Feature Story                                                       September 2011 

How much do we know about the impacts of invasive species?

Introduced species may be dramatically changing local communities without our notice. A recent study by Dr Gregory Ruiz, Dr Paul Fofonoff, and Brian Steves from Smithsonian Environmental Research Center’s (SERC) Marine Invasions Lab and Alisha Dahlstrom from the University of Tasmania, Australia (2011) found that for the crustaceans, the most abundant group of introduced marine invertebrates, there is surprisingly little known about their impacts.

Amphipodes are the most abundant group of introduced marine/estuarine crustaceans in North America. Photo by Monaca Noble, SERC.

Crustaceans are a large group of mostly aquatic animals that include crabs, lobsters, crayfish, shrimp, krill, barnacles, copepods and others. Of the 381 non-native invertebrates and algae known to have established themselves in North America, 108 (28%) are crustaceans. Most of these are small and go largely unnoticed. They are the amphipods, isopods, and copepods, and together they include 64% of the introduced crustaceans. Decapods, which include crabs, crayfish, lobsters, and shrimp, and barnacles (Cirripedia), make up 14% and 7% of the introduced crustaceans. Dr. Ruiz and his team combed through the literature for reported impacts and found that an impact was reported for 30 of 108 species (28%). In order for a species to have an impact, it had to cause a detectable change in the composition or population size of a resident species, or have an economic impact on fisheries resources, agricultural products, infrastructure (docks, dams, water supply, etc.), power plants, shipping or recreation. Barnacles were the most likely to have a reported impact (75%), followed by copepods (57%) and decapods (crabs, etc.) (33%). Many of the impacts reported were competition between or predation on a resident species resulting in a change in its composition or population size or an economic impact, but there were several other types of impacts, including habitat alteration and parasitism.

The Japanese Skeleton Shrimp, Caprella mutica. Photo by Jeff R. Cordell, University of Washington.

With only 28% of non-native marine crustaceans having a reported impact, you might wonder what the big deal is. After all, for 72% of the species there were no reported impacts. But in reality, there is simply a lack of study to evalute potential effects. Many of these groups are small and tend to go unnoticed, but could be changing the local community and ecosystem. One example is the Japanese Skeleton Shrimp, Caprella mutica. This successful invader is considered a potentially harmful invader due to its large population size in its introduced region and ability to outcompete native species, but its impacts are largely unknown. Caprella mutica is native to the northwest Pacific from Eastern Russia to Japan. It was discovered in California in 1973 and can now be found from Southern California to Alaska. It was seen on the East Coast in 2000 and can be found from Connecticut to New Brunswick, Canada. We know that this species is abundant on oil platforms off Santa Barbara, California and a major component of the diet of native fish in the area, but little else is know in spite of its large range.

What we’ve found is that some introduced crustaceans do have an impact on the local communities through competition, predation, habitat alteration and parasitism, but for most species there are no studies that quantify their impact in a meaningful way. Just as species invasions occur without notice, introduced species may be dramatically changing local communities without our notice. We need more studies that assess impact; otherwise we could fail to notice the invaders right in front of us.

 

Isopod from San Franscisco Bay. Photo by Monaca Noble, SERC.

An introduced copopoda, Pseudodiaptomus forbesi. Photo by Jeff R. Cordell, University of Washington.

Ruiz, GM, PW Fofonoff, B Steves, A Dahlstrom. 2011. Marine Crustracean Invasions in North America: A Synthesis of Historical Records and Documented Impacts. In Galil, B., PF Clark, JT Carlton (eds.). In the Wrong Place - Alien Marine Crustaceans: Distribution, Biology and Impacts. Invading Nature - Springer Series in Invasion Ecology, Vol. 6, ISBN: 978-94-007-0590-6