Shifts in the marine fish assemblage on tropicalised east Australian reefs

Miss Shannen Smith1, Dr. Ezequiel Marzinelli3,4,5, Dr. Arthur  Shultz2, Prof. Peter Steinberg1,5, Dr.  Hamish  Malcolm2, A/Prof. Adriana Vergés1,5

1Centre for Marine Science and Innovation; Ecology and Evolution Research Centre; University of New South Wales, Sydney, Australia, 2Marine Ecosystem Research, Fisheries NSW, Department of Primary Industries, Coffs Harbour, Australia, 3The University of Sydney, Faculty of Science, School of Life and Environmental Sciences, Sydney, Australia, 4Singapore Centre for Environmental Life Sciences Engineering; Nanyang Technological University, , Singapore, 5Sydney Institute of Marine Sciences, Sydney , Australia

Temperate reefs around the world are becoming tropicalised as global species redistributions are causing novel species interactions and leading to profound community shifts. For species that move to higher latitudes, survival depends not only on physiological capacity but also the ability to coexist or be competitive within the established community. The consequences of novel communities however are only beginning to be understood. For the marine environment, the range expansion of tropical herbivorous fishes is leading to the tropicalisation of some temperate reefs and the decline of kelp as a dominant habitat-former. This is true for the Solitary Islands Marine Park (SIMP), a critical tropical/subtropical/temperate transition zone on the east coast of Australia and ocean warming hotspot. We used baited remote underwater video surveys (2002-2018) to examine changes in fish biodiversity on reefs within SIMP where kelp has been lost and not recovered for almost a decade. In addition to a marked increase in tropical herbivorous fishes, we found an overall increase in fish abundance and in the occurrence of both tropical and temperate-associated piscivores and invertivorous fishes. On the species level, we also identified four temperate-associated species that appear to have declined on the reefs in this study, three of which are endemic to the southern half of Australia. This study highlights meaningful changes in fish community structure over a period of striking environmental change.


I am a second year PhD candidate in the Seagrass, Algae, Tropicalisation Lab at the University of New South Wales, Sydney, Australia. My research focus is in understanding the mechanisms of tropicalisation, i.e the climate induced changes that occur on temperate reefs that cause them to shift towards a more tropical state. I completed my undergraduate and honours degrees at the University of Technology, Sydney, Australia with specific interest in the behavioural ecology of range expanding marine fishes. For my PhD, I work primarily in the Solitary Islands, New South Wales, where an influx of tropical marine fishes and large scale macroalgal loss has been recorded. I am interested in the role of range expanding species in directly altering and maintaining a novel ecosystem state.

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