Ontogeny of in situ behaviours relevant to dispersal and population connectivity in larvae of coral-reef fishes

Abstract

Behaviour during the pelagic larval stage of coral-reef fishes can strongly influence dispersal, yet little is known of behavioural ontogeny. Speed, orientation and vertical distribution of larvae of 4 coral-reef fishes (Platax teira, Ephippidae; Lutjanus malabaricus, Lutjanidae; Epinephelus coioides, E. fuscoguttatus, Serranidae; 6 to 23 mm) were measured in situ off Taiwan. In E. coioides and E. fuscoguttatus, speed was 2 to 30 cm s -1 (4 to 19 body lengths s -1 , BL s -1 ), and increased at 1.4 to 2.3 cm s -1 mm -1 . In P. teira and L. malabaricus, speed was 11.2 to 16.6 cm s -1 (4 to 20 BL s -1 ) across the size range. All but the smallest, slowest larvae had Reynolds numbers >1000, and so swam in an inertial environment. In situ speeds were 39 to 87% of critical speeds, and smaller larvae swam nearer to critical speed than larger larvae. Of the larvae 71 to 90% swam directionally, but neither percentage of directional individuals nor orientation precision increased with size. P. teira swam toward the southwest (offshore). Epinephelus species undertook ontogenetic changes in orientation. Neither orientation nor ontogenetic changes were found in L. malabaricus. Horizontal swimming can influence dispersal directly. Vertical distribution, which differed among species, can influence dis- persal indirectly. P. teira became surface orientated, ascending 0.8 m per mm increase in length. L. malabaricus descended 0.5 m per mm increase in length. E. coioides ascended 0.4 m per mm increase in length. E. fuscoguttatus preferred greater depths, and lacked ontogenetic changes. The behaviours and their development show these larval reef fishes can influence dispersal in species- specific ways.