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Reef-building crustose coralline algae (CCA) are known to facilitate the settlement and metamorphosis of scleractinian coral larvae. In recent decades, CCA coverage has fallen globally and degrading environmental conditions continue to reduce coral survivorship, spurring new restoration interventions to rebuild coral reef health. In this study, naturally produced chemical compounds (metabolites) were collected from two pantropical CCA genera to isolate and classify those that induce coral settlement. In experiments using four ecologically important Caribbean coral species, we demonstrate the applicability of extracted, CCA-derived metabolites to improve larval settlement success in coral breeding and restoration efforts. Tissue-associated CCA metabolites induced settlement of one coral species,Orbicella faveolata, while metabolites exuded by CCA (exometabolites) induced settlement of three species:Acropora palmata,Colpophyllia natansandOrbicella faveolata. In a follow-up experiment, CCA exometabolites fractionated and preserved using two different extraction resins induced the same level of larval settlement as the unfractionated positive control exometabolites. The fractionated CCA exometabolite pools were characterized using liquid chromatography tandem mass spectrometry, yielding 145 distinct molecular subnetworks that were statistically defined as CCA-derived and could be classified into 10 broad chemical classes. Identifying these compounds can reveal their natural prevalence in coral reef habitats and facilitate the development of new applications to enhance larval settlement and the survival of coral juveniles.
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Composite substrates for coral larval settlement and reef restoration based on natural hydraulic lime and inorganic strontium and magnesium compounds
Coral reefs face unprecedented threats from climate change and human activities, making reef restoration increasingly important for the preservation of marine biodiversity and the sustainability of coastal communities. One promising restoration method relies on coral breeding and larval settlement, but this approach requires further innovation to achieve high rates of settlement and survival. In this study, we built on our previous work engineering lime mortar-based coral settlement substrates by investigating three different compositions of a natural hydraulic lime (NHL) base material as well as composite NHL substrates containing alkaline earth metals. These materials were tested with larvae of three reef-building Caribbean coral species: Orbicella faveolata (Mountainous star coral), Diploria labyrinthiformis (Grooved brain coral), and Colpophyllia natans (Boulder brain coral). We found that the base material composition, including its silicate and calcium carbonate (CaCO3) content, as well as the addition of the inorganic additives strontium carbonate (SrCO3), magnesium carbonate (MgCO3), and magnesium sulfate (MgSO4), all influenced coral larval settlement rates. Overall, NHL formulations with lower concentrations of silicate and higher concentrations of calcium, strontium, and magnesium carbonates significantly increased coral settlement. Further, when dissolved ions of magnesium and strontium were added to seawater, both had a significant effect on larval motility, with magnesium promoting settlement and metamorphosis in C. natans larvae, supporting the observation that these additives are also bioactive when incorporated into substrates. Our results demonstrate the potential benefits of incorporating specific inorganic ion additives such as Mg2+ and Sr2+ into substrates to facilitate early coral life history processes including settlement and metamorphosis. Further, our results highlight the importance of optimizing multiple aspects of coral substrate design, including material composition, to promote settlement and survival in coral propagation and reef restoration.
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- PAR ID:
- 10536926
- Editor(s):
- NA
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Ecological Engineering
- Volume:
- 202
- Issue:
- C
- ISSN:
- 0925-8574
- Page Range / eLocation ID:
- 107236
- Subject(s) / Keyword(s):
- Settlement substrates Coral reef restoration Substrate design Coral propagation Settlement rates Inorganic additives Ion release Bioactive materials Larval settlement Larval motility Natural hydraulic lime (NHL) mortar-based substrate
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.ecoleng.2024.107236
