Abstract：
The aquaculture of Manila clam (Ruditapes philippinarum) is under threat due to its high mortality in summer. To investigate the environmental influence on mortality of the species, we have conducted field surveys in the aquaculture area in Laizhou Bay, during the summers of 2019 and 2020. Environmental and biological data were collected. The results of data analysis have shown that in 2020, large-scale mortality events were not recorded and spatial variations of environmental variables were no significant within the survey area. However, in August 2019, significant variations of environmental variables were detected in the middle tidal area. This area was charactered with relatively high-water temperature (with maximum temperature of 31.49 °C and mean value of 26.17 ± 1.62 °C), elevated hydrogen sulfide concentrations (with a maximum concentration of 24.72 μmol/L and a mean concentration of 7.89 ± 4.14 μmol/L), and low dissolved oxygen concentrations (with a minimum concentration of 3.35 mg/L and a mean concentration of 6.27 ± 0.42 mg/L). Correspondingly, high mortality of the clam was recorded in the area, the abundance of live Manila clams has decreased by 80%. No significant abnormalities of environmental variables and clam growth were observed in other regions in 2019. Glycogen content and condition index of the clam were analyzed to investigate the relationship between environmental stress and the health of the clam. Compared to the condition index, glycogen content is a more sensitive indicator of the health status of the clam because changes in glycogen content appeared earlier than changes in condition index and mortality. A principal component analysis further indicated that the high mortality of the clam corresponds with a few environmental variables, including elevated temperature, hypoxia and the concentration of hydrogen sulfide. The simultaneous presence of these multiple environmental stressors could have triggered alterations in the physiological responses of the clam.
摘要：
由于夏季的高死亡率，马尼拉蛤类（Ruditapesphilippinarum）的水产养殖受到威胁。为了调查环境对物种死亡率的影响，我们在莱州湾水产养殖区进行了实地调查，在2019年和2020年的夏天。收集了环境和生物数据。数据分析结果表明，在2020年，没有记录到大规模的死亡事件，并且在调查区域内环境变量的空间变化没有显着。然而,2019年8月,在潮中地区检测到环境变量的显著变化.该区域的特征是水温相对较高（最高温度为31.49°C，平均值为26.17±1.62°C），硫化氢浓度升高（最大浓度为24.72μmol/L，平均浓度为7.89±4.14μmol/L），和低溶解氧浓度（最低浓度为3.35mg/L，平均浓度为6.27±0.42mg/L）。相应地,该地区记录到了高死亡率，马尼拉蛤仔的数量减少了80%。2019年，其他地区未观察到环境变量和蛤类生长的显著异常。通过对蛤仔糖原含量和条件指标的分析,探讨环境胁迫与蛤仔健康的关系。与条件指数相比，糖原含量的变化比病情指数和死亡率的变化更早，因此糖原含量的变化是反映蛤类健康状况的更敏感指标。主成分分析进一步表明，蛤类的高死亡率与一些环境变量相对应，包括升高的温度，缺氧和硫化氢的浓度。这些多种环境应激源的同时存在可能触发了蛤仔生理反应的改变。
