Rockweed Isopod

Pentidotea wosnesenskii

The Rockweed isopod, Pentidotea wosnesenskii, is a marine crustacean found along the rocky shores of the Northern Pacific, from British Columbia and Washington down to San Francisco. It typically inhabits the intertidal zone, often hiding under rockweed like Fucus distichus. Although it can be found at depths up to 919 meters, most occurrences are in shallower waters, with 90% being less than 20 meters deep. This species can grow up to 4 centimeters in length and is usually green, which helps it blend into its seaweed surroundings. The Rockweed isopod's life cycle involves indirect sperm transfer, with eggs brooded in a specialized pouch called the marsupium. These eggs hatch into manca postlarvae, which eventually develop into adults. The isopod is preyed upon by the surf scoter, a type of sea duck. Divers encountering this isopod may find it camouflaged among seaweed, making it a subtle presence rather than a prominent sight.