Acidified algae, not larvae, block coral settlement
Six weeks of ocean acidification on crustose coralline algae halved Acropora settlement, but larvae still settled on ambient-conditioned CCA even at low pH.
Source
Ocean acidification reduces induction of coral settlement by crustose coralline algae
What they did
Authors pretreated CCA for 42 days at pH 8.1–7.5 (464–1638 μatm pCO2), then offered Acropora larvae those CCA, ambient-conditioned CCA at the same pH levels, or CCA extracts after acute larval OA exposure.
What they found
CCA held at pH 7.5 induced only 12% settlement (about half of control). pH 7.9 and 7.7 were 20% and 24% below control. Ambient-conditioned CCA still induced ~31% settlement across pH. Acute larval OA did not block extract-induced metamorphosis.
The limits
What it doesn't show
Tank assays on two Acropora species do not prove reef-scale recruitment collapse, and they do not identify the exact chemical cue that CCA lost.
Key terms
- Crustose coralline algae (CCA)
- Calcifying red algae that provide preferred coral settlement surfaces and chemical cues.
- Ocean acidification
- Falling seawater pH and carbonate saturation as the ocean takes up CO2.
- Settlement induction
- CCA-driven cue that makes swimming coral larvae attach and metamorphose.
- Acropora millepora
- Broadcast-spawning reef coral used as the main larval species here.
- Magnesium calcite
- CCA skeleton mineral more soluble than coral aragonite under acidification.
Flashcards
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Quiz yourself
OA reduced coral settlement mainly by:
Common questions
What failed first under OA?
The CCA settlement cue after weeks of low pH, not the larvae’s ability to settle.
Settlement at pH 7.5 CCA?
About 12% of larvae, half of control.
Did acute larval OA block extract cues?
No significant effect in 24 h tests.
Why are CCA vulnerable?
Their Mg-calcite is more soluble than coral carbonate.
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