Elevated estuary water temperature drives fish gut dysbiosis and increased loads of pathogenic vibrionaceae

Analysis of Differential Alternative Splicing in Largemouth Bass After High Temperature Exposure

Temperature is one of the critical factors affecting the physiological functions of fish. With ongoing global warming, changes in water temperature have a profound impact on fish species. Alternative splicing, being a significant mechanism for gene expression regulation, facilitates fish to adapt and thrive in dynamic and varied aquatic environments. Our study used transcriptome sequencing to analyze alternative splicing in largemouth bass gills at 34 °C for 24 h. The findings indicated an increase in both alternative splicing events and alternative splicing genes after high temperature treatment. Specifically, the comparative analysis revealed a total of 674 differential alternative splicing events and 517 differential alternative splicing genes. Enrichment analysis of differential alternative splicing genes revealed significant associations with various gene ontology (GO) terms and KEGG pathways, particularly in immune-related pathways like necroptosis, apoptosis, and the C-type lectin receptor signaling pathway. These results emphasize that some RNA splicing-related genes are involved in the response of largemouth bass to high temperatures.

Thermally Primed Zostera muelleri Seeds Exhibit Higher Germination Rates Than Those From Ambient Conditions

Seagrasses provide critical ecosystem services such as carbon sequestration, sediment stabilisation and nursery habitat for juvenile fish. Zostera muelleri is ubiquitous within Australian and New Zealand estuaries, however, as a species is relatively understudied. We sourced seeds from a thermally affected east Australian estuary and investigated whether germination rates differed between ambient and thermally affected seeds over a variety of temperatures (16°C-28°C) to determine how seagrass systems might react in a warming climate. Germination for the experiment was low and totalled 5% of all seeds; however, similar numbers are typical in seed germination studies. Germination was highest at 16°C and was enhanced through the simulation of a 48-h freshwater pulse. Thermally affected sites germinated faster and had greater mean maximum germination when compared to control sites regardless of experimental temperature. These findings indicate that Z. muelleri in this system may be exhibiting transgenerational plasticity due to the thermal stress the parent experiences. This result provides an alternate viewpoint to the current literature by suggesting that unknown transgenerational effects may provide Z. muelleri with greater germination plasticity against temperatures expected under predicted climate change scenarios than previously expected.

Spatial and environmental drivers of temperate estuarine archaeal communities

Archaea play a crucial role in the global biogeochemical cycling of elements and nutrients, helping to maintain the functional stability of estuarine systems. This study characterised the abundance and diversity of archaeal communities and identified the environmental conditions shaping these microbial communities within six temperate estuaries along approximately 500 km of the New South Wales coastline, Australia. Estuarine sediments were found to exhibit significantly higher species richness than planktonic communities, with representative sequences from the Crenarchaeota phylum characterising each environment. Ordinate analyses revealed catchment characteristics as the strongest drivers of community variability. Our results also provide evidence supporting distance-decay patterns of archaeal biogeography across intermediate scales within and between temperate estuaries, contributing to a growing body of evidence revealing the extent spatial scales play in shaping microbial communities. This study expands our understanding of microbial diversity in temperate estuaries, with a specific focus on archaeal community structure and their role in maintaining ecosystem stability.

Diseases of marine fish and shellfish in an age of rapid climate change

A recurring trend in evidence scrutinized over the past few decades is that disease outbreaks will become more frequent, intense, and widespread on land and in water, due to climate change. Pathogens and the diseases they inflict represent a major constraint on seafood production and yield, and by extension, food security. The risk(s) for fish and shellfish from disease is a function of pathogen characteristics, biological species identity, and the ambient environmental conditions. A changing climate can adversely influence the host and environment, while augmenting pathogen characteristics simultaneously, thereby favoring disease outbreaks. Herein, we use a series of case studies covering some of the world's most cultured aquatic species (e.g., salmonids, penaeid shrimp, and oysters), and the pathogens (viral, fungal, bacterial, and parasitic) that afflict them, to illustrate the magnitude of disease-related problems linked to climate change.

Multigenerational effects of elevated temperature on host-microbiota interactions in the marine water flea Diaphanosoma celebensis exposed to micro- and nanoplastics

Rising ocean temperatures are driving unprecedented changes in global marine ecosystems. Meanwhile, there is growing concern about microplastic and nanoplastic (MNP) contamination, which can endanger marine organisms. Increasing ocean warming (OW) and plastic pollution inevitably cause marine organisms to interact with MNPs, but relevant studies remain sparse. Here, we investigated the interplay between ocean warming and MNP in the marine water flea Diaphanosoma celebensis. We found that combined exposure to MNPs and OW induced reproductive failure in the F2 generation. In particular, the combined effects of OW and MNPs on the F2 generation were associated with key genes related to reproduction and stress response. Moreover, populations of predatory bacteria were significantly larger under OW and MNP conditions during F2 generations, suggesting a potential link between altered microbiota and host fitness. These results were supported by a host transcriptome and microbiota interaction analysis. This research sheds light on the complex interplay between environmental stressors, their multigenerational effects on marine organisms, and the function of the microbiome.

Integration of metagenome and metabolome analysis reveals the correlation of gut microbiota, oxidative stress, and inflammation in Coilia nasus under air exposure stress and salinity mitigation

Due to the strong response to air exposure, high mortality was occurred in Coilia nasus. Previous studies reported that 10 ‰ NaCl could significantly reduce mortality in C. nasus under air exposure. To investigate the mechanisms that 10 ‰ NaCl can alleviate stress, community structure and metabolism of the intestinal flora of C. nasus were detected via metagenome and metabolome. In this study, C. nasus were divided into control group (C), air exposure group without 10 ‰ NaCl (AE), and air exposure group with 10 ‰ NaCl (AES). After air exposure stress and salinity mitigation, the mortality, intestinal microorganisms, metabolites, and physiological biomarkers were analyzed. The results showed that the mortality rate of C. nasus was reduced after salinity reduction; the antioxidant capacity was elevated compared to the AE group; and anti-inflammatory capacity was increased in the AES group compared to the AE group. Metagenomic sequencing results showed that the levels of harmful bacteria (E. coli, Aeromonas) in the Candida nasus gut increased after air exposure; beneficial bacteria (Actinobacteria, Corynebacteria) in the C. nasus gut increased after salinity reduction. Metabolomics analyses showed that AE decreased the expression of beneficial metabolites and increased the expression of harmful metabolites; AES increased beneficial metabolites and decreased harmful metabolites. Correlation analysis showed that in the AE group, beneficial metabolites were negatively correlated with oxidative stress and inflammatory response, while harmful metabolites were positively correlated with oxidative stress and inflammatory response, and were associated with bacterial communities such as Gillisia, Alkalitalia, Avipoxvirus, etc.; the correlation of metabolites with oxidative stress and inflammatory response was opposite to that of AE in the case of AES, and was associated with Lentilactobacillus, Cyanobacterium, and other bacterial communities. Air exposure caused damage to Candida rhinoceros and 10 ‰ salinity was beneficial in alleviating C. nasus stress. These results will provide new insights into methods and mechanisms to mitigate stress in fish.

Tissue-specific transcriptional response of post-larval clownfish to ocean warming

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.