Monterey Bay Aquarium Research Institute
Marine Botany

Sargassum muticum distribution and natural history

Sargassum muticum is originally from Japan, and was brought to the Pacific Northeast in the 1930's. In North America its range stretches from British Columbia to Baja California, and it has also succeeded in invading the coasts of England, France, Scandinavia, and the Iberian peninsula. The species was most likely transmitted via Japanese oysters (Crassostrea gigas) rather than by ships, as its distribution is not concentrated around ports and the holdfast mechanism is not strong enough to remain attached to a moving vessel (Deysher 1982.)

Pacific Northeast temperatures range from 9 to 13 degrees Celsius, with central California on the cooler end due to upwelling. Because S. muticum prefers warmer water, this stretch of coast is free from invasion. This raises the question of how S. muticum managed to migrate 1100 km from Northern California to Southern California in one leap. It most likely travelled along the California Current, which flows southward and shoreward from March to July, while the rest of the year algal branches tend to be carried out to sea. But S. muticum is described as being fertile only in July and August, and even the earliest reproductive branch would not have time to travel 1100 km and still release germlings. Fortunately for S. muticum, it survives as a pelagic organism and is both monoecious and self-fertile, which means that a single vegetative branch could float down to Southern California and establish a new population by itself (Deysher 1982.)

While not S. muticum, the most well-known population of Sargassum is that characterizing the Sargasso Sea in the Atlantic Ocean. This community is not attached to a substratum, but rather is purely pelagic, forming enormous floating mats. No one knows if the pelagic alga is a separate species or if it is an attached species that has become detached and reproduces asexually by thallus division.

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Last updated: 05 January 2005         copyright Jacqueline Pratt 1999.  All rights reserved.