Climate drives coupled regime shifts across subtropical estuarine ecosystems.

Ecological regime shifts are expected to increase this century as climate change propagates cascading effects across ecosystems with coupled elements. Here, we demonstrate that the climate-driven salt marsh-to-mangrove transition does not occur in isolation but is linked to lesser-known oyster reef-to-mangrove regime shifts through the provision of mangrove propagules. Using aerial imagery spanning 82 y, we found that 83% of oyster reefs without any initial mangrove cover fully converted to mangrove islands and that mean (± SD) time to conversion was 29.1 ± 9.6 y. In situ assessments of mangrove islands suggest substantial changes in ecosystem structure during conversion, while radiocarbon dates of underlying reef formation indicate that such transitions are abrupt relative to centuries-old reefs. Rapid transition occurred following release from freezes below the red mangrove (Rhizophora mangle) physiological tolerance limit (-7.3 °C) and after adjacent marsh-to-mangrove conversion. Additional nonclimate-mediated drivers of ecosystem change were also identified, including oyster reef exposure to wind-driven waves. Coupling of regime shifts arises from the growing supply of mangrove propagules from preceding and adjacent marsh-to-mangrove conversion. Climate projections near the mangrove range limit on the Gulf coast of Florida suggest that regime shifts will begin to transform subtropical estuaries by 2070 if propagule supply keeps pace with predicted warming. Although it will become increasingly difficult to maintain extant oyster habitat with tropicalization, restoring oyster reefs in high-exposure settings or active removal of mangrove seedlings could slow the coupled impacts of climate change shown here.

Characterization of the genome and cell invasive phenotype of Vibrio diabolicus Cg5 isolated from mass mortality of Pacific oyster, Crassostrea gigas.

Vibrio is an important group of aquatic animal pathogens, which has been identified as the main pathogenic factor causing mass summer mortality of Crassostrea gigas in northern China. This study aims to investigate the potential pathogenic mechanisms of Vibrio Cg5 isolate in C. gigas. We sequenced and annotated the genome of Vibrio Cg5 to analyze potential virulence factors. The gentamicin protection assays were performed with C. gigas primary cells to reveal the cell-invasive behavior of Cg5. The genome analysis showed that Cg5 was a strain of human disease-associated pathogen with multiple antibiotic resistance, and four virulence factors associated with intracellular survival were present in the genome. The gentamicin protection assays showed that Cg5 could potentially invade the cells of C. gigas, indicating that Cg5 could be a facultative intracellular pathogen of C. gigas. These results provide insights into the pathogenic mechanism of V. diabolicus, an emerging pathogenic Vibrio on aquatic animals, which would be valuable in preventing and controlling diseases in oysters.

Cloning, expression and characterisation of a novel mollusc α-1,2-Fucosyltransferase from Crassostrea gigas (CgFUT2).

Glycans containing fucose play crucial roles in cell biology, particularly in recognition processes. In humans, fucose found in H-blood group antigens is recognized by various pathogens, thereby influencing host-pathogen interactions. However, in invertebrate biology the specific functions of these modifications and the corresponding glycosyltransferases are not fully elucidated. Therefore, cloning these glycosyltransferases from different model systems will provide valuable insights into this process. Little is known about fucosyltransferases in molluscs. For this study, a sequence of the Pacific oyster, Crassostrea gigas, based on amino acid sequence homologies with rabbit and human α-1,2-fucosyltransferases, was chosen. The recombinant enzyme (350 amino acids) was able to transfer fucose from GDP-fucose to the galactose residue of type II disaccharides, terminal galactoses in complex N-glycan structures and several linear and branched galactans which were tested using a glycan microarray. The α-1,2-linkage formed was confirmed by NMR analysis. The enzyme was active in a broad pH-range, it was relatively stable upon storage conditions and its activity was not dependent on the presence of divalent cations. In this study, we were able to clone, express and characterise a novel α-1,2-fucosyltrasferase from Crassostrea gigas (CgFUT2).

Determination, expression and characterization of an UDP-N-acetylglucosamine:α-1,3-D-mannoside ß-1,2-N-acetylglucosaminyltransferase I (GnT-I) from the Pacific oyster, Crassostrea gigas.

Molluscs are intermediate hosts for several parasites. The recognition processes, required to evade the host's immune response, depend on carbohydrates. Therefore, the investigation of mollusc glycosylation capacities is of high relevance to understand the interaction of parasites with their host. UDP-N-acetylglucosamine:α-1,3-D-mannoside ß-1,2-N-acetylglucosaminyltransferase I (GnT-I) is the key enzyme for the biosynthesis of hybrid and complex type N-glycans catalysing the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the α-1,3 Man antenna of Man5GlcNAc2. Thereby, the enzyme produces a suitable substrate for further enzymes, such as α-mannosidase II, GlcNAc-transferase II, galactosyltransferases or fucosyltransferases. The sequence of GnT- I from the Pacific oyster, Crassostrea gigas, was obtained by homology search using the corresponding human enzyme as the template. The obtained gene codes for a 445 amino acids long type II transmembrane glycoprotein and shared typical structural elements with enzymes from other species. The enzyme was expressed in insect cells and purified by immunoprecipitation using protein A/G-plus agarose beads linked to monoclonal His-tag antibodies. GnT-I activity was determined towards the substrates Man5-PA, MM-PA and GnM-PA. The enzyme displayed highest activity at pH 7.0 and 30 °C, using Man5-PA as the substrate. Divalent cations were indispensable for the enzyme, with highest activity at 40 mM Mn2+, while the addition of EDTA or Cu2+ abolished the activity completely. The activity was also reduced by the addition of UDP, UTP or galactose. In this study we present the identification, expression and biochemical characterization of the first molluscan UDP-N-acetylglucosamine:α-1,3-D-mannoside ß-1,2-N-acetylglucosaminyltransferase I, GnT-I, from the Pacific oyster Crassostrea gigas.

Discovery and biochemical characterization of two hexokinases from Crassostrea gigas.

Hexokinases (HKs) play a vital role in glucose metabolism, which controls the first committed step catalyzing the production of glucose-6-phosphate from glucose. Two HKs (CGIHK1 and CGIHK2) from the Pacific oyster Crassostrea giga were cloned and characterized. CGIHK1 and CGIHK2 were recombinantly expressed in Escherichia coli and successfully purified by the Ni-NTA column. The optimum pH of the two enzymes was pH 8.0 and 8.5, respectively. The optimum temperature of the two enzymes was 42 °C and 50 °C, respectively. Both enzymes showed a clear requirement for divalent magnesium and were strongly inhibited by SDS. CGIHK1 exhibited highly strict substrate specificity to glucose, while CGIHK2 could also catalyze other 11 monosaccharide substrates. This is the first report on the in vitro biosynthesis of glucose-6-phosphate by the hexokinases from Crassostrea gigas. The facile expression and purification procedures combined with different substrate specificities make CGIHK1 and CGIHK2 candidates for the biosynthesis of glucose-6-phosphate and other sugar-phosphates.

An optimized protocol for routine development of cell culture from adult oyster, Crassostrea madrasensis.

Marine molluscan cell lines, required for virus screening and cultivation, form essential tools for developing health management strategies for these animals in the blue economy. Moreover, they are also crucial to develop cultivated seafood. As there is no valid marine molluscan cell line, primary cell cultures are relied upon for all investigations. A sound protocol for generating primary cell cultures from molluscs is entailed, but existing protocols often involve heavy antibiotic usage and depuration that invariably affect gene expression and cell health. This work presents an easy-to-adopt, time-saving protocol using non-depurated mollusc Crassostrea madrasensis, which requires only initial antibiotic treatment and minimal exposure or no use of antibiotics in the cell culture medium. The important experimental considerations for arriving at this protocol have been elucidated. Accordingly, sodium hypochlorite and neomycin sulfate were chosen for disinfecting tissues. The study is the first to use shrimp cell culture medium (SCCM) as a cell culture medium for molluscan cell culture. Despite being osmoconformers, the oysters exhibited stable intracellular osmotic conditions and pH, which, when provided in vitro, promoted effective cardiomyocyte formation. The cell viability could be enhanced using 10% fetal bovine serum (FBS), but healthy cell culture could also be obtained using SCCM without FBS. The optimized culture conditions allowed for regular beating cardiomyocyte clusters that could be retained for a month. Limited cell proliferation, as shown by the BrdU assay, demands further interventions, such as possibly producing induced pluripotent stem cells. The optimized protocol and culture conditions also align with some requirements for producing cultivated meat from marine molluscs.

An LPS-induced TNF-α factor involved in immune response of oyster Crassostrea gigas by regulating haemocytes apoptosis.

LPS induced TNF-α Factor (LITAF) is a transcription factor widely involving in activation of Tumor Necrosis Factor (TNF) and other cytokines in the inflammatory response. In the present study, a homologue of LITAF with a conserved LITAF domain was identified from the Pacific oyster Crassostrea gigas. The transcripts of CgLITAF were detected in all examined tissues with highest expression in hepatopancrease. The immunofluorescence assay and Western blot showed that LPS stimulation induced an obvious nucleus translocation of CgLITAF protein in haemocytes. While the mRNA level of CgLITAF changed slightly after LPS stimulation. When the siRNA of CgLITAF was injected to inhibit its expression, the apoptotic level of haemocytes decreased observably after LPS stimulation. Consistently, the transcripts of CgTNF3 and CgTNF4 (LOC105343080, LOC105341146), the apoptotic-related molecules including CgBax, CgCytochrome c, CgCaspase9 and CgCaspase3, were significantly suppressed in the CgLITAF-RNAi oysters. While the mRNA expression level of CgBcl was enhanced significantly in the CgLITAF-RNAi oysters. These results indicated that CgLITAF promoted haemocyte apoptosis by regulating the expression of apoptotic-related factors, suggesting its important role in the immune response of oysters.

Molecular confirmation and functional study of signal transducer and activator of transcription genes in the Pacific oyster Crassostrea gigas.

The JAK (Janus kinase)-STAT (Signal transducer and activator of transcription) is a well-known functional signaling pathway that plays a key role in several important biological activities such as apoptosis, cell proliferation, differentiation, and immunity. However, limited studies have explored the functions of STAT genes in invertebrates. In the present study, the gene sequences of two STAT genes from the Pacific oyster (Crassostrea gigas), termed CgSTAT-Like-1 (CgSTAT-L1) and CgSTAT-Like-2 (CgSTAT-L2), were obtained using polymerase chain reaction (PCR) amplification and cloning. Multiple sequence comparisons revealed that the sequences of crucial domains of these proteins were conserved, and the similarity with the protein sequence of other molluscan STAT is close to 90 %. The phylogenetic analyses indicated that CgSTAT-L1 and CgSTAT-L2 are novel members of the mollusk STAT family. Quantitative real-time PCR results implied that CgSTAT-L1 and CgSTAT-L2 mRNA expression was found in all tissues, and significantly induced after challenge with lipopolysaccharide (LPS), peptidoglycan (PGN), or poly(I:C). After that, dual-luciferase reporter assays denoted that overexpression of CgSTAT-L1 and CgSTAT-L2 significantly activated the NF-κB signaling, and, interestingly, the overexpressed CgSTAT proteins potentiated LPS-induced NF-κB activation. These results contributed a preliminary analysis of the immune-related function of STAT genes in oysters, laying the foundation for deeper understanding of the function of invertebrate STAT genes.

Involvement of metabotropic glutamate receptors in regulation of immune response in the Pacific oyster Crassostrea gigas.

Metabotropic glutamate receptors (mGluRs) play a pivotal role in the neuroendocrine-immune regulation. In this study, eight mGluRs were identified in the Pacific Oyster Crassostrea gigas, which were classified into three subfamilies based on genetic similarity. All CgmGluRs harbor variable numbers of PBP1 domains at the N-terminus. The sequence and structural features of CgmGluRs are highly similar to mGluRs in other species. A uniformly upregulated expression of CgmGluRs was observed during D-shaped larval stage compared to early D-shaped larval stage. The transcripts of CgmGluRs were detectable in various tissues of oyster. Different CgmGluR exhibited diverse expression patterns response against different PAMP stimulations, among which CgmGluR5 was significantly downregulated under these stimulations, reflecting its sensitivity and broad-spectrum responsiveness to microbes. Following LPS stimulation, the mRNA expression of CgmGluR5 and CgCALM1 in haemocytes was suppressed within 6 h and returned to normal levels by 12 h. Inhibition of CgmGluR5 activity resulted in a significant reduction in CgCALM1 expression after 12 h. Further KEGG enrichment analysis suggested that CgmGluR5 might modulate calcium ion homeostasis and metabolic pathways by regulating CgCALM1. This research delivers the systematic analysis of mGluR in the Pacific Oyster, offering insights into evolutionary characteristics and immunoregulatory function of mGluR in mollusks.

The phytoplankton community affects the energy metabolism and immunomodulation strategy of oyster during breeding seasons.

The mass mortality of Pacific oyster Crassostrea gigas has become a severe ecological and economic concern to Chinese aquaculture, which is proposed to be linked to the phytoplankton community in the farming waters. In the present study, both field and laboratory experiments were conducted to identify the phytoplankton taxa associated with oyster mortality and explore the molecular mechanism by which they affect the physiological health of oysters. The field experiment showed that more serious mortality of oysters was observed in the North Yellow Sea from July to September in 2018 (average survival rate of 75.11 %) than in 2019 (average survival rate of 85.78 %), with the proportion of Bacillariophyta (diatoms) in the phytoplankton community in 2018 lower than that in 2019. In comparison to 2019, reduced dry weight, lower glycogen and triglyceride contents in hepatopancreas, lower 17ß-estradiol and testosterone concentrations in gonad, as well as a generally weaker immune response against Vibrio splendidus stimulation were detected in the oysters sampled in 2018. The treatment of oysters with either starvation (starvation group) or Nitzschia closterium f. minutissima feeding (N. closterium group) was conducted to verify the field findings, with individuals reared in natural seawater as control. After 40 days of N. closterium feeding, dry weight, glycogen and triglyceride contents in hepatopancreas significantly increased, as well as the biosynthesis of sex hormones and gonadal maturation were promoted compared to the control and starvation groups. Moreover, a much stronger immune response against V. splendidus stimulation was observed in the oysters of N. closterium group, with the fold-changes of norepinephrine content in serum, SOD activity in hepatopancreas, and the mRNA expression level of IL17-5 and HSP70 in haemocytes higher than those in the control and starvation groups. Collectively, these results suggested that lack of diatoms in the farming waters suppressed the energy storage and gonadal maturation of adult oysters, and also resulted in a compromised immune response against bacterial infection, which may be a leading cause of the mass mortality of oysters living in diatom-deficient waters during breeding seasons.

Whole-genome DNA methylation profiling revealed epigenetic regulation of NF-κB signaling pathway involved in response to Vibrio alginolyticus infection in the Pacific oyster, Crassostrea gigas.

DNA methylation, an essential epigenetic alteration, is tightly linked to a variety of biological processes, such as immune response. To identify the epigenetic regulatory mechanism in Pacific oyster (Crassostrea gigas), whole-genome bisulfite sequencing (WGBS) was conducted on C. gigas at 0 h, 6 h, and 48 h after infection with Vibrio alginolyticus. At 6 h and 48 h, a total of 11,502 and 14,196 differentially methylated regions (DMRs) were identified (p<0.05, FDR<0.001) compared to 0 h, respectively. Gene ontology (GO) analysis showed that differentially methylated genes (DMGs) were significantly enriched in various biological pathways including immunity, cytoskeleton, epigenetic modification, and metabolic processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that transcription machinery (ko03021) is one of the most important pathways. Integrated transcriptome and methylome analyses allowed the identification of 167 and 379 DMG-related DEGs at 6 h and 48 h, respectively. These genes were significantly enriched in immune-related pathways, including nuclear factor kappa B (NF-κB) signaling pathway (ko04064) and tumor necrosis factor (TNF) signaling pathway (ko04668). Interestingly, it's observed that the NF-κB pathway could be activated jointly by TNF Receptor Associated Factor 2 (TRAF2) and Baculoviral IAP Repeat Containing 3 (BIRC3, the homolog of human BIRC2) which were regulated by DNA methylation in response to the challenge posed by V. alginolyticus infection. Through this study, we provided insightful information about the epigenetic regulation of immunity-related genes in the C. gigas, which will be valuable for the understanding of the innate immune system modulation and defense mechanism against bacterial infection in invertebrates.

A novel surface marker CD49d promotes TNF expression in oyster agranulocytes by mediating the MAPK pathway.

CD49d, encoded by the gene Integrin α4, is a significant member of cell adhesion receptors, which is widely expressed in various immune cells to trigger immune responses against invading pathogens. In the present study, the expression of CgCD49d and its regulatory role in TNF expression were investigated in the Pacific oyster Crassostrea gigas. There were five Int-alpha domains, an Integrin_alpha2 region and a unique FG-GAP repeat region inserted identified in CgCD49d. CgCD49d transcript was specifically expressed in haemocytes, and its mRNA expression level in haemocytes increased after LPS and Vibrio splendidus stimulation. After CgCD49d was blocked by using its antibody, the phosphorylation level of CgJNK in the MAPK signaling pathway and CgTNF transcripts decreased significantly post V. splendidus stimulation. After phosphorylation level of CgJNK was inhibited by using its inhibitor, the nuclear translocation of CgRel was restrained and CgTNF transcripts also decreased significantly post V. splendidus stimulation. Furthermore, CgCD49d was found to be mainly expressed in the agranulocyte subpopulation, and Alexa Fluor 488-conjugated CgCD49d antibody labeled agranulocytes with a circle of green fluorescence signals on CgCD49d+ agranulocyte surface under Confocal microscopy, which accounted for 24.9 ± 4.53% of total haemocytes. Collectively, these results suggested that CgCD49d promoted TNF expression in oyster haemocytes against bacterial invasion by mediating MAPK pathway, and it could be used as a surface marker to type and sort a subset of agranulocyte subpopulation among haemocytes.

MicroRNA transcriptome analysis reveals the immune regulatory mechanism of Crassostrea hongkongesis against Vibrio harveyi infection.

MicroRNAs (miRNAs) are small non-coding RNA molecules that modulate target-genes expression and play crucial roles in post-transcriptional regulation and immune system regulation. The Hong Kong oyster (Crassostrea hongkongesis), as the main marine aquaculture shellfish in the South China Sea, not only has high economic and ecological value, but also is an ideal model for conducting research on pathogen host interaction. Vibrio harveyi, a Gram negative luminescent marine bacterium, is widely distributed in coastal water environments and can cause large-scale death of C. hongkongesis. However, little in formation is available on the immune regulatory mechanisms of C. hongkongesis infected with V. harveyi. Therefore, we performed microRNA transcriptome analysis for elucidating the immunoregulation mechanism of C. hongkongesis infected with V. harveyi. The results show that a total of 308468208 clean reads and 288371159 clean tags were obtained. 222 differentially expressed miRNAs were identified. A total of 388 target genes that were differentially expressed and negatively correlated with miRNA expression were predicted by 222 DEmiRs. GO enrichment analysis of 388 DETGs showed that they were mainly enriched in the immune-related term of membrane-bounded vesicle, endocytic vesicle lumen, antigen processing and presentation of exogenous peptide antigen via MHC class I, antigen processing and presentation of peptide antigen via MHC class I, and other immune-related term. KEGG enrichment analysis showed that DETGs were mainly enriched in the Complement and coagulation cascades, Herpes simplex virus 1 infection, Bacterial invasion of epithelial cells, Antigen processing and presentation and NOD-like receptor signaling pathway. The 16 key DEmiRs and their target genes form a regulatory network for seven immune-related pathways. These results suggest that V. harveyi infection induces a complex miRNA response with wide-ranging effects on immune gene expression in the C. hongkongesis. This study explored the immune response of C. hongkongesis to V. harveyi infection at the level of miRNAs, which provides new ideas for the healthy culture and selective breeding of C. hongkongesis.

CgADAR1 involved in regulating the synthesis of interferon-like protein in Crassostrea gigas.

Adenosine deaminases acting on RNA 1 (ADAR1) is a dsRNA adenosine (A)-to-inosine (I) editing enzyme that regulates the innate immune response against virus invasion. In the present study, a novel CgADAR1 was identified from the oyster Crassostrea gigas. The open reading frame (ORF) of CgADAR1 was of 3444 bp encoding a peptide of 1147 amino acid residues with two Zα domains, one dsRNA binding motif (DSRM) and one RNA adenosine deaminase domain (ADEAMc). The mRNA transcripts of CgADAR1 were detected in all the examined tissues, with higher expression levels in mantle and gill, which were 7.11-fold and 4.90-fold (p < 0.05) of that in labial palp, respectively. The mRNA transcripts of CgADAR1 in haemocytes were significantly induced at 24 h and 36 h after Poly (A: U) stimulation, which were 6.03-fold (p < 0.01) and 1.37-fold (p < 0.001) of that in control group, respectively. At 48 h after Poly (A:U) stimulation, the mRNA expression of CgRIG-Ⅰ, CgIRF8 and CgIFNLP significantly increased, which were 4.36-fold (p < 0.001), 1.82-fold (p < 0.05) and 1.92-fold (p < 0.05) of that in control group. After CgADAR1 expression was inhibited by RNA interference (RNAi), the mRNA expression levels of CgMDA5, CgRIG-Ⅰ, CgTBK1, CgIRF8 and CgIFNLP were significantly increased, which were 11.88-fold, 11.51-fold, 2.22-fold, 2.85-fold and 2.52-fold of that in control group (p < 0.001), and the phosphorylation level of CgTBK1 was also significantly increased. These results suggested that CgADAR1 played a regulation role in the early stages of viral infection by inhibiting the synthesis of interferon-like protein.

CgSHIP2 negatively regulates the mRNA expressions of CgIL-17s in response to Vibrio splendidus stimulation in Crassostrea gigas.

SH2 domain containing inositol polyphosphate5-phosphatase-2 (SHIP2) is a member of the 5-phosphatase family, acting as a vital negative regulator of immune response in vertebrates. In the present study, a SHIP2 homologue (designed as CgSHIP2) was identified from Pacific oyster, Crassostrea gigas. There was a SH2 domain, an IPPc domain and a SAM domain in CgSHIP2. The mRNA transcripts of CgSHIP2 were widely expressed in all the tested tissues with the highest expression in haemolymph. The mRNA expressions of CgSHIP2 in haemocytes increased significantly at 6, 12, 48 and 72 h after Vibrio splendidus stimulation. The positive green signals of CgSHIP2 protein were mainly located in cytoplasm of haemocytes. After the expression of CgSHIP2 was inhibited by RNA interference, the mRNA transcripts of interleukin 17s (CgIL-17-1, CgIL-17-2, CgIL-17-3 and CgIL-17-6) in the haemocytes increased significantly at 24 h after V. splendidus stimulation, which were 8.15-fold (p < 0.001), 3.44-fold (p < 0.05), 2.15-fold (p < 0.01) and 4.63-fold (p < 0.05) compared with that in NC-RNAi group, respectively. Obvious branchial swelling and cilium shedding in gills were observed in CgSHIP2-RNAi group at 24 h after V. splendidus stimulation. The results suggested that CgSHIP2 played an important role in controlling inflammatory response induced by bacteria in oysters.

CgIκB2 negatively regulates the expression of interferon-like protein by Rel/NF-κB signal in Crassostrea gigas.

Inhibitors of NF-κB (IκBs) have been implicated as major components of the Rel/NF-κB signaling pathway, playing an important negative regulatory role in host antiviral immunity such as in the activation of interferon (IFN) in vertebrates. In the present study, the immunomodulatory effect of IκB (CgIκB2) on the expression of interferon-like protein (CgIFNLP) was evaluated in Pacific oyster (Crassostrea gigas). After poly (I:C) stimulation, the mRNA expression level of CgIκB2 in haemocytes was significantly down-regulated at 3-12 h while up-regulated at 48-72 h. The mRNA expression of CgIκB2 in haemocytes was significantly up-regulated at 3 h after rCgIFNLP stimulation. In the CgIκB2-RNAi oysters, the mRNA expression of CgIFNLP, interferon regulatory factor-8 (CgIRF8) and NF-κB subunit (CgRel), the abundance of CgIFNLP and CgIRF8 protein in haemocytes, as well as the abundance of CgRel protein in nucleus were significantly increased after poly (I:C) stimulation. Immunofluorescence assay showed that nuclear translocation of CgIRF8 and CgRel protein was promoted in CgIκB2-RNAi oysters compared with that in EGFP-RNAi group. In the CgRel-RNAi oysters, the mRNA and protein expression level of CgIFNLP significantly down-regulated after poly (I:C) stimulation. The collective results indicated that CgIκB2 plays an important role in regulating CgIFNLP expression through its effects on Rel/NF-κB and IRF signaling pathways.

Hurricanes temporarily weaken human-ecosystem linkages in estuaries.

Intense disturbances such as hurricanes may drastically affect ecosystems, producing both acute and long-term changes along coastlines. By disrupting human activities (e.g., fishing), hurricanes can provide an opportunity to quantify the effects of these activities on coastal ecosystems. We performed predator-exclusion experiments on oyster reefs in 2016, one-year before a category-4 hurricane ("Harvey") and again in 2018 one-year post-hurricane where the storm made landfall. Additionally, we examined 8 years (2011-2018) of fisheries-independent data to gauge how fishing pressure and fish populations were affected by the storm in three locations that varied in storm impacts. In the month following Hurricane Harvey, fishing effort dropped by 90% in the area with wind and flooding damage, and predatory fish species commonly targeted by anglers were 300% more abundant than the year prior to the hurricane. The locations without damage to fishing infrastructure did not experience declines in fishing pressure or changes in fish abundance, regardless of flooding disturbance. Reef fish and invertebrate communities directly affected by the storm were significantly different after the hurricane and were ~ 30% more diverse. With low fishing pressure, sportfish CPUE were 1.7-6.9 × higher immediately after the hurricane. Intermediate consumers, such as crabs that prey on oysters, were 45% less abundant and 10% smaller. These results indicate that hurricanes can temporarily disrupt human-ecosystem linkages and reconstitute top-down control by sportfish in estuarine food webs. Disturbance events that interrupt or weaken those interactions may yield indirect ecological benefits and provide insights into the effects of human activities on food webs.

The role of the balance between energy production and ammonia detoxification mediated by key amino acids in divergent hypersaline adaptation among crassostrea oysters.

Global ocean salinity is changing under rapid climate change and intensified anthropogenic activity. Increased differences in salinity threaten marine biodiversity, organismal survival, and evolution, particularly sessile invertebrates dwelling in highly fluctuating intertidal and estuarine environments. Comparing the responses of closely related species to salinity changes can provide insights into the adaptive mechanisms underlying inter- and intraspecific divergence in salinity tolerance, but are poorly understood in marine bivalves. We collected wild individuals of four Crassostrea species, in addition to two populations of the same species from their native habitats and determined the dynamics of hydrolyzed amino acids (HAAs) and transcriptional responses to hypersaline stress. In response to hypersaline stress, species/populations inhabiting natural high-salinity sea environments showed higher survival and less decline in HAAs than that of congeners inhabiting low-salinity estuaries. Thus, native environmental salinity shapes oyster tolerance. Notably, a strong negative correlation between the decline in HAAs and survival indicated that the HAAs pool could predict tolerance to hypersaline challenge. Four HAAs, including glutamine (Glu), aspartic acid (Asp), alanine (Ala) and glycine (Gly), were identified as key amino acids that contributed substantially to the emergency response to hypersaline stress. High-salinity-adapted oyster species only induced substantial decreases in Glu and Asp, whereas low-salinity-adapted congeners further incresaed Ala and Gly metabolism under hypersaline stress. The dynamics of the content and gene expression responsible for key amino acids pathways revealed the importance of maintaining the balance between energy production and ammonia detoxification in divergent hypersaline responses among oyster species/populations. High constructive or plastic expression of evolutionarily expanded gene copies in high-salinity-adapted species may contribute to their greater hypersaline tolerance. Our findings reveal the adaptive mechanism of key amino acids in salinity adaptation in marine bivalves and provide new avenues for the prediction of adaptive potential and aquaculture with high-salinity tolerant germplasms.

Perkinsus spp. Occurrence in South America: A review.

Marine mollusk production is increasing worldwide, and this trend is being evidenced in South American countries, where several species of bivalves are produced, exploited, and traded. This activity brings benefits either for the ecosystem, as it is a less impactful and polluting than other aquaculture practices, and to coastal human communities, as it provides food and income. However, emergence of outbreaks by pathogens is a major concern and can put an entire developing sector at risk. Perkinsosis is a disease caused by Perkinsus spp. protozoans that affect mollusks worldwide. In this review we provide information on Perkinsus spp. among bivalves from South America. Infections by these parasites were only reported to date among coastal Atlantic bivalves of Argentina, Uruguay, and Brazil. The vast majority of cases and studies are reported from Brazil. We comprehensively review those results here. Finally, we suggest some considerations for future investigations that may expand our knowledge of these parasites.

First report of Perkinsus marinus occurrence associated with wild Pacific oysters Crassostrea gigas from the west coast of Korea.

This study reports the occurrence of Perkinsus marinus associated with wild Pacific oyster (Crassostrea gigas) specimens collected along the west coast of Korea. Confirmation of P. marinus presence was achieved by conventional PCR using World Organization of Animal Health (WOAH)-recommended primers that specifically targeted regions of the rDNA locus (ITS1, 5.8S, and ITS2). Sequencing of 10 samples revealed two distinct sequences differing by a single base pair, indicating potential haplotype variability. One sequence closely resembled the P. marinus strain found in Maryland, USA, whereas the other exhibited divergence, indicative of species diversity in the Korean strain, as was evident from the haplotype network analysis. Further validation involved the Ray's Fluid Thioglycollate Medium (RFTM) assay, which initially yielded inconclusive results, possibly due to low infection intensity. Subsequently, RFTM and 2 M NaOH assays conducted on the isolates in the present study, cultured P. marinus cells in standard DMEM/F12 medium, and a positive P. marinus strain (ATCC 50509), revealed characteristic hypnospores of P. marinus upon Lugol's iodine staining. These comprehensive investigations underscore the conclusive confirmation of P. marinus in Korean waters and mark a significant milestone in our understanding of the distribution and characteristics of this parasite in previously unreported regions.