Speed Presentation 2024 Australian Marine Sciences Association Annual Meeting combined with NZMSS

Temperate Marine Ecosystems under Tropicalisation: Ecological Function Changes at the Warmer Edge of Western Australia's Kelp Forests (#497)

Oceane Attlan 1 , Albert Pessarrodona 1 , Thomas Wernberg 1 2
  1. School of Biological Sciences and UWA Oceans Institute, University of Western Australia, Perth, Western Australia, Australia
  2. Institute of Marine Research, Nye Flødevigveien 20, His 4817, Norway

The loss of kelp forests across sections of the Western Australian coastline following the 2011 marine heat wave has advanced the tropicalisation of its temperate reefs1. As a consequence, scattered coral colonies and turfs or warm-affinity seaweeds now dominate areas previously occupied by kelp forests2. This shift of habitat-forming species modifies the associated calcifying community, which impacts the ecological functioning of temperate reefs3. Here, we aim to quantify how a shift in habitat-forming species alters the carbonate production of temperate reefs under the scenario of tropicalisation4. To do so, we surveyed the calcifying community (corals and calcifying algae) of twelve different reefs in Port Gregory (~29ºS) and Kalbarri (~30ºS) which are characterised by either unusual high cover of warm-affinity seaweeds, turfs or coral colonies compared to a kelp forest. We then calculated the carbonate production at the site level following the Indo-Pacific ReefBudget method5. To understand the ecology of carbonate production main drivers at coral dominated sites, we determined the calcification rates of five coral species commonly found in the reef. This research provides key insights into how ocean warming is changing the carbonate dynamics of temperate reefs, which may have consequences for the geo-ecological functions they provide.

  1. Wernberg, T. et al. An extreme climatic event alters marine ecosystem structure in a global biodiversity hotspot. Nature Climate Change 3, 78-82, doi:10.1038/nclimate1627 (2012).
  2. Wernberg, T. et al. Climate-driven regime shift of a temperate marine ecosystem localization. Science 353, 169-172, doi:10.1126/science.aaf4009 (2016).
  3. Harney, J. N. & Fletcher, C. H. A Budget of Carbonate Framework and Sediment Production, Kailua Bay, Oahu, Hawaii. Journal of Sedimentary Research 73, 856-868, doi:10.1306/051503730856 (2003).
  4. Vergés, A. et al. Tropicalisation of temperate reefs: Implications for ecosystem functions and management actions. Functional Ecology 33, 1000-1013, doi:10.1111/1365-2435.13310 (2019).
  5. Perry, C.T., Lange, I. & Januchowski-Hartley, F.A. ReefBudget Indo Pacific: online resource and methodology. Retrieved from http://geography.exeter.ac.uk/reefbudget/ (2018).