Food availability outweighs ocean acidification effects in juvenileMytilus edulis: laboratory and field experiments

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless in many coastal areas high pCO2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg-1) and CO2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO2 variability in this habitat and the combined effects of elevated pCO2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal pCO2 variability. During summer, maximal pCO2 values of 2500 μatm were observed at the surface and >3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO2 inner fjord field station (mean pCO2 ca. 1000 μatm) in comparison to a low pCO2 outer fjord station (ca. 600 μatm). In addition, mussels were able to outcompete the barnacle Amphibalanus improvisus at the high pCO2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO2. At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification

Effects of elevated seawater pCO2 on gene expression patterns in the gills of the green crab, Carcinus maenas

Background: The green crab Carcinus maenas is known for its high acclimation potential to varying environmental abiotic conditions. A high ability for ion and acid-base regulation is mainly based on an efficient regulation apparatus located in gill epithelia. However, at present it is neither known which ion transport proteins play a key role in the acid-base compensation response nor how gill epithelia respond to elevated seawater pCO2 as predicted for the future. In order to promote our understanding of the responses of green crab acid-base regulatory epithelia to high pCO2, Baltic Sea green crabs were exposed to a pCO2 of 400 Pa. Gills were screened for differentially expressed gene transcripts using a 4,462-feature microarray and quantitative real-time PCR. Results: Crabs responded mainly through fine scale adjustment of gene expression to elevated pCO2. However, 2% of all investigated transcripts were significantly regulated 1.3 to 2.2-fold upon one-week exposure to CO2 stress. Most of the genes known to code for proteins involved in osmo- and acid-base regulation, as well as cellular stress response, were were not impacted by elevated pCO2. However, after one week of exposure, significant changes were detected in a calcium-activated chloride channel, a hyperpolarization activated nucleotide-gated potassium channel, a tetraspanin, and an integrin. Furthermore, a putative syntaxin-binding protein, a protein of the transmembrane 9 superfamily, and a Cl-/HCO3 - exchanger of the SLC 4 family were differentially regulated. These genes were also affected in a previously published hypoosmotic acclimation response study. Conclusions: The moderate, but specific response of C. maenas gill gene expression indicates that (1) seawater acidification does not act as a strong stressor on the cellular level in gill epithelia; (2) the response to hypercapnia is to some degree comparable to a hypoosmotic acclimation response; (3) the specialization of each of the posterior gill arches might go beyond what has been demonstrated up to date; and (4) a re-configuration of gill epithelia might occur in response to hypercapnia

Near-future CO2 levels impair the olfactory system of a marine fish

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordData availability: All raw sequence data are accessible at the NCBI Sequence Read Archive through accession number SRP097118. Water chemistry, behaviour and electrophysiology data are available through Pangaea (https://doi.pangaea.de/10.1594/PANGAEA.884674).Survival of marine fishes that are exposed to elevated near-future CO2levels is threatened by their altered responses to sensory cues. Here we demonstrate a physiological and molecular mechanism in the olfactory system that helps to explain altered behaviour under elevated CO2. We combine electrophysiology measurements and transcriptomics with behavioural experiments to investigate how elevated CO2affects the olfactory system of European sea bass (Dicentrarchus labrax). When exposed to elevated CO2(approximately 1,000 µatm), fish must be up to 42% closer to an odour source for detection, compared with current CO2levels (around 400 µatm), decreasing their chances of detecting food or predators. Compromised olfaction correlated with the suppression of the transcription of genes involved in synaptic strength, cell excitability and wiring of the olfactory system in response to sustained exposure to elevated CO2levels. Our findings complement the previously proposed impairment of γ-aminobutyric acid receptors, and indicate that both the olfactory system and central brain function are compromised by elevated CO2levels.This study was supported by grants from Association of European Marine Biology Laboratories (227799), the Natural Environment Research Council (R.W.W.; NE/H017402/1), the Biotechnology and Biological Sciences Research Council (R.W.W.; BB/D005108/1), Fundação para a Ciência e Tecnologia (Portuguese Science Ministry) (UID/Multi/04326/2013) and a Royal Society Newton International Fellowship to C.S.P. C.S.P. is also a beneficiary of a Starting Grant from AXA

Impact of high CO2 concentrations on marine life: Molecular mechanisms and physiological adaptations of pH and ion regulation in marine fish.

In this thesis, the impact of hypercapnia (elevated PCO2) on the mechanisms of ion regulation and on energy metabolism, as well as the patterns of genetic regulation in marine fish was studied. Hypercapnia had no impact on oxygen consumption of whole animals and isolated gills. However, the energy allocation in gills shifted significantly towards ion regulation, protein- and RNA-biosynthesis. From regulation patterns of branchial ion transporters a biphasic acclimation model was elaborated: Within the initial phase, pH recovery is supported by transient downregulation of Na /H -exchanger (NHE1), Na /HCO3--cotransporter (NBC1) and Cl-/HCO3--exchanger (AE1) and increase of Na /K -ATPase (NKA), while long-term elevated levels of NKA and NBC1 maintain the new ion equilibrium. Acute response of the total branchial transcriptome was studied by differentially regulated genes obtained from cDNA libraries. Further processes responsive to hypercapnia were identified, such as stress responses and shifts in metabolic fluxes. The key processes of hypercapnia acclimation identified in the present thesis may serve as sensitive biomarkers for future studies

Auswirkungen erhöhter CO2-Konzentrationen auf das Leben im Meer: Molekulare Mechanismen physiologischer Anpassungen der pH- und Ionenregulation mariner Fische

In this thesis, the impact of hypercapnia (elevated PCO2) on the mechanisms of ion regulation and on energy metabolism, as well as the patterns of genetic regulation in marine fish was studied. Hypercapnia had no impact on oxygen consumption of whole animals and isolated gills. However, the energy allocation in gills shifted significantly towards ion regulation, protein- and RNA-biosynthesis. From regulation patterns of branchial ion transporters a biphasic acclimation model was elaborated: Within the initial phase, pH recovery is supported by transient downregulation of Na /H -exchanger (NHE1), Na /HCO3--cotransporter (NBC1) and Cl-/HCO3--exchanger (AE1) and increase of Na /K -ATPase (NKA), while long-term elevated levels of NKA and NBC1 maintain the new ion equilibrium. Acute response of the total branchial transcriptome was studied by differentially regulated genes obtained from cDNA libraries. Further processes responsive to hypercapnia were identified, such as stress responses and shifts in metabolic fluxes. The key processes of hypercapnia acclimation identified in the present thesis may serve as sensitive biomarkers for future studies