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

Decadal Demographic Shifts and Size-dependent Disturbance Responses of Corals in a Subtropical Warming Hotspot (#426)

Brigitte Sommer 1 , Jessica M Hodge 2 , Liam Lachs 3 , James Cant 2 , John M Pandolfi 4 , Maria Beger 2
  1. The University of Sydney, Sydney, NSW, Australia
  2. The University of Leeds, Leeds, United Kingdom
  3. Newcastle University, Newcastle upon Tyne, United Kingdom
  4. The University of Queensland, Brisbane, Queensland, Australia

Focusing on subtropical reefs in eastern Australia, we examine trends in the size-structure of corals with contrasting life-histories and zoogeographies surrounding the 2016 coral bleaching event (2010-2019) to determine their resilience and recovery capacity. Specifically, we use ImageJ and the SizeExtractR workflow to extract planar area of individual corals from transect photographs and use a size-based approach to investigate responses of different life stages to disturbance and the potential mechanisms that influence recovery trajectories. We document demographic shifts, with disproportionate declines in the number of small corals and long-term persistence of larger corals. The incidence of bleaching and partial mortality increased with coral size. While endemic Pocillopora experienced marked declines, decadal stability of Turbinaria despite bleaching, coupled with abundance increase and bleaching resistance in Acropora indicate remarkable resilience of these taxa in the subtropics. Declines in the number of small corals and variable associations with environmental drivers indicate bottlenecks to recovery mediated by inhibitory effects of thermal extremes for Pocillopora(heat stress) and Acropora (heat and cold stress), and stimulatory effects of chlorophyll-a for Turbinaria. Although our study reveals signs of resilience, it foreshadows the vulnerability of subtropical corals to changing disturbance regimes.