Standard Presentation (15 mins) Australian Marine Sciences Association 2022

Impacts of Natural Recruitment and Asexual Propagation on Coral Population Size Structure (#321)

Christine D Roper 1 , Emma F Camp 1 , John Edmondson 2 , David J Suggett 1
  1. Climate Change Cluster, University of Technology Sydney, Ultimo, NSW, Australia
  2. Wavelength Reef Cruises, Port Douglas, QLD, Australia

Coral populations on the Great Barrier Reef are experiencing long-term shifts in size structure, including steep declines in the abundance of small colonies due to the depleting supply of new recruits. In 2018, tourism operators in the northern GBR initiated planting of asexual coral fragments (>5cm) to aid recovery at high-value sites. We examined how this activity alongside natural recruitment collectively contributed to local site recovery and in turn the influence on coral population size structure. We examined two sites which were differentially impacted by the 2016/2017 mass bleaching, and consequently subject to distinct outplant efforts (14,100 versus 5,800 outplants). From 2018-2021 coral cover increased from 15% to 27% at Rayban (high-effort site), and 38% to 51% at Mojo (low-effort). Natural recovery was characterised by a settlement rate of 6.6 (±3.4) and 3.7 (±1.7) recruits/tile, while the density of established recruits was 10.7/m2 (±1.8) and 6.5/m2 (±0.8) at Rayban and Mojo, respectively. Size-frequency distributions of key taxa showed a higher frequency of small to mid-sized colonies (4cm2 – 150cm2) in outplant compared to control areas. We discuss how the combined monitoring of natural versus intervention-based recovery is essential to understanding the impact of coral propagation efforts on local site recovery.