Ocean warming and marine heatwaves are predicted to have adverse impacts on marine organisms. Yet, knowledge of the molecular mechanisms that underpin successful or failed acclimation to increasing temperatures remains incomplete. We conducted an aquaria-based study of early-life stage clownfish comprising of six thermal regimes, measuring the metabolic, and multi-tissue transcriptional response of Amphiprion ocellaris using seven tissues. Sampling at 31°C increased metabolic rates in fish reared at 28°C; however, these effects were reduced with increasing developmental rearing at 31°C. Transcriptomic analysis revealed multi-tissue reprogramming of metabolic processes at +3°C, particularly in the liver-pancreas axis. Importantly, chronic larval-juvenile exposure to +3°C induced the acclimation of metabolic rates and caused the upregulation of oxidative phosphorylation (liver) and the downregulation of insulin secretion (pancreas). These results indicate that temperature increase will drive tissue-wide metabolic reprogramming in fish, with changes in key energetic pathways underpinning fish's ability to acclimate to warming.

Increasing ocean temperatures have been demonstrated to have a range of negative impacts on coral reef fishes. However, despite a wealth of studies of juvenile/adult reef fish, studies of how early developmental stages respond to ocean warming are limited. As overall population persistence is influenced by the development of early life stages, detailed studies of larval responses to ocean warming are essential. Here, in an aquaria-based study we investigate how temperatures associated with future warming and present-day marine heatwaves (+3 °C) impact the growth, metabolic rate, and transcriptome of 6 discrete developmental stages of clownfish larvae (Amphiprion ocellaris). A total of 6 clutches of larvae were assessed, with 897 larvae imaged, 262 larvae undergoing metabolic testing and 108 larvae subject to transcriptome sequencing. Our results show that larvae reared at +3 °C grow and develop significantly faster and exhibit higher metabolic rates than those in control conditions. Finally, we highlight the molecular mechanisms underpinning the response of larvae from different developmental stages to higher temperatures, with genes associated with metabolism, neurotransmission, heat stress and epigenetic reprogramming differentially expressed at +3 °C. Overall, these results indicate that clownfish development could be altered under future warming, with developmental rate, metabolic rate, and gene expression all affected. Such changes may lead to altered larval dispersal, changes in settlement time and increased energetic costs.

Background Most researches on sponge holobionts focus primarily on symbiotic microbes, yet data at the level of the sponge hologenome are still relatively scarce. Understanding of the sponge host and its microbial gene expression profiles and the host-microbes interplay in different niches represents a key aspect of sponge hologenome. Using the Hawaiian demosponge Mycale grandis in different niches as a model, i.e. on rocks, on the surface of coral Porites compressa, under alga Gracilaria salicornia, we compared the bacterial and fungal community structure, functional gene diversity, expression pattern and the host transcriptome by integrating open-format (deep sequencing) and closed-format (GeoChip microarray) high-throughput techniques. Results Little inter-niche variation in bacterial and fungal phylogenetic diversity was detected for M. grandis in different niches, but a clear niche-dependent variability in the functional gene diversity and expression pattern of M. grandis host and its symbiotic microbiota was uncovered by GeoChip microarray and transcriptome analyses. Particularly, sponge host genes related to innate immunity and microbial recognition showed a strong correlation with the microbial symbionts' functional gene diversity and transcriptional richness in different niches. The cross-niche variability with respect to the symbiont functional gene diversity and the transcriptional richness of M. grandis holobiont putatively reflects the interplay of niche-specific selective pressure and the symbiont functional diversity. Conclusions Niche-dependent gene expression profiles of M. grandis hologenome and the host-microbes interplay were suggested though little inter-niche variation in bacterial and fungal diversity was detected, particularly the sponge innate immunity was found to be closely related to the symbiotic microbes. Altogether, these findings provide novel insights into the black box of one sponge holobiont in different niches at the hologenome level.

Anthropogenically driven climate change is predicted to increase average sea surface temperatures, as well as the frequency and intensity of marine heatwaves in the future. This increasing temperature is predicted to have a range of negative physiological impacts on multiple life-stages of coral reef fish. Nevertheless, studies of early-life stages remain limited, and tissue-specific transcriptomic studies of post-larval coral reef fish are yet to be conducted. Here, in an aquaria-based study we investigate the tissue-specific (brain, liver, muscle, and digestive tract) transcriptomic response of post-larval (20 dph) Amphiprion ocellaris to temperatures associated with future climate change (+3 °C). Additionally, we utilized metatranscriptomic sequencing to investigate how the microbiome of the digestive tract changes at +3 °C. Our results show that the transcriptional response to elevated temperatures is highly tissue-specific, as the number of differentially expressed genes (DEGs) and gene functions varied amongst the brain (102), liver (1785), digestive tract (380), and muscle (447). All tissues displayed DEGs associated with thermal stress, as 23 heat-shock protein genes were upregulated in all tissues. Our results indicate that post-larval clownfish may experience liver fibrosis-like symptoms at +3 °C as genes associated with extracellular matrix structure, oxidative stress, inflammation, glucose transport, and metabolism were all upregulated. We also observe a shift in the digestive tract microbiome community structure, as Vibrio sp. replace Escherichia coli as the dominant bacteria. This shift is coupled with the dysregulation of various genes involved in immune response in the digestive tract. Overall, this study highlights post-larval clownfish will display tissue-specific transcriptomic responses to future increases in temperature, with many potentially harmful pathways activated at +3 °C.

This is the first report of the transcriptome assemblies of the deep-sea octocorals Calyptrophora lyra and Chrysogorgia stellata, which were collected in a survey of the West Pacific seamounts area. We sequenced the transcriptomes of C. lyra and C. stellata using the Illumina NovaSeq 6000 System. De novo assembly and analysis of the coding regions predicted 193,796 unigenes from the total 116,441,796 reads of C. lyra and 235,513 unigenes from the total 122,031,866 reads of C. stellata. Our data are a valuable resource with which to understand the ecological and biological characteristics of the West Pacific deep-sea corals. The data will also contribute to the study of deep-sea environments as extreme and limited habitats and provide direction for future research and further insight into the organismal responses of deep-sea corals to environmental changes.

Anemonefish are an emerging group of model organisms for studying genetic, ecological, evolutionary, and developmental traits of coral reef fish. The yellowtail clownfish Amphiprion clarkii possesses species-specific characteristics such as inter-species co-habitation, high intra-species color variation, no anemone specificity, and a broad geographic distribution, that can increase our understanding of anemonefish evolutionary history, behavioral strategies, fish-anemone symbiosis, and color pattern evolution. Despite its position as an emerging model species, the genome of A. clarkii is yet to be published. Using PacBio long-read sequencing and Hi-C chromatin capture technology, we generated a high-quality chromosome-scale genome assembly initially comprised of 1,840 contigs with an N50 of 1,203,211 bp. These contigs were successfully anchored into 24 chromosomes of 843,582,782 bp and annotated with 25,050 protein-coding genes encompassing 97.0% of conserved actinopterygian genes, making the quality and completeness of this genome the highest among all published anemonefish genomes to date. Transcriptomic analysis identified tissue-specific gene expression patterns, with the brain and optic lobe having the largest number of expressed genes. Further analyses revealed higher copy numbers of erbb3b (a gene involved in melanocyte development) in A. clarkii compared with other anemonefish, thus suggesting a possible link between erbb3b and the natural melanism polymorphism observed in A. clarkii. The publication of this high-quality genome, along with A. clarkii's many unique traits, position this species as an ideal model organism for addressing scientific questions across a range of disciplines.

The false clownfish Amphiprion ocellaris is a popular fish species and an emerging model organism for studying the ecology, evolution, adaptation, and developmental biology of reef fishes. Despite this, high-quality genomic resources for this species are scarce, hindering advanced genomic analyses. Leveraging the power of PacBio long-read sequencing and Hi-C chromosome conformation capture techniques, we constructed a high-quality chromosome-scale genome assembly for the clownfish A. ocellaris. The initial genome assembly comprised of 1,551 contigs of 861.42 Mb, with an N50 of 863.85 kb. Hi-C scaffolding of the genome resulted in 24 chromosomes containing 856.61 Mb. The genome was annotated with 26,797 protein-coding genes and had 96.62% completeness of conserved actinopterygian genes, making this genome the most complete and high quality among published anemonefish genomes. Transcriptomic analysis identified tissue-specific gene expression patterns, with the brain and optic lobe having the largest number of expressed genes. Further, comparative genomic analysis revealed 91 genome elements conserved only in A. ocellaris and its sister species Amphiprion percula, and not in other anemonefish species. These elements are close to genes that are involved in various nervous system functions and exhibited distinct expression patterns in brain tissue, potentially highlighting the genetic toolkits involved in lineage-specific divergence and behaviors of the clownfish branch. Overall, our study provides the highest quality A. ocellaris genome assembly and annotation to date, whilst also providing a valuable resource for understanding the ecology and evolution of reef fishes.

Anemonefish consists of 30 species and are likely the most recognizable fishes to the public due to their unique colour patterns, easy captive breeding, and the animation film Finding Nemo. They are also important species to biologists owing to their symbiotic relationship with anemones as well as sequential hermaphroditism and hence serve as emerging model organisms in ecology, evolution, and development. The latest advancements in high-throughput sequencing technologies and bioinformatic analysis have facilitated studies in anemonefish research. In this chapter, we first show the recent genomics studies that unveil the genomic architecture and underlying evolutionary processes in anemonefish. We also cover how state-of-the-art transcriptomic and proteomic techniques have been utilized to capture and uncover the fundamental molecular mechanisms driving dynamic changes in biological processes throughout development and under various environmental changes.

This is the first report of a transcriptome assembly of a newly discovered hydrothermal vent mussel, Gigantidas vrijenhoeki (Bivalvia: Mytilidae), on the Central Indian Ridge. Gigantidas vrijenhoeki was identified from material collected at the newly discovered Onnuri Vent Field (OVF) on the Central Indian Ridge in 2018, and was reported as a new species, distinct from another dominant hydrothermal vent mussel, Bathymodiolus marisindicus, in 2020. We sequenced the transcriptome of G. vrijenhoeki using the Illumina HiSeq X System. De novo assembly and analysis of the coding regions predicted 25,405 genes, 84.76% of which was annotated by public databases. The transcriptome of G. vrijenhoeki will be a valuable resource in studying the ecological and biological characteristics of this new species, which is distinct from other deep-sea mussels. These data should also support the investigation of the relationship between the environmental conditions of hydrothermal vents and the unique distribution of G. vrijenhoeki in the OVF of the Central Indian Ridge.

Elevated temperature can have detrimental effects on the physiological performance of many marine organisms. However, phenotypic plasticity may enable some populations to maintain their performance under thermal stress. Two longitudinally separated populations of the coral reef fish, Acanthochromis polyacanthus from the Great Barrier Reef have shown differing capacities for thermal plasticity - the southernmost Heron Island population restored aerobic scope within one generation at a higher temperature, whereas the northernmost Palm Island population restored aerobic scope only when two generations were exposed to warmer conditions. We recently discovered an epigenetic signature associated with transgenerational plasticity in the Palm Island population. Here, we aimed to determine if epigenetic changes are also associated with the within-generational plasticity observed in the Heron Island population and, if so, how this epigenetic signature compares to the Palm Island transgenerational epigenome. By sequencing and analyzing the genome-wide DNA methylome of fish reared at control (+0 degrees C) or elevated temperatures (+1.5 and +3 degrees C) since early life, we identified 480 differentially methylated genomic regions and 372 adjacent protein-coding genes associated with within-generational plasticity in the Heron Island population. Functions related to insulin, cardiovascular capacity, development, and heat response were significantly enriched in differentially methylated genes, suggesting that these functions are the core mechanisms for within-generational restoration of aerobic scope. Comparison to the differentially methylated genes identified from F2 Palm Island population revealed little overlap of genes and enriched functions, indicating that distinct genetic toolkits may be used for within- and between-generational plasticity to ocean warming in the same species from different latitudes.

Eleutherobia rubra (Brundin, 1896) is a temperate asymbiotic octocoral, distributed around Korea, Japan, the west coast of the USA, and northwest Australia. This soft coral is particularly found in the East, West, and South Seas around the Korean Peninsula, so it is useful for investigating the stress responses of corals to rising seawater temperatures around the Korean Peninsula simultaneously and the effects of climate change on coral ecosystems in temperate regions. One individual of E. rubra (Anthozoa: Alcyonacea: Alcyoniidae) was collected around Pohang, South Korea (36°00′17.7”N, 129°35′12.1″E) and extracted total RNA to construct the transcriptome assembly. The Illumina HiSeq3000 platform was used for the transcriptome sequencing and 32,624 coding sequences were predicted by the de novo assembly and analysis of the coding regions. This is the first transcriptome assembly for the genus Eleutherobia. The transcriptome information for E. rubra will be a valuable resource for studying the transcriptomic changes in temperate and cold-water corals in response to environmental stresses.

Climate change rapidly warms the ocean and marine species often move northwards for suitable habitats. Stony coral, Alveopora japonica, is observed more frequently for the last few years in temperate sea like Jeju Island, South Korea. To understand the ecological consequences such as habitat formation and fate of this species in changing environment, unraveling the genetic makeup of the species is essential. We sequenced the transcriptome of the A. japonica holobionts using Illumina HiSeq2000 platform. De novo assembly and analysis of coding regions predicted 108,636 coding sequences consisted of the coral host and residing Symbiodinium. Homology analysis showed the gene contents from our assembly are comparable to other sequenced corals and Symbiodiniums. The reference assembly of A. japonica will be a valuable resource to study the ecological characteristics of this species in the marine benthic ecosystem.

Neolepas marisindica (Arthropoda; Scalpellomorpha; Eolepadidae) is a deep-sea stalked barnacle, previously reported as a new species, found along the Central Indian Ridge. It is morphologically distinct from N. zevinae and N. rapanuii, which are found in the Pacific. We sequenced the transcriptome assembly of N. marisindica from individuals collected at a depth of 2022 m off the Onnuri Vent Field on the Central Indian Ridge by video-guided hydraulic grab from the research vessel ISABU (RV ISABU). We sequenced the transcriptome using the rilumina HiSeq X System. De novo assembly and analysis of coding regions predicted 26,201 coding sequences. The reference assembly of N. marisindica will be a valuable resource for future investigations into the ecological characteristics of this species in hydrothermal vent ecosystems. Furthermore, examining the features of hydrothermal vents with functional gene analyses will provide useful information regarding environmental interactions or evolution processes in organisms that inhabit deep-sea hydrothermal vents.

Background: Coral reefs composed of stony corals are threatened by global marine environmental changes. However, soft coral communities composed of octocorallian species, appear more resilient. The genomes of several species of cnidarians have been published, including stony corals, sea anemones, and hydra, but as of yet no octocoral species. To fill this phylogenetic gap within the cnidarian, we sequenced the octocoral, Dendronephthya gigantea, a non-symbiotic soft coral, commonly known as the carnation coral. Findings: The D. gigantea genome size is approximately 276 Mb. A high-quality genome assembly was constructed using 29.85Gb (108x coverage) of PacBio long reads and 35.54Gb (128x coverage) of Illumina short paired-end reads resulting in the largest N50 value reported among cnidarian of 1.4 Mb. About 12 % of the genome consisted of repetitive elements. We found 28,879 protein-coding genes. This gene set contained about 94% metazoan single-copy orthologs, indicating the gene models were predicted with high quality compared to other cnidarians. Based on molecular phylogenetic analysis, octocoral and hexacoral divergence occurred approximately 544 million years ago. Moreover, there is a clear difference in Hox gene composition: unlike in hexacorals, Antp superclass member Evx gene was absent in D. gigantea. Conclusions: We present the first genome assembly of a non-symbiotic octocoral, D. gigantea to aid in the comparative genomic analysis of cnidarians, including comparisons of stony and soft corals and symbiotic and non-symbiotic corals. In addition, the genome of this species may provide clues about differential genetic coping mechanisms between soft and stony coral regarding the global warming.

Global warming will have far-reaching consequences for marine species over coming decades, yet the magnitude of these effects may depend on the rate of warming across generations. Recent experiments show coral reef fishes can compensate the metabolic challenges of elevated temperature when warm conditions are maintained across generations. However, the effects of a gradual temperature increase across generations remain unknown. In the present study, we analysed metabolic and molecular traits in the damselfish Acanthochromis polyacanthus that were exposed to +1.5 degrees C in the first generation and +3.0 degrees C in the second (Step +3.0 degrees C). This treatment of stepwise warming was compared to fish reared at current-day temperatures (Control), second-generation fish of control parents reared at +3.0 degrees C (Developmental +3.0 degrees C) and fish exposed to elevated temperatures for two generations (Transgenerational +1.5 degrees C and Transgenerational +3.0 degrees C). Hepatosomatic index, oxygen consumption and liver gene expression were compared in second-generation fish of the multiple treatments. Hepatosomatic index increased in fish that developed at +3.0 degrees C, regardless of the parental temperature. Routine oxygen consumption of Step +3.0 degrees C fish was significantly higher than Control; however, their aerobic scope recovered to the same level as Control fish. Step +3.0 degrees C fish exhibited significant upregulation of genes related to mitochondrial activity and energy production, which could be associated with their increased metabolic rates. These results indicate that restoration of aerobic scope is possible when fish experience gradual thermal increase across multiple generations, but the metabolic and molecular responses are different from fish reared at the same elevated thermal conditions in successive generations.

Extreme thermal events are increasing in frequency and duration as the climate continues to warm, with potential detrimental effects on marine organisms. However, the effects of heatwaves may differ among geographically separated populations depending on their capacity for thermal plasticity. Here, we compared the response to simulated summer heatwave temperatures (+1.5 and +3.0 ˚C above average) in two populations of a coral reef damselfish with different capacities for thermal plasticity. We found that the more thermally tolerant population had greater plasticity of gene expression and had significantly more downregulated genes, which may provide more energy to repair damage associated with thermal stress and to maintain basic functions at these extreme temperatures. In contrast, the thermally sensitive population exhibited higher basal levels of heat shock proteins and had three times fewer changes in gene expression overall. The limited changes in gene regulation suggest that individuals have reduced genome plasticity to tolerate thermal fluctuations and consequently may not have enough energy to repair damage and resume cellular homeostasis at extreme temperatures. Thus, we have identified the molecular signatures of how two genetically distinct fish populations cope with an extreme thermal event, and why they differ in their capacity for thermal plasticity.

Epigenetic inheritance is a potential mechanism by which the environment in one generation can influence the performance of future generations 1 . Rapid climate change threatens the survival of many organisms; however, recent studies show that some species can adjust to climate-related stress when both parents and their offspring experience the same environmental change 2 , 3 . Whether such transgenerational acclimation could have an epigenetic basis is unknown. Here, by sequencing the liver genome, methylomes and transcriptomes of the coral reef fish, Acanthochromis polyacanthus , exposed to current day (+0 °C) or future ocean temperatures (+3 °C) for one generation, two generations and incrementally across generations, we identified 2,467 differentially methylated regions (DMRs) and 1,870 associated genes that respond to higher temperatures within and between generations. Of these genes, 193 were significantly correlated to the transgenerationally acclimating phenotypic trait, aerobic scope, with functions in insulin response, energy homeostasis, mitochondrial activity, oxygen consumption and angiogenesis. These genes may therefore play a key role in restoring performance across generations in fish exposed to increased temperatures associated with climate change. Our study is the first to demonstrate a possible association between DNA methylation and transgenerational acclimation to climate change in a vertebrate.

Scleractinian corals are the foundation species of the coral-reef ecosystem. Their calcium carbonate skeletons form extensive structures that are home to millions of species, making coral reefs one of the most diverse ecosystems of our planet. However, our understanding of how reef-building corals have evolved the ability to calcify and become the ecosystem builders they are today is hampered by uncertain relationships within their subclass Hexacorallia. Corallimorpharians have been proposed to originate from a complex scleractinian ancestor that lost the ability to calcify in response to increasing ocean acidification, suggesting the possibility for corals to lose and gain the ability to calcify in response to increasing ocean acidification. Here, we employed a phylogenomic approach using whole-genome data from six hexacorallian species to resolve the evolutionary relationship between reef-building corals and their noncalcifying relatives. Phylogenetic analysis based on 1,421 single-copy orthologs, as well as gene presence/absence and synteny information, converged on the same topologies, showing strong support for scleractinian monophyly and a corallimorpharian sister clade. Our broad phylogenomic approach using sequence-based and sequence-independent analyses provides unambiguous evidence for the monophyly of scleractinian corals and the rejection of corallimorpharians as descendants of a complex coral ancestor.

MicroRNAs (miRNAs) are small regulatory RNAs that are involved in many biological process in eukaryotes. They play a crucial role in modulating genetic expression of their targets, which makes them integral components of transcriptional regulatory networks. As sponges (phylum Porifera) are commonly considered the most basal metazoan, the in-depth capture of miRNAs from these organisms provides additional clues to the evolution of miRNA families in metazoans. Here, we identified the core proteins involved in the biogenesis of miRNAs, and obtained evidence for bona fide miRNA sequences for two marine sponges Stylissa carteri and Xestospongia testudinaria (11 and 19 respectively). Our analysis identified several miRNAs that are conserved amongst demosponges, and revealed that all of the novel miRNAs identified in these two species are specific to the class Demospongiae.

Assigning functions to uncultivated environmental microorganisms continues to be a challenging endeavour. Here, we present a new microscopy protocol for fluorescence in situ hybridisation-correlative light and electron microscopy (FISH-CLEM) that enabled, to our knowledge for the first time, the identification of single cells within their complex microenvironment at electron microscopy resolution. Members of the candidate phylum Poribacteria, common and uncultivated symbionts of marine sponges, were used towards this goal. Cellular 3D reconstructions revealed bipolar, spherical granules of low electron density, which likely represent carbon reserves. Poribacterial activity profiles were retrieved from prokaryotic enriched sponge metatranscriptomes using simulation-based optimised mapping. We observed high transcriptional activity for proteins related to bacterial microcompartments (BMC) and we resolved their subcellular localisation by combining FISH-CLEM with immunohistochemistry (IHC) on ultra-thin sponge tissue sections. In terms of functional relevance, we propose that the BMC-A region may be involved in 1,2-propanediol degradation. The FISH-IHC-CLEM approach was proven an effective toolkit to combine -omics approaches with functional studies and it should be widely applicable in environmental microbiology.