[Coral-List] Settlement patterns of the coral Acropora millepora on sediment-laden surfaces

[Gerard Ricardo]

Dear Coral Listers,


 
We would like to bring to your attentionour new (open access) paper “Settlement patterns of the coral Acroporamillepora on sediment-laden surfaces”, available at http://www.sciencedirect.com/science/article/pii/S0048969717318569


 
Abstract

Successful recruitment in corals is important for thesustenance of coral reefs, and is considered a demographic bottleneck in therecovery of reef populations following disturbance events. Yet several factorsinfluence larval settlement behaviour, and here we quantified thresholdsassociated with light attenuation and accumulated sediments on settlementsubstrates. Sediments deposited on calcareous red algae (CRA) directly andindirectly impacted coral settlement patterns. Although not avoiding directcontact, Acropora millepora larvae were very reluctant to settle on surfaceslayered with sediments, progressively shifting their settlement preference fromupward to downward facing (sediment-free) surfaces under increasing levels ofdeposited sediment. When only upward-facing surfaces were presented, 10% ofsettlement 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) veneerof sediment that occurs within background levels on reefs. Grooves withinsettlement surfaces slightly improved options for settlement on sediment-coatedsurfaces (EC10: 29 mg cm− 2), but were quickly infilled at higher depositedsediment levels. CRA that was temporarily smothered by sediment for 6 d becamebleached (53% surface area), and inhibited settlement at ~ 7 mg cm− 2 (EC10). Aminor decrease in settlement was observed at high and very low lightintensities when using suboptimal concentrations of a settlement inducer (CRAextract); however, no inhibition was observed when natural CRA surfaces alongwith more realistic diel-light patterns were applied. The low depositedsediment thresholds indicate that even a thin veneer of sediment can haveconsequences for larval settlement due to a reduction of optimal substrate. Andwhile grooves and overhangs provide more settlement options in high depositionareas, recruits settling at these locations may be subject to ongoing stressfrom shading, competition, and sediment infilling.


 
Cheers,

Gerard Ricardo