Beschreibung: This dataset results from two, month-long global change laboratory experiments conducted in Sitka, Alaska from February 12 to March 18, 2020 (winter experiment) and August 15 to September 16, 2020 (summer experiment). These experiments were used to tease apart the effects of seasonal variation in light availability and nutrients on the response of three high-latitude kelp species (Macrocystis pyrifera, Hedophyllum nigripes, and Neoagarum fimbriatum) to pH and temperature. Experimental controls were designed to approximate current environmental conditions in Sitka Sound, and treatments were based on projected end-of-century scenarios of ocean acidification (OA) and warming (OW) for this region. At the end of the experiments, the investigators assessed the seasonal impact of OW and OA on kelp growth rates, thallus nitrogen content, and carbon acquisition strategy based on thallus δ13C values. Finally, to test whether kelp palatability was impacted by future warming and acidification, tissue of H. nigripes and N. fimbriatum grown during the experiments was used to perform feeding assays with a common kelp forest consumer.

Beschreibung: We present measured and estimated seawater physiochemical parameters at CO2 vents and ambient pH sites along the coast of Ischia (Italy) across water depths from 1 m to 40 m. We characterized the physical and chemical parameters in four CO2 venting sites (vent 1 to vent 4) and reference sites with ambient pH with no venting activity (two reference sites for each CO2 vent). SeaFETTM Ocean pH sensors (Satlantic) were deployed to quantify variation in pH at the CO2 vents and their corresponding ambient pH sites at the same depths where benthic surveys were performed from May to October 2019. Before deployment, the SeaFETs were calibrated with ambient pH water. The mean offset between calibration samples and calibrated SeaFET pH was ± 0.006 units (n= 44 water samples), indicating a high-quality pH dataset. The pH sensors were deployed in the recently discovered CO2 vents (Vent 2, Vent 3, Vent 4) and one of the corresponding reference areas with no visible vent activity during the same period (ambient 2a, ambient 3a, ambient 4a). The pH and seawater physicochemical parameters for vent 1 and their corresponding ambient sites (site Castello Aragonese) are also included here. This data from the Castello Aragonese site was originally reported by Kroeker et al., 2011. Discrete water samples were collected using Niskin bottles at the vent and reference areas with ambient pH to measure: i) the carbonate system parameters during the pH sensor deployment, and ii) the dissolved inorganic nutrients. Salinity was measured using a CTD (CTD Sea-Bird Electronics SBE 19 Plus Seacat). Discrete water samples for total alkalinity (AT) were collected within 0.25 m of the pH sensors using standard operating protocols. Precision of the AT measurements of CRMs was 〈 2 μmol kg-1 from nominal values. AT and pHT along with in situ temperature and depth were used to determine the remaining carbonate system parameters for each sampling period using the R package seacarb v3.2.12 (Gattuso et al., 2023).

Beschreibung: Acidification-induced changes in neurological function have been documented in several tropical marine fishes. Here, we investigate whether similar patterns of neurological impacts are observed in a temperate Pacific fish that naturally experiences regular and often large shifts in environmental pH/pCO2. In two laboratory experiments, we tested the effect of acidification, as well as pH/pCO2 variability, on gene expression in the brain tissue of a common temperate kelp forest/estuarine fish, Embiotoca jacksoni. Experiment 1 employed static pH treatments (target pH = 7.85/7.30), while Experiment 2 incorporated two variable treatments that oscillated around corresponding static treatments with the same mean (target pH = 7.85/7.70) in an eight-day cycle (amplitude ± 0.15). We found that patterns of global gene expression differed across pH level treatments. Additionally, we identified differential expression of specific genes and enrichment of specific gene sets (GSEA) in comparisons of static pH treatments and in comparisons of static and variable pH treatments of the same mean pH. Importantly, we found that pH/pCO2 variability decreased the number of differentially expressed genes detected between high and low pH treatments, and that inter-individual variability in gene expression was greater in variable treatments than static treatments. These results provide important confirmation of neurological impacts of acidification in a temperate fish species and, critically, that natural environmental variability may mediate the impacts of ocean acidification.

Beschreibung: It is well understood that differences in the cues used by consumers and their resources in fluctuating environments can give rise to trophic mismatches governing the emergent effects of global change. Trophic mismatches caused by changes in consumer energetics during periods of low resource availability have received far less attention, although this may be common for consumers during winter when primary producers are limited by light. Even less is understood about these dynamics in marine ecosystems, where consumers must cope with energetically costly changes in CO2‐driven carbonate chemistry that will be most pronounced in cold temperatures. This may be especially important for calcified marine herbivores, such as the pinto abalone (Haliotis kamschatkana). H. kamschatkana are of high management concern in the North Pacific due to the active recreational fishery and their importance among traditional cultures, and research suggests they may require more energy to maintain their calcified shells and acid/base balance with ocean acidification. Here we use field surveys to demonstrate seasonal mismatches in the exposure of marine consumers to low pH and algal resource identity during winter in a subpolar, marine ecosystem. We then use these data to test how the effects of exposure to seasonally relevant pH conditions on H. kamschatkana are mediated by seasonal resource identity. We find that exposure to projected future winter pH conditions decreases metabolism and growth, and this effect on growth is pronounced when their diet is limited to the algal species available during winter. Our results suggest that increases in the energetic demands of pinto abalone caused by ocean acidification during winter will be exacerbated by seasonal shifts in their resources. These findings have profound implications for other marine consumers and highlight the importance of considering fluctuations in exposure and resources when inferring the emergent effects of global change.

Beschreibung: Percent cover of 215 benthic species was quantified using two approaches with scuba diving: i) visual census techniques in Shallow Reef (benthic surveys were performed from 0.5 to 3 m depth) and Reef habitats (benthic surveys at ~10 m depth) dominated by algae and ii) photographic surveys in Caves (benthic surveys at ~3 m depth) and Deep Reef habitats (benthic surveys at ~ 40 m depth) dominated by sessile invertebrate animals. For visual censuses, 12 quadrats (25x25 cm) were haphazardly placed at Vent 1 and Vent 3 and the two corresponding ambient pH sites (n = 3 sites per habitat, n = 36 quadrats for Shallow Reefs and Reefs, respectively). For photographic surveys, 48–54 and 24 photoquadrats (25x25 cm) were taken at Vent 2 and Vent 4 and the two corresponding reference sites with ambient pH for each habitat (n = 3 sites per habitat, n = 144 photographic quadrats for Caves and n = 72 photographic quadrats for Deep Reefs, respectively). Both types of quadrats (visual censuses in the field and photographs in the lab) were divided into a grid of 25 squares (5 cm x 5 cm each). Percentage cover was quantified by counting the number of squares filled in the grid by the species and expressing the final values as relative percentages.

Beschreibung: Ocean acidification is predicted to impact all areas of the oceans and affect a diversity of marine organisms. However, the diversity of responses among species prevents clear predictions about the impact of acidification at the ecosystem level. Here, we used shallow water CO2 vents in the Mediterranean Sea as a model system to examine emergent ecosystem responses to ocean acidification in rocky reef communities. We assessed in situ benthic invertebrate communities in three distinct pH zones (ambient, low, and extreme low), which differed in both the mean and variability of seawater pH along a continuous gradient. We found fewer taxa, reduced taxonomic evenness, and lower biomass in the extreme low pH zones. However, the number of individuals did not differ among pH zones, suggesting that there is density compensation through population blooms of small acidification-tolerant taxa. Furthermore, the trophic structure of the invertebrate community shifted to fewer trophic groups and dominance by generalists in extreme low pH, suggesting that there may be a simplification of food webs with ocean acidification. Despite high variation in individual species' responses, our findings indicate that ocean acidification decreases the diversity, biomass, and trophic complexity of benthic marine communities. These results suggest that a loss of biodiversity and ecosystem function is expected under extreme acidification scenarios.

Beschreibung: Understanding species' responses to upwelling may be especially important in light of ongoing environmental change. Upwelling frequency and intensity are expected to increase in the future, while ocean acidification and deoxygenation are expected to decrease the pH and dissolved oxygen of upwelled waters. However, the acute effects of a single upwelling event and the integrated effects of multiple upwelling events on marine organisms are poorly understood. Here, we use in situ measurements of pH, temperature, and dissolved oxygen to characterize the covariance of environmental conditions within upwelling-dominated kelp forest ecosystems. We then test the effects of acute (0-3 days) and chronic (1-3 month) upwelling on the performance of two species of kelp forest grazers, the echinoderm, Mesocentrotus franciscanus, and the gastropod, Promartynia pulligo. We exposed organisms to static conditions in a regression design to determine the shape of the relationship between upwelling and performance and provide insights into the potential effects in a variable environment. We found that respiration, grazing, growth, and net calcification decline linearly with increasing upwelling intensity for M. francicanus over both acute and chronic timescales. Promartynia pulligo exhibited decreased respiration, grazing, and net calcification with increased upwelling intensity after chronic exposure, but we did not detect an effect over acute timescales or on growth after chronic exposure. Given the highly correlated nature of pH, temperature, and dissolved oxygen in the California Current, our results suggest the relationship between upwelling intensity and growth in the 3-month trial could potentially be used to estimate growth integrated over long-term dynamic oceanographic conditions for M. franciscanus. Together, these results indicate current exposure to upwelling may reduce species performance and predicted future increases in upwelling frequency and intensity could affect ecosystem function by modifying the ecological roles of key species.

Beschreibung: Despite a growing interest in identifying tipping points in response to environmental change, our understanding of the ecological mechanisms underlying non-linear ecosystem dynamics is limited. Ecosystems governed by strong species interactions can provide important insight into how non-linear relationships between organisms and their environment propagate through ecosystems, and the potential for environmentally mediated species interactions to drive or protect against sudden ecosystem shifts. Here, we experimentally determine the functional relationships (i.e., the shapes of the relationships between predictor and response variables) of a seagrass assemblage with well-defined species interactions to ocean acidification (enrichment of CO2) in isolation and in combination with nutrient loading. We demonstrate that the effect of ocean acidification on grazer biomass (Phyllaplysia taylori and Idotea resecata) was quadratic, with the peak of grazer biomass at mid-pH levels. Algal grazing was negatively affected by nutrients, potentially due to low grazer affinity for macroalgae (Ulva intestinalis), as recruitment of both macroalgae and diatoms were favored in elevated nutrient conditions. This led to an exponential increase in macroalgal and epiphyte biomass with ocean acidification, regardless of nutrient concentration. When left unchecked algae can cause declines in seagrass productivity and persistence through shading and competition. Despite quadratic and exponential functional relationships to stressors that could cause a non-linear decrease in seagrass biomass, productivity of our model seagrass – the eelgrass (Zostera marina)- remained highly resilient to increasing acidification. These results suggest that important species interactions governing ecosystem dynamics may shift with environmental change, and ecosystem state may be decoupled from ecological responses at lower levels of organization.

Beschreibung: Variation in environmental conditions across a species' range can alter their responses to environmental change through local adaptation and acclimation. Evolutionary responses, however, may be challenged in ecosystems with tightly coupled environmental conditions, where changes in the covariance of environmental factors may make it more difficult for species to adapt to global change. Here, we conduct a 3-month-long mesocosm experiment and find evidence for local adaptation/acclimation in populations of red sea urchins, Mesocentrotus franciscanus, to multiple environmental drivers. Moreover, populations differ in their response to projected concurrent changes in pH, temperature, and dissolved oxygen. Our results highlight the potential for local adaptation/acclimation to multivariate environmental regimes but suggest that thresholds in responses to a single environmental variable, such as temperature, may be more important than changes to environmental covariance. Therefore, identifying physiological thresholds in key environmental drivers may be particularly useful for preserving biodiversity and ecosystem functioning.

Beschreibung: We report on fine taxonomic and functional analyses of polychaetes associated with rocky reefs along a gradient of ocean acidification (OA) at the volcanic CO2 vent system off the Castello Aragonese (Ischia Island, Italy). Percent cover of algae and sessile invertebrates (a determinant of polychaete distribution) was classified into functional groups to disentangle the direct effects of low pH on polychaete abundance from the indirect effects of pH on habitat and other species associations. A total of 6459 polychaete specimens belonging to 83 taxa were collected. Polychaete species richness and abundance dramatically dropped under the extreme low pH conditions due to the disappearance of both calcifying and non-calcifying species. Differences in distribution patterns indicate that the decreasing pH modified the structure and biological traits of polychaete assemblages independent of changes in habitat. A detailed taxonomic analysis highlighted species-specific responses to OA, with closely related species having opposing responses to decreasing pH. This resulted in an increase in the abundance of filter feeders and herbivores with decreasing pH, while sessile polychaetes disappeared in the extreme low pH zones, and were replaced by discretely motile forms. Reproductive traits of the polychaete assemblages changed as well, with brooding species dominating the most acidified zones. The few taxa that were abundant in extreme low pH conditions showed high tolerance to OA (e.g. Amphiglena mediterranea, Syllis prolifera, Platynereis cf. dumerilii, Parafabricia mazzellae, Brifacia aragonensis), and are promising models for further studies on the responses of benthic organisms to the effects of reduced pH.