The Coral Proto - Free Ocean Carbon Enrichment system (CP-FOCE): Engineering and development

Ocean acidification is driven by increasing atmospheric CO₂ and represents a key threat to the Great Barrier Reef (GBR) and other coral reefs globally. Previous investigations have depended on studies in aquaria that are compromised by reduced ecological complexity and buffering capacity, and problems associated with containment. These aquaria studies also include artifacts such as artificial flow, light, temperature, and water quality conditions. In order to avoid these issues a new technology was needed for in situ science. This need was the driver behind development of the Free Ocean Carbon Enrichment (FOCE) approach. FOCE is similar in approach to the Free Air Carbon Enrichment (FACE) experiments pursued on land for almost two decades. FOCE as a systems concept was developed at the Monterey Bay Aquarium Research Institute (MBARI) to perform controlled in situ studies on the effects of increased carbon dioxide on ocean environments. FOCE systems inject carbon dioxide enriched water into the desired control volume to lower the environmental pH to a specified value. The challenge of maintaining reef conditions while manipulating the carbonate chemistry further advanced the FOCE concept. A shallow water reef version of FOCE was needed to perform this research at the University of Queensland. Working with MBARI the University of Queensland developed the Coral Proto - Free Ocean Carbon Dioxide Enrichment (CP - FOCE) system. Although the CP-FOCE does not differ conceptually from the original FOCE it is different in a couple of respects. First, it requires that a region of the coral flat be semi-enclosed in the chamber section of CP-FOCE. This allows the required amount of CO₂ to be optimised. Second, by closing the enclosure off fully for a short time, the oxygen levels and carbonate chemistry can be accurately measured to determine net production/respiration as well as the calcification/dissolution rates of the organisms living within the chamber. In this paper we present the engineering details of the CP-FOCE system design. This paper details the unique engineering design and challenges of the CP-FOCE system The paper briefly outlines the chemical and biological requirements that provided the technical specifications for CP-FOCE to successfully study the impacts of the changing water chemistry on the physiology of calcareous reef organisms including corals and calcareous algae. We have also a brief outline of the methods used to perform measurements of calcification and dissolution rates. Additionally, we include discussion on production and respiration rates in CP-FOCE systems when maintained at ambient and two different increased pCO₂ scenarios. We present technical results of this first deployment and address future plans for modifications and deployments of CP-FOCE. Forthcoming peer reviewed papers will describe the biological, chemical, and geochemical responses.