Fish are critical ecologically and socioeconomically for subsistence economies in the Arctic, an ecosystem undergoing unprecedented environmental change. Our understanding of the responses of nearshore Arctic fishes to environmental change is inadequate because of limited research on the physicochemical drivers of abundance occurring at a fine scale. Here, high-frequency in situ measurements of pH, temperature, salinity, and dissolved oxygen were paired with daily fish catches in nearshore Alaskan waters of the Beaufort Sea. Due to the threat that climate change poses to high-latitude marine ecosystems, our main objective was to characterize the abiotic drivers of abundance and elucidate how nearshore fish communities may change in the future. We used generalized additive models (GAMs) to describe responses to the nearshore environment for 18 fish species. Relationships between abundance and the physicochemical environment were variable between species and reflected life history. Each abiotic covariate was significant in at least one GAM, exhibiting both nonlinear and linear associations with abundance. Temperature was the most important predictor of abundance and was significant in GAMs for 11 species. Notably, pH was a significant predictor of abundance for six species: Arctic cod (Boreogadus saida), broad whitefish (Coregonus nasus), Dolly Varden (Salvelinus malma), ninespine stickleback (Pungitius pungitius), saffron cod (Eleginus gracilis), and whitespotted greenling (Hexagrammos stelleri). Broad whitefish and whitespotted greenling abundance was positively associated with pH, while Arctic cod and saffron cod abundance was negatively associated with pH. These results may be a bellwether for future nearshore Arctic fish community change by providing a foundational characterization of the relationships between abundance and the abiotic environment, particularly in regard to pH, and demonstrate the importance of including a wider range of physicochemical habitat covariates in future research.
Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity.
In light of the chronic stress and mass mortality reef-building corals face under climate change, it is critical to understand the processes essential to reef persistence and replenishment, including coral reproduction and development. Here we quantify gene expression and size sensitivity to ocean acidification across a set of developmental stages in the rice coral, Montipora capitata. Gametes and then embryos and swimming larvae were exposed to three pH treatments ranging from 7.8 (Ambient), 7.6 (Low) and 7.3 (Xlow) from fertilization to 9 days post-fertilization. Embryo development and size, planula volume, and stage-specific gene expression were compared between treatments at each stage to determine the effects of acidified seawater on early development. While there was no measurable size differentiation between fertilized eggs and embryos at the prawn chip stage exposed to ambient, low, and extreme low pH, early gastrula and planula raised in reduced pH treatments were significantly smaller than those raised in ambient seawater, suggesting an energetic cost to developing under low pH. However, no differentially expressed genes emerged between treatments at any time point, except swimming larvae. Larvae from pH 7.6 showed upregulation of genes involved in cell division, regulation of transcription, lipid metabolism, and oxidative stress in comparison to the other two treatments, and smallest sizes in this treatment. While low pH appears to increase energetic demands and trigger oxidative stress, the developmental process is robust to this at a molecular level, with swimming larval stage reached in all pH treatments.
- High CO2 conditions profoundly affected biofilm community composition
- Species turnover explained differences in community composition
- Biofilm communities were more homogeneous under high CO2 conditions
- Toxin producing and turf-forming algae were enriched under high CO2 conditions
Biofilms harbour a wealth of microbial diversity and fulfil key functions in coastal marine ecosystems. Elevated carbon dioxide (CO2) conditions affect the structure and function of biofilm communities, yet the ecological patterns that underpin these effects remain unknown. We used high-throughput sequencing of the 16S and 18S rRNA genes to investigate the effect of elevated CO2 on the early successional stages of prokaryotic and eukaryotic biofilms at a CO2 seep system off Shikine Island, Japan. Elevated CO2 profoundly affected biofilm community composition throughout the early stages of succession, leading to greater compositional homogeneity between replicates and the proliferation of the potentially harmful algae Prymnesium sp. and Biddulphia biddulphiana. Species turnover was the main driver of differences between communities in reference and high CO2 conditions, rather than differences in richness or evenness. Our study indicates that species turnover is the primary ecological pattern that underpins the effect of elevated CO2 on both prokaryotic and eukaryotic components of biofilm communities, indicating that elevated CO2 conditions represent a distinct niche selecting for a distinct cohort of organisms without the loss of species richness.
Ocean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed “tropicalization”. A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral-dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral-dominated ecosystems. We show that increased herbivory by warm-water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf-dominated ecosystems, rather than the complex coral-dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO2 levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.
The objective of this study was to assess experimentally the potential impact of anthropogenic pH perturbation (ApHP) on concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as processes governing the microbial cycling of sulfur compounds. A summer planktonic community from surface waters of the Lower St. Lawrence Estuary was monitored in microcosms over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1,850 µatm), and 3 × pCO2 (2,700 µatm). A mixed phytoplankton bloom comprised of diatoms and unidentified flagellates developed over the course of the experiment. The magnitude and timing of biomass buildup, measured by chlorophyll a concentration, changed in the 3 × pCO2 treatment, reaching about half the peak chlorophyll a concentration measured in the 1 × pCO2 treatment, with a 2-day lag. Doubling and tripling the pCO2 resulted in a 15% and 40% decline in average concentrations of DMS compared to the control. Results from 35S-DMSPd uptake assays indicated that neither concentrations nor microbial scavenging efficiency of dissolved DMSP was affected by increased pCO2. However, our results show a reduction of the mean microbial yield of DMS by 34% and 61% in the 2 × pCO2 and 3 × pCO2 treatments, respectively. DMS concentrations correlated positively with microbial yields of DMS (Spearman’s ρ = 0.65; P < 0.001), suggesting that the impact of ApHP on concentrations of DMS in diatom-dominated systems may be strongly linked with alterations of the microbial breakdown of dissolved DMSP. Findings from this study provide further empirical evidence of the sensitivity of the microbial DMSP switch under ApHP. Because even small modifications in microbial regulatory mechanisms of DMSP can elicit changes in atmospheric chemistry via dampened efflux of DMS, results from this study may contribute to a better comprehension of Earth’s future climate.
In the past decades, the impacts of ocean acidification (OA) on marine animals have gained much attention. To date, numerous works in the literature have shown that OA can affect a variety of biological processes of marine animals, and our knowledge about its effects on marine organisms is mainly focused on the following aspects: (1) fertilization and early development; (2) biomineralization, metabolism, and growth; and (3) immunity and behaviors. However, there are still some limitations that currently exist in research on OA, which include (1) performing experiments with “constant acidification” rather than natural pH fluctuations that may not fully reflect their future true living conditions; (2) using pCO2 levels that were predicted to be reached in a hundred years in the future for experiments with relatively short exposure times, thus overlooking marine organisms’ potential for genetic adaptation or acclimation to the acidified seawater; (3) large amounts of experiments examining OA’s physiological impacts while leaving the potential affecting mechanisms largely unstudied; and (4) a lack of experiments investigating indirect effects of OA on marine organisms and the whole ecosystem. After providing a summary of the current knowledge of OA’s impacts on marine animals, this review aims to highlight potential directions for future studies.
The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO2) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO2). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.
Global change driven by anthropogenic carbon emissions is altering ecosystems at unprecedented rates, especially coral reefs, whose symbiosis with algal endosymbionts ise particularly vulnerable to increasing ocean temperatures and altered carbonate chemistry. Here, we assess the physiological responses of the coral holobiont (animal host + algal symbiont) of three Caribbean coral species from two reef environments after exposure to simulated ocean warming (28, 31 °C), acidification (300 – 3290 μatm), and the combination of stressors for 93 days. We used multidimensional analyses to assess how multiple coral holobiont physiological parameters respond to ocean acidification and warming. Our results demonstrate significantly diminishing holobiont physiology in S. siderea and P. astreoides in response to projected ocean acidification, while future warming elicited severe declines in P. strigosa. Offshore S. siderea fragments exhibited higher physiological plasticity than inshore counterparts, suggesting that this offshore population has the capacity to modulate their physiology in response to changing conditions, but at a cost to the holobiont. Plasticity of P. strigosa and P. astreoides was not clearly different between natal reef environments, however, temperature evoked a greater plastic response in both species. Interestingly, while these species exhibit unique physiological responses to ocean acidification and warming, when data from all three species are modeled together, convergent stress responses to these conditions are observed, highlighting the overall sensitivities of tropical corals to these stressors. Our results demonstrate that while ocean warming is a severe acute stressor that will have dire consequences for coral reefs globally, chronic exposure to acidification may also impact coral physiology to a greater extent than previously assumed. The variety of responses to global change we observe across species will likely manifest in altered Caribbean reef assemblages in the future.
Prior exposure to variable environmental conditions is predicted to influence the resilience of marine organisms to global change. We conducted complementary 4-month field and laboratory experiments to understand how a dynamic, and sometimes extreme, environment influences growth rates of a tropical reef-building crustose coralline alga and its responses to ocean acidification (OA). Using a reciprocal transplant design, we quantified calcification rates of the Caribbean coralline Lithophyllum sp. at sites with a history of either extreme or moderate oxygen, temperature, and pH regimes. Calcification rates of in situ corallines at the extreme site were 90% lower than those at the moderate site, regardless of origin. Negative effects of corallines originating from the extreme site persisted even after transplanting to more optimal conditions for 20 weeks. In the laboratory, we tested the separate and combined effects of stress and variability by exposing corallines from the same sites to either ambient (Amb: pH 8.04) or acidified (OA: pH 7.70) stable conditions or variable (Var: pH 7.80-8.10) or acidified variable (OA-Var: pH 7.45-7.75) conditions. There was a negative effect of all pH treatments on Lithophyllum sp. calcification rates relative to the control, with lower calcification rates in corallines from the extreme site than from the moderate site in each treatment, indicative of a legacy effect of site origin on subsequent response to laboratory treatment. Our study provides ecologically relevant context to understanding the nuanced effects of OA on crustose coralline algae, and illustrates how local environmental regimes may influence the effects of global change.
Coccolithophores are unicellular phytoplanktonic organisms characterized by a covering of calcite plates, the coccoliths, which are produced intracellularly. These calcifiers, as one of the main planktonic functional groups, play an important role in the inorganic carbon cycle and possibly as ballast that sinks organic carbon to the deep-sea. Most efforts to understanding coccolithophore response to ocean acidification (OA) –or the raise in atmospheric CO2 reduces ocean pH and saturation states (Ω) of CaCO3– have been through lab experiments, mostly using a small set of strains of the cosmopolitan, easily cultivated species Emiliania huxleyi. This species is especially interesting because it is young (~ 291,000 years) and has adapted to a wide range of marine environments. However, it is not the only coccolithophore and even within that species there is a lot of phenotypic and genetic diversity and diverse responses to OA in the lab. Despite the efforts made it is unclear how the physiological effects under controlled conditions translate to community-level responses in the field. This thesis aimed to contribute to understanding this issue by studying the distribution, composition and realized niches of coccolithophore assemblages and E. huxleyi morphotypes in contrasting pCO2/pH/Ωcalcite environments of the Eastern South Pacific, and to evaluate the responses of different E. huxleyi23 morphotypes to targeted pCO2/pH levels set in the lab. For this, the coccolithophores were surveyed in a coastal-oceanic section, mesotrophic waters, upwelling systems, and fjords-channels of Patagonia. From a total of 40 species, E. huxleyi was the most prevalent (30-100 % relative abundance). Within this taxon, several morphotypes has been described as stable in culture and genetically differentiated (e.g., the A and R morphotypes). The moderately-calcified A morphotype dominated the E. huxleyi populations being only surpassed by the R hyper-calcified morphotype in upwelling systems with high pCO2/low pH. This abrupt shift in the composition of E. huxleyi populations suggested that these coastal environments hold genetic reservoirs for their adaptation to OA. Therefore, the hypothesis was tested that these forms are adapted to resist high pCO2/low pH conditions. Unexpectedly, the morphotypes from the Eastern South Pacific were not more sensitive than the R hyper-calcified strains from neighboring high pCO2/low pH waters (lowering growth rates and PIC/POC ratios). On the other hand, realized-niche analysis showed that the A morphotype has a broader niche that is more tolerant to environmental-change (i.e., generalist) than the R morphotype’s niche, specialized to high pCO2/low pH waters. The lack of evidence for local adaptation to high pCO2/low pH conditions in E. huxleyi, might be explained by a narrow unimodal niche response to Ωcalcite revealed by niche analysis that was not tested experimentally. Alternatively, the R hyper-calcified morphotype might be selected by an unidentified condition particular to the Eastern South Pacific that correlates with temperature, salinity, and Ωcalcite of its realized-niche. Overall, despite their rapid turnover and large population sizes, oceanic planktonic microorganisms do not necessarily exhibit adaptations to high-pCO2 upwelled waters, and this ubiquitous coccolithophore may be near the limit of its capacity to adapt to ongoing OA.
Symbiosis establishment is a milestone in the life cycles of most broadcast-spawning corals; however, it remains largely unknown how initial symbiont infection is affected by ocean warming and acidification, particularly for massive corals. This study investigated the combined effects of elevated temperature (29 vs. 31 °C) and pCO2 (~ 450 vs. ~ 1000 μatm) on the recruits of a widespread massive coral, Platygyra daedalea. Results showed that geometric diameter and symbiosis establishment were unaffected by high pCO2, while elevated temperature significantly reduced successful symbiont infection by 50% and retarded the geometric diameter by 6%. Although neither increased temperature, pCO2, nor their interaction affected survival or algal pigmentation of recruits, there was an inverse relationship between symbiont infection rates and survivorship, especially at high temperatures, possibly as a result of oxidative stress caused by algal symbionts under increased temperature. Intriguingly, the proportion of Durusdinium did not increase in recruits at 31 °C, while recruits reared under high pCO2 hosted less Breviolum and more Durusdinium, indicating a high degree of plasticity of early symbiosis and contrasting to the previous finding that heat stress usually leads to the prevalence of thermally tolerant Durusdinium in coral recruits. These results suggest that ocean warming is likely to be more deleterious for the early success of P. daedalea than ocean acidification and provide insights into our understanding of coral-algal symbiotic partnerships under future climatic conditions.
The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment and the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge–microbe interactions. In this study, we compared the bacterial diversity and immune repertoire of the demosponge, Neopetrosia compacta, and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress based on climate scenarios predicted for 2100. Neopetrosia compacta harbors a diverse microbial community and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and immune response-related genes. Upon exposure to RCP 8.5 conditions, the microbiome composition and host transcriptome of N. compacta remained stable, which correlated with high survival (75%). In contrast, tissue necrosis and low survival (25%) of L. chagosensis was accompanied by microbial community shifts and downregulation of host immune-related pathways. Meta-analysis of microbiome diversity and immunological repertoire across poriferan classes further highlights the importance of host–microbe interactions in predicting the fate of sponges under future ocean conditions.
Ocean acidification has been broadly recognised to have effects on the structure and functioning of marine benthic communities. The selection of tolerant or vulnerable species can also occur during settlement phases, especially for calcifying organisms which are more vulnerable to low pH–high pCO2 conditions. Here, we use three natural CO2 vents (Castello Aragonese north and south sides, and Vullatura, Ischia, Italy) to assess the effect of a decrease of seawater pH on the settlement of Mollusca in Posidonia oceanica meadows, and to test the possible buffering effect provided by the seagrass. Artificial collectors were installed and collected after 33 days, during April–May 2019, in three different microhabitats within the meadow (canopy, bottom/rhizome level, and dead matte without plant cover), following a pH decreasing gradient from an extremely low pH zone (pH < 7.4), to ambient pH conditions (pH = 8.10). A total of 4659 specimens of Mollusca, belonging to 57 different taxa, were collected. The number of taxa was lower in low and extremely low pH conditions. Reduced mollusc assemblages were reported at the acidified stations, where few taxa accounted for a high number of individuals. Multivariate analyses revealed significant differences in mollusc assemblages among pH conditions, microhabitat, and the interaction of these two factors. Acanthocardia echinata, Alvania lineata, Alvania sp. juv, Eatonina fulgida, Hiatella arctica, Mytilys galloprovincialis, Musculus subpictus, Phorcus sp. juv, and Rissoa variabilis were the species mostly found in low and extremely low pH stations, and were all relatively robust to acidified conditions. Samples placed on the dead matte under acidified conditions at the Vullatura vent showed lower diversity and abundances if compared to canopy and bottom/rhizome samples, suggesting a possible buffering role of the Posidonia on mollusc settlement. Our study provides new evidence of shifts in marine benthic communities due to ocean acidification and evidence of how P. oceanica meadows could mitigate its effects on associated biota in light of future climate change.
Prior to fertilization, mothers provision their oocytes with mRNA that regulates the early stages of development and may additionally include transcripts for proteins that support embryonic stress response early on. At some point during embryogenesis, however, these maternal transcripts are degraded as zygotic transcription activates and intensifies during a phenomenon known as the maternal-to-zygotic transition (MZT). Some evidence suggests that as the MZT progresses, and the effects of maternal transcripts are waning while the zygotic expression is being established, offspring of marine broadcast spawners become more vulnerable to environmental perturbations. In light of escalating threats to marine broadcast spawners, it is critical to understand their reproduction and development, which are essential processes for species resilience by repopulating and replenishing existing populations. Reef building corals, in particular, are under threat from multiple stressors at the local and global scales. Mass mortality has occurred in recent years due to a series of marine heatwaves. In addition, there is chronic stress occurring in the form of ocean acidification, or the decline in pH in surface waters due to the uptake of atmospheric carbon dioxide of anthropogenic origin. Here, we characterize the function of maternal mRNAs, the timeline of the MZT, and sensitivity of gene expression to ocean acidification (OA) in the reef- building coral, Montipora capitata to investigate role of the MZT in embryonic stress response in reef-building corals.
Elevated atmospheric carbon dioxide (CO2) is causing global ocean changes and drives changes in organism physiology, life-history traits, and population dynamics of natural marine resources. However, our knowledge of the mechanisms and consequences of ocean acidification (OA) – in combination with other climatic drivers (i.e., warming, deoxygenation) – on organisms and downstream effects on marine fisheries is limited. Here, we explored how the direct effects of multiple changes in ocean conditions on organism aerobic performance scales up to spatial impacts on fisheries catch of 210 commercially exploited marine invertebrates, known to be susceptible to OA. Under the highest CO2 trajectory, we show that global fisheries catch potential declines by as much as 12% by the year 2100 relative to present, of which 3.4% was attributed to OA. Moreover, OA effects are exacerbated in regions with greater changes in pH (e.g., West Arctic basin), but are reduced in tropical areas where the effects of ocean warming and deoxygenation are more pronounced (e.g., Indo-Pacific). Our results enhance our knowledge on multi-stressor effects on marine resources and how they can be scaled from physiology to population dynamics. Furthermore, it underscores variability of responses to OA and identifies vulnerable regions and species.
Rapid evolution may provide a buffer against extinction risk for some species threatened by climate change; however, the capacity to evolve rapidly enough to keep pace with changing environments is unknown for most taxa. The ecosystem-level consequences of climate adaptation are likely to be the largest in marine ecosystems, where short-lived phytoplankton with large effective population sizes make up the bulk of primary production. However, there are substantial challenges to predicting climate-driven evolution in marine systems, including multiple simultaneous axes of change and considerable heterogeneity in rates of change, as well as the biphasic life cycles of many marine metazoans, which expose different life stages to disparate sources of selection. A critical tool for addressing these challenges is experimental evolution, where populations of organisms are directly exposed to controlled sources of selection to test evolutionary responses. We review the use of experimental evolution to test the capacity to adapt to climate change stressors in marine species. The application of experimental evolution in this context has grown dramatically in the past decade, shedding light on the capacity for evolution, associated trade-offs, and the genetic architecture of stress-tolerance traits. Our goal is to highlight the utility of this approach for investigating potential responses to climate change and point a way forward for future studies.
Oyster microbiomes are integral to healthy function and can be altered by climate change conditions. Genetic variation among oysters is known to influence the response of oysters to climate change and may ameliorate any adverse effects on oyster microbiome, however, this remains unstudied. Nine full-sibling selected breeding lines of the Sydney rock oyster (Saccostrea glomerata) were exposed to predicted warming (ambient = 24°C, elevated = 28°C) and ocean acidification (ambient pCO2 = 400, elevated pCO2 = 1000 µatm) for four weeks. The haemolymph bacterial microbiome was characterised using 16S rRNA (V3-V4) gene sequencing and varied among oyster lines in the control (ambient pCO2, 24°C) treatment. Microbiomes were also altered by climate change dependent on oyster lines. Bacterial α-diversity increased in response to elevated pCO2 in two selected lines, while bacterial β-diversity was significantly altered by combinations of elevated pCO2 and temperature in four selected lines. Climate change treatments caused shifts in the abundance of multiple Amplicon Sequence Variants (ASVs) driving change in the microbiome of some selected lines. We show that oyster genetic background may influence the Sydney rock oyster haemolymph microbiome under climate change and that future assisted evolution breeding programs to enhance resilience should consider the oyster microbiome.
- More simplified and modularized bacterial networks of rearing seawater under elevated pCO2.
- Changed abundances of CNPS cycling genes of seawater microbiome under elevated pCO2.
- Changed C, N, and P chemistry of rearing seawater under elevated pCO2.
- Seawater C, N, and P chemistry may be affected by future elevated pCO2 via seawater microbiome.
Mean oceanic CO2 values have already risen and are expected to rise further on a global scale. Elevated pCO2 (eCO2) changes the bacterial community in seawater. However, the ecological association of seawater microbiota and related geochemical functions are largely unknown. We provide the first evidence that eCO2 alters the interaction patterns and functional potentials of microbiota in rearing seawater of the swimming crab, Portunus trituberculatus. Network analysis showed that eCO2 induced a simpler and more modular bacterial network in rearing seawater, with increased negative associations and distinct keystone taxa. Using the quantitative microbial element cycling method, nitrogen (N) and phosphorus (P) cycling genes exhibited the highest increase after one week of eCO2 stress and were significantly associated with keystone taxa. However, the functional potential of seawater bacteria was decoupled from their taxonomic composition and strongly coupled with eCO2 levels. The changed functional potential of seawater bacteria contributed to seawater N and P chemistry, which was highlighted by markedly decreased NH3, NH4+-N, and PO43--P levels and increased NO2−-N and NO3−-N levels. This study suggests that eCO2 alters the interaction patterns and functional potentials of seawater microbiota, which lead to the changes of seawater chemical parameters. Our findings provide new insights into the mechanisms underlying the effects of eCO2 on marine animals from the microbial ecological perspective.
The sponge-associated microbial community contributes to the overall health and adaptive capacity of the sponge holobiont. This community is regulated by the environment, as well as the immune system of the host. However, little is known about the effect of environmental stress on the regulation of host immune functions and how this may, in turn, affect sponge-microbe interactions. In this study, we compared the microbiomes and immune repertoire of two sponge species, the demosponge, Neopetrosia compacta and the calcareous sponge, Leucetta chagosensis, under varying levels of acidification and warming stress. Neopetrosia compacta harbors a diverse bacterial assemblage and possesses a rich repertoire of scavenger receptors while L. chagosensis has a less diverse microbiome and an expanded range of pattern recognition receptors and proteins with immunological domains. Upon exposure to warming and acidification, the microbiome and host transcriptome of N. compacta remained stable, which correlated with high survival. In contrast, the bacterial community of L. chagosensis exhibited drastic restructuring and widespread downregulation of host immune-related pathways, which accompanied tissue necrosis and mortality. Differences in microbiome diversity and immunological repertoire of diverse sponge groups highlight the central role of host-microbe interactions in predicting the fate of sponges under future ocean conditions.