| In
2003, resource managers in the 28 states of the Mississippi
River drainage basin were surveyed about the aquatic invasive
species that were ranked “most troublesome.”
They identified 46 plants, microorganisms, mollusks, fish
and mammals. The list includes some of the species that
have been causing major problems in Louisiana, such as the
water weeds Hydrilla and Salvinia and the Asian carps (grass,
silver, bighead and black carps).
Some
folks may find it odd that the list also includes the red
swamp crawfish Procambarus clarkii. Yes, that’s
the main one in everyone’s crawfish boil around here.
But this species isn’t welcome in areas that haven’t
been part of its native range. In those places, the red
swamp crawfish causes problems through burrowing –
damaging irrigation systems, levees, dams and water control
structures. It also acts as an intermediate host for some
helminth parasites that may be limited in their reproductive
capacity without this “new” species.
By this
example, we see that the term “invasive species”
has a lot in common with the term “weed.” According
to gardeners, a weed is any plant that is growing somewhere
where it isn’t wanted.
Unfortunately,
plants and animals and even disease organisms are now traveling
to more places where they are definitely not wanted. As
an example of how fast species are being moved around the
world now, the 2003 species list does not mention two of
Louisiana’s newest aquatic invaders: the apple snail
(genus Pomacea) and the Rio Grande cichlid fish
(Herichthys cyanoguttatus).
Infestations
of apple snails have occurred in several places in south
Louisiana. Reports have described the invaders as one of
two very similar species within the group called channeled
apple snails: Pomacea canaliculata and Pomacea
insularum. Originally from South America, this genus
has been popular for food and for use in aquaria. Wild populations
now cause tremendous damage to rice crops in Southeast Asia
and the Dominican Republic. In the United States, this pest
has become established in Florida, California, Texas, Georgia,
Alabama and Hawaii. Even in locations where rice crops aren’t
threatened, wetland vegetation can be damaged. Since 2006,
the U.S. Department of Agriculture has banned the importation
and interstate transport of most apple snails. However,
some biologists have reported seeing the banned species
in stores this year.
In 2006,
apple snails were found near New Orleans in canals in Gretna.
Attempts were made to control this infestation by aggressive
removal and destruction of egg masses. Finding the bubble-gum-pink
egg masses attached above the waterline on trees and pilings
is a sure indication of the species’ presence, even
where the fist-sized snail isn’t apparent. In the
past few months, P. insularum has been found in
huge numbers at locations near Houma. This outbreak is probably
too extensive to control manually. Hoping for cold weather
to kill this species won’t help, either. P. insularum
is native to the Buenos Aires region of Argentina, where
their average minimum monthly temperature in winter is 4–6
degrees Celsius (39–43 degrees Fahrenheit), which
is actually colder than north Louisiana. In addition, channeled
apple snails are relatively tolerant of estuarine salinity
concentrations. We may be in the situation of hoping that
there is an unknown factor which will limit this species
in Louisiana.
Should
they become established, the question will be raised on
their edibility. Apple snails are popular as food in parts
of Asia, but they are the intermediate host of several parasites.
Anyone who tries one of the published recipes will want
to cook them thoroughly.
Since
about 1995, the Rio Grande cichlid is becoming more common
in the waters in and around New Orleans. Known as the Texas
Blue in the aquarium trade, this fish breeds readily in
aquaria, and a number of folks have admitted to dumping
excess fish into the canals. Now, people fishing for bluegills
in City Park or Bayou St. John are as likely to pull up
a Rio Grande as a native bream, and Rio Grandes have been
found in bayous outside of the metropolitan area, including
LaBranche. UNO researchers have found that the fish have
no trouble living in Lake Pontchartrain at least long enough
to infest nearby freshwater habitats. While this species
originates from warmer locales, it seems to be doing fine
in south Louisiana. And researchers are also finding that
the Rio Grande can defend territory more aggressively than
native bluegills, possibly leading to total displacement
of native bream. While there is still some hope that conditions
will develop that limit this species, people may want to
investigate recipes for this one.
To learn
more about preventing the spread of aquatic invasive species,
visit www.protectyourwaters.net
where the following procedures are explained:
- Remove
any visible mud, plants, fish or animals before transporting
equipment
- Eliminate
water from equipment before transporting
- Clean
and dry anything that came in contact with water (boats,
trailers, equipment, clothing, dogs, etc.)
- Never
release plants, fish or animals into a body of water unless
they came out of that body of water
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