Lying in wait: "Sleeper" barnacles

The most vulnerable place in Hawai'i for the arrival of new invasive species may be our harbors and waterways.

While air passengers' luggage and carryons are inspected and crew check for brown tree snakes in cargo containers, the bottoms of ships arrive daily covered with wildlife.

“We really have no protection against hull fouling, and travel through the freshwater lake (Lake Gatun) in the middle of the Panama Canal isn't sufficient to kill most barnacles. They just close up and wait, and the wait isn't that long for getting through Panama,” wrote Michael Hadfield, Professor of Zoology at the University of Hawaii at Manoa.

And a some of those animals may be “sleeper species,” getting comfortable in the Hawaiian environment before they make the genetic shifts required to become real pests.

Hadfield and co-author John Zardus review the issue of marine alien invasions in a couple of recent papers:“Multiple origins and incursions of the Atlantic barnacle Chthamalus proteus in the Pacific,” in Molecular Ecology in 2005; and “A tale of three seas: consistency of natural history traits in a Caribean-Atlantic barnacle introduced to Hawaii,” in Biological Invasions in 2006, with additional co-authors Chela Zabin, Fabio Bettini Pitombo and Vanessa Fread.

Using mitochondrial DNA, they tested Chthamalus in Hawai'i and found evidence that Hawai'i specimens are related to Atlantic representatives from several different areas. It shows that there were multiple immigrants that are now interbreeding.

The researchers also tested representatives of the barnacle in other south Pacific and western Pacific harbors, and found similar results.

“We found compelling evidence that it has arrived multiple times in the Pacific from several areas in its native range,” they wrote.

One of the odd things they found is that a significant proportion come from the coast of Brazil well south of Panama. It suggests that a fair number of the imports came around Cape Horn rather than through the Panama Canal. That may be because Chthamalus isn't as tolerant of the fresh water bath in Lake Gatun, and that some of the potential barnacle immigrants from that route died.

Although it's an invader, thus far there haven't been significant impacts from it, the authors say. But Hadfield said it seems to have the potential of some other weedy species: They simply hold on for a while, over time make an adaptation to their new environment, and then become problem species.

“In the case of introduced animals, its clear that a lot of predatory species have quickly undergone prey and even habitat shifts in new locales. Witness the predatory snail, Euglandina rosea, that came from relatively low, moist habitats in the U.S. Southeast where it ate a variety of other snails from soil litter or low trees. In Hawaii, it not only eats a variety of new prey (including all of our native tree snails), but also has ascended the mountains and ravines to live in habitats the likes of which don't occur in North and South Carolina, Georgia and Florida,” he said.

“Some people call these invaders 'sleeper species,' meaning that their introduction appears to be benign, until they finally 'adapt' and take off to become a major problem,” Hadfield said.

© 2007 Jan W. TenBruggencate