera, 8 species, 49 individuals), lethrinids (1 genus, similar to 4 species, 11 individuals), nemipterids (1 genus , 2 species, 10 individuals), serranids (2 genera, 2 species, 14 indiv iduals) and acanthurids (2 genera, similar to 4 species, 13 individual s). Numbers of individuals per species ranged from 1 to 25. Speeds wer e remarkably high for such small fishes (0.7 to 5.5 cm). Average speed was 20.6 cm s(-1) (range 2 to 65), or 13.7 body lengths s(-1) (range 2 to 34). SE for species with n > 4 ranged from 0.8 to 5.3 cm s(-1) (4 .1 to 25.0% of mean speed), but speed of the fastest individual of eac h species averaged 144% of mean speed. A taxonomic component was evide nt, with apogonids the slowest (2 to 13 cm s(-1)), followed by nemipte rids (10 cm s(-1)). Speed of pomacentrids and chaetodontids varied wid ely among species (7 to 35 cm s(-1)), whereas acanthurids, lethrinids and serranids were fast (19 to 55 cm s(-1)). Except for apogonids and nemipterids, nearly all species had mean swimming speeds greater than average ambient current speeds in the Lizard island area. Mean speed w as positively correlated with size (slope 8.2, r(2) = 0.43) when all t axa were included, but was not correlated with size for the Pomacentri dae and Chaetodontidae when each were considered alone. The speeds rep orted here combined with data on swimming endurance recently reported by Stobutzki & Bellwood (1997; Mar Ecol Prog Ser 149:35-41) reveal rem arkable swimming abilities for late-stage pelagic larvae of coral-reef fishes which could either greatly enhance dispersal or eliminate it.