The influence of phase of the moon and physical processes on the input of presettlement fishes to coral reefs

At One Tree Island, Great Barrier Reef, Australia, large numbers of reef fish, of sizes that were considered potential settlers, were caught in ichthyoplankton nets that were tethered on the reef crest at night. Comparisons were made, among lunar phases, with wind direction and strength, rate of water flow over the reef crest (facilitated by tide and wind) and changes in local water masses. Analyses for total reef fish and separately, the Gobiidae, Blenniidae, Lutjanidae, Apogonidae, Pomacentridae, Mullidae, Labridae and Scaridae, all showed considerable variation in abundance with time, but peaks in abundance were not concurrent for most families of fish. Differences in temporal patterns were also found at the species level for the Labridae. Although high catches of many fishes were found just after new and full moons, peaks in abundance were also found at other times and therefore the model that patterns of input were fully explained by semi‐lunar or lunar cycles was rejected. Peaks in abundance, for some groups, were not concordant with semilunar or lunar periods but were found at times when the wind was strong and onshore. Thus, a combination of lunar phase and wind explained a greater proportion of variation in replenishment of reefs for some groups than lunar phase alone. Single physical variables, or combinations of them (based on multivariate analyses), explained variation in abundance of some groups (e.g. Labridae and Gobiidae), but there was still unexplained variation in the abundance of fish caught in nets. Multispecies models of larval supply were generally inadequate and it was concluded that unexplained variation in fish abundance was partly due to pooling fish at the level of family and above (e.g. total reef fishes), when resolution at the species level is required. It is argued that a knowledge of production of fish (spawning/hatching), length of presettlement phase, swimming abilities and behaviour, as well as the biological and physical phenomena influencing survival, are required to explain variation in the replenishment of reefs.