Standard Presentation (15 mins) Australian Marine Sciences Association 2022

Boosting Reef Health Through Removal of Macroalgae (#427)

Hillary A Smith 1 2 , Stella E Fulton 1 , Neil Mattocks 3 , Adam K Smith 4 , Lisa Boström-Einarsson 5 6 , Ian M McLeod 6 7 , David G Bourne 1 7
  1. College of Science and Engineering, James Cook University, Townsville
  2. University of New South Wales, Sydney
  3. Great Barrier Reef Marine Park Authority, Townsville
  4. Reef Ecologic, Townsville
  5. Lancaster Environment Centre, Lancaster, UK
  6. TropWater, James Cook University, Townsville
  7. Australian Institute of Marine Science, Townsville

Declining coral cover on tropical coral reefs often results in a concomitant increase in macroalgae. When proliferation of macroalgae persists outside regular seasonal growth, it can shift the ecosystem dominance away from corals into a permanently altered system. Such an altered system is unlikely to recover naturally, despite ample supply of coral larvae, as coral settlement and survival is reduced by the presence of macroalgae. Physical removal of macroalgae has been proposed to overcome this biotic barrier to recovery, although empirical evidence demonstrating the effects of removal on phase-shifted reefs is lacking. In this presentation, I will show evidence that four years of manual removal of macroalgae has resulted in significant positive increases in coral recruitment, and that other metrics of reef health show promising signs of recovery following intervention. Four months after each spawning event, we found a threefold increase in coral recruits to tiles in plots where macroalgae had been removed. Furthermore, benthic coral cover has increased at a faster rate where algae were removed compared to control areas. These results suggest that, at small scales, macroalgae removal may be a useful intervention to boost recruitment on degraded reefs.