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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13778

Partitioning of marine transition zone reefs among temperate, sub-tropical and tropical fishes is more related to depth and habitat than temperature

D. V. Fairclough

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ABSTRACT: Understanding changes in fish communities as oceans warm, and cool and competition for space between established and novel species, can be evaluated in biogeographic transition zones, such as the west coast of Australia. At ~30°S in this region, a cool anomaly occurred in the 2000s, between marine heatwaves. Over two years of that anomaly, surveyed reef fishes were 57% temperate, 18% sub-tropical and 25% tropical. The most numerous fishes included a wrasse, herring, bullseye, drummer and damselfish. Based on similarities in the composition of fishes, seven significant clusters of reefs were identified along a gradation from deep, exposed to shallow, protected lagoonal reefs. Endemic sub-tropical and temperate wrasses and damselfishes typified all reefs. Some of these were ubiquitous over deep and lagoonal reefs and others prevalent in only one reef type, demonstrating habitat preferences and partitioning among closely-related species. This was reflected in the differing order of importance of fishes that typified reefs. Linear modelling indicated that abiotic (depth, distance from shore) and biotic factors (e.g. algae) explained the majority of variation in the fish community among reefs. Additional variation, particularly within lagoonal reefs, was related to relief, turf and corals, rather than water temperature. Occurrence and reproductive activity of a group of tropical/sub-tropical wrasses and damselfish in some lagoonal reefs with abundant tropical habitats (e.g. corals), suggested that they supported novel communities during cool anomalies. Better predictions of future change and interactions between existing and novel species with environmental cycles requires knowledge of species-specific habitat relationships and biology.