A study explores how a drastic reduction in kelp forests led to shifts in sea otter and sea urchin behavior, restructuring mechanisms that control the ecosystem. Ecosystems worldwide are subject to both predation-driven and resource-driven influences on community structure and functioning. Joshua G. Smith and colleagues examined how climate, disease, and disturbance eroded the strength of predation-driven control in a marine ecosystem through changes in prey traits and predator behavior. In 2014, in kelp forests along the west coast of North America, sea star wasting disease abruptly reduced the number of sunflower sea stars, which are predators of purple sea urchins, around the same time that climatic stressors reduced the amount of kelp, on which urchins graze. The urchins' shift to active foraging led to a mosaic of kelp forests and urchin-grazed barrens, with food-limited urchins showing declines in energetically demanding gonad production. Following the urchin outbreak, sea otters increased their urchin consumption; however, the authors report, the otters largely ignored starved urchins in barrens, preferring energetically profitable urchins in forests in good condition. Hence, the authors suggest, otter preference for the forest-based urchins enhanced kelp patch resistance to overgrazing. However, because otters did not forage for urchins in the barrens, they did not enhance kelp recovery, according to the authors.
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Article #20-12493: "Behavioral responses across a mosaic of ecosystem states restructure a sea otter-urchin trophic cascade," by Joshua G. Smith et al.
MEDIA CONTACT: Joshua G. Smith, University of California, Santa Cruz, CA; tel: 559-999-0332; email: JogSmith@ucsc.edu
Proceedings of the National Academy of Sciences