Biodiversityhttp://nbepstatus-trends.squarespace.com/marine-invasive-species/en-US2009-12-05T02:10:23ZSquarespace Site Server v5.8.4 (http://www.squarespace.com/)Marine Invasive Specieshttp://nbepstatus-trends.squarespace.com/marine-invasive-species/2008/11/7/marine-invasive-species.htmlNBEP2008-11-07T19:10:09ZBiodiversity is an important measure of the condition of an ecosystem. Biodiversity can be reduced-i.e., species can be lost in an ecosystem-due to a variety of disturbances, such as land development and pollution. Among the most potent threats to marine biodiversity are invasive species.
Invasive species are non-native species which can exhibit population explosions or displace native species upon introduction into a new ecosystem. Invasives can cause significant disruption to a system such as Narragansett Bay, and can cause economic harm through interference with fisheries and other human uses. Invasive species can rapidly proliferate within an area, entering due to man’s intervention rather than natural spreading mechanisms. In the marine environment, this often involves species that “hitchhike” a ride from far-off ports on the hulls or in ballast compartments of ships, including recreational and commercial vessels. Some organisms may drop off a ship to establish a population in a new location, while others, such as barnacles, may reproduce and release young colonizers while still attached to the ship. When such species do not have local predators controlling their growth, their population may explode, causing significant disturbance to native flora or fauna. They may out-compete native species for space and food sources. Some invasive species come from polluted harbors, and are more resistant to pollution impacts like hypoxia (low oxygen). Others may suddenly be at an advantage as the ecosystem changes due to climate shifts (warmer water, etc.). This has become an issue of global concern, with federal laws now developed to control introductions through sources (called vectors) such as ballast water from large ships.
Invasives can be a major threat to commercial aquaculture in various areas of the country. Introduced green crabs impacted the ecology of Narragansett Bay over 100 years ago. They are now a serious threat to shellfish aquaculture in both the U.S. Northwest and the Maine coast.
In 2000 and 2003, NBEP, R.I. Coastal Resources Management Council and the Narragansett Bay National Estuarine Research Reserve coordinated a “Rapid Assessment Survey” of marine invasive species in Narragansett Bay. The team studied local “fouling organisms”-plants and animals which attach themselves to pilings, docks and other underwater structures. The survey found 124 species, of which 92 were identified as native, 17 were clearly introduced from Europe or the Pacific, and 15 were “cryptogenic” (origin unknown). The study suggests that as many as 26% of the Bay’s fouling community is comprised of non-native species, of which some are known invasives.
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Some of the most commonly observed invasive species in Narragansett Bay are the green crab (Carcinus maenus), which arrived here long ago, as well as the Asian shore crab (Hemigrapsus sanguineus), which is a more recent introduction. Common invasive algae include dead man’s fingers (Codium fragile), and Grateloupia turuturu. Invasive tunicates-encrusting organisms made up of colonies of primitive animals-include Styela clava, Botrylloides diagensis, and Didemnum spp. Didemnum has become a threat to shellfish aquaculture in New Zealand. The consequences of these introductions on Narragansett Bay’s ecosystem are as yet unknown.
The Chinese mitten crab (Eriocheir sinensis) is another potential invader-not yet identified in Narragansett Bay, but recently found in the Hudson River estuary and highly likely to enter the Bay system within a decade. This migratory catadromous species can be extremely destructive to shoreline habitats, as it establishes dense populations which burrow deeply into riverbanks, accelerating erosion. Its population exploded in Europe after introduction there in the early 1900’s; in the late 20th century, it was introduced to the San Francisco Bay area, and quickly became widely established.
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