Lomentaria hakodatensis is a red alga with a wide native distribution in the Northwest Pacific. It grows in purple globular asses of entangled gelatinous branches, 50–100 mm tall. The plants are attached to a rock by a fibrous holdfast, but also grow epiphytically and also occur in the drift community. This species has a wide native range, from Pacific Russia to Vietnam, Australia, and the Marshall Islands. In 1944 it was collected near Ensenada, Mexico. It has become established at many locations on the West Coast, from Haida Gwai (Queen Charlotte Islands, British Columbia) to Costa Rica. The first record in California was in San Francisco Bay in 1992. This seaweed has introduced to the Netherlands, Brittany, Atlantic Spain, and lagoons in France and Italy. Transplants of Pacific oysters may have been the primary vector for L. hakodatensis, but hull fouling and ballast water have also been involved in its introduction.