Caging experiment to examine mortality, during metamorphosis of coral reeffish larvae

All previous attempts to estimate early postsettlement mortality of coral r eef fishes using either caging experiments or disappearance of new recruits have examined fish that had already settled, and therefore did not include the metamorphosis process Crest nets capture unharmed transparent larvae d uring their migration from the open ocean to lagoon reefs before metamorpho sis. We released these presettlement larvae at night into cages surrounding patch reefs and measured larval survivorship after two nights. This caging experiment involved cages enclosing the natural resident fish fauna, inclu ding predators, and others cleared of fish before releasing the larvae. The analyses of variance showed that (1) there was no difference in survivorsh ip between the seven trials, (2) there was a significant difference between cleared and uncleared cages, and (3); there were significant differences b etween larval species tested. For the seven species that had a significant difference in survivorship between cleared and uncleared cages, average mor tality of the larvae was 14% (range 0-26%) in cleared cages and 67% (range 29-76%) in cages with predators. The difference in mortality between specie s was related to the size of the larvae, as larger species exhibited reduce d mortality compared to smaller species. Mortality was related to the abund ance of resident fish that could act as predators or competitors. Predation can have a significant impact on the survival of metamorphosing fish larva e on coral reefs.