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Free Ocean CO2 Enrichment (FOCE) experiments are a relatively recent development in ocean acidification research, designed to address the need for in situ, long-term, community level experiments. FOCE studies have been conducted across different marine benthic habitats and regions, from Antarctica to the tropics. Based on this previous research we have formed some core operating principles that will aid those embarking on future FOCE experiments. FOCE studies have potential to provide important insight into the effects of ocean acidification that can add to or refine conclusions drawn from laboratory or single species studies because they are conducted in situ on intact assemblages. Scaling up from sub-organismal and individual effects to also include indirect impacts on the ecosystem and ecosystem services, make FOCE experiments essential in filling in current knowledge gaps in our understanding of ocean acidification. While FOCE systems are complex, relatively costly, and somewhat difficult to operate, the challenges they pose are tractable and they have proven to be a useful approach in ocean acidification research. The aim of this paper is to draw from the experiences of past FOCE experiments and provide practical advice for designing, building and operating a FOCE experiment. Some of the most important recommendations include: field testing the system design; having a backup power supply; using replicate treatment enclosures; monitoring and maintaining the chemistry appropriately; allowing sufficient time to achieve near CO2 equilibrium conditions; and having a scientific focus with a core set of hypotheses. Future FOCE experiments could focus on longer durations, multiple factors, and testing more intact benthic marine communities and ecosystems. We hope this paper will encourage further FOCE deployments and experiments, as well as provide some guidelines to improve future FOCE studies and advance ocean acidification research.

Free-ocean CO2 enrichment (FOCE) experiments have been deployed in marine ecosystems to manipulate carbonate system conditions to those predicted in future oceans. We investigated whether the pH/carbonate chemistry of extremely cold polar waters can be manipulated in an ecologically relevant way, to represent conditions under future atmospheric CO2 levels, in an in-situ FOCE experiment in Antarctica. We examined spatial and temporal variation in local ambient carbonate chemistry at hourly intervals at two sites between December and February and compared these with experimental conditions. We successfully maintained a mean pH offset in acidified benthic chambers of −0.38 (±0.07) from ambient for approximately 8 weeks. Local diel and seasonal fluctuations in ambient pH were duplicated in the FOCE system. Large temporal variability in acidified chambers resulted from system stoppages. The mean pH, Ωarag and fCO2 values in the acidified chambers were 7.688 ± 0.079, 0.62 ± 0.13 and 912 ± 150 µatm, respectively. Variation in ambient pH appeared to be mainly driven by salinity and biological production and ranged from 8.019 to 8.192 with significant spatio-temporal variation. This experiment demonstrates the utility of FOCE systems to create conditions expected in future oceans that represent ecologically relevant variation, even under polar conditions.

Reactive oxygen species (ROS) are implicated in the pathogenesis of stress-induced gastrointestinal injury. In the present study, we have investigated the effects of acute stress and chronic stress on the enhanced production of superoxide anion as determined by cytochrome c reduction assay, and correlated the enhanced production of superoxide anion with increased lipid peroxidation, DNA fragmentation and membrane microviscosity, indices of oxidative tissue injury, in gastric mucosa and intestinal mucosa, and determined the protective effects of a novel IH636 grape seed proanthocyanidin extract (GSPE) against mucosal injury. Acute stress was induced by water-immersion restraint stress for 90 min, while chronic stress was induced by water-immersion restraint stress for 15 min/day for 15 consecutive days. Half of the animals exposed to acute stress were pretreated orally with 100 mg GSPE/kg/day for 15 consecutive days. Similarly, half of the animals exposed to chronic stress were pretreated orally with 100 mg GSPE/kg/day for 15 consecutive days. Acute stress produced maximal injury to both gastric mucosa and intestinal mucosa as compared to chronic stress. Acute stress and chronic stress increased cytochrome c reduction by 12.2- and 4.8-fold, respectively, in the gastric mucosa, and 12.1- and 4.6-fold in the intestinal mucosa. Acute stress increased lipid peroxidation, DNA fragmentation and membrane microviscosity by 3.3-, 4.1- and 11.6-fold, respectively, in the gastric mucosa, and 4.4-, 5.2- and 16.6-fold, respectively, in intestinal mucosa. GSPE decreased acute stress-induced lipid peroxidation, DNA fragmentation and membrane microviscosity by 15%, 12% and 13%, respectively, in the gastric mucosa, and by 13%, 14% and 16%, respectively, in the intestinal mucosa. Chronic stress increased lipid peroxidation, DNA fragmentation and membrane microviscosity by 2.9-, 3.3- and 6.3- fold, respectively, in the gastric mucosa, and 3.3-, 4.2- and 9.3-fold, respectively, in the intestinal mucosa. GSPE decreased chronic stress-induced lipid peroxidation, DNA fragmentation and membrane microviscosity by 23%, 21% and 25%, respectively, in the gastric mucosa, and by 26%, 26% and 25%, respectively, in the intestinal mucosa. These results demonstrate that acute stress and chronic stress can induce gastrointestinal oxidative stress and mucosal injury through enhanced production of ROS, and that GSPE provides significant protection against gastrointestinal oxidative stress and mucosal injury by scavenging these ROS.

We demonstrate an electro-optic phase modulator based demodulation system for acoustic frequency modulated optical signals. The system is free from polarisation fading and is capable of retrieving high frequency signals, ultimately limited by the time of flight of the interferometer itself. Digital interrogation method is based on the Carre algorithm and does not require fine tuning of the introduced phase and is suitable for simultaneous phase retrieval at multiple wavelengths without the need for correction transfer filters.

A 16 element wavelength division multiplexed linear array of distributed feedback fibre lasers (DFB FL), pumped at 980 nm is reported. The array incorporates DFB FL technology specifically developed for optimal array multiplexing performance. This technology has important applications to all- optical underwater acoustic sensing. An overview of key technical issues in DFB FL multiplexing is also included.

A new fibre optic hydrophone based on a distributed feedback fibre laser (DFB FL) sensor is described. The sensor is designed to achieve ocean noise limited pressure sensitivity. Unlike previous fibre laser acoustic sensors, this device is acceleration insensitive making it less susceptible to vibrational noise. Experimental results for one implementation of the sensor are presented.