Abstracts Category : Other

Habitat preferences and associations of juvenile algal-associated fishes on coral reefs

by Oda Ravnaas Waldeland

Macroalgae are an important and diverse component of tropical inshore reefs, providing a range of ecological and functional services. Most of the research emphasis has focused on the negative effects of increased macroalgae on coral reefs to the growth and persistence of corals and fishes. However, on undisturbed reefs, macroalgal beds provide important habitats for newly settled fishes, many of which have ontogenetic changes to coral reefs and replenish adult populations that help control macroalgal growth. The few studies that have investigated macroalgal associations of juvenile fishes have treated macroalgae as a single entity. In doing so, any associations of fishes with taxonomic or functional groups cannot be discerned. The objective of this thesis was to undertake observational and experimental studies to investigate the patterns and mechanisms of habitat selection and preferences in algal-associated juvenile fishes on coastal reefs.In Chapter 2, I investigated the availability, use and selectivity of microhabitats on the reef flat of an inshore reef by recently settled coral reef fishes. Fish and benthic communities were quantified along three 50m transects at each of six reef flat sites along the leeward side of Orpheus Island, an inshore island on the central Great Barrier Reef (GBR). Benthic communities were quantified using the point-intercept method, recording the benthos directly underneath the transect every 0.5m. Recently settled fish were surveyed within a 2m belt along each transect. All recently settled fishes were identified to species, and the microhabitat they were associated with was recorded. A total of 22 species of recently settled fish were recorded across all transects, with the majority of the species being herbivorous as adults. Examination of the microhabitat preferences of the six most abundant species revealed that the two herbivorous rabbitfish species, Siganus lineatus and S. canaliculatus, appeared to associate with large fleshy macroalgae (namely Padina and Sargassum). In contrast, three herbivorous damselfishes, Pomacentrus wardi, P. adelus and P. chrysurus, and the invertebrate feeding cardinalfish Apogon cookii showed no apparent selection for any of the microhabitats examined. These findings suggest that macroalgae are important habitats for some newly settled coral reef fishes, and the availability and composition of macroalgae may shape juvenile populations. Both habitat selection at settlement and/or post-settlement processes may contribute to the establishment of these patterns.The objective of Chapter 3 was to investigate the specific habitat and olfactory preferences of two rabbitfishes (S. lineatus and S. canaliculatus) and two herbivorous damselfishes (P. wardi and P. adelus) at settlement. Nave settlement-stage fishes were collected in light traps and used in a series of aquarium-based settlement choice experiments in which an individual larva was introduced into the centre of a 500L aquarium and allowed to choose among four habitat options. The fishes were