Natural pH/pCO2 variability along Chilean coast, and the response of local populations of marine organisms upon future ocean acidification scenarios

Chair: Gretchen Hofmann

Cristian A. Vargas(1,2), Nelson A. Lagos(2,3) Marco A. Lardies(2,4) Cristian Duarte(2,5) Patricio H. Manríquez(6) & Víctor M. Aguilera(7)

1 Department of Aquatic System, Faculty of Environmental Sciences, Universidad de Concepcion, Concepcion, Chile & Millennium Institute of Oceanography (IMO), Universidad de Concepcion, Concepcion, Chile
2 Center for the Study of Multiple-Drivers on Marine Socio-Ecological Systems (MUSELS), Chile
3 Centro de Investigación e Innovación para el Cambio Climático (CiiCC), Facultad de Ciencias, Universidad Santo Tomás, Santiago, Chile
4 Facultad de Ingeniería y Facultad de Artes Liberales, Universidad Adolfo Ibáñez, Santiago, Chile
5 Departamento de Ecología y Biodiversidad, Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, Santiago Chile
6
Laboratorio de Ecología y Conducta de la Ontogenia Temprana (LECOT), Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, Chile 6 Instituto de Ciencias Naturales Alexander von Humboldt, Universidad de Antofagasta, Antofagasta, Chile

Background
Chilean coast is characterized by a by spatial-environmental heterogeneity in oceanographic conditions. Coastal upwelling areas and estuaries are commonly characterised by a strong CO2 outgassing. Acidic riverine waters, and/or low alkalinity waters from glacier melting, influence tidal inlets, fjords, and channels, which in turns results in high pCO2 surface waters. Marine biota inhabiting coastal environments are exposed to wide range of natural fluctuations of pH/pCO2, which may determine a tolerance level based on their natural range of exposure. This is highly relevant, when the scientific community consider standard pCO2 levels in ocean acidification (OA) experiments, which in turns might only reflect the natural variability to which the biota is exposed. Here, we analysed the environmental information available for different coastal ecosystems in order to characterise the pCO2 levels, and then to contextualize the responses of different marine organisms collected in these environments and exposed to high pCO2 levels at the laboratory (1000 atm).

Methods
Carbonate system information was collected through different field campaigns and scientific programs in order to estimate pCO2 upon seasonal contrasting conditions. Study sites involved coastal areas influenced by different oceanographic processes: river plumes, estuaries, upwelling areas, tidal inlets, river-influenced and glacier-influenced fjords, and from 23º-55º S. We have re-analysed information regarding the intraspecific variability in the physiological response of different taxa (i.e. copepods, gastropods and mussels) collected in these different environments upon exposition at high pCO2 conditions at the laboratory. The different physiological responses have been analysed in the context of the natural variability of their respective habitat.

Findings
Most coastal environments along Chilean coast are characterised by high pCO2 levels (400 up to 1000 atm). Therefore, the medium and high level of pCO2 typically used in many OA experiments worldwide (i.e. 750 to 1000-1200 µatm) represent a natural condition which can be observed along coastal areas.
The environmental history of pCO2 exposure at the different selected sites in our study could induce differential physiological resilience across the different taxa and may explain the differential responses upon high pCO2 observed in this study.

Conclusions
Ensuring realistic scenarios requires a step change in how experiments are design, communicated, and utilized elsewhere. Habitat-specific potential OA scenarios must be estimated in order to design experiments at realistic pCO2 levels for each environment.

Funding: NC120086, IC120019, FONDECYT 1130254
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Natural variability and anthropogenic change revealed by moored time series observations of pCO2 and pH

Sutton A, Sabine C, Feely R