Diel patterns of abundance of presettlement reef fishes and pelagic larvaeon a coral reef

Most presettlement reef fish settled at night at One Tree Island, Great Bar rier Reef. Fish were sampled day and night using channel nets located on th e reef crest? and a plankton-mesh purse-seine net in the lagoon (1992-1994) . Catches of fish at night were generally tens to hundreds of times greater than those taken during the day. Preflexion fish, as well as postflexion a nd pelagic juveniles, were taken in greater numbers at night. Preflexion fo rms were a combination of those that had hatched from demersal eggs and lat er stages that had been transported over the reef crest. Highest numbers of postflexion and pelagic juvenile forms of Apogonidae, Blenniidae, Gobiesoc idae, Gobiidae, Labridae, Lutjanidae, Mugiloididae, Mullidae, Pomacentridae , Scaridae, Serranidae and Tripterygiidae were found at night. Observations , while SCUBA diving, and purse-seine samples in the lagoon indicated that the only resident larvae were of the genera Spratelloides and Hypoatherina; most of the fishes caught in nets, therefore, were immigrants. Patch reefs , sampled for new settlers early in the morning and late in the day. indica ted that the majority of apogonids (Apogon doederleini, > 95%) settled at n ight. Although greater numbers of pomacentrids were found in morning counts (e.g. Pomacentrus wardi), if data were converted to an hourly rate, many p omacentrids showed a similar hourly late of settlement day and night. Depth -stratified sampling in waters near One Tree Island (to 20 m) indicated tha t some taxa rise to the surface at night. This behaviour, perhaps combined with avoidance of diurnal predators may explain on-reef movement of potenti al settlers soon after dark. Studies on settlement cues, therefore, need to focus on night-related phenomena.