Award: OCE-1041062

Over the past 25 years changes in ocean circulation, coastal upwelling and atmospheric carbon dioxide have caused decline in the oxygen concentration and pH of NE Pacific coastal waters. To understand the ecological consequences of these changes we must know animal exposures. This study sought geochemical proxies (representative geochemical signatures) in carbonate structures (shells and statoliths, Fig. 1) to reflect the exposure of larval molluscs and squid embryos to low pH and low oxygen. Through a series of laboratory exposure experiments we identified the Uranium:Calcium (U:Ca) ratio as a valuable indicator of pH and carbonate ion concentration in 2 species of larval mussel shells. This performed better than any of the other (Mg:Ca, Cu:Ca, Zn:Ca, Sr:Ca, Ba:Ca, Pb:Ca) trace elements examined, alone or in combination. The U:Ca ratio was not altered by fluctuating pH (around the same mean) or by low oxygen. A field test using U:Ca and temperature data from previously outplanted larvae supported elevated U:Ca ratios under upwelling (low pH conditions). Zn:Ca was positively correlated with oxygen concentration in the open coast California mussel but no elements varied with oxygen in larval shells of the bay mussel. The U:Ca ratio was elevated in embryonic market squid statoliths (balance organs) reared under combined low pH and low oxygen conditions, but not under low pH alone. Normally squid can regulate conditions experienced by statoliths, which are isolated from the external environment by capsules, chorions and statocysts. Thus their chemistry is less likely to reflect pH stress, unless additional stress (e.g. low oxygen) inhibits acid-base regulations. Last Modified: 08/08/2014 Submitted by: Lisa A Levin