Ecology. 2014 Jan;95(1):164-72. doi: 10.1890/13-0014.1.
Marine ecosystems are increasingly at risk from overexploitation and fisheries collapse. As managers implement recovery plans, shifts in species interactions may occur broadly with potential consequences for ecosystem structure and function. In kelp forests off San Nicolas Island, California, USA, we describe striking changes in size structure and life history traits (e.g., size at maturation and sex change) of a heavily fished, ecologically important predator, the California sheephead (Semicossyphus pulcher). These changes occurred in two phases: (1) after intense commercial fishery exploitation in the late 1990s and (2) following recovery in the late 2000s, nearly a decade after management intervention. Using gut contents and stable-isotope values of sheephead and their prey, we found evidence for a dietary niche expansion upon recovery of population size structure to include increased consumption of sea urchins and other mobile invertebrate grazers by larger sized fish. By examining historical diet data and a time series of benthic community composition, we conclude that changes in dietary niche breadth are more likely due to the recovery of size structure from fishing than major shifts in prey availability. Size-dependent predator-prey interactions may have ecosystem consequences and management measures that preserve or restore size structure, and therefore historical trophic roles of key predators, could be vital for maintaining kelp forest ecosystem health.
海洋生态系统越来越受到过度开发和渔业崩溃的威胁。随着管理者实施恢复计划，物种相互作用可能会广泛发生，这可能对生态系统结构和功能产生潜在影响。在美国加利福尼亚州圣尼古拉斯岛外的海草林中，我们描述了一种受过度捕捞影响的、具有重要生态意义的捕食者——加利福尼亚羊头鱼（Semicossyphus pulcher）的大小结构和生活史特征（如成熟大小和性别转变）的惊人变化。这些变化分两个阶段发生：（1）在 20 世纪 90 年代末密集的商业渔业捕捞之后，（2）在 21 世纪后期，即管理干预近十年后，种群大小结构恢复后。通过检查羊头鱼及其猎物的肠道内容物和稳定同位素值，我们发现，在种群大小结构恢复后，其饮食生态位有扩张的迹象，包括体型较大的鱼类增加了对海胆和其他移动无脊椎草食动物的消耗。通过研究历史饮食数据和底栖群落组成的时间序列，我们得出结论，饮食生态位宽度的变化更可能是由于捕捞导致的大小结构恢复，而不是猎物可利用性的重大变化。基于大小的捕食者-猎物相互作用可能对生态系统产生影响，而保护或恢复大小结构的管理措施，对于维持海草林生态系统的健康可能至关重要。
