Life on the Edge: Two Dissimilar Extreme Events Alter Food Webs Through Modification of Top-Down Control

Climate change is causing rapid, unexpected changes to ecosystems through alteration of environmental regimes, modification of species interactions, and increased frequency and magnitude of disturbances. Yet how the type of disturbance affects food webs remains ambiguous. Long-term studies capturing ecosystem responses to extreme events are necessary to understand climate effects on species interactions and ecosystem resilience but remain rare. In the Gulf of Mexico, our 8-year study captured two disturbances that had contrasting effects on predator abundance and cascading effects to estuarine food webs. In 2017, Hurricane Harvey destroyed fishing infrastructure, fishing activity declined, and sportfish populations increased ~40% while intermediate trophic levels that sportfish prey upon declined ~50%. Then in 2021, a fish kill caused by freezing temperatures during Winter Storm Uri reduced sportfish populations by ~60% and intermediate trophic levels increased 250%. Sportfish abundance affected the abundance and size of oyster reef mesopredators. Excluding fish predators significantly altered oyster reef community structure. These results demonstrate how extreme events shape communities and influence their resilience based upon their effects on top predators. Moreover, top-down forces from sportfish are important in estuaries, persist through disturbances, and influence community resilience, highlighting the necessity of proper recreational fisheries management through extreme events.

气候变化通过改变环境格局、调整物种相互作用以及提升干扰事件的发生频率与强度，正快速且出乎意料地改变着生态系统（ecosystems）。然而，不同类型的干扰事件如何影响食物网（food webs），目前仍尚不明确。开展长期研究以记录生态系统对极端事件的响应，是理解气候变化对物种相互作用及生态系统恢复力影响的必要手段，但此类研究依然较为匮乏。在墨西哥湾（Gulf of Mexico），我们为期8年的研究记录了两起对捕食者种群丰度产生相反影响、并对河口食物网产生级联效应的干扰事件。2017年，飓风哈维（Hurricane Harvey）摧毁了渔业基础设施，渔业活动随之下降，游钓鱼类（sportfish）种群数量增长约40%，而其捕食的中间营养级（intermediate trophic levels）生物量则下降约50%。随后在2021年，冬季风暴乌里（Winter Storm Uri）引发的低温导致大规模鱼类死亡，致使游钓鱼类种群减少约60%，中间营养级生物量则增长250%。游钓鱼类的种群丰度会影响牡蛎礁（oyster reef）中型捕食者（mesopredators）的丰度与体型。移除鱼类捕食者会显著改变牡蛎礁群落的结构。这些研究结果揭示了极端事件如何通过作用于顶级捕食者（top predators）来塑造群落并影响其恢复力。此外，游钓鱼类介导的下行控制（top-down forces）作用在河口生态系统中至关重要，且能在干扰事件中持续存在，进而影响群落恢复力，这凸显了在极端事件期间开展合理休闲渔业（recreational fisheries）管理的必要性。