ALIEN SPECIES

The environmental changes caused by marine invaders are known for only a few of the legions of introductions. Around the world, introduced algae, marsh grasses, fishes, molluscs, crustaceans, worms and many other invertebrates are now often the dominant members of coastal communities.

 

 

 

 

 

 

 

Examples of the impact of marine aliens include the invasion of North America by the European periwinkle in the early 19^th century, which led to profound changes in the community composition of rocky shores, mudflats and salt marshes on North America's east coast. The dramatic appearance in the late 1950’s of the Asian green alga, also on the US east coast had an extensive impact on mollusc fisheries. In the 1960's Asian eelgrass colonized estuaries on the US west coast creating vast areas of rooted vegetation where there were once only mudflats. The introduced West Atlantic ctenophore (a voracious predator of plankton) has devastated fisheries in the Azov and Black seas, and is now spreading through the Sea of Mamara towards the Mediterranean.

A spectacular example happened in 1984 in the western Mediterranean. The tropical algae Caulerpa taxiolia was accidentally introduced from the Monaco Aquarium. In this new ecosystem the algae grew to a great size and multiplied at an alarming rate. It has invaded more than 30,000 acres of seafloor in Spain, France, Italy, Croatia and Tunisia, displacing the local flora and fauna in the process.

 

 

 

 

 

 

 

 

 

More than a dozen marine fishes have been introduced to the Hawaiian Islands, including the bluestripe     snapper, which has become an abundant predator in shallow waters. Terrestrial aliens have also had their impact on marine species. Domestic cats introduced on Baltra, in the Galapagos Islands helped to eliminate the marine iguana. The same fate befell the Guadalupe storm petrel on Guadalupe Island, and they have killed thousands of seabirds annually on Marion Island in the Prince Edward Islands. Rabbits introduced to Laysan Island so devastated the vegetation that they nearly eliminated the Laysan teal. But the worst terrestrial aliens have been rats, which have affected seabird species worldwide.