Effects of seawater pCO2 and temperature on shell growth, shell stability, condition and cellular stress of Western Baltic Sea Mytilus edulis (L.) and Arctica islandica (L.)@en

Acidification of the World's oceans may directly impact reproduction, performance and shell formation of marine calcifying organisms. In addition, since shell production is costly and stress in general draws on an organism's energy budget, shell growth and stability of bivalves should indirectly be affected by environmental stress. The aim of this study was to investigate whether a combination of warming and acidification leads to increased physiological stress (lipofuscin accumulation and mortality) and affects the performance [shell growth, shell breaking force, condition index (Ci)] of young Mytilus edulis and Arctica islandica from the Baltic Sea. We cultured the bivalves in a fully-crossed 2-factorial experimental setup (seawater (sw) pCO2 levels \"low\", \"medium\" and \"high\" for both species, temperature levels 7.5, 10, 16, 20 and 25 °C for M. edulis and 7.5, 10 and 16 °C for A. islandica) for 13 weeks in summer. Mytilus edulis and A. islandica appeared to tolerate wide ranges of sw temperature and pCO2. Lipofuscin accumulation of M. edulis increased with temperature while the Ci decreased, but shell growth of the mussels only sharply decreased while its mortality increased between 20 and 25 °C. In A. islandica, lipofuscin accumulation increased with temperature, whereas the Ci, shell growth and shell breaking force decreased. The pCO2 treatment had only marginal effects on the measured parameters of both bivalve species. Shell growth of both bivalve species was not impaired by under-saturation of the sea water with respect to aragonite and calcite. Furthermore, independently of water temperatures shell breaking force of both species and shell growth of A. islandica remained unaffected by the applied elevated sw pCO2 for several months. Only at the highest temperature (25 °C), growth arrest of M. edulis was recorded at the high sw pCO2 treatment and the Ci of M. edulis was slightly higher at the medium sw pCO2 treatment than at the low and high sw pCO2 treatments. The only effect of elevated sw pCO2 on A. islandica was an increase in lipofuscin accumulation at the high sw pCO2 treatment compared to the medium sw pCO2 treatment. Our results show that, despite this robustness, growth of both M. edulis and A. islandica can be reduced if sw temperatures remain high for several weeks in summer. […]全球海洋酸化可能直接对海洋钙化生物（marine calcifying organisms）的繁殖、生存表现及贝壳形成造成影响。此外，贝壳合成本身耗能极高，且各类胁迫通常会消耗生物的能量储备，因此双壳类（bivalves）的贝壳生长与结构稳定性会间接受到环境胁迫的影响。本研究旨在探究增温与酸化的联合作用是否会加剧生理胁迫（包括脂褐素积累（lipofuscin accumulation）与死亡率），并影响采自波罗的海（Baltic Sea）的幼年紫贻贝（Mytilus edulis）与冰岛北极蛤（Arctica islandica）的生存表现，具体测定指标包括贝壳生长、贝壳抗折强度（shell breaking force）与条件指数（condition index, Ci）。本研究采用完全交叉双因子实验设计，于夏季开展为期13周的培养实验：设置适用于两种物种的海水（seawater, sw）二氧化碳分压（pCO2）水平梯度（低、中、高）；其中紫贻贝的培养温度设置为7.5、10、16、20和25 ℃，冰岛北极蛤的培养温度设置为7.5、10和16 ℃。实验结果显示，紫贻贝与冰岛北极蛤均可耐受较宽范围的海水温度与二氧化碳分压条件。紫贻贝的脂褐素积累量随温度升高而上升，但其条件指数（Ci）则呈下降趋势；而在20至25 ℃的温度区间内，紫贻贝的贝壳生长仅出现显著下降，死亡率同步升高。对于冰岛北极蛤而言，其脂褐素积累量同样随温度升高而上升，但条件指数（Ci）、贝壳生长速率与贝壳抗折强度均出现显著下降。二氧化碳分压处理对两种双壳类的各项测定参数仅存在微弱影响。当海水相对于文石（aragonite）与方解石（calcite）处于不饱和状态时，两种双壳类的贝壳生长均未受到抑制。此外，无论培养温度如何，两种双壳类的贝壳抗折强度以及冰岛北极蛤的贝壳生长速率，在长达数月的高二氧化碳分压海水处理下均未受到显著影响。仅在最高培养温度（25 ℃）下，高二氧化碳分压海水处理组的紫贻贝出现生长停滞；且中二氧化碳分压海水处理组的紫贻贝条件指数（Ci）略高于低、高二氧化碳分压海水处理组。高二氧化碳分压海水处理对冰岛北极蛤的唯一显著影响，是相较于中二氧化碳分压海水处理组，高分压组的脂褐素积累量出现上升。本研究结果表明，尽管两种双壳类具备较强的环境耐受能力，但如果夏季海水温度持续偏高达数周，紫贻贝与冰岛北极蛤的生长均会受到抑制。[…]