Seawater carbonate chemistry and calcification rate of eastern oyster Crassostrea virginica, 2011@en

Anthropogenic carbon dioxide (CO2) emissions reduce pH of marine waters due to the absorption of atmospheric CO2 and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed 23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures. Biocalcification declined significantly with a reduction of ~0.5 pH units and higher temperature and salinity mitigated the decrease in biocalcification.

人为二氧化碳（CO₂）排放可通过大气CO₂的溶解与碳酸形成过程，降低海水的pH值。河口水域更易发生酸化，因其存在多种酸化源，且缓冲能力弱于海水。因此，河口造壳生物可能比海洋生物更早遭遇酸化胁迫，但目前学界对河口钙化生物的pH变化耐受度仍知之甚少。
本研究分析了切萨皮克湾（Chesapeake Bay）23年的水质监测数据，结果显示：尽管中盐水域（mesohaline waters）的pH无显著变化，但高盐水域（polyhaline waters）的日间平均pH已显著降低。部分曾孕育大规模牡蛎种群的支流，其pH值却呈上升趋势。不过，部分支流当前的平均水环境条件，已达到本研究实验室实验中观测到的、会降低牡蛎生物钙化速率或导致壳体净溶解的临界值。
本研究采用三因素析因实验设计（three-way factorial design），设置3个pH梯度、2个盐度梯度与2个温度梯度，在实验室中测定了幼年东部牡蛎（Crassostrea virginica）的钙化速率。
生物钙化速率随pH降低约0.5个单位后显著下降，而更高的温度与盐度可缓解这一下降趋势。