, Volume 421, Issue 1, pp 25–30

Invasion by a Japanese marine microorganism in western North America

  • Mary McGann
  • Doris Sloan
  • Andrew N. Cohen

DOI: 10.1023/A:1003808517945

Cite this article as:
McGann, M., Sloan, D. & Cohen, A.N. Hydrobiologia (2000) 421: 25. doi:10.1023/A:1003808517945


The earliest record in western North America of Trochammina hadai Uchio, a benthic foraminifer common in Japanese estuaries, is from sediment collected in Puget Sound in 1971. It was first found in San Francisco Bay in sediment samples taken in 1983, and since 1986 has been collected at 91% of the sampled sites in the Bay, constituting up to 93% of the foraminiferal assemblage at individual sites. The species is also present in recent sediment samples from 12 other sites along the west coast of North America. The evidence indicates that T. hadai is a recent introduction to San Francisco Bay, and is probably also not native to the other North American sites. Trochammina hadai was probably transported from Japan in ships' ballast tanks, in mud associated with anchors, or in sediments associated with oysters imported for mariculture. Its remarkable invasion of San Francisco Bay suggests the potential for massive, rapid invasions by other marine microorganisms.

foraminifers non-indigenous species Trochammina hadai San Francisco Bay estuaries Pacific Coast 

Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Mary McGann
    • 1
  • Doris Sloan
    • 2
  • Andrew N. Cohen
    • 3
  1. 1.U.S. Geological SurveyMenlo ParkU.S.A.
  2. 2.Department of Geology and GeophysicsUniversity of CaliforniaBerkeleyU.S.A.
  3. 3.San Francisco Estuary InstituteRichmondU.S.A.

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