Marine reserves contribute to multiple objectives stated in the UNESCO's 2030 Sustainability Agenda, for example, capturing CO₂ and regulating the climate, providing food and jobs, and increasing cultural heritage and biodiversity. At the central-northern Chilean coast, there is the national reserve Pingüino de Humboldt involving marine reserves in three small islands (Choros, Damas y Chañaral de Aceituno). The reserve was declared in 1990 becoming part of the National System of Protected Areas, having a management plan (Decree No. 159) since 2016 aimed at promoting scientific knowledge to generate baseline information for the conservation, management and marine exploitation of the natural resources of the marine reserve. However, till now, little is known about hydrographic and oceanographic processes regulating the productivity and biodiversity of the marine reserve, especially on basal trophic groups like plankton species. This information is critical to design the management and conservation efforts besides elucidating adaptive processes determining the tolerance to current and future environmental changes. The marine reserve is affected year-round by coastal upwelling promoting the irruption of cold, oxygen-poor and CO₂ rich (>800 µatm) subsurface waters. While oxygen deficient water might impact aerobic metabolism, high acidity water might constrain the metabolism of calcifying organisms and hence, the efficiency of the biological pump supporting higher trophic levels. Furthermore, the region is also affected by El Niño Southern Oscillation (ENSO) which, through high temperature waters, can synergistically impact basal biological processes supporting the biodiversity of the reserve. By means of discrete oceanographic campaigns and continuous measurements of temperature, oxygen, pH and salinity at two depths, the ENSO-Climate Change and the Carbon cycle in the Pacific South East (ECLIPSE) project is devoted to characterize the interannual pH variability in the marine reserve, as well as delineate biological responses to current and future progression of ocean acidification. Here we show preliminary results corresponding to eight months of observations during a period dominated by La Niña. Quality control tests and validation with reference material and higher accuracy measurements of pH, oxygen and salinity were carried before analysis. Stronger changes on hydrographic drivers occurred beyond the diurnal cycle such that under active upwelling, the marine reserve is exposed at either the surface (10 m) or depth (30 m) to pH levels as low as 7.77 and 7.62 pH_T, respectively. Periods with low pH conditions can last up to ten days, and variability and magnitude of pH changes are attenuated with depth. Low pH events were also associated (r²>0.6) with cold (12°C) and hypoxic (<1 mg/L) conditions suggesting upwelling might be the main local forcing of hydrographic fluctuations affecting the marine reserve. The influence of this local natural pH variability affecting adaptive processes of keystone plankton species is being currently assessed by means of grazing experiments. Together with environmental information, these biological observations will allow a more comprehensive understanding of processes determining the productivity and biodiversity of the marine reserve.

Primary Presenter: Victor Aguilera, Centro de Estudios Avanzados en Zonas Aridas (victor.aguilera@ceaza.cl)

Authors:

Linda Barranco, Centro de Estudios Avanzados en Zonas Aridas  (linda.barranco@gmail.com)

Katerin Aniñir, Centro de Estudios Avanzados en Zonas Aridas  (kataninir@gmail.com)

Carlos Henriquez, Centro de Estudios Avanzados en Zonas Aridas  (carlos.henriquez@ceaza.cl)

Victor Aguilera, Centro de Estudios Avanzados en Zonas Aridas  (victor.aguilera@ceaza.cl)