Tropicalisation of temperate reefs: implications for nursery habitat function for juvenile fishes

Miss Erin McCosker1, Dr Adriana Vergés1,2, Dr Peter Steinberg1,2,4, Dr Hamish Malcolm3

1The University of New South Wales, Sydney, Australia, 2Sydney Institute of Marine Science, Sydney, Australia, 3Department of Primary Industries, New South Wales Fisheries, Coffs Harbour, Australia, 4Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technical University, Singapore, Singapore


Temperate reefs around the world are becoming tropicalised, as range shifting warm-water species increase in dominance, while cool-water species recede. This has already caused profound shifts in dominant habitat-forming species, such as the transformation of lush kelp forests to depauperate barrens, or in some cases, the emergence of novel coral reefs. However, the consequences of habitat shifts for fish recruitment, and hence sustaining biodiversity on tropicalised reefs, requires an understanding of the importance of these habitats as nurseries for juvenile fishes. This study utilised underwater surveys to quantify the nursery value of temperate reef habitats for juvenile fishes along 1,200km of rocky reef in south-eastern Australia, a region that has emerged as a hot spot for change. Variation in the overall juvenile fish assemblage and species-habitat relationships were examined to identify critical nursery habitats for juvenile fishes. Strong species preference or avoidance of specific habitats indicated that juvenile fishes of some species were dependent on specialised resources, such as kelp forests, and these resources may be limited on tropicalised reefs. The availability of species’ preferred nursery habitats will influence both localised population replenishment and the likelihood of species to successfully expand their range as waters warm. This study highlights that changes in the identity and relative abundance of habitat-formers on tropicalised temperate reefs may differentially compromise or enhance their nursery function for fish species, altering reef community structure.


Erin is currently a PhD student supervised by Dr Adriana Vergés, Dr Peter Steinberg and Dr Hamish Malcolm at the University of New South Wales in Sydney, Australia. Erin’s research focuses on understanding the consequences of, and identifying the potential opportunities arising from, the tropicalisation of temperate reefs. This process is an increasingly rapid and visible re-organisation of temperate reefs as warm-water species shift their ranges towards the poles, causing changes in recipient ecosystems. Erin’s PhD aims to quantify the impacts of these tropicalisation-induced changes on two key ecosystem functions – nursery function for juvenile fish and productivity.  Having never been SCUBA diving in temperate waters before starting her PhD, Erin’s research has allowed her to discover the underwater beauty of Australia’s Great Southern Reef. Prior to commencing her PhD, Erin obtained her Masters of Environmental Science at Murdoch University in Perth, Western Australia.

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