Poster Presentation Australian Society for Fish Biology Conference 2022

The impact of foraging and predation on the shoaling behaviours of tropical vagrant fish and their potential for range expansion (#207)

Lucas LD Djurichkovic 1 , David DB Booth 1 , Alex AR Rigg 1
  1. University of Technology Sydney, Waterloo, NSW, Australia

Rising sea surface temperatures and concurrent strengthening of poleward boundary currents are driving the redistribution and expansion of tropical marine organism’s ranges into novel temperate habitats, resulting in a restructuring of ecological interactions in recipient communities. An increasing number of temperate marine ecosystems globally have become regions of tropicalisation, an example is the seasonal displacement of coral reef fishes from natal lower latitude tropical ecosystems. This arrival of low-density populations of juvenile tropical fish (termed ‘vagrant’ fishes) results in changes to local fish communities, as critical behavioural functions such as shoaling are potentially comprised as the trade-offs (foraging and mitigating predation) that define such functions are altered. Over-winter survival rates of vagrants however still remain low due to cold water exposure, restricting the successful establishment of populations in temperate habitats. Previous research has shown that the vagrant tropical damselfish Abudefduf vaigiensis benefited from shoaling with temperate species through the mitigation of predation risk, allowing increased foraging opportunities and attaining larger body sizes than when shoaling with conspecifics. This study aims to compare how different shoaling forms influence shoaling of A. vaigiensis and how this impacts their fitness. Preliminary results suggest physiological and behavioural plasticity by A. vaigiensis juveniles when shoaling with conspecifics or heterospecifics. At a shoal ratio of 80% conspecifics, A. vaigiensis juveniles exhibited a significant increase in somatic growth rate compared to 100% conspecifics. Results from predation and foraging trade-off lab experiments have also indicated that novel predators can induce risk-aversive behaviours that can compromise feeding rates, as we found dramatically reduced boldness when exposed to a live predator (Sepia plangon). Shoaling strategies may be predominant factor in the range expansion potential of tropical fishes, and therefore it is imperative that we better understand how they are employed and what factors exert the greatest influence over them.