A note on larvae with potential transpacific distribution
Questions often arise as to why we see the larvae of species currently only known to the NW Pacific here in the NE Pacific. Coos Bay and other NE Pacific bays are hubs for shipping. In Coos Bay, large ships leave the bay loaded with stripped fir trees or wood chips, head across the Pacific and return with ballast water. Current regulations (Oregon Revised Statute 783.620-640; Murphy et al. 2004) require that they conduct mid-oceanic ballast exchanges such that species cannot be transported from one bay to another. However, it is known that many species have been transported around the world this way before these regulations were in place (Carlton and Geller 1991; Carlton and Cohen 2007) and is just as possible for nemerteans.
It is unlikely that the larvae we collect are directly derived from ballast water for a several reasons: 1) When we find larvae, we usually find them repeatedly and seasonally; 2) In many instances, larvae identified to species from the NW Pacific were too young to have traveled 5,500 miles by boat, taking usually around two weeks; and finally 3) The likelihood of finding a single larva from a ballast of, at most, 100,000 tons diluted into Coos Bay, the largest Bay in Oregon, is very low. However, while it is unlikely we would encounter ballast larvae directly, it is possible that nemertean species were established in Coos Bay by this mechanism.
No matter how species arrived initially, once species are established here one cannot know if they were transported here from elsewhere or vise versa. A description from the NW Pacific does not imply place of origin and instead, often reflects the first location in which a species was found. Species invasions and population dynamics are particularly difficult to measure without an appropriate baseline for biodiversity from which to begin.