Mixed-species shoaling as a behavioural mechanism facilitating the redistribution of tropical fishes.

Mr Kai Paijmans1, Professor David Booth2, Dr Marian Wong1

1University of Wollongong, Wollongong, Australia, 2University of Technology, Sydney, Sydney, Australia

Tropical fishes recruiting to temperate regions outside of their native range (hereafter termed vagrants) provide an exciting opportunity to investigate how novel behavioural interactions between displaced and native species are likely to structure future climate change driven redistributions. For gregarious tropical vagrants, a lack of conspecific recruits and exposure to novel environments imposes significant limitations on growth and survival. However, for some gregarious vagrant species these limitations may be overcome via the formation of mixed-species shoals with native heterospecifics. Each year, small numbers of larval damselfish (Abudefduf vaigiensis) are transported from the equatorial coral sea before settling in temperate south-eastern Australia. I have undertaken extensive underwater visual surveys and found that most vagrant A. vaigiensis form shoals with temperate heterospecifics and that A. vaigiensis in exposed habitats are within larger shoals containing more species than those in sheltered habitats. Considering these findings, I have conducted aquarium based shoal choice experiments and in situ behavioural observations to test the hypothesis that mixed-species shoaling facilitates A. vaigiensis predation avoidance and access to exposed but profitable foraging areas. This research exemplifies the importance of mixed-species shoaling behaviour for displaced gregarious fishes. More broadly, it highlights the need for novel behavioural interactions between displaced and native species to be considered as both facilitators or inhibitors of successful climate change driven species redistributions.


Kai Paijmans is a PhD candidate at the University of Wollongong (NSW, Australia). His broad interests lie in the application of behavioural ecology for understanding community and ecosystem scale dynamics, working with fish communities as model systems. Kai’s current research and PhD thesis is on mixed-species shoaling behaviour. The formation of mixed-species shoals (social groups) by fish has important implications for the growth and survival of individuals, however isn’t well understood due to a historical focus on single-species shoaling. South Eastern Australia, where Kai is based, is an ocean warming hotspot, therefore providing important opportunities to investigate species redistributions. By investigating how mixed-species shoaling behaviour displayed by displaced tropical fishes in association with native temperate fishes impacts the growth and survival of individuals, Kai’s research not only has implications in understanding the redistribution of fishes to higher latitudes, but also provides insight into how interspecific behavioural interactions influence and are influenced by the broader community and ecosystem in which they are occurring.

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