By Bianca T. Esposito, NWNL Research Intern
(Edited by Alison M. Jones, NWNL Director)
Bianca T. Esposito is a Syracuse University senior studying Biology and Economics. Her summer research for NWNL was on biodiversity and water resources. Her past NWNL blogs are: Wild v Hatchery Salmon; Buffalo & Bison; Papyrus & Phragmites; & Deer & Elephants.
Invasive species are those that threaten to overtake other species. Whether flora or fauna, native or introduced, invasive species pose aggressive threats to the quality of lakes and ponds. “Introduced species” aren’t necessarily invasive; and “native species” can become invasive. Introduced species that are aggressive to the point of creating potential problems are termed “non-native invasives.” This blog discusses the impacts of two non-native invasive populations: water hyacinth (flora); and zebra mussels (fauna).
TO WATER HYACINTH
Water Hyacinth at the Montreal Botanical Garden, Canada.
Water hyacinth (Eichhornia crassipes) is a perennial, free-floating aquatic weed, native to South America’s Amazon River, but carried overseas for ornamental use. Today the water hyacinth is considered to be the “world’s worst aquatic weed.” This aggressive, invasive species spreads rapidly over entire surfaces of lakes and ponds and can double its coverage in just two weeks. Yet its ability to withstand drastic fluctuations in flow rates, acidity and low nutrient levels makes it a viable and popular water-garden plant.
Since imported to North America in 1884, it has invaded the Columbia and Mississippi River Basins, two NWNL case-study watersheds. Also introduced into East Africa, it is present in three NWNL basins: those of the Omo, Nile and Mara Rivers. Recorded in Egypt as early as the 1890’s, water hyacinth became a “plague” in the late 1900’s. River control schemes, such as dams, barrages and irrigation canals have encouraged its growth and spread. Furthermore, climate change, a combination of higher temperatures and CO₂ fertilization, is significantly increasing water hyacinth proliferation.
IMPACTS TO NATIVE RIVERINE SPECIES
On the positive side, water hyacinth cleans contaminated waters by absorbing large amounts of heavy metals into its tissue. However, once established, its degradation of waterways crowds out an ecosystem’s native species. Ergo, it becomes a “pest species.”
Water Hyacinth with Papyrus in Masurua Swamp, Tanzania
On Mississippi River waterways, water hyacinth becomes a mesh of dense mats ─ some spanning hundreds of acres of water. These mats cluster and cause a chain reaction that block sunlight from reaching native submerged plants, deplete oxygen in the water and kill aquatic wildlife, including fish. Ultimately, these mats prevent the growth and abundance of phytoplankton and other rooted benthic, aquatic plants that rely on sunlight and release O2. This negatively impacts fisheries, since phytoplankton is the basis of many aquatic food webs.
Kenyan fishermen on Lake Victoria, source of the White Nile Basin, have seen a 45% decrease in fish-catch rates after water hyacinth mats blocked access to fishing grounds, and thus delay delivery to markets. These consequences have increased costs of fishing efforts and materials. This hurts all who rely on fishing, and decreases the quality of fish in local markets.
In sum, the presence of water hyacinth within water bodies means: No Sunlight – No Photosynthesis – No Oxygen – No Fish. Ultimately, through this chain reaction, water hyacinth destroys the native ecosystems it invades.
EXTENDED WATERSHED DAMAGE BY WATER HYACINTH
Water Hyacinth with Papyrus in Masurua Swamp, Tanzania
─ Wind, water currents and boat traffic can break off pieces of water hyacinth mats that then can drift or blow away into new territories.
─ In sub-freezing Mississippi River Basin winters, water hyacinth mats decompose and literally tons of dead plant matter sink at once to the bottom, creating shallower rivers after several years of this build-up.
─ Water hyacinth disrupts critical values and services by blocking boater access; impeding commercial and recreational boat navigation; reducing water flow; and interfering with hydroelectric power generation.
─ Water hyacinth also affects drainage and irrigation canals by clogging intake pumps and reducing water flow. This causes floods and damage to canal banks. In recreational waters, water hyacinth invasion negatively impacts anglers, water-skiers and swimmers.
WATER HYACINTH SOLUTIONS
Water hyacinth management costs are close to US$100 million/year in both the US and Africa. Thus, it is clear that prevention is the most effective and cheapest control.
Another approach is to control expansion. This is usually, but controversially, done with low-cost chemical herbicides labeled “For aquatic use,” such as Glyphosate 5,4. However, application of this herbicide creates decomposition of dead plant material, thus fostering oxygen depletion which kills fish and other aquatic species.
Other methods of control include mechanically raking and harvesting the plant ─ as well as hand removal, biocontrol insects (such as the Neochetina beetle) and summer drawdowns. When harvesting and removing the plant, it is crucial to not discard it into a natural water way, but rather contain it in protected compost.
INTRODUCTION TO ZEBRA MUSSELS
Zebra mussels line Green Bay, Red River County Park, WI (Creative Commons)
Zebra mussels (Dreissena polymorpha), native to lakes in southeast Russia, are another non-native invasive species. In the 19th century, zebra mussels accidentally expanded into western Europe, the UK and N. America through trade. They entered N. America in the 1980’s when a trading boat came into the Great Lakes unaware of zebra mussels in its ballast water. Fortunately, invasive zebra mussels have yet to spread to Africa; but it could happen in the near future through trade.
Zebra mussels are the only freshwater bivalves able to attach to hard substrates in high densities. They reside in larger estuaries, inland rivers and lakes, adapting to hard- and soft-bottom habitats with surfaces suitable for attachment. Their entry into new ecosystems occurs through accidental transportation when attached to the bottom of boats. Once attached to a surface, zebra mussels are nearly impossible to remove. However, juvenile zebra mussels, with their ability to move freely in water, pose an additional threat to uncontaminated waters.
In some areas of the Mississippi River, there are as many as 20,000 zebra mussels per square yard. Since 1986, they have invaded 20 states east of the Mississippi River. There is no detection yet of zebra mussels in the NWNL case-study Raritan and Columbia River Basins. According to the State of NJ, “Zebra mussels have not yet been detected in New Jersey waters, but it is probable that invasion will occur in the near future.”
The Columbia River Basin, as of Aug 6, 2018, is the only major western US watershed not yet invaded by zebra and quagga mussels. Montana’s Flathead Lake, which drains into the Clark and Pend Oreille River tributaries to the Columbia River, is the last barrier against zebra mussels slipping into the the Columbia River system. One means of protection at the lake, and throughout the Columbia watershed, is extensive warning via signage and implementation of inspection stations, such as one on US Highway 93, that pressure-washes contaminated boats if they are found with mussels.
ZEBRA MUSSELS: NATIVE SPECIES IMPACTS & LOSSES
Zebra Mussels growing up a native mussel (Creative Commons)
Since zebra mussels have no natural predators in new ecosystems, they easily and dramatically reduce native species in US and Canadian fishing communities, by consuming and decreasing the amounts of food traditionally available for native species, such as algae. Zebra mussels also attach themselves to native species, such as crayfish, turtle shells and other mussels. In limiting the ability of native species to move, feed, breath and breed, they prevent reproduction and threaten their survival, as happened with the native “Higgins eye pearlymussel.”
EXTENDED WATERSHED DAMAGE BY ZEBRA MUSSELS
Sign warning for invasive Zebra Mussels at Eisenhower State Park, Texas
In aggregating on hard surfaces, zebra mussels cause economic impacts on municipal, industrial and private water systems. Since they grow in dense colonies, they can clog intake pipes and change the ecology of their new ecosystems. Zebra mussels also damage ecosystem services; change and alter habitat; decrease oxygen concentration when they respirate; modify natural benthic communities and modify nutrient regime. They negatively impact human health, aquaculture/fisheries, tourism and disrupt transportation. Even outside of the water, this invasive species destroys beaches with its extremely foul smell upon decaying.
Economic costs to manage zebra mussels impacts the Midwest and eastern US annually at an estimated $1 billion dollars. The Great Lakes region alone spends an estimated $500 million/year scrubbing zebra mussels from docks, pipes and intake pumps. While zebra mussels have not yet spread to NJ waterways, management costs hypothetically would run approximately $336 million/ year. If zebra mussels reach the Columbia River Basin their damage could cost hydroelectric facilities alone anywhere from $250 million to $300 million/ year.
ZEBRA MUSSEL SOLUTIONS
Sign warning boaters of invasive Zebra Mussels in Goose Lake, Arizona
Currently, zebra mussels are routinely removed from raw water systems where they create a bio-fouling nuisance, and are then discarded in landfills. Mechanical removal of attached zebra mussels is done using high-pressure water cleaning and micro-encapsulated BioBullets. Rigorous boating equipment maintenance by all boat owners is critical in stopping the spread of zebra mussels. Signs in most harbors and ports now warn that boats be cleaned with warm soapy water when entering from another body of water. Additionally, boaters are told not to dump water from one body of water into another body of water, since juvenile mussels move freely. Two critical solutions are 1) every boat owner assuming responsibility and 2) signage that spreads awareness of this invasive species.
Clearly invasive species pose major problems to the new habitats they invade, whether flora, such as hyacinth, or fauna, such as zebra mussels. In N. America and Africa, water hyacinth has hindered the growth of native aquatic flora and phytoplankton, depleting the aquatic food chain. Adult zebra mussels degrade watersheds by clogging irrigation pipes, and crowding out of native species. Additionally, unattached juvenile mussels easily spread this species to uncontaminated waters. Although invasive species can have some beneficial traits to the watersheds they dominate, degradation by water hyacinth and zebra mussels outweighs their benefits. It is imperative to spread awareness on how to prevent the spread of these and other non-native invasive species in order to protect the health of all impacted watersheds.
All photos © Alison M. Jones unless otherwise noted.