Articles | Volume 15, issue 8
Biogeosciences, 15, 2349–2360, 2018
Biogeosciences, 15, 2349–2360, 2018

Research article 19 Apr 2018

Research article | 19 Apr 2018

Natural ocean acidification at Papagayo upwelling system (north Pacific Costa Rica): implications for reef development

Celeste Sánchez-Noguera1,2, Ines Stuhldreier1,3, Jorge Cortés2, Carlos Jiménez4,5, Álvaro Morales2,6, Christian Wild3, and Tim Rixen1,7 Celeste Sánchez-Noguera et al.
  • 1Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany
  • 2Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Universidad de Costa Rica, San José, Costa Rica
  • 3Faculty of Biology and Chemistry (FB2), University of Bremen, Bremen, Germany
  • 4Energy, Environment and Water Research Center (EEWRC) of the Cyprus Institute (CyI), Nicosia, Cyprus
  • 5Enalia Physis Environmental Research Centre (ENALIA), Aglanjia, Nicosia, Cyprus
  • 6Escuela de Biología, University of Costa Rica, San José, Costa Rica
  • 7Institute of Geology, University Hamburg, Hamburg, Germany

Abstract. Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the 2009 upwelling season. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive intra- and interseasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH  =  7.8, pCO2  =  643.5 µatm), unveiling that natural acidification also occurs sporadically in the non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During the non-upwelling season, the aragonite saturation state (Ωa) rises to values of  >  3.3 and during the upwelling season falls below 2.5. The Ωa threshold values for coral growth were derived from the correlation between measured Ωa and coral linear extension rates which were obtained from the literature and suggest that future ocean acidification will threaten the continued growth of reefs in Bahía Culebra. These data contribute to building a better understanding of the carbonate system dynamics and coral reefs' key response (e.g., coral growth) to natural low-pH conditions, in upwelling areas in the eastern tropical Pacific and beyond.

Short summary
The Papagayo upwelling system is a natural laboratory for studying ecosystems' response to ocean acidification (OA). We measured pH and pCO2 in situ with high temporal resolution and compared them with data available from upwelling season. Local coral reefs are exposed to acidic and undersaturated waters in upwelling and non-upwelling events. These restrictive conditions occur alongside local stressors, potentially decreasing reefs' resilience and increasing their vulnerability under future OA.
Final-revised paper