Inorganic carbon dynamics in the upwelling system off the Oregon coast and implications for commercial shellfish hatcheries

The increasing absorption of anthropogenic CO2 by the global ocean and concomitant decrease in pH will alter seawater carbonate chemistry in ways that may negatively impact calcifying organisms. In particular, the change in saturation state (Ω) of calcium carbonate minerals calcite and aragonite may be energetically unfavorable for shell formation while favoring shell dissolution. Eastern boundary upwelling systems may provide insights into how ecosystems respond to future conditions of ocean acidification when deep water with high dissolved inorganic carbon (DIC), low pH and low Ω is forced toward the surface. Mortality in commercial seed stock and reduced wild set of the oyster Crassostrea gigas in the northeast Pacific during 2005-2009 reinforced the need for understanding biological responses to acidified ocean water. In response, a long-term strategy to understand local carbonate chemistry dynamics, seasonal perturbations and the effects on development of calcifying bivalves was developed. At present, a time-series of pCO2 measurements was implemented in April 2010 in Netarts Bay, Oregon at Whiskey Creek Shellfish Hatchery (WCH). The intake sits at a depth of 0.5-8ft and water is pumped in at 100gpm. A line taken off the intake is run continuously through a thermosalinograph at approximately 1.5gpm into a showerhead style equilibrator in which the headspace is recirculated by aerating the water for enhanced gas exchange. CO2 in equilibrated air is analyzed by NDIR. Additionally two discrete samples of intake seawater were taken across tidal cycles weekly and analyzed for total CO2 (TCO2) according to the methods of Hales et al. (2004) and pCO2 for quality control. The pCO2 in the bay exhibits a diurnal cycle representative of daytime photosynthesis and nighttime respiration. However, the phasing and profiles of these cycles are dominated by tidal mixing and are affected by the introduction of high pCO2 water during upwelling events. Diurnal pCO2 during periods of low wind stress ranges from 100-700µatm. When strong equatorward winds induce upwelling, pCO2 levels exhibit a higher daily range of 300-2000µatm. The saturation state was calculated from the pCO2/TCO2 measurements of the discrete samples. The Ω for calcite and aragonite ranged from 2.07 and 1.15 to 8.58 and 4.69 respectively from April through August. Increased pCO2 and decreased pH have been shown to negatively impact larval development in C. gigas (Kurihara, 2007). Periods of elevated pCO2 in May and June 2010 correlated with commercial losses at WCH. The use of precise pCO2 measurements in real time has proven to be a valuable tool for use in aquaculture. As a commercial practice WCH has elected to only use source water that is below empirical pCO2 thresholds for spawning and culturing larvae. This has resulted in continued production and cost saving in an industry crucial to coast economies. A continuous TCO2/pCO2 monitoring system will be integrated into this long time-series to constrain inorganic carbon providing insight into carbonate chemistry dynamics in Netarts Bay, effects of ocean acidification on bivalve development and possible water treatment approaches for commercial aquaculture.

Vance, J. M. & Hales, B. R., 2010. Inorganic carbon dynamics in the upwelling system off the Oregon coast and implications for commercial shellfish hatcheries. American Geophysical Union, Fall Meeting 2010, abstract #OS31E-07. Abstract.

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