Climate change is introducing new stressors into already stressed ecosystems. Among these, extreme events such as heat waves play a crucial role in determining the structure of ecosystems. We tested single and combined effects of overgrazing, burial and heat waves on the seedlings of the habitat-forming species Posidonia oceanica. At current heat wave temperatures, overgrazing in isolation had more deleterious effects than seed burial, and effects were synergistic and additive when both factors co-occurred. The combined effect of overgrazing and seed burial with current heat waves could hamper P. oceanica seedling development, with similar or even higher levels than the sole effect of heat waves in the near future (29 °C). The effects of overgrazing and seed burial are expected to be overridden if heat waves temperatures exceed 29 °C. These results suggest that co-occurring environmental stressors, in combination with current heat waves, could compromise the sexual recruitment of this seagrass.

气候变化将新的压力因素引入已经压力很大的生态系统中。其中，诸如热浪之类的极端事件在决定生态系统的结构中起着至关重要的作用。我们测试了过度放牧，埋葬和热浪对生境形成物种大洋波塞冬的幼苗的单一和联合作用。在目前的热浪温度下，单独放牧过度放牧比种子埋葬更具有害作用，并且当两个因素同时发生时，其协同作用和累加作用。过度放牧和种子埋葬与当前的热浪共同作用可能会阻碍大洋P幼苗发育，在不久的将来（29°C），其水平将超过热浪的唯一影响。如果热浪温度超过29°C，过度放牧和种子埋葬的影响预计将被忽略。这些结果表明，共同出现的环境压力加上当前的热浪可能会损害该海草的性繁殖。