Project description:The association with photosymbiotic algae is crucial for the proliferation of many coral reef organisms, but increases their sensitivity to environmental changes. Large benthic foraminifera (LBF) are a diverse group of carbonate producers harboring algal photosymbionts. They act as key ecological engineers and are widely used as bioindicators. As in corals, elevated temperatures and light intensities are known to induce bleaching in LBF, but the combined effects of ocean acidification and warming remain unclear. To shed light into the adaptive physiology of LBF, we linked the assessment of the holobiont and photosymbiont physiological condition (mortality, growth, coloration, and chlorophyll a) to a bottom-up proteomics approach that allows the examination of cellular responses of host and symbionts simultaneously. In a two-months experiment, we exposed Amphistegina lobifera to the combined effects of ocean acidification (400, 1000 and 2800 ppm pCO2) and warming (28-control and 31°C). More than 1,000 proteins were identified by label-free mass spectrometry-based whole proteome analysis and assigned to the host or photosymbionts. Photopigment concentrations declined in response to elevated pCO2, visible by discoloration. These indicate the reduction of photosymbiont densities under ocean acidification, despite the fertilizing effects suggested for high inorganic carbon availability, and imply metabolic adjustments. Increases of proteolytic proteins suggest active host regulation of photosymbiont density in order to maintain homeostasis with its algal photosymbionts. Growth rates, however, were unaffected by elevated pCO2 levels at control temperatures, but high pCO2 levels (2800 ppm, pH 7.52) combined with thermal stress (31°C) impaired growth, though mortality and shell dissolution was negligible. While growth was unaffected by intermediate pCO2 levels (1000 ppm, pH 7.98) combined with ocean warming, this treatment induced the most distinct proteome responses. These include the regulation of ion transporters and host cytoplasmic proteins that likely abet calcification under ocean acidification. This study reveals a highly complex cellular response in both the host and the photosymbiont, which appears to facilitate a high resilience potential of A. lobifera to end of the century ocean conditions. Nevertheless, our results imply that when pCO2 levels rise above 1000 ppm during persistent ocean warming or extreme heating events these adaptive mechanisms become disrupted.

Project description:Increasing atmospheric CO2 concentrations are causing decreased pH over vast expanses of the ocean. This decreasing pH may alter biogeochemical cycling of carbon and nitrogen via the microbial process of nitrification, a key process that couples these cycles in the ocean, but which is often sensitive to acidic conditions. Recent reports indicate a decrease in oceanic nitrification rates under experimentally lowered pH. How composition and abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA) assemblages respond to decreasing oceanic pH, however, is unknown. We sampled microbes from two different acidification experiments and used a combination of qPCR and functional gene microarrays for the ammonia monooxygenase gene (amoA) to assess how acidification alters the structure of ammonia oxidizer assemblages. We show that despite widely different experimental conditions, acidification consistently altered the community composition of AOB by increasing the relative abundance of taxa related to the Nitrosomonas ureae clade. In one experiment this increase was sufficient to cause an increase in the overall abundance of AOB. There were no systematic shifts in the community structure or abundance of AOA in either experiment. These different responses to acidification underscore the important role of microbial community structure in the resiliency of marine ecosystems. amoA gene diversity from two ocean acidification experiments, Monterey Bay experiment (two time points, ambient and acidified) and Vineyard Sound experiment (ambient and acifidied, with and without nutrients) examined with 2 two-color arrays (Cy3 and Cy5): the universal standard 20-mer oligo is printed to the slide with a 70-mer oligo (an archetype). Environmental DNA sequences (fluoresced with Cy3) within 15% of the 70-mer conjugated to a 20-mer oligo (fluoresced with Cy5) complementary to the universal standard will bind to the oligo probes on the array. Signal is the ratio of Cy3 to Cy5.

Project description:In recent years, increasing levels of dissolved carbon dioxide in seawater have led to an increase of ocean acidification (OA), which constitutes a major threat to marine ecosystems. As an important economically marine bivalve, Mactra veneriformis is highly susceptible to ocean acidification. In this study, we recorded and observed the mortality rate, oxygen consumption rate and ammonia excretion rate of different shell colour groups of M. veneriformis under the stress of ocean acidification (pH=7.6), and conducted transcriptome analysis of the mantle tissues of M. veneriformis with white and purple shell colours in the acidified group (pH=7.6) and the control group (pH=8.1) under the two conditions, which showed that there was a significant difference in mortality rate between the acidified group and the control group at day 30, but there was a significant difference in mortality rate between the white colors group and the purple colors group at day 30, which was not significant. The results showed that there was a significant difference in mortality between the acidified and control groups at day 30, but the difference in mortality between the white and purple shell colour groups at day 30 was not significant. In the transcriptome analysis, fatty acid synthase gene was up-regulated in two shell colours of M. veneriformis under acidification stress, which may be a molecular compensatory mechanism to reduce the susceptibility of organisms to oxidative damage of lipids; tyrosinase gene was up-regulated, which may be a compensatory mechanism of Tyr's regulatory mechanism to the formation of shell damages under acidification; carbonic anhydrase gene was up-regulated in the purple group of M. veneriformis under acidification stress, which may be a compensatory mechanism for the acidity of M. veneriformis to cope with environmental stress; the white group of M. veneriformis under acidification stress was up-regulated. The carbonic anhydrase gene was up-regulated in the purple group under acidification stress, which may be an acidity compensation mechanism of M. veneriformis in response to the environmental stress.

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