Recovering populations of the southern sea otters suppress a global marine invader

Understanding the role of apex predators on ecosystems is essential for
designing effective conservation strategies. Supporting recovery of apex
predators can have many benefits; one that has been rarely examined is
control of invasive prey. We investigated whether a recovering apex
predator, the southern sea otter (Enhydra lutris nereis), can exert local
control over a global marine invader, the green crab (Carcinus maenas). We
determined that southern sea otters in Elkhorn Slough estuary in
California can consume large numbers of invasive green crabs and found
strong negative relationships in space and time between otter and green
crab abundance. Green crabs persisted at highest abundance in this estuary
at sites with artificial tidal restriction that were not accessible to
otters. Green crab abundance remained lower in this estuary than in all
other estuaries in the region, which lack resident sea otters.
Conservation organizations and agencies have invested heavily in recovery
of southern sea otters, increasing their numbers in this estuary.
Restoration of natural tidal exchange and lost marshes and seagrass beds
further supports their populations. We have demonstrated that these
investments in top predator recovery and habitat restoration have reduced
the impacts of a global invader. Our investigation highlights that
investment in recovery of top predators can increase beneficial food web
interactions and resilience of the entire ecosystem.