Wave-sheltered embayments are recruitment hotspots for tropical fishes on temperate reefs

© Inter-Research 2016. Poleward redistribution of species, facilitated by global warming, will be compromised if habitats at higher latitudes do not support the species' early life stages. For tropical reef fishes, reef structure may mediate colonisation of temperate regions; however, an understanding of key habitat requirements for colonisation is currently lacking. We show that density, diversity (taxonomic and trophic) and species richness of newly recruited tropical reef fishes were greater in embayed than exposed reefs in 2 mid-latitude temperate zones, where coastal waters are rapidly warming: southeastern Australia (30.5-33° S) and western Japan (32-33.5° N). Dietary generalists (e.g. planktivores and herbivores) and specialists (corallivores) associated more commonly with embayed reefs. Wave exposure was a stronger predictor of the density and richness of dietary generalists than water temperature, latitude, predatory fish densities, reef rugosities, benthos and distance to river mouths. Corallivores were strongly associated with branching corals, which were exclusive to highly sheltered reefs. We also explored habitat associations of 7 focal species within a coral reef, One Tree Island (OTI), Great Barrier Reef. Four species associated with wave - sheltered over exposed reef on OTI and temperate Australian reef. However, Abudefduf vaigiensis, Pomacentrus coelestis and Acanthurus triostegus associated more with wave-sheltered reef in temperate regions. We hypothesise that cool temperate waters promote greater sheltering of some warm-adapted, tropical fishes by impacting their swimming/physiological performance. Results suggest availability of embayed temperate reefs may influence where some tropical fishes colonise with warming waters, through impacting recruitment. Wave exposure of reefs should be considered when predicting geographic responses of tropical fishes to climate change