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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. 

Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts. 

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. 

Reversing coral reef decline requires reducing environmental threats while actively restoring reef ecological structure and function. A promising restoration approach uses coral breeding to boost natural recruitment and repopulate reefs with genetically diverse coral communities. Recent advances in predicting spawning, capturing spawn, culturing larvae, and rearing settlers have enabled the successful propagation, settlement, and outplanting of coral offspring in all of the world's major reef regions. Nevertheless, breeding efforts frequently yield low survival, reflecting the type III survivorship curve of corals and poor condition of most reefs targeted for restoration. Furthermore, coral breeding programs are still limited in spatial scale and species diversity. Here, we highlight four priority areas for research and cooperative innovation to increase the effectiveness and scale of coral breeding in restoration: (1) expanding the number of restoration sites and species, (2) improving broodstock selection to maximize the genetic diversity and adaptive capacity of restored populations, (3) enhancing culture conditions to improve offspring health before and after outplanting, and (4) scaling up infrastructure and technologies for large‐scale coral breeding and restoration. Prioritizing efforts in these four areas will enable practitioners to address reef decline at relevant ecological scales, re‐establish self‐sustaining coral populations, and ensure the long‐term success of restoration interventions. Overall, we aim to guide the coral restoration community toward actions and opportunities that can yield rapid technical advances in larval rearing and coral breeding, foster interdisciplinary collaborations, and ultimately achieve the ecological restoration of coral reefs.