ALBERT

Description: Deep-sea sediments constitute a unique archive of ocean change, fueled by a permanent rain of mineral and organic remains from the surface ocean. Until now, paleo-ecological analyses of this archive have been mostly based on information from taxa leaving fossils. In theory, environmental DNA (eDNA) in the sediment has the potential to provide information on non-fossilized taxa, allowing more comprehensive interpretations of the fossil record. Yet, the process controlling the transport and deposition of eDNA onto the sediment and the extent to which it preserves the features of past oceanic biota remains unknown. Planktonic foraminifera are the ideal taxa to allow an assessment of the eDNA signal modification during deposition because their fossils are well preserved in the sediment and their morphological taxonomy is documented by DNA barcodes. Specifically, we re-analyze foraminiferal-specific metabarcodes from 31 deep-sea sediment samples, which were shown to contain a small fraction of sequences from planktonic foraminifera. We confirm that the largest portion of the metabarcode originates from benthic bottom-dwelling foraminifera, representing the in situ community, but a small portion (〈10 %) of the metabarcodes can be unambiguously assigned to planktonic taxa. These organisms live exclusively in the surface ocean and the recovered barcodes thus represent an allochthonous component deposited with the rain of organic remains from the surface ocean. We take advantage of the planktonic foraminifera portion of the metabarcodes to establish to what extent the structure of the surface ocean biota is preserved in sedimentary eDNA. We show that planktonic foraminifera DNA is preserved in a range of marine sediment types, the composition of the recovered eDNA metabarcode is replicable and that both the similarity structure and the diversity pattern are preserved. Our results suggest that sedimentary eDNA could preserve the ecological structure of the entire pelagic community, including non-fossilized taxa, thus opening new avenues for paleoceanographic and paleoecological studies.

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: Environmental transitions leading to spatial physical-chemical gradients are of ecological and evolutionary interest because they are able to induce variations in phenotypic plasticity. Thus, the adaptive variability to low-pH river discharges may drive divergent stress responses [ingestion rates (IR) and expression of stress-related genes such as Heat shock protein 70 (Hsp70) and Ferritin] in the neritic copepod Acartia tonsa facing changes in the marine chemistry associated to ocean acidification (OA). These responses were tested in copepod populations inhabiting two environments with contrasting carbonate system parameters (an estuarine versus coastal area) in the Southern Pacific Ocean, and assessing an in situ and 96-h experimental incubation under conditions of high pressure of CO2 (PCO2 1200 ppm). Adaptive variability was a determining factor in driving variability of copepods' responses. Thus, the food-rich but colder and corrosive estuary induced a traits trade-off expressed as depressed IR under in situ conditions. However, this experience allowed these copepods to tolerate further exposure to high PCO2 levels better, as their IRs were on average 43% higher than those of the coastal individuals. Indeed, expression of both the Hsp70 and Ferritin genes in coastal copepods was significantly higher after acclimation to high PCO2 conditions. Along with other recent evidence, our findings confirm that adaptation to local fluctuations in seawater pH seems to play a significant role in the response of planktonic populations to OA-associated conditions. Facing the environmental threat represented by the inter-play between multiple drivers of climate change, this biological feature should be examined in detail as a potential tool for risk mitigation policies in coastal management arrangements.

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.