OOS 31-10 - Sea otters, biodiversity, and ecosystem services: The good, the bad, and ugly role of keystone predators

Wednesday, August 9, 2017: 4:40 PM
D136, Oregon Convention Center
Edward J. Gregr and Kai Ming A. Chan, Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, BC, Canada

Given that top predators have been extinguished from many working landscapes, it is reasonable to ask to what degree keystone predators improve or degrade ecosystem services. Sea otters on Canada's west coast have been both maligned as ‘rats of the ocean’ for their competitive predation on lucrative invertebrate fisheries (e.g., urchins, clams, crabs, abalone), and praised for their contribution (via this predation) to the recovery of biodiverse, highly productive, kelp forest ecosystems. However, previous work has examined these effects at local scales. We conducted the first-ever analysis of the regional consequences of sea otter recovery on coastal ecosystem services by integrating field and remote sensing data using ecosystem and habitat suitability models.


Local field observations of kelp forests in otter-present and otter-absent study sites confirmed significant increases in biomass of kelp, kelp-associated grazers and invertebrates, and coastal rockfish. An increase in biodiversity was also observed in invertebrate and rockfish communities. Translating these results to the landscape scale required estimates of the proportion of the landscape that each ecosystem service provider occupied. Remote sensing data contributed to descriptions of habitat suitability which, combined with conservative assumptions, allowed the difference between the two systems to be compared at regional extents. These landscape predictions confirm that the otter-present system has a significantly lower abundance of several commercially important invertebrate species, it also contains over 30% more biomass than the otter-absent system. Kelp comprised the bulk of this additional biomass, but it also included a 3-fold increase in lingcod (a proxy for commercial rockfish) and several invertebrate groups. Translated to ecosystem services, this putative ecological success results in losses to the invertebrate fishery estimated at (-6.7 M$/yr), with tourism benefits predicted to be over +30 M$/year. The value of secondary production (+11.6M$/yr, estimated as the increased abundance of commercial finfish) is at least partially attributable to increased biodiversity.

Things get ugly when the beneficiaries, and the social and cultural values, are considered. For example, the projected outcomes above pit two groups of beneficiaries (commercial fishers and tourists) against each other, and omits the socially- and culturally-crucial subsistence fishery, which will also suffer losses.

Keystone predators may in fact be key for ecosystem services, but this needs confirmation via landscape-level analyses (e.g., with ecosystem models) to extend local field studies, and the integration of beneficiary perspectives of the value of those services.