Free-ocean CO<sub>2</sub> enrichment (FOCE) systems: present status and future developments

Abstract

Abstract. Free-ocean CO 2 enrichment (FOCE) systems are designed to assess the impact of ocean acidification on biological communities in situ for extended periods of time (weeks to months). They overcome some of the drawbacks of laboratory experiments and field observations by enabling (1) precise control of CO 2 enrichment by monitoring pH as an offset of ambient pH, (2) consideration of indirect effects such as those mediated through interspecific relationships and food webs, and (3) relatively long experiments with intact communities. Bringing perturbation experiments from the laboratory to the field is, however, extremely challenging. The main goal of this paper is to provide guidelines on the general design, engineering, and sensor options required to conduct FOCE experiments. Another goal is to introduce xFOCE, a community-led initiative to promote awareness, provide resources for in situ perturbation experiments, and build a user community. Present and existing FOCE systems are briefly described and examples of data collected presented. Future developments are also addressed as it is anticipated that the next generation of FOCE systems will include, in addition to pH, options for oxygen and/or temperature control. FOCE systems should become an important experimental approach for projecting the future response of marine ecosystems to environmental change.

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“…Although information from long-term laboratory experiments is vital to reveal sensitivities of marine organisms, even they can still only predict responses from exposures of relatively short durations, of months or even a few years, to environmentally unrealistic conditions experiments, including in situ mesocosms (Nagelkerken & Munday, 2015) and CO 2 vent sites (Fabricius et al, 2011;Hall-Spencer et al, 2008;Uthicke et al, 2016), are another common approach which allows for the investigation of impacts on more long-term scales and also often include responses at the community level and the physical, chemical and biological variability in their natural environments that cannot be recreated in laboratory experiments. This method, however, has a lack of control of treatment conditions where organisms, for instance near vent sites, are locally exposed to significant short-term variation in pH levels as well as vents releasing other harmful substances (Gattuso et al, 2014). The newest methods in ocean acidification research are the free-ocean CO 2 enrichment (FOCE) systems, which are designed to assess the impact of lowered pH on biological communities in situ over weeks to months (Gattuso et al, 2014).…”

“…This method, however, has a lack of control of treatment conditions where organisms, for instance near vent sites, are locally exposed to significant short-term variation in pH levels as well as vents releasing other harmful substances (Gattuso et al, 2014). The newest methods in ocean acidification research are the free-ocean CO 2 enrichment (FOCE) systems, which are designed to assess the impact of lowered pH on biological communities in situ over weeks to months (Gattuso et al, 2014).…”

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“…However, day/night trends of dimethylated sulfur benthic flux across habitat types were less consistent, reflecting the increase in community complexity as one moves through ecological scales-intracellular DMSP concentrations were determined from the holobiont of individual organisms, whilst benthic exchange fluxes were determined at the ecosystem community level, i.e., integrating the interactive effect of multiple organisms and holobionts across multiple trophic levels. This underlines the importance of in situ measurements conducted at the community level, rather than on isolated individuals in controlled laboratory environments, for appreciating the true biological and biogeochemical complexity of natural marine systems (Gattuso et al, 2014).…”

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“…A FOCE system consists of one or more partially open mesocosms placed on the seabed in a natural ocean habitat and connected to a flume that directs the flow of ambient (control) or CO 2 -enriched (experimental) seawater through the mesocosm(s) (Gattuso et al, 2014). For experimental treatments, CO 2 -enriched seawater (produced by various methods) is injected into the flume upstream of the mesocosm location to permit equilibration of seawater carbonate chemistry prior to its entry into the mesocosm(s) (Kirkwood et al, 2015).…”

“…MBARI engineers and scientists developed a FOCE system for deep-sea studies ( Figure 5) and were involved in FOCE development at several global locations (Kline et al, 2012;Barry et al, 2014;Gattuso et al, 2014;Kirkwood et al, 2015). A FOCE system for nearshore, subtidal use in Monterey Bay is under development.…”