ALBERT

Description: Anthropogenic modification watersheds and climate change have altered export from fluvial systems causing changes to the carbonate chemistry of river-influenced near shore environments. To determine the possible effects of riverine discharges on the mussel Perumytilus purpuratus, we performed in situ transplant experiments between river-influenced and open coastal habitats with contrasting seawater carbonate chemistries (i.e., pCO2, pH, Omega ar) across four regions covering a wide latitudinal range (32°55'S-40°10'S). The river-influenced habitats selected for transplant experiments were different than open coastal habitats; with higher pCO2 (354-1313 µatm), lower pH (7.6?7.9) and Omega ar values (0.4?1.4) than in open coastal area. Growth, calcification, metabolism were measured in a reciprocal transplant experiment to determine physiological responses associated with river-influenced sites and non-influenced control sites. Growth and calcification rates were higher in river-influenced habitats; however the organisms in this area also had lower metabolic rates, possibly due to enhanced food supply from river systems. Further analysis of carbon isotopic composition (delta 13C) indicated that the relative contribution of seawater dissolved inorganic carbon (DIC) to the carbonate shells of P. purpuratus was much higher than respiratory carbon. Nevertheless, P. purpuratus incorporated between 7% and 26% of metabolic carbon in the shell depending on season. There was a strong, significant relationship between delta 13C POC and delta 13C Tissue, which likely influenced the isotopic composition of the shell carbon.

Description: Future ocean acidification (OA) will affect physiological traits of marine species, with calcifying species being particularly vulnerable. As OA entails high energy demands, particularly during the rapid juvenile growth phase, food supply may play a key role in the response of marine organisms to OA. We experimentally evaluated the role of food supply in modulating physiological responses and biomineralization processes in juveniles of the Chilean scallop, Argopecten purpuratus, that were exposed to control (pH 8.0) and low pH (pH 7.6) conditions using three food supply treatments (high, intermediate, and low). We found that pH and food levels had additive effects on the physiological response of the juvenile scallops. Metabolic rates, shell growth, net calcification, and ingestion rates increased significantly at low pH conditions, independent of food. These physiological responses increased significantly in organisms exposed to intermediate and high levels of food supply. Hence, food supply seems to play a major role modulating organismal response by providing the energetic means to bolster the physiological response of OA stress. On the contrary, the relative expression of chitin synthase, a functional molecule for biomineralization, increased significantly in scallops exposed to low food supply and low pH, which resulted in a thicker periostracum enriched with chitin polysaccharides. Under reduced food and low pH conditions, the adaptive organismal response was to trade-off growth for the expression of biomineralization molecules and altering of the organic composition of shell periostracum, suggesting that the future performance of these calcifiers will depend on the trajectories of both OA and food supply. Thus, incorporating a suite of traits and multiple stressors in future studies of the adaptive organismal response may provide key insights on OA impacts on marine calcifiers.

Description: Increased carbon dioxide levels (CO2) in the atmosphere triggered a cascade of physical and chemical changes in the ocean surface. Marine organisms producing carbonate shells are regarded as vulnerable to these physical (warming), and chemical (acidification) changes occurring in the oceans. In the last decade, the aquaculture production of the bivalve scallop Argopecten purpuratus (AP) showed declined trends along the Chilean coast. These negative trends have been ascribed to ecophysiological and biomineralization constraints in shell carbonate production. This work experimentally characterizes the biomechanical response of AP scallop shells subjected to climate change scenarios (acidification and warming) via quasi-static tensile and bending tests. The experimental results indicate the adaptation of mechanical properties to hostile growth scenarios in terms of temperature and water acidification. In addition, the mechanical response of the AP subjected to control climate conditions was analyzed with finite element simulations including an anisotropic elastic constitutive model for a two-fold purpose: Firstly, to calibrate the material model parameters using the tensile test curves in two mutually perpendicular directions (representative of the mechanical behavior of the material). Secondly, to validate this characterization procedure in predicting the material's behavior in two mechanical tests.

Description: We present experimental data obtained from an experiment with newly hatched veliger larvae of the gastropod Concholepas concholepas exposed to three pCO2 levels. Egg capsules were collected from two locations in northern and central Chile, and then incubated throughout their entire intra-capsular life cycle at three nominal pCO2 levels, 400, 700 and 1000 ppm (i.e. corresponding to 8.0, 7.8 and 7.6 pH units, respectively). Hatched larvae were fed with natural food assemblages. Food availability at time zero did not vary significantly with pCO2 level. Our results clearly showed a significant effect of elevated pCO2 on the intensity of larval feeding, which dropped by 〉60%. Incubation also showed that pCO2-driven ocean acidification (OA) may radically impact the selectivity of ingested food by C. concholepas larvae. Results also showed that larvae switched their clearance rate based on large cells, such as diatoms and dinoflagellates to tiny and highly abundant nanoflagellates and cyanobacteria as pCO2 levels increased. Thus, this study reveals the important effect of low pH conditions on larval feeding behavior, in terms of both ingestion magnitude and selectivity. These findings support the notion that larval feeding is a key physiological process susceptible to the effects of OA.

Description: Changes in phenotypic traits, such as mollusc shells, are indicative of variations in selective pressure along environmental gradients. Recently, increased sea surface temperature (SST) and ocean acidification (OA) due to increased levels of carbon dioxide in the seawater have been described as selective agents that may affect the biological processes underlying shell formation in calcifying marine organisms. The benthic snail Concholepas concholepas (Muricidae) is widely distributed along the Chilean coast, and so is naturally exposed to a strong physical-chemical latitudinal gradient. In this study, based on elliptical Fourier analysis, we assess changes in shell morphology (outlines analysis) in juvenile C. concholepas collected at northern (23°S), central (33°S) and southern (39°S) locations off the Chilean coast. Shell morphology of individuals collected in northern and central regions correspond to extreme morphotypes, which is in agreement with both the observed regional differences in the shell apex outlines, the high reclassification success of individuals (discriminant function analysis) collected in these regions, and the scaling relationship in shell weight variability among regions. However, these extreme morphotypes showed similar patterns of mineralization of calcium carbonate forms (calcite and aragonite). Geographical variability in shell shape of C. concholepas described by discriminant functions was partially explained by environmental variables (pCO2, SST). This suggests the influence of corrosive waters, such as upwelling and freshwaters penetrating into the coastal ocean, upon spatial variation in shell morphology. Changes in the proportion of calcium carbonate forms precipitated by C. concholepas across their shells and its susceptibility to corrosive coastal waters are discussed.

Description: This study evaluated the impact of medium-term exposure to elevated pCO2 levels (750-1200 ppm) on the physiological processes of juvenile Mytilus chilensis mussels over a period of 70 d in a mesocosm system. Three equilibration tanks filled with filtered seawater were adjusted to three pCO2 levels: 380 (control), 750 and 1200 ppm by bubbling air or an air-CO2 mixture through the water. For the control, atmospheric air (with aprox. 380 ppm CO2) was bubbled into the tank; for the 750 and 1200 ppm treatments, dry air and pure CO2 were blended to each target concentration using mass flow controllers for air and CO2. No impact on feeding activity was observed at the beginning of the experiment, but a significant reduction in clearance rate was observed after 35 d of exposure to highly acidified seawater. Absorption rate and absorption efficiency were reduced at high pCO2 levels. In addition, oxygen uptake fell significantly under these conditions, indicating a metabolic depression. These physiological responses of the mussels resulted in a significant reduction of energy available for growth (scope for growth) with important consequences for the aquaculture of this species during medium-term exposure to acid conditions. The results of this study clearly indicate that high pCO2 levels in the seawater have a negative effect on the health of M. chilensis. Therefore, the predicted acidification of seawater associated with global climate change could be harmful to this ecologically and commercially important mussel.

Description: Coastal upwelling regions already constitute hot spots of ocean acidification as naturally acidified waters are brought to the surface. This effect could be exacerbated by ocean acidification and warming, both caused by rising concentrations of atmospheric CO2. Along the Chilean coast, upwelling supports highly productive fisheries and aquaculture activities. However, during recent years, there has been a documented decline in the national production of the native scallop Argopecten purpuratus. We assessed the combined effects of temperature and pCO2-driven ocean acidification on the growth rates and shell characteristics of this species farmed under the natural influence of upwelling waters occurring in northern Chile (30°S, Tongoy Bay). The experimental scenario representing current conditions (14 °C, pH 8.0) were typical of natural values recorded in Tongoy Bay, whilst conditions representing the low pH scenario were typical of an adjacent upwelling area (pH 7.6). Shell thickness, weight, and biomass were reduced under low pH (pH 7.7) and increased temperature (18 °C) conditions. At ambient temperature (14 °C) and low pH, scallops showed increased shell dissolution and low growth rates. However, elevated temperatures ameliorated the impacts of low pH, as evidenced by growth rates in both pH treatments at the higher temperature treatment that were not significantly different from the control treatment. The impact of low pH at current temperature on scallop growth suggests that the upwelling could increase the time required for scallops to reach marketable size. Mortality of farmed scallops is discussed in relation to our observations of multiple environmental stressors in this upwelling-influenced area.

Description: Ocean Acidification (OA) has become one of the most studied global stressors in marine science during the last fifteen years. Despite the variety of studies on the biological effects of OA with marine commercial species, estimations of these impacts over consumers' preferences have not been studied in detail, compromising our ability to undertake an assessment of market and economic impacts resulting from OA at local scales. Here, we use a novel and interdisciplinary approach to fill this gap. We experimentally test the impact of OA on commercially relevant physical and nutritional attributes of mussels, and then we use economic discrete choice models to assess the marginal effects of these impacts over consumers' preferences and wellbeing. Results showed that attributes, which were significantly affected by OA, are also those preferred by consumers. Consumers are willing to pay on average 52% less for mussels with evidences of OA and are willing to increase the price they pay to avoid negative changes in attributes due to OA. The interdisciplinary approach developed here, complements research conducted on OA by effectively informing how OA economic impacts can be analyzed under the lens of marginal changes in market price and consumer' welfare. Thereby, linking global phenomena to consumers' wellbeing, and shifting the focus of OA impacts to assess the effects of local vulnerabilities in a wider context of people and businesses.

Description: We assess the role of direct and indirect effects of coastal environmental drivers (including the parameters of the carbonate system) on energy expenditure (MR) and body mass (M) of the intertidal mussel, Perumytilus purpuratus, across 10 populations distributed over 2800 km along the Southern Eastern Pacific (SEP) coast. We find biogeographic and local variation in carbonate system variables mediates the effects of latitude and temperature on metabolic rate allometry along the SEP coast. Also, the fitted Piecewise Structural Equation models (PSEM) have greater predictive ability (conditional R2 = 0.95) relative to the allometric scaling model (R2 = 0.35). The largest standardized coefficients for MR and M were determined by the influence of temperature and latitude, followed by pCO2, pH, total alkalinity, and salinity. Thus, physiological diversity of P. purpuratus along the SEP coast emerges as the result of direct and indirect effects of biogeographic and local environmental variables.