Ocean acidification and seasonal temperature alter the behaviour and fitness of range-extending coral reef fish under future climate

Climate-driven invasions of ecosystems by range-extending animals are often mediated by behavioural modifications that increase their chances of establishment in novel biological communities. This creates novel ecological interactions that can also affect the behaviour of native species in recipient ecosystems. However, this key question has seldom been addressed in marine systems, in particular with the additive effect of ocean acidification and the mediating effects of seasonal climate variability. Here, we performed a laboratory experiment to evaluate how novel species interactions, ocean acidification, and future summer vs winter temperatures could affect the behaviour and fitness of a range-extending tropical and co-shoaling temperate fish. Compared to current summer temperatures, tropical fish became more active, more aggressive, and increased their feeding and fitness during future summers in their novel poleward ranges, but reduced their aggression, boldness and feeding during future winters. Tropical fish became more active under ocean acidification. Temperate fish behaviour was unaffected by climate treatment but their growth rates were higher under future winter vs current and future summer temperatures. We conclude that future winter conditions in temperate ecosystems still reduce the performance of range-extending fishes in temperate fish communities and hence slow down tropicalisation of higher latitudes.

气候变化驱动的动物生态系统范围扩张入侵，往往通过行为上的适应性改变，从而提高其在新型生物群落中定居的机会。这种适应性改变创造了新的生态相互作用，也可能影响接收生态系统中本地物种的行为。然而，这一关键问题在海洋系统中鲜有研究，特别是在考虑海洋酸化作用的叠加效应以及季节性气候变率的调节作用。在本研究中，我们通过实验室实验评估了新型物种相互作用、海洋酸化以及未来夏季与冬季温度如何影响范围扩张的热带和共群温带鱼类的行为和适应性。与当前夏季温度相比，热带鱼在未来的夏季在新扩展的北极范围内变得更加活跃、更具侵略性，并增加了其摄食和适应性，但在未来的冬季则减少了其侵略性和大胆程度，并降低了摄食。在海洋酸化条件下，热带鱼的行为变得更加活跃。温带鱼的行为不受气候处理的影响，但其在未来冬季、当前和未来夏季温度下的生长速率更高。我们得出结论，未来冬季的温带生态系统条件仍会降低范围扩张鱼类在温带鱼类群落中的表现，从而减缓高纬度的热带化进程。