Settlement patterns of the coral Acropora millepora on sediment-laden surfaces

Gerard F. Ricardo, Ross J. Jones, Mikaela Nordborg, Andrew P. Negri

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Abstract

Successful recruitment in corals is important for the sustenance of coral reefs, and is considered a demographic bottleneck in the recovery of reef populations following disturbance events. Yet several factors influence larval settlement behaviour, and here we quantified thresholds associated with light attenuation and accumulated sediments on settlement substrates. Sediments deposited on calcareous red algae (CRA) directly and indirectly impacted coral settlement patterns. Although not avoiding direct contact, Acropora millepora larvae were very reluctant to settle on surfaces layered with sediments, progressively shifting their settlement preference from upward to downward facing (sediment-free) surfaces under increasing levels of deposited sediment. When only upward-facing surfaces were presented, 10% of settlement was inhibited at thresholds from 0.9 to 16 mg cm− 2 (EC10), regardless of sediment type (carbonate and siliciclastic) or particle size (fine and coarse silt). These levels equate to a very thin (< 150 μm) veneer of sediment that occurs within background levels on reefs. Grooves within settlement surfaces slightly improved options for settlement on sediment-coated surfaces (EC10: 29 mg cm− 2), but were quickly infilled at higher deposited sediment levels. CRA that was temporarily smothered by sediment for 6 d became bleached (53% surface area), and inhibited settlement at ~ 7 mg cm− 2 (EC10). A minor decrease in settlement was observed at high and very low light intensities when using suboptimal concentrations of a settlement inducer (CRA extract); however, no inhibition was observed when natural CRA surfaces along with more realistic diel-light patterns were applied. The low deposited sediment thresholds indicate that even a thin veneer of sediment can have consequences for larval settlement due to a reduction of optimal substrate. And while grooves and overhangs provide more settlement options in high deposition areas, recruits settling at these locations may be subject to ongoing stress from shading, competition, and sediment infilling.

LanguageEnglish
Pages277-288
Number of pages12
JournalScience of the Total Environment
Volume609
DOIs
StatePublished - 31 Dec 2017

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settlement pattern
coral
Sediments
sediment
calcareous alga
red alga
Algae
Reefs
Veneers
larval settlement
reef
substrate
light attenuation
Silt
Carbonates
Substrates
background level
shading
light intensity
coral reef

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Ricardo, Gerard F. ; Jones, Ross J. ; Nordborg, Mikaela ; Negri, Andrew P./ Settlement patterns of the coral Acropora millepora on sediment-laden surfaces. In: Science of the Total Environment. 2017 ; Vol. 609. pp. 277-288
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abstract = "Successful recruitment in corals is important for the sustenance of coral reefs, and is considered a demographic bottleneck in the recovery of reef populations following disturbance events. Yet several factors influence larval settlement behaviour, and here we quantified thresholds associated with light attenuation and accumulated sediments on settlement substrates. Sediments deposited on calcareous red algae (CRA) directly and indirectly impacted coral settlement patterns. Although not avoiding direct contact, Acropora millepora larvae were very reluctant to settle on surfaces layered with sediments, progressively shifting their settlement preference from upward to downward facing (sediment-free) surfaces under increasing levels of deposited sediment. When only upward-facing surfaces were presented, 10{\%} of settlement was inhibited at thresholds from 0.9 to 16 mg cm− 2 (EC10), regardless of sediment type (carbonate and siliciclastic) or particle size (fine and coarse silt). These levels equate to a very thin (< 150 μm) veneer of sediment that occurs within background levels on reefs. Grooves within settlement surfaces slightly improved options for settlement on sediment-coated surfaces (EC10: 29 mg cm− 2), but were quickly infilled at higher deposited sediment levels. CRA that was temporarily smothered by sediment for 6 d became bleached (53{\%} surface area), and inhibited settlement at ~ 7 mg cm− 2 (EC10). A minor decrease in settlement was observed at high and very low light intensities when using suboptimal concentrations of a settlement inducer (CRA extract); however, no inhibition was observed when natural CRA surfaces along with more realistic diel-light patterns were applied. The low deposited sediment thresholds indicate that even a thin veneer of sediment can have consequences for larval settlement due to a reduction of optimal substrate. And while grooves and overhangs provide more settlement options in high deposition areas, recruits settling at these locations may be subject to ongoing stress from shading, competition, and sediment infilling.",
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Settlement patterns of the coral Acropora millepora on sediment-laden surfaces. / Ricardo, Gerard F.; Jones, Ross J.; Nordborg, Mikaela; Negri, Andrew P.

In: Science of the Total Environment, Vol. 609, 31.12.2017, p. 277-288.

Research output: Contribution to journalArticle

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Ricardo GF, Jones RJ, Nordborg M, Negri AP. Settlement patterns of the coral Acropora millepora on sediment-laden surfaces. Science of the Total Environment. 2017 Dec 31;609:277-288. Available from, DOI: 10.1016/j.scitotenv.2017.07.153