Sea Otters Are Saving Coastal Ecosystems

GS 3 – Environment – Species

The recovering population of sea otters in California, especially in the Elkhorn Slough National Estuarine Research Reserve, has played a critical role in controlling the proliferation of invasive green crabs.

Sea Otters:

History:

• • Heavily hunted in the 18th and 19th centuries for their dense fur.
  • Declared a fully protected mammal in California in 1913, but faced challenges like oil spills and habitat loss.
  • Population recovery began after being listed as threatened and federally protected in 1977.

Role in Ecosystem:

• • Consume 50,000 to 120,000 green crabs annually, offering a natural solution to the invasive species problem on the U.S. West Coast.
  • Unique Adaptations:

• • • High metabolism instead of blubber for insulation.
    • Consume 25% of their body weight daily, making them effective predators.

Green Crab (Portunus sanguinolentus):

Habitat and Spread:

• • Native to the Atlantic Ocean and Baltic Sea, now invasive in Australia, South America, and South Africa.
  • Known globally as shore crab or green shore crab.

Physical Features:

• • Size: Carapace width up to 90 mm at maturity.
  • Coloration: Ranges from green, brown, and grey to red (red coloration indicates delayed moulting and increased aggression).

Diet: Feeds on small crustaceans, molluscs, and worms.

Impact on Coastal Ecosystems:

• • Damages seagrass beds, vital habitats for marine species.
  • Over-predation of prey species disrupts native species survival.
  • Outcompetes native species for resources like food and habitat.