We look around our environment and we see things as they are – but not as they were. Over the centuries settlers brought with them to America, intentionally and unintentionally, hundreds of species that are not native to this continent.
Alabama has a project in operation along the Gulf that is cataloging the presence and distribution of introduced species. In the Gulf of Mexico area alone the last accounting showed that there were 483 introduced species of plants, 50 invertebrates, 38 fish, eight viruses, five reptiles, four amphibians, four birds and three mammals.
Some of these included the hog, Norway rat, starling, house sparrow, common carp, Zebra mussel, three species of tilapia and the peacock bass just to name a few. A total of 138 fish species have been introduced into the United States with most of these taking up residence in states with climates like Florida’s (50), California (56) and Hawaii (33). Because of these introductions 44 native fish species are threatened or endangered.
These non-native fish alter the ecology of aquatic ecosystems. For example, the grass carp (Ctenopharyngodon idella) is a vegetarian and eats aquatic vegetation (duck weed among others), which is used by other species and the common carp (Cyprinus carpio), which decreases water clarity and reduces algal growth. As the overall biomass of these introduced species increases their effects are multiplied, because for a given ecosystem only a fixed level of biomass can be supported.
If it’s tied up in these introduced species the diversity of the system is reduced and its venerability to collapse caused by changing environmental conditions goes up. Changes made by these introduced species have caused the extinction of some native fish with a few of the introduced species interbreeding with native fish and producing hybrids with unknown ecological effects.
Even taking into account some of the economic benefits from introduced species such as the brown trout, the more than 40 non-indigenous species that have negatively affected native fishes and other aquatic organisms cause conservatively speaking, an estimated economic loss of more than $1 billion annually.
Recently, we’ve been alarmed by press coverage of introduced species like the “Snake Head” and the Zebra mussel, which could lead to the wholesale destruction of entire ecosystems. The “Snake Head”, which was released into the wild as an unwanted aquarium fish, could eat its way through our ponds and lakes. While the Zebra mussel, brought into the Great Lakes in the ballast tanks of freighters from the Baltic Sea, has no natural predators and it numbers in the billions in our lakes and rivers.
This mussel feeds low on the food chain and will tie up nutrients that would have been washed down the river systems to the Gulf. Over time the result will be reduced productivity in our estuaries with fewer fish, crabs and oysters. Steps are now being taken to deal with these problems by the federal government.
In 1990 the Non-indigenous Aquatic Nuisance Prevention and Control Act (NANPCA) was passed by congress in an effort to control previously introduced species including the Zebra mussel among others. This authorization was expanded in 1996 with the passage of the National Invasive Species Act of (NISA) which required NOAA to examine the threats posed by multiple aquatic invasive species and to take steps to address the problem. This includes methods to clear the ballast water of all ships entering US ports of living organisms.
Think Global – Act Local!