BALLAST SEDIMENT: A LIKELY MECHANISM FOR NONINDIGENOUS FORAMINIFERAL INTRODUCTIONS

At least five nonindigenous foraminiferal species have been reported worldwide, all in active shipping ports, and all are suspected of having been introduced by transoceanic vessels, including tankers and bulk carriers. These vessels take on water to maintain their stability during transit, incidentally pumping sediment into their holding tanks. Entrained in this sediment are a wide array of aquatic organisms (foraminifera, amphipods, bivalves, gastropods, diatoms, ostracods, sponges spicules, echinoid spines, fish), plant debris (seeds, fibers), and man-made or natural objects (metal chips, paint balls, glass, tar balls) which may be discharged into distant ports when the vessels release their ballast. In this study, we investigated the presence of foraminifera in ballast sediment samples from three locations in the U.S.

Most of the vessels arriving in Prince William Sound, Alaska are tankers which originate in west coast U.S. ports (Long Beach, San Francisco, Puget Sound), although a few are from overseas (Korea, China, Japan). Thirty ballast tanks from 12 vessels were sampled, 20 of which contained foraminifera. Twelve benthic and 3 planktonic species were recovered, including the invasive Japanese species Trochammina hadai,which was present in 11 samples. Most of these species were also present in ballast sediment obtained from a vessel in San Francisco Bay.

Transoceanic vessels arriving in the Great Lakes commonly originate in European ports and are required to pump out their ballast before entering U.S. or Canadian ports. Although these No-Ballast-On-Board (NOBOB) vessels are supposed to be devoid of ballast, left behind is the mud that accumulates next to the steel framing in the tanks and residual amounts of water that cannot be removed due to the geometry of the pumping systems. We sampled 19 of these vessels over a two year period. All of the 13 sediment samples collected in 2001 contain foraminifera, including 32 benthic and 6 planktonic species. Foraminifera were also present in 14 of 19 sediment samples collected in 2002, represented by 22 benthic and 7 planktonic taxa. Maximum foraminiferal abundance was >65,000 specimens/g dry sediment, 21% of which were alive at the time of collection. Clearly, both ballasted and NOBOB vessels are potential vectors for nonindigenous foraminiferal introductions.