Data from: Sudden collapse of a mesopredator reveals its complementary role in mediating rocky reef regime shifts

While changes in the abundance of keystone predators can have cascading effects resulting in regime shifts, the role of mesopredators in these processes remains underexplored. We conducted annual surveys of rocky reef communities that varied in the recovery of a keystone predator (sea otters Enhydra lutris) and the mass mortality of a mesopredator (sunflower sea star Pycnopodia helianthoides) due to an infectious wasting disease. By fitting a population model to empirical data, we show that sea otters had the greatest impact on the mortality of large sea urchins, but that Pycnopodia decline corresponded to a 311% increase in medium urchins and a 30% decline in kelp densities. Our results reveal predator complementarity in size-selective prey consumption strengthens top-down control on urchins, affecting the resilience of alternative reef states by reinforcing kelp forests and eroding urchin barrens. We reveal previously underappreciated species interactions within a 'classic' trophic cascade and regime shift, highlighting the critical role of middle-level predators in mediating rocky reef state transitions.

尽管关键捕食者（keystone predator）的丰度变化可引发级联效应并导致生态系统状态转换，但中型捕食者（mesopredator）在这一过程中的作用仍未得到充分探索。我们针对岩礁群落开展了年度调查，该群落的关键捕食者——海獭（Enhydra lutris）的恢复情况，以及因传染性消耗病导致的中型捕食者——向日葵海星（Pycnopodia helianthoides）的大规模死亡状况均存在差异。通过将种群模型拟合至实测数据，我们发现海獭对大型海胆的死亡率影响最为显著；而向日葵海星的种群衰退则对应中型海胆数量增长311%、巨藻密度下降30%。研究结果表明，捕食者在体型选择性猎物取食中的互补作用，强化了对海胆的下行控制效应，通过巩固巨藻林、削弱海胆荒漠，进而影响不同岩礁状态的恢复力。本研究揭示了‘经典’营养级联与生态系统状态转换中此前未被充分认知的物种相互作用，凸显了中层捕食者在调控岩礁群落状态转换中的关键作用。