August 20, 2012

From Invader To Dominator: Understanding The New Species In A Habitat

Brett Smith for - Your Universe Online

Hawaiian researchers can now add fish to the phrase “the best laid-plans of mice and men, often go awry," as John Steinbeck once translated from a famous Robert Burns´ poem. An avid fisherman himself, Steinbeck would no doubt appreciate the problems caused by three invasive species of fish introduced to the Pacific archipelago 55 years ago.

In an attempt to better understand how an invasive species comes to dominate a habitat, Michelle Gaither, Robert Toonen, and Brian Bowen of the Hawaii Institute of Marine Biology (HIMB) used genetic sequencing to study the spread of these species and to identify changes in their genetic diversity following their introduction into a new habitat.

In the 1950s, Hawaii's Division of Fish and Game conducted surveys and found the local marine fauna was dominated by herbivorous fish, which were "a useless end in the food chain."

So to bolster local fisheries and fill a perceived empty niche in the local ecosystem, government officials introduced eleven different species of snappers and groupers to boost recreational and commercial fishing. Of the eleven species introduced, only three survived, however these fish-- Lutjanus fulvus (Blacktail Snapper, to℠au), Cephalopholis argus (Peacock Hind, roi) and Lutjanus kasmira (Bluestripped Snapper, ta℠ape)–came to overrun the indigenous aquatic populations.

In their research, the HIMB team used historical records and genetic analysis to construct genetic architectures of the sampled fish. They found that the invasive species have thrived to different degrees in the waters around the main Hawaiian islands.

Ta´ape, the most successful species, was able to maintain a high level of genetic diversity, similar to its parent population in French Polynesia. Meanwhile, the to´au population lost much of the genetic diversity found in the introductory group and has not become as widespread or as abundant as the other two species.

Team member Michelle Gaither explained that the results have implications for scientists and policymakers that deal with invasive species or the introduction of a new species into a habitat.

“We now have a better idea of why some species are more successful invaders than others,” she said.

“The faster a species becomes established in its new environment, the faster it finds food and begins to reproduce the more likely it is to maintain the genetic diversity that is so important to its long term success as an alien species.”

In addition to the direct impact these species have on the ecosystem, conservationists fear that a parasitic nematode, Spirocamallanus istiblenni, may have been introduced to Hawaiian waters when the fish were initially released.

Hawaii has instituted many policies to combat the three invasive fish species that have failed to gain traction in the market because of low prices and that most fisheries view them as a pest. Since 2008, the state has sponsored competitive spearfishing of the roi, ta´ape, and to´au. In 2010,event organizers reported that out of the 271 fish caught, 254 were roi, 12 ta´ape and five to´au. They added that the removal of these predators could have saved 40,000 indigenous reef fish.