An unrecognized role for predators: Digging sea otters promote eelgrass genetic diversity

The physical disturbances caused by recovering sea otter populations as they forage the seafloor for food increase the genetic diversity of surrounding eelgrass plants, according to a new study. The findings reveal an underappreciated evolutionary process through which predators promote genetic diversity and ecological resilience. While it’s well known that predators can have profound effects on ecosystems, most related knowledge is derived from observed changes in community structure as driven by trophic interactions, between predators and organisms in their food chain. The nontrophic genetic consequences of predation, particularly how indirect disturbance by predators affects the genetic diversity and evolution of plant communities, are not well understood. Erin Foster and colleagues hypothesized the physical disturbances from foraging sea otters, who routinely dig for clams and small crabs in eelgrass meadows, could promote conditions that facilitate reproduction of the eelgrass plant, increasing the community’s genetic diversity. By comparing genetic analyses from meadows where sea otters had been absent for more than a century, to meadows where sea otters had been recently reintroduced (within the past 10 years), or to meadows where they’d been present for decades, Foster et al. discovered that eelgrass genetic diversity was significantly higher – up to 30% – in meadows where otters had been present for 20-30 years. The authors demonstrate that the longer otters were present in an area, the more genetically diverse the eelgrass communities were. “The findings of Foster et al. come at a prescient time. The need to protect and monitor genetic diversity has often been overlooked in global communities such as the Convention on Biological Diversity,” writes Joe Roman in a related Perspective. “Research on the effects of disturbance and species interactions on genetic diversity could help inform the restoration efforts of trophic rewilding.”