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Marine Ecology Progress Series

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MEPS 362:129-137 (2008)  -  DOI:

Chemical effects of macroalgae on larval settlement of the broadcast spawning coral Acropora millepora

Chico L. Birrell1, Laurence J. McCook2,3,*, Bette L. Willis1,3, Lindsay Harrington1

1School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
2Great Barrier Reef Marine Park Authority, PO Box 1379, Townsville, Queensland 4810, Australia
3ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia
*Corresponding author. Email:

ABSTRACT: Recovery of degraded reefs is dependent on the settlement of coral larvae into habitats typically dominated by benthic algae, so that benthic algae may play pivotal roles in coral settlement and reef recovery. Here we demonstrate that waterborne influences of macroalgae could affect coral settlement before larvae contact reef substrata and that such effects vary between macroalgae. We tested for waterborne effects of algae on both pre-settlement behaviour and settlement of larvae of the coral Acropora millepora onto live fragments of the crustose coralline alga Hydrolithon reinboldii. Treatments comprised seawater collected from aquaria that had previously contained 1 of 3 macroalgae common on degraded reefs. The foliose brown macroalga, Lobophora variegata, enhanced coral settlement by 40% relative to substratum control treatments. In contrast, the filamentous green macroalga Chlorodesmis fastigiata (‘turtle weed’), hindered coral settlement by delaying settlement of larvae, although final settlement was similar to that in control treatments. Padina sp., a foliose brown macroalga closely related to L. variegata, reduced coral settlement by 30% compared with substratum controls. The demonstration of waterborne effects suggests that macroalgae can influence coral settlement before larvae reach reef substrata, even on a crustose coralline alga known to induce settlement, and even where the immediate settlement location is free of macroalgal cover. These results demonstrate the complexity in the mechanisms underlying the effects that over-abundant macroalgal growth may have on reef recovery. These effects have critical implications for the ecological resilience of coral reefs, especially as climate change increases the frequency and severity of disturbances to reefs.

KEY WORDS: Coral · Macroalgae · Recruitment · Resilience · Settlement · Allelopathy

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Cite this article as: Birrell CL, McCook LJ, Willis BL, Harrington L (2008) Chemical effects of macroalgae on larval settlement of the broadcast spawning coral Acropora millepora. Mar Ecol Prog Ser 362:129-137.

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