Miss Sahira Bell1,2, Miss Shannen Smith3, Associate Professor Thomas Wernberg1, Dr Hamish Malcolm5, Dr Ezequiel Marzinelli6,7, Associate Professor Adriana Verges3,4
1University Of Western Australia, Perth, Australia, 2Balu Blue Foundation, Port Lincoln, Australia, 3University of New South Wales, Sydney, Australia, 4Sydney Institute of Marine Science, Sydney, Australia, 5Department of Primary Industries, Coffs Harbour, Australia, 6National University of Singapore, , Singapore, 7University of Sydney, Sydney, Australia
As climate change warms the oceans and species shift their distributions to stay within optimal thermal ranges, novel species interactions are starting to emerge. For the ecologically important kelp Ecklonia radiata found along Australia’s Great Southern Reef this is especially relevant, as range-shifting tropical fishes who overgraze kelps are adapting to ocean warming in this way. The east and west coasts of Australia have recorded dramatic declines in kelp forests near the warm edge of their distribution, and increases in the abundance of tropical herbivorous fishes. However, the region specific impact of herbivory and other mechanisms that may be driving kelp loss in these areas are not fully understood. Here, we experimentally quantify the relative importance of kelp recruitment processes and herbivory in driving persistent regime shifts from kelp to turf-alga dominance. Herbivore exclusion cages and recruitment tiles were deployed in situ along the east and west coasts to assess benthic community changes and kelp recruitment in the absence of herbivory pressure. Evidence of kelp recruitment viability on both coasts was observed, indicating that when herbivory pressure is removed oceanographic conditions remain suitable for kelp recovery. Benthic community composition was also significantly impacted by cage protection, with an increase in large, habitat forming, brown macro-algae, and a decrease in turf-alga observed within herbivore excluded areas. This study disentangles the roles that recruitment and herbivorous fishes play in limiting recovery of degraded kelp forests, and can further our capacity to predict, prevent and restore loss of services from these ecosystems.
Sahira Bell is a PhD Candidate at the University of Western Australia studying the impacts of climate change and tropicalisation on kelp forests. She also works alongside the conservation not-for-profit group, the Balu Blue Foundation, on campaigns to raise awareness and increase protection for Australia’s Great Southern Reef.