The giant salvinia is taking over Texas waters.
There is very little true “wilderness” in America. I’ve hiked around absolutely desolate patches of Wyoming, thinking I was at the end of the world, only to find a rusty beer can or a .30-.30 cartridge on the top of some windy bluff, left behind by the last person to pass through.
The fact is, humans interact with and are a part of what we often think of as “nature.” Our responsibility to it, therefore, extends beyond our time out there in it, and we need to think about the lasting effects our presence can have.
A case in point is our continuing and expanding problem with human-introduced invasive species. Nothing in nature is stable, and evolution occurs as a result of perturbations in the dynamic equilibrium that occur as a result of species introduction and migration. However, human activity has resulted in dramatic events unprecedented in the history of the earth, introducing species of widely disparate ecologies and histories into settings half a world away. The results can be dramatic and disastrous.
While animals, like zebra mussels or the snakehead, are prominent, flashy exemplars of the invasive species problem, introduced plants have the potential to wreak havoc on our environment at similarly catastrophic scales. Texas, like much of the southern US, faces just such a problem in the incredibly aggressive Giant Salvinia (Salvinia molesta).
Giant salvinia is a floating water fern native to Brazil. It is used in aquaria as a decorative plant and was likely introduced into America when someone cleaned out their fish tank. They were first identified in Texas in 1998, and have been found in several reservoirs in the state since then. Salvinia reproduces rapidly and can quickly cover a waterway. They easily spread on boats, boat trailers, or even on the feet of water fowl.
The danger of salvinia is threefold. First, its rapid growth and the absence of any organisms that eat it means that salvinia can rapidly overwhelm native plants by simply outcompeting them for space and resources. This can negatively impact native fish and birds as well, as many of the native plants choked out by salvinia are important food resources for them.
Secondly, salvinia mats can completely block out the sunlight in any invaded bodies of water, killing the photosynthetic plants and algae and reducing available oxygen. Thirdly, the explosive growth of salvinia provides a large influx of dead plant matter that, when it decays, results in further oxygen depletion in the pond, lake, or river where it has come to live.
Waterways infested with salvinia can quickly become monospecific wastes, a green-capped desert where only salvinia can live. Thickly grown floating mats of the plant also provide navigation and boating hazards, and can even confuse waterfowl. Birds flying overhead may think that the green sward under them is a meadow or patch of plants, completely missing the presence of a pond or lake under all that green. This can have a disastrous effect on migratory populations.
Management of salvinia is still in its early stages, and includes the introduction of a weevil that preferentially feeds on the fern. However, the best line of defense is preventing its spread to further waterways.
Boaters and anglers should learn to recognize the distinct fronds of this invasive and carefully clean them from any boats, trailers, or gear that may have come in contact with the plant. Hopefully, an effective removal strategy will be devised, but until then: keep watching the water!
Featured image via PassportToTexas.org