Invasion threat of benthic marine algae arriving on Japanese tsunami marine debris in Oregon and Washington, USA

Abstract

:Recognisable debris from the Great Tōhoku Earthquake and Tsunami of March 2011 began arriving on the coasts of Oregon and Washington, USA in June 2012. This debris often carried fouling Japanese marine algae, and there was concern that these species might recruit and invade northeast Pacific shores. From June 2012 to July 2016, we examined 42 heavily fouled debris items and, using both morphology and sequencing data, identified 84 species and varieties of marine algae and cyanobacteria on the debris. Many of these taxa had features that indicated a high invasion potential: 83% were reproductive, 48% were ephemeral, and 75% were opportunistic forms. Naturally widespread species and 13 well-known global invaders were present. However, 61% of the species or their genetic variants had been reported from the northeast Pacific before the tsunami. Although the invasion risk was still deemed high, preventative debris removal appears to have been effective in averting many potential introductions.