ALBERT

Description: The emission of anthropogenic carbon dioxide leads to the lowering of seawater pH. Ocean acidification is a major problem for marine calcifying organisms. There is a need to study short- and long-term effects of lowered pH on marine organisms such as oysters. Oysters are an important food source and useful for nutrients recycling in the coastal estuarine environments. The coastal estuarine environment such as mangrove ecosystems connected to the Sargasso Sea, Ferry Reach, Bermuda, has a natural variation of pH according to the changes in tidal regime (thus low and high tide activities). The unique environment serves as a model place to carry out the effect of changing pH on a marine organism such as flat tree oysters inhabiting this coastal ecosystem. For the laboratory experiment, a total of 84 specimens of the flat tree oyster, Isognomon alatus, were randomly collected on 21 January 2009 from rocks exposed at low tide in Mullet Bay, an intertidal mudflat, St. George, Bermuda (latitude: 32° 22' 30'' N, longitude: 64° 41' 35''W). An experiment was performed to test the effect of projected future pH decrease in a seawater flow-through system at Bermuda Institute of Ocean Sciences (BIOS) for a short period (February to April 2009). Physicochemical conditions (seawater temperature, salinity, pH and oxygen concentration) in three control tanks (C1, C2, C3, pH = 8.1 - 8.2) and three acidification tanks (T1, T2, T3, pH = 7.8 - 7.9) used for the culture of the oysters were recorded. Changes in shell morphometrics of the oysters were determined. For the field experiment, 42 specimens of I. alatus were randomly placed in 6 tanks (approx. n = 7 oysters/tank). Two tanks were then positioned along the transect at each station (A, B ,C) in Mangrove Bay, Bermuda. The shell parameters of flat tree oysters and physicochemical conditions were monitored biweekly.

Description: Seawater changing chemistry has consequences on coastal ecosystems and their living resources. Future projections suggest the pH could drop 0.2-0.3 pH units by the year 2100 under a business-as-usual (BAU) CO2 emission scenario. Marine calcifying organisms such as corals, calcifying algae, crustaceans, mussels, oysters and clams are most likely to be impacted by ocean acidification. The Isognomon alatus (flat tree oyster) is an important species that can be negatively affected by the lowering of seawater pH. Isognomon alatus is an important food source, a substrate for other benthic organisms (e.g., stone crab, Menippe mercenaria) and contribute to nutrients recycling in coastal ecosystems. The study was conducted to test the impacts acidified seawater CO2 on the growth of I. alatus under controlled laboratory conditions as well as field experiment. The Isognomon alatus lost weight and experienced negative growth rates of –0.56 +- 0.36 mg /g/day under average pH values of 7.8 expected by the end of this century compared to a loss of –0.26 +- 0.23 mg/g/day under ambient pH (value 8.1) conditions. In contrast, I. alatus incubated in a field experiment showed a gain in weight and positive growth of 3.30 +- 0.23 mg/g/day despite exposure to pH levels (7.4) during low tide significantly lower than those experienced in the laboratory. Overall, the results showed concern on the impacts of acidification flat tree oyster (Bivalvia:Isognomonidae). A decline of calcifying bivalves populations can impact coastal ecosystems function and indirectly affect the human beings that depend on them as a food source.