Selden Rebecca L, Gaines Steven D, Hamilton Scott L, Warner Robert R
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA
Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA.
Proc Biol Sci. 2017 Jan 25;284(1847). doi: 10.1098/rspb.2016.1936.
Where predator-prey interactions are size-dependent, reductions in predator size owing to fishing has the potential to disrupt the ecological role of top predators in marine ecosystems. In southern California kelp forests, we investigated the size-dependence of the interaction between herbivorous sea urchins and one of their predators, California sheephead (Semicossyphus pulcher). Empirical tests examined how differences in predator size structure between reserve and fished areas affected size-specific urchin mortality. Sites inside marine reserves had greater sheephead size and biomass, while empirical feeding trials indicated that larger sheephead were required to successfully consume urchins of increasing test diameter. Evaluations of the selectivity of sheephead for two urchin species indicated that shorter-spined purple urchins were attacked more frequently and successfully than longer-spined red urchins of the same size class, particularly at the largest test diameters. As a result of these size-specific interactions and the higher biomass of large sheephead inside reserves, urchin mortality rates were three times higher inside the reserve for both species. In addition, urchin mortality rates decreased with urchin size, and very few large urchins were successfully consumed in fished areas. The truncation of sheephead size structure that commonly occurs owing to fishing will probably result in reductions in urchin mortality, which may reduce the resilience of kelp beds to urchin barren formation. By contrast, the recovery of predator size structure in marine reserves may restore this resilience, but may be delayed until fish grow to sizes capable of consuming larger urchins.
在捕食者与猎物的相互作用取决于体型大小的情况下，因捕捞导致捕食者体型减小，有可能扰乱顶级捕食者在海洋生态系统中的生态作用。在南加利福尼亚海带森林中，我们研究了草食性海胆与其捕食者之一加州羊头鱼（Semicossyphus pulcher）之间相互作用的体型依赖性。实证测试考察了保护区和捕捞区之间捕食者体型结构的差异如何影响特定体型海胆的死亡率。海洋保护区内的羊头鱼体型更大、生物量更高，而实证摄食试验表明，需要成功需要更大体型的羊头鱼才能成功捕食测试直径不断增大的海胆。对羊头鱼对两种海胆物种选择性的评估表明，短棘紫海胆比相同体型等级的长棘红海胆更容易且更成功地受到攻击，尤其是在最大测试直径时。由于这些特定体型的相互作用以及保护区内大型羊头鱼的生物量更高，两种海胆在保护区内的死亡率是捕捞区的三倍。此外，海胆死亡率随海胆体型增大而降低，在捕捞区很少有大型海胆被成功捕食。因捕捞常见的羊头鱼体型结构截断可能会导致海胆死亡率降低，这可能会降低海带床对海胆荒漠形成的恢复力。相比之下，海洋保护区内捕食者体型结构的恢复可能会恢复这种恢复力，但可能会延迟到鱼类生长到能够捕食更大海胆的体型时。
