In California, southern sea otters have become unexpected defenders against invasive green crabs, which were originally introduced from Europe. These crabs, known for displacing native species and damaging sensitive ecosystems, have met their match in the voracious otters of the Elkhorn Slough National Estuarine Research Reserve. Scientists are astonished by the otters’ effectiveness in restoring balance to the estuary.
By August Roberts
The Threat of Green Crabs
Green crabs are among the most destructive invasive species in U.S. coastal waters. Since their arrival in the 19th century, likely through ballast water from European merchant ships, they have wreaked havoc by destroying eelgrass beds, preying on juvenile salmon, and outcompeting native crabs. Efforts to manage the infestation in states like Washington and Oregon cost millions annually, but these measures have had limited success in halting their spread.
Otters as Natural Predators
Since the year 2000, green crab populations in the Elkhorn Slough estuary have declined significantly without human intervention. This unexpected shift is attributed to southern sea otters, which rely on high-calorie diets to maintain body heat. Protected since 1913 after near-extinction, the otter population in Elkhorn Slough now numbers about 120 individuals. Their appetite for green crabs has helped curb the invasive species and restored ecological stability.
Positive Impact on the Ecosystem
With fewer green crabs, eelgrass beds have begun to recover, improving water quality and supporting the otters’ habitat. According to estuarine ecologist Rikke Jeppesen, the situation in 2003–2004 seemed dire, with green crabs poised to overrun the estuary. Today, researchers report catching fewer than five green crabs in traps that previously captured hundreds. This turnaround underscores the critical role otters play in maintaining the ecosystem.
A Hopeful Future
Although the current population of southern sea otters in U.S. waters remains around 3,000, their gradual recovery offers hope for reversing decades of damage caused by green crabs. The otters’ natural ability to control invasive species could serve as a model for restoring balance in other ecosystems threatened by similar invasions.
The resurgence of southern sea otters in California demonstrates how natural predators can effectively combat invasive species and restore ecological balance. By controlling green crab populations, otters have not only protected eelgrass beds but also improved water quality and biodiversity. This success story highlights the importance of conservation efforts in addressing environmental challenges and preserving delicate ecosystems.
Based on content from www.goodnewsnetwork.org and additional research.