Removal of macroalgae from degraded reefs enhances coral recruitment

Smith, Hillary A., Brown, Dylan A., Arjunwadkar, Chaitanya V., Fulton, Stella E., Whitman, Taylor, Hermanto, Bambang, Mastroianni, Elissa, Mattocks, Neil, Smith, Adam K., Harrison, Peter L., Boström-Einarsson, Lisa, McLeod, Ian M., and Bourne, David G. (2022) Removal of macroalgae from degraded reefs enhances coral recruitment. Restoration Ecology. (In Press)

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Abstract

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. Here, we manually removed macroalgae from twelve 25 m(2) experimental plots (88.5 +/- 6.2 kg wet weight per plot; 90% benthic cover decrease) on a degraded reef prior to coral mass spawning across 2 years and recorded the number of coral recruits to settlement tiles and natural substrata. Four months after each spawning event, we found a threefold increase in coral recruits to tiles in plots where macroalgae had been removed (n = 12 plots; February 2019: mean 45.9 +/- 12.7 recruits per tile; February 2020: mean 53.9 +/- 5.9 recruits per tile) compared to control plots where macroalgae remained (n = 12 plots; February 2019 mean: 13.6 +/- 2.8 recruits per tile; February 2020 mean: 17.5 +/- 3.5 recruits per tile). These results suggest that, at small scales, macroalgae removal may be a useful intervention to boost recruitment on degraded reefs. Longer-term monitoring is needed to document if coral survivorship, growth, and subsequent reef recovery occurs.

Item ID: 72253
Item Type: Article (Research - C1)
ISSN: 1526-100X
Keywords: citizen science,coral recruitment,Great Barrier Reef,macroalgae removal,phase shift,reef restoration
Copyright Information: © 2021 Society for Ecological Restoration.
Date Deposited: 09 Feb 2022 11:58
FoR Codes: 31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 50%
41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410405 Environmental rehabilitation and restoration @ 50%
SEO Codes: 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180507 Rehabilitation or conservation of marine environments @ 50%
18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180501 Assessment and management of benthic marine ecosystems @ 50%
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