Towards an in-depth characterization of Symbiodiniaceae in tropical giant clams via metabarcoding of pooled multi-gene amplicons

Filamentous virus-like particles are present in coral dinoflagellates across genera and ocean basins

Filamentous viruses are hypothesized to play a role in stony coral tissue loss disease (SCTLD) through infection of the endosymbiotic dinoflagellates (Family Symbiodiniaceae) of corals. To evaluate this hypothesis, it is critical to understand the global distribution of filamentous virus infections across the genetic diversity of Symbiodiniaceae hosts. Using transmission electron microscopy, we demonstrate that filamentous virus-like particles (VLPs) are present in over 60% of Symbiodiniaceae cells (genus Cladocopium) within Pacific corals (Acropora hyacinthus, Porites c.f. lobata); these VLPs are more prevalent in Symbiodiniaceae of in situ colonies experiencing heat stress. Symbiodiniaceae expelled from A. hyacinthus also contain filamentous VLPs, and these cells are more degraded than their in hospite counterparts. Similar to VLPs reported from SCTLD-affected Caribbean reefs, VLPs range from ~150 to 1500 nm in length and 16-37 nm in diameter and appear to constitute various stages in a replication cycle. Finally, we demonstrate that SCTLD-affected corals containing filamentous VLPs are dominated by diverse Symbiodiniaceae lineages from the genera Breviolum, Cladocopium, and Durusdinium. Although this study cannot definitively confirm or refute the role of filamentous VLPs in SCTLD, it demonstrates that filamentous VLPs are not solely observed in SCTLD-affected corals or reef regions, nor are they solely associated with corals dominated by members of a particular Symbiodiniaceae genus. We hypothesize that filamentous viruses are a widespread, common group that infects Symbiodiniaceae. Genomic characterization of these viruses and empirical tests of the impacts of filamentous virus infection on Symbiodiniaceae and coral colonies should be prioritized.

Viruses of a key coral symbiont exhibit temperature-driven productivity across a reefscape

Viruses can affect coral health by infecting their symbiotic dinoflagellate partners (Symbiodiniaceae). Yet, viral dynamics in coral colonies exposed to environmental stress have not been studied at the reef scale, particularly within individual viral lineages. We sequenced the viral major capsid protein (mcp) gene of positive-sense single-stranded RNA viruses known to infect symbiotic dinoflagellates ('dinoRNAVs') to analyze their dynamics in the reef-building coral, Porites lobata. We repeatedly sampled 54 colonies harboring Cladocopium C15 dinoflagellates, across three environmentally distinct reef zones (fringing reef, back reef, and forereef) around the island of Moorea, French Polynesia over a 3-year period and spanning a reef-wide thermal stress event. By the end of the sampling period, 28% (5/18) of corals in the fringing reef experienced partial mortality versus 78% (14/18) of corals in the forereef. Over 90% (50/54) of colonies had detectable dinoRNAV infections. Reef zone influenced the composition and richness of viral mcp amino acid types ('aminotypes'), with the fringing reef containing the highest aminotype richness. The reef-wide thermal stress event significantly increased aminotype dispersion, and this pattern was strongest in the colonies that experienced partial mortality. These findings demonstrate that dinoRNAV infections respond to environmental fluctuations experienced in situ on reefs. Further, viral productivity will likely increase as ocean temperatures continue to rise, potentially impacting the foundational symbiosis underpinning coral reef ecosystems.

Building consensus around the assessment and interpretation of Symbiodiniaceae diversity

Within microeukaryotes, genetic variation and functional variation sometimes accumulate more quickly than morphological differences. To understand the evolutionary history and ecology of such lineages, it is key to examine diversity at multiple levels of organization. In the dinoflagellate family Symbiodiniaceae, which can form endosymbioses with cnidarians (e.g., corals, octocorals, sea anemones, jellyfish), other marine invertebrates (e.g., sponges, molluscs, flatworms), and protists (e.g., foraminifera), molecular data have been used extensively over the past three decades to describe phenotypes and to make evolutionary and ecological inferences. Despite advances in Symbiodiniaceae genomics, a lack of consensus among researchers with respect to interpreting genetic data has slowed progress in the field and acted as a barrier to reconciling observations. Here, we identify key challenges regarding the assessment and interpretation of Symbiodiniaceae genetic diversity across three levels: species, populations, and communities. We summarize areas of agreement and highlight techniques and approaches that are broadly accepted. In areas where debate remains, we identify unresolved issues and discuss technologies and approaches that can help to fill knowledge gaps related to genetic and phenotypic diversity. We also discuss ways to stimulate progress, in particular by fostering a more inclusive and collaborative research community. We hope that this perspective will inspire and accelerate coral reef science by serving as a resource to those designing experiments, publishing research, and applying for funding related to Symbiodiniaceae and their symbiotic partnerships.

Does plastic type matter? Insights into non-indigenous marine larvae recruitment under controlled conditions

Marine plastic debris (MPD) are a global threat to marine ecosystems. Among countless ecosystem impacts, MPD can serve as a vector for marine 'hitchhikers' by facilitating transport and subsequent spread of unwanted pests and pathogens. The transport and spread of these non-indigenous species (NIS) can have substantial impacts on native biodiversity, ecosystem services/functions and hence, important economic consequences. Over the past decade, increasing research interest has been directed towards the characterization of biological communities colonizing plastic debris, the so called Plastisphere. Despite remarkable advances in this field, little is known regarding the recruitment patterns of NIS larvae and propagules on MPD, and the factors influencing these patterns. To address this knowledge gap, we used custom-made bioassay chambers and ran four consecutive bioassays to compare the settlement patterns of four distinct model biofouling organisms' larvae, including the three notorious invaders Crassostrea gigas, Ciona savignyi and Mytilus galloprovincialis, along with one sessile macro-invertebrate Spirobranchus cariniferus, on three different types of polymers, namely Low-Linear Density Polyethylene (LLDPE), Polylactic Acid (PLA), Nylon-6, and a glass control. Control bioassay chambers were included to investigate the microbial community composition colonizing the different substrates using 16S rRNA metabarcoding. We observed species-specific settlement patterns, with larvae aggregating on different locations on the substrates. Furthermore, our results revealed that C. savignyi and S. cariniferus generally favoured Nylon and PLA, whereas no specific preferences were observed for C. gigas and M. galloprovincialis. We did not detect significant differences in bacterial community composition between the tested substrates. Taken together, our results highlight the complexity of interactions between NIS larvae and plastic polymers. We conclude that several factors and their potential interactions influenced the results of this investigation, including: (i) species-specific larval biological traits and ecology; (ii) physical and chemical composition of the substrates; and (iii) biological cues emitted by bacterial biofilm and the level of chemosensitivity of the different NIS larvae. To mitigate the biosecurity risks associated with drifting plastic debris, additional research effort is critical to effectively decipher the mechanisms involved in the recruitment of NIS on MPD.

Cryopreservation of six Symbiodiniaceae genera and assessment of fatty acid profiles in response to increased salinity treatments

Symbiodiniaceae are a diverse group of dinoflagellates, the majority of which are free-living and/or associated with a variety of protists and other invertebrate hosts. Maintenance of isolated cultures is labour-intensive and expensive, and cryopreservation provides an excellent avenue for their long-term storage. We aimed to cryopreserve 15 cultured isolates from six Symbiodiniaceae genera using dimethyl sulfoxide (DMSO) as the cryoprotectant agent (CPA). Under 15% DMSO, 10 isolates were successfully cryopreserved using either rapid freezing or controlled-rate freezing. Cultures that failed or had low survival, were subjected to (1) a reduction of CPA to 10%, or (2) increased salinity treatment before freezing. At 10% DMSO, three further isolates were successfully cryopreserved. At 15% DMSO there were high cell viabilities in Symbiodinium pilosum treated with 44 parts per thousand (ppt) and 54 ppt culture medium. An isolate of Fugacium sp. successfully cryopreserved after salinity treatments of 54 ppt and 64 ppt. Fatty acid (FA) analyses of S. pilosum after 54 ppt salinity treatment showed increased saturated FA levels, whereas Fugacium sp. had low poly-unsaturated FAs compared to normal salinity (34 ppt). Understanding the effects of salinity and roles of FAs in cryopreservation will help in developing protocols for these ecologically important taxa.

Ammonia transporter 2 as a molecular marker to elucidate the potentials of ammonia transport in phylotypes of Symbiodinium, Cladocopium and Durusdinium in the fluted giant clam, Tridacna squamosa

Giant clams harbor coccoid Symbiodiniaceae dinoflagellates that are phototrophic. These dinoflagellates generally include multiple phylotypes (species) of Symbiodinium, Cladocopium, and Durusdinium in disparate proportions depending on the environmental conditions. The coccoid symbionts can share photosynthate with the clam host, which in return supply them with nutrients containing inorganic carbon, nitrogen and phosphorus. Symbionts can recycle nitrogen by absorbing and assimilating the endogenous ammonia produced by the host. This study aimed to use the transcript levels of ammonia transporter 2 (AMT2) in Symbiodinium (Symb-AMT2), Cladocopium (Clad-AMT2) and Durusdinium (Duru-AMT2) as molecular indicators to estimate the potential of ammonia transport in these three genera of Symbiodiniaceae dinoflagellates in different organs of the fluted giant clam, Tridacna squamosa, obtained from Vietnam. We also determined the transcript levels of form II ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcII) and nitrate transporter 2 (NRT2) in Symbiodinium (Symb-rbcII; Symb-NRT2), Cladocopium (Clad-rbcII; Clad-NRT2) and Durusdinium (Duru-rbcII; Duru-NRT2), in order to examine the potential of ammonia transport with reference to the potentials of phototrophy or NO₃^- uptake independent of the quantities and proportion of these Symbiodiniaceae phylotypes. Our results indicated for the first time that phylotypes of Symbiodinium and Cladocopium could have different potentials of ammonia transport, and that phylotypes of Symbiodinium might have higher potential of NO₃^- transport than ammonia transport. They also suggested that Symbiodiniaceae phylotypes residing in different organs of T. squamosa could have disparate potentials of ammonia transport, alluding to the functional diversity among phylotypes of coccoid Symbiodinium, Cladocopium, and Durusdinium.

Molecular characterization, immunofluorescent localization, and expression levels of two bicarbonate anion transporters in the whitish mantle of the giant clam, Tridacna squamosa, and the implications for light-enhanced shell formation

Giant clams conduct light-enhanced shell formation, which requires the increased transport of Ca²⁺ and inorganic carbon (C_i) from the hemolymph through the shell-facing epithelium of the whitish inner mantle to the extrapallial fluid where CaCO₃ deposition occurs. The major form of C_i in the hemolymph is HCO₃^-, but the mechanisms of HCO₃^- transport through the basolateral and apical membranes of the shell-facing epithelial cells remain unknown. This study aimed to clone from the inner mantle of Tridacna squamosa the complete coding cDNA sequences of electrogenic Na⁺-HCO₃^-cotransporter 1 homolog (NBCe1-like-b) and electrogenic Na⁺-HCO₃^-cotransporter 2 homolog (NBCe2-like). NBCe1-like-b comprised 3360 bp, encoding a 125.7 kDa protein with 1119 amino acids. NBCe1-like-b was slightly different from NBCe1-like-a of the ctenidium reported elsewhere, as it had a serine residue (Ser¹⁰²⁵), which might undergo phosphorylation leading to the transport of Na⁺: HCO₃^- at a ratio of 1: 2 into the cell. NBCe1-like-b was localized at the basolateral membrane of the shell-facing epithelial cells, and its gene and protein expression levels increased significantly in the inner mantle during illumination, indicating a role in the light-enhanced uptake of HCO₃^- from the hemolymph. The sequence of NBCe2-like obtained from the inner mantle was identical to that reported previously for the outer mantle. In the inner mantle, NBCe2-like had an apical localization in the shell-facing epithelial cells, and its protein abundance was upregulated during illumination. Hence, NBCe2-like might take part in the light-enhanced transport of HCO₃^- through the apical membrane of these cells into the extrapallial fluid.

Alignment-Free Analysis of Whole-Genome Sequences From Symbiodiniaceae Reveals Different Phylogenetic Signals in Distinct Regions

Dinoflagellates of the family Symbiodiniaceae are predominantly essential symbionts of corals and other marine organisms. Recent research reveals extensive genome sequence divergence among Symbiodiniaceae taxa and high phylogenetic diversity hidden behind subtly different cell morphologies. Using an alignment-free phylogenetic approach based on sub-sequences of fixed length k (i.e. k-mers), we assessed the phylogenetic signal among whole-genome sequences from 16 Symbiodiniaceae taxa (including the genera of Symbiodinium, Breviolum, Cladocopium, Durusdinium and Fugacium) and two strains of Polarella glacialis as outgroup. Based on phylogenetic trees inferred from k-mers in distinct genomic regions (i.e. repeat-masked genome sequences, protein-coding sequences, introns and repeats) and in protein sequences, the phylogenetic signal associated with protein-coding DNA and the encoded amino acids is largely consistent with the Symbiodiniaceae phylogeny based on established markers, such as large subunit rRNA. The other genome sequences (introns and repeats) exhibit distinct phylogenetic signals, supporting the expected differential evolutionary pressure acting on these regions. Our analysis of conserved core k-mers revealed the prevalence of conserved k-mers (>95% core 23-mers among all 18 genomes) in annotated repeats and non-genic regions of the genomes. We observed 180 distinct repeat types that are significantly enriched in genomes of the symbiotic versus free-living Symbiodinium taxa, suggesting an enhanced activity of transposable elements linked to the symbiotic lifestyle. We provide evidence that representation of alignment-free phylogenies as dynamic networks enhances the ability to generate new hypotheses about genome evolution in Symbiodiniaceae. These results demonstrate the potential of alignment-free phylogenetic methods as a scalable approach for inferring comprehensive, unbiased whole-genome phylogenies of dinoflagellates and more broadly of microbial eukaryotes.

Ingested microplastics impair the metabolic relationship between the giant clam Tridacna crocea and its symbionts

Microplastics are emerging as widespread pollutants in coral reef ecosystems worldwide; however, there is limited knowledge regarding their impact on giant clams, which are important reef builders. In the present study, the cytological, physiological, and molecular response of the giant clam Tridacna crocea to a 5 d exposure of microplastics was investigated. The concentration of microplastics in the intestine and outer mantle increased significantly and gradually after the exposure to microplastics. There were no significant changes in the density of symbiotic Symbiodiniaceae throughout the exposure period, but symbiont chlorophyll content increased significantly after 1 d of exposure. There was a significant increase in symbiont superoxide dismutase (SOD) activity, but a decrease in giant clam SOD activity and symbiont glutathione S-transferase (GST) activity. No significant changes in catalase (CAT) activity and caspase3 activation level were observed in the two symbiotic partners. Transcriptomic analysis of the giant clam revealed 138 significantly upregulated and 1390 significantly downregulated genes after 5 d of microplastic exposure. The top 20 GO terms overrepresented by these significantly downregulated genes were related to primary metabolic processes and cellular metabolic processes. No significantly upregulated genes were observed in symbionts, but 28 genes were significantly downregulated, including chloroplast oxygen-evolving enhancer, photosystem I reaction center subunit II, peptide/nitrate transporter, sodium-coupled neutral amino acid transporter, beta-glucosidase, and TPA: lipase. These results suggest that T. crocea ingests microplastics through the outer mantle and intestine, and these microplastics can suppress the photosynthesis, organic nutrient transportation, and detoxification ability of the symbionts, as well as the primary metabolism of the giant clam. This eventually could threaten their metabolic relationship and long-term survival.

The colorful mantle of the giant clam Tridacna squamosa expresses a homolog of electrogenic sodium: Bicarbonate cotransporter 2 that mediates the supply of inorganic carbon to photosynthesizing symbionts

Giant clams live in symbiosis with phototrophic dinoflagellates, which reside extracellularly inside zooxanthellal tubules located mainly in the colourful and extensible outer mantle. As symbiotic dinoflagellates have no access to the ambient seawater, they need to obtain inorganic carbon (C_i) from the host for photosynthesis during illumination. The outer mantle has a host-mediated and light-dependent carbon-concentrating mechanism to augment the supply of C_i to the symbionts during illumination. Iridocytes can increase the secretion of H⁺ through vacuolar H⁺-ATPase to dehydrate HCO₃⁻ present in the hemolymph to CO₂. CO₂ can permeate the basolateral membrane of the epithelial cells of the zooxanthellal tubules, and rehydrated back to HCO₃⁻ in the cytoplasm catalysed by carbonic anhydrase 2. This study aimed to elucidate the molecular mechanism involved in the transport of HCO₃⁻ across the apical membrane of these epithelial cells into the luminal fluid surrounding the symbionts. We had obtained the complete cDNA coding sequence of a homolog of electrogenic Na⁺-HCO₃⁻cotransporter 2 (NBCe2-like gene) from the outer mantle of the fluted giant clam, Tridacna squamosa. NBCe2-like gene comprised 3,399 bp, encoding a protein of 1,132 amino acids of 127.3 kDa. NBCe2-like protein had an apical localization in the epithelial cells of zooxanthellal tubules, denoting that it could transport HCO₃⁻ between the epithelial cells and the luminal fluid. Furthermore, illumination augmented the transcript level and protein abundance of NBCe2-like gene/NBCe2-like protein in the outer mantle, indicating that it could mediate the increased transport of HCO₃⁻ into the luminal fluid to support photosynthesis in the symbionts.

Direct evidence of sex and a hypothesis about meiosis in Symbiodiniaceae

Dinoflagellates in the family Symbiodiniaceae are obligate endosymbionts of diverse marine invertebrates, including corals, and impact the capacity of their hosts to respond to climate change-driven ocean warming. Understanding the conditions under which increased genetic variation in Symbiodiniaceae arises via sexual recombination can support efforts to evolve thermal tolerance in these symbionts and ultimately mitigate coral bleaching, the breakdown of the coral-Symbiodiniaceae partnership under stress. However, direct observations of meiosis in Symbiodiniaceae have not been reported, despite various lines of indirect evidence that it occurs. We present the first cytological evidence of sex in Symbiodiniaceae based on nuclear DNA content and morphology using Image Flow Cytometry, Cell Sorting and Confocal Microscopy. We show the Symbiodiniaceae species, Cladocopium latusorum, undergoes gamete conjugation, zygote formation, and meiosis within a dominant reef-building coral in situ. On average, sex was detected in 1.5% of the cells analyzed (N = 10,000-40,000 cells observed per sample in a total of 20 samples obtained from 3 Pocillopora colonies). We hypothesize that meiosis follows a two-step process described in other dinoflagellates, in which diploid zygotes form dyads during meiosis I, and triads and tetrads as final products of meiosis II. This study sets the stage for investigating environmental triggers of Symbiodiniaceae sexuality and can accelerate the assisted evolution of a key coral symbiont in order to combat reef degradation.

Basolateral Na+/Ca2+ exchanger 1 and Na+/K+-ATPase, which display light-enhanced gene and protein expression levels, could be involved in the absorption of exogenous Ca2+ through the ctenidium of the giant clam, Tridacna squamosa

Giant clams perform light-enhanced shell formation (calcification) and therefore need to increase the uptake of exogenous Ca²⁺ during illumination. The ctenidium of the fluted giant clam, Tridacna squamosa, is involved in light-enhanced Ca²⁺ uptake. It expresses the pore-forming voltage-gated calcium channel (VGCC) subunit alpha 1 (CACNA1) in the apical membrane of the epithelial cells, and the protein expression level of CACNA1 is upregulated in the ctenidium during illumination. This study aimed to elucidate the mechanism involved in the transport of the absorbed Ca²⁺ across the basolateral membrane of the ctenidial epithelial cells into the hemolymph. We obtained a homolog of Na⁺/Ca²⁺exchanger 1 (NCX1-like) from the ctenidium of T. squamosa, which comprised 2418 bp, encoding a protein of 806 amino acids (88.9 kDa). NCX1-like had a basolateral localization in the epithelial cells of the ctenidial filaments and tertiary water channels. Illumination resulted in significant increases in the transcript and protein levels of NCX1-like/NCX1-like in the ctenidium. Hence, NCX1-like could operate in conjunction with VGCC to increase the transport of Ca²⁺ from the ambient seawater into the hemolymph during illumination. Illumination also resulted in the upregulation of the gene and protein expression levels of Na⁺/K⁺-ATPase (NKA) α-subunit (NKAα/NKAα) in the ctenidium of T. squamosa. As light-enhanced extrusion of Ca²⁺ into the hemolymph through NCX1-like would lead to a greater influx of extracellular Na⁺, the increased expression of the basolateral NKA was required to augment the capacity of intracellular Na⁺ homeostasis.

The fluted giant clam (Tridacna squamosa) increases the protein abundance of the host's copper-zinc superoxide dismutase in the colorful outer mantle, but not the whitish inner mantle, during light exposure

The colorful outer mantle of giant clams contains abundance of symbiotic dinoflagellates (zooxanthellae) and iridocytes, and has direct exposure to light. In light, photosynthesizing dinoflagellates produce O₂, and the host cells in the outer mantle would be confronted with hyperoxia-related oxidative stress. In comparison, the whitish inner mantle contains few symbiotic dinoflagellates and no iridocytes. It is involved in shell formation, and is shaded from light. CuZnSOD is a cytosolic enzyme that scavenges intracellular O₂^-. We had obtained from the outer mantle of the fluted giant clam, Tridacna squamosa, the complete cDNA coding sequence of a host-derived copper zinc superoxide dismutase (CuZnSOD), which comprised 462 bp and encoded for 154 amino acids with a calculated MW of 15.6 kDa. CuZnSOD was expressed strongly in the outer mantle, ctenidium, hepatopancreas and kidney. The transcript level of CuZnSOD remained unchanged in the outer mantle during light exposure, but the protein abundance of CuZnSOD increased ~3-fold after exposure to light for 6 or 12 h. By contrast, 12 h of light exposure had no significant effects on the gene and protein expression levels of CuZnSOD/CuZnSOD in the inner mantle. Hence, the increased expression of CuZnSOD in the outer mantle of T. squamosa was probably a host's response to ameliorate oxidative stress related to photosynthesis in the symbionts, and not simply due to increased metabolic rate in the host cells. Evidently, the host clam must possess light- or O₂-responsive anti-oxidative defenses in order to align with the light-dependent photosynthetic activity of its symbionts.

Metabarcoding reveals distinct microbiotypes in the giant clam Tridacna maxima

BACKGROUND

Giant clams and scleractinian (reef-building) corals are keystone species of coral reef ecosystems. The basis of their ecological success is a complex and fine-tuned symbiotic relationship with microbes. While the effect of environmental change on the composition of the coral microbiome has been heavily studied, we know very little about the composition and sensitivity of the microbiome associated with clams. Here, we explore the influence of increasing temperature on the microbial community (bacteria and dinoflagellates from the family Symbiodiniaceae) harbored by giant clams, maintained either in isolation or exposed to other reef species. We created artificial benthic assemblages using two coral species (Pocillopora damicornis and Acropora cytherea) and one giant clam species (Tridacna maxima) and studied the microbial community in the latter using metagenomics.

RESULTS

Our results led to three major conclusions. First, the health status of giant clams depended on the composition of the benthic species assemblages. Second, we discovered distinct microbiotypes in the studied T. maxima population, one of which was disproportionately dominated by Vibrionaceae and directly linked to clam mortality. Third, neither the increase in water temperature nor the composition of the benthic assemblage had a significant effect on the composition of the Symbiodiniaceae and bacterial communities of T. maxima.

CONCLUSIONS

Altogether, our results suggest that at least three microbiotypes naturally exist in the studied clam populations, regardless of water temperature. These microbiotypes plausibly provide similar functions to the clam host via alternate molecular pathways as well as microbiotype-specific functions. This redundancy in functions among microbiotypes together with their specificities provides hope that giant clam populations can tolerate some levels of environmental variation such as increased temperature. Importantly, the composition of the benthic assemblage could make clams susceptible to infections by Vibrionaceae, especially when water temperature increases. Video abstract.

Considerations for maximizing the adaptive potential of restored coral populations in the western Atlantic

Active coral restoration typically involves two interventions: crossing gametes to facilitate sexual larval propagation; and fragmenting, growing, and outplanting adult colonies to enhance asexual propagation. From an evolutionary perspective, the goal of these efforts is to establish self-sustaining, sexually reproducing coral populations that have sufficient genetic and phenotypic variation to adapt to changing environments. Here, we provide concrete guidelines to help restoration practitioners meet this goal for most Caribbean species of interest. To enable the persistence of coral populations exposed to severe selection pressure from many stressors, a mixed provenance strategy is suggested: genetically unique colonies (genets) should be sourced both locally as well as from more distant, environmentally distinct sites. Sourcing three to four genets per reef along environmental gradients should be sufficient to capture a majority of intraspecies genetic diversity. It is best for practitioners to propagate genets with one or more phenotypic traits that are predicted to be valuable in the future, such as low partial mortality, high wound healing rate, high skeletal growth rate, bleaching resilience, infectious disease resilience, and high sexual reproductive output. Some effort should also be reserved for underperforming genets because colonies that grow poorly in nurseries sometimes thrive once returned to the reef and may harbor genetic variants with as yet unrecognized value. Outplants should be clustered in groups of four to six genets to enable successful fertilization upon maturation. Current evidence indicates that translocating genets among distant reefs is unlikely to be problematic from a population genetic perspective but will likely provide substantial adaptive benefits. Similarly, inbreeding depression is not a concern given that current practices only raise first-generation offspring. Thus, proceeding with the proposed management strategies even in the absence of a detailed population genetic analysis of the focal species at sites targeted for restoration is the best course of action. These basic guidelines should help maximize the adaptive potential of reef-building corals facing a rapidly changing environment.