Record high damselfish recruitment at Rottnest Island, Western Australia, and the potential for climate-induced range extension

Three-decades of observations of tropical fish recruitment on the south coast of Rottnest Island, Western Australia (WA), have indicated that settlement of two tropical damselfish (Abudefduf sexfasciatus and A. vaigiensis) peaks each autumn with the seasonal strengthening of the Leeuwin Current (LC). Historically these fish have not bred at Rottnest Island or at other adjacent coastal locations although an active breeding population exists at the Houtman Abrolhos Islands some 330 km to the north. Record levels of recruitment in early 2011 followed extremely strong southward advection in the LC accompanied by unprecedented high water temperatures associated with a marine heat wave. Settlement numbers the following year were almost as high, again associated with a very strong LC and high water temperatures, while 2013 saw lower but still above average recruitment. Against a background of gradual ocean warming along the WA coast, one of the world's 30 hotspots for increasing ocean temperature, the potential for these species to establish a breeding population at Rottnest Island is explored by comparing the water temperatures during the presumed spawning period at the Abrolhos Islands with those at Rottnest Island together with winter temperatures and the abundance of what are believed to be mature Abudefduf successfully over-wintering at Rottnest Island. “The results indicate that establishment of a breeding population at Rottnest Island does not appear to be limited by water temperatures, and raises the question as to why a breeding population does not already exist as the settlement habitat appears very similar to that at the Abrolhos Islands.