Scottish Marine and Freshwater Science Volume 5 Number 1: UK Ocean Acidification Coastal Monitoring Network - Expanding the Network - Defra Contract C5801/ME5309

Introduction

Ocean acidification is the decrease in the pH of the earth's oceans as a result of uptake of anthropogenic carbon dioxide (CO ₂) from the atmosphere ^[1] . It has been reported that a third of the anthropogenic CO ₂ (from activities such as fossil fuel burning) produced over the past 200 years has been absorbed by the oceans, resulting in a decrease in pH of 0.1 units ^[2] . By 2100 the pH is predicted to decrease by 0.4 units. Although the input of CO ₂ from the atmosphere has only small spatial variation, some marine regions will be more rapidly affected; the susceptibility of water chemistry to change is dependent on the chemical composition and temperature of the water. The limited data available worldwide shows that acidification does not occur uniformly. Spatial, seasonal and annual variations have been reported ^[3-5] , with variability naturally highest in coastal regions. It is, therefore, important to establish these natural variations by routine monitoring before changes due to anthropogenic inputs can be assessed. Ocean acidification and climate change share a common cause, increasing carbon dioxide (CO ₂) in the atmosphere. However, ocean acidification must be distinguished from climate change as it is not a climate process but rather an alteration to the chemistry of seawater.

There has been a great deal of interest in ocean acidification in recent years because of its potential effects on marine biogeochemistry and ecosystems. Atmospheric CO ₂ is in equilibrium with CO ₂ in the aqueous phase. As concentrations of CO ₂ increase in the atmosphere, DIC will increase resulting in an alteration to the carbonate system such that HCO ^-3 and CO ₂ will increase while CO ₃ ^-2 and pH will decrease ( Figure 1). CaCO ₃ saturation decreases with water depth, therefore, any reduction of CO ₃ ^-2 will potentially result in lowered saturation levels with increased dissolution and reduced saturation depths of marine carbonates such as aragonite, calcite and magnesian calcites ^[6,7] .

The effects of the decrease in seawater pH and changes to the saturation states of carbonates may be corrosive to the shells and skeletons of marine organisms, while the decrease in carbonate ions may affect organisms' abilities to build skeletons and shells, particularly among calcifying organisms ^[7] . In planktonic and benthic communities many may require more energy to obtain and produce the calcium carbonate required for skeletal or shell production. This may impact on other energy using functions such as fertilisation, development and growth. Studies have shown a decreased calcification when pH is decreased, with early life stages being particularly sensitive to acidification. CO ₂ effects will impact the metabolism and physiology of organisms in many ways, since factors such as acid - base balances and oxygen transport in cells and body fluids are affected by their pH.

Cold-water corals found in coastal areas, such as Mingulay reef complex in the Hebrides, may also be particularly sensitive to decreases in pH and CO ₂ ^-3. These coral colonies serve as shelter, feeding and breeding habitats for fish. Changes to coral habitats may, therefore, also impact the fish and other organisms living within them. Organisms which produce calcium carbonate from aragonite and magnesian calcite may be more susceptible to increases in CO ₂ concentrations because of the increasing solubility of these in acidifying seawater ^[7-10] .

Ocean acidification may also have socio-economic implications for the UK economy. Estimating the impact of ocean acidification to the economy, however, is difficult because the ability of marine species to adapt is unknown. Any impact on fertilisation, development and growth of marine species, as a result of ocean acidification, may impact fisheries as a food resource. It is estimated that 20% of the world's protein intake is from marine sources ^[11] . In 2010, 606,295 tonnes fish and 245,856 tonnes shellfish, were landed in the UK and Ireland. It is estimated that 30,000 people in the UK, alone, are dependent on fishing for their livelihoods ^[12] . The Marine Climate Change Impacts Partnership ( MCCIP) 2013 science review ^[13] predicted that ocean acidification (assuming a doubling of atmospheric CO ₂ and a 10-25% reduction in growth calcification) would result in a 10-25% loss in shellfish landings, equating to a loss of £100-500 million per year by 2080 from the UK economy. Coastal areas are also an important part of the UK leisure and recreation industry supporting employment and small businesses for activities such as diving, kayaking, sea angling, and marine mammal observations. Any change in coastal marine biodiversity as a result of ocean acidification may impact potential revenue. The effects of ocean acidification may, therefore, impact those involved in the fisheries and aquaculture industry, retailers, consumers and coastal communities.

In September 2010 the UK signed up to the OSPAR Bergen Statement, to which effect ministers have agreed to respond to new challenges and priorities including ocean acidification. Following on from the Bergen statement the OSPAR Coordination Group (CoG) met and agreed that ocean acidification will be a requirement of the Joint Assessment and Monitoring Programme ( JAMP) 2010-2014 ^[14] . The UK also has a commitment to fulfill Marine Strategy Framework Directive ( MSFD) requirements. Annex 3 of the Directive includes 'pH, pCO ₂ profiles or equivalent information used to measure marine acidification' as a characteristic under physical and chemical features.

The OSPAR Quality Status Report, published in September 2010 ^[5] , identified ocean acidification as an emerging concern for ecosystems and indicated that ecosystem-wide effects would be observed in the next 50 years. ICES highlighted the lack of data on seasonal and inter-annual variability, and advised that measurements should cover a range of waters ^[15] . Charting Progress 2 also highlighted 'the lack of baseline measurements of pH against which changes can be judged' and indicated that there was an upward trend in ocean acidification which could pose a threat to marine species and ecosystems. Both the OSPAR/ ICES Study Group on Ocean Acidification ( SGOA) ^[16] and the Global Ocean Acidification Observing Network (GOA-ON) ¹⁷ have identified particular gaps in data for coastal and inshore waters.

Limited monitoring of the changes in ocean acidification is undertaken in coastal waters around the UK. The UK Ocean Acidification Programme ( UKOA) funded a baseline study of carbonate chemistry parameters in UK waters, which included monitoring at the Cefas SmartBuoy sites over a 3 year period. It was agreed that additional monitoring would be undertaken for a short period in 2013 as a UK- IMON demonstration study.

The project was divided into two distinct parts, firstly a preliminary feasibility study to examine the use of moored water samplers to collect water samples for the analysis of dissolved inorganic carbon ( DIC) and secondly discrete sampling for TA and DIC analysis at five locations around the UK. Reported here are the results of both parts of the project.