Diet and nocturnal foraging in cardinalfishes (Apogonidae) at One Tree Reef, Great Barrier Reef, Australia

Cardinalfishes (family Apogonidae) form a major component of nocturnal planktivore assemblages on coral reefs. In order to assess their trophic role on reefs, we examined diet, diel feeding behaviour and nocturnal foraging in 7 species in the lagoon at One Tree Reef, Great Barrier Reef, Australia. Between 64 and 93% of fish collected at dawn had identifiable material in the stomach compared with 5 to 36% of fish collected at dusk, suggesting that all 7 species were predominantly nocturnal feeders. The movement of apogonids between resting sites and feeding grounds was examined using day and night visual surveys. Apogonids shared restricted resting habitats by day but moved into a range of habitats at night. Species were spatially segregated at night, both horizontally and vertically in the water column. Most species had generalised diets containing primarily demersal plankton and benthic invertebrates, suggesting a role in recycling rather than importation of nutrients and energy on reefs. Dietary differences among species appeared to be driven largely by their feeding positions in the water column at night. Since apogonids feed in a range of habitats, then return to restricted resting sites during the day, they are likely to play an important role in concentrating nutrients and energy on reefs, providing localised and predictable resources for both predators and detritivore communities.