Other Invaders on Maine's Radar Screen
While much focus has been on learning how to recognize Maine's "eleven most unwanted" invasive aquatic plants, and to distinguish them from their native Maine look alikes, it is important not to lose sight of the bigger picture. Maine's lakes, ponds, streams and wetlands are threatened by a wide array of non-native invaders, some plant, some animal. Some have been here in Maine for decades; others are relatively new to our region and are only now beginning to appear on Maine's radar screen. Here is an introduction to some of the other invaders to be aware of as you are out and about on your favorite lake, pond, or stream. If an invasive organism or plant is detected, please follow the guidelines for "Reporting Suspicious Plants" and fill out the Suspicious Aquatic Plant Form or Suspicious Organism Form and send it in to the CIAP. Invasive Prevention, early Detection and rapid Response are key to protecting Maine water from the spread of these invaders. Please see An Ounce of Prevention.
The Asian (or Asiatic) clam is a freshwater bivalve mollusk native to southern and eastern Asia and Africa. The source of introduction to the United States is unknown, but it is suspected that this species was brought from China by immigrants as a food source and subsequently released. The popularity of these small clams as aquarium specimens and as bait may have further exacerbated their spread. The Asian clam is now found in fresh waters throughout much of the United States including New England. (As of 2007, Asian clam populations have been discovered in Massachusetts and Connecticut.)
The clams thrive in sandy lake bottoms where they form dense communities; the population in a single waterbody may easily reach into the billions. The sexes are normally distinct; however hermaphrodites exist that are capable of self fertilization. When the second stage larvae, called veligers, reach approximately 1mm in size they are discharged from the gills of the parent to begin life as juveniles on the bottom sediments. (Under ideal conditions a single clam can release hundreds or even thousands of baby clams a day, up to 70,000 a year!) Asian clams reach maturity at about 6 to 10mm. Adults may reach up to 4cm in length during their lifespan of one to four years. The shell of the Asian clam is ovate, and normally yellow-green to brown in color with thick concentric rings. The inside of the shell is layered with polished, light purple material called nacre. Other shell colors (called morphs) do occur. Like other bivalves Asian clams are filter feeders; and collectively they eat plankton in vast quantities.
Asian clam infestations may clog power plant and industrial water systems, cause problems in irrigation canals and pipes, and foul boating equipment. Ecologically, this species can alter benthic substrates and compete with native zooplankton, mussel and fish species for food and/or space. Asian clams appear to be capable of tolerating polluted environments better than many native bivalves. In cases where Asian clam infestations have been intentionally controlled by a cold weather draw-down the clams have produced ammonia in high enough quantities to be lethal to other fish and wildlife.
Chinese mitten crabs are native to parts of China and Korea (where they are considered a culinary delicacy). The first record of this species in the United States was in 1965 in the Great Lakes region; the likely vector was the ballast tanks of commercial vessels. Mitten crabs have since been sighted in regions of the US as far a field as the Mississippi River delta and San Francisco Bay. In 2005, mitten crabs were caught in crab pots in Chesapeake Bay. This was the first reported sighting of this invasive crab in the eastern United States. In May of 2007, the crabs were found in Delaware Bay
Chinese mitten crabs occur in both fresh and salt water. At the age of two to five years old the crabs leave their burrows along the riverbankds of freshwater rivers and tributaries to mate and spawn in saltwater estuaries, migrating overland when necessary. Once the crabs have mated, the males are believed to die, leaving the females to brood the eggs. In the spring the eggs hatch into larvae and after about six to seven weeks these metamorphose into juvenile crabs, which then migrate back up the river into freshwater to complete the life cycle. These migrations can be extensive. It is the only crab known to occur in fresh waters of North America. Its claws are equal in size and covered with fur-like setae (soft bristles), or mittens, and eight sharp-tipped walking legs (no swimming legs). The adult carapace (body shell) is 8-10cm wide, and light brown to olive green in color.
The mitten crab is an omnivorous predator that will devour just about anything it can catch and swallow, including native freshwater crayfish. Mitten crabs also burrow, and in large numbers can cause substantial damage to unprotected riverbanks.
Chinese mystery snails, native to parts of Southeast Asia, were brought to this country as a food source for Asian markets. It is believed that imported snails were intentionally released in some ares to create a locally-harvestable supply. Since their introduction, Chinese mystery snails have spread to many parts of the United States, and can now be found in a number of Maine lakes and ponds.
Chinese mystery snails are distinctively large; at the size of a walnut or golf ball, the are half-again as large as Maine's largest native freshwater snail. Though they spend a good portion of their lives under the water surface, half buried in the bottom sediments, Chinese mystery snails may also be encountered with their trap doors sealed up tight, floating along at the water's surface. When these large snails die, they often wash up on shore, where their dark, olive-colored shells can be easily seen and (unpleasantly) smelled. Chinese mystery snails prefer the quiet water of lakes, ponds, roadside ditches and slower portions of streams.
Once in a body of water, the Chinese mystery snail may be transported, as adults or tiny juveniles, via bait buckets and water holding areas on boats. Like other snail species, this species may serve as a vector for various parasites and diseases. Chinese mystery snails occur in a number of Maine waterbodies, but the full distribution of this snail in Maine is unknown. MVLMP/CIAP currently manages a statewide database on reported sightings of C. chinesis malleatus. You can assist the effort to get a better ahndle on this invasive organism by reporting any sightings to MVLMP/CIAP at 207-783-7733 or email@example.com.
1. Martin, Scott M. 1999. Freshwater snails (Mollusca: Gastropoda) of Maine. Northeastern Naturalist.
2. Cipangopaludina chinensis (Reeve, 1863). Fact sheet by Gulf States Marine Fisheries Commission.http://nis.gsmfc.org/nis_factsheet.php?toc_id=125
Northern pike are native to parts of Eurasia and North America, but are not native to Maine. This popular "sport fish" was illegally introduced into the Belgrade Chain of Lakes in the 1970's and is now present in at least sixteen lakes in the Kennebec, Androscoggin, and coastal river drainages. It also is suspected to occur in several additional waters.
Esox lucius can inhabit almost every type of freshwater, from cold deep lakes, to warm shallow ponds, to sluggish streams. Having a broad range of tolerances for various water conditions such as temperature, clarity and dissolved oxygen, E. lucius is considered to be one of the most adaptable freshwater species.
Northern pike are voracious predators and spend much of their time stealthfully hunting in quiet weed beds. Pike ambush their prey by holding perfectly still for long periods, then striking with remarkable acceleration and precision. The fish has a distinctive habit of catching its prey sideways in the mouth, killing or immobilizing it with needlelike teeth, and then turning the prey lengthwise to swallow it. An average pike consumes three to four times its weight during the course of a year. Besides fish, its diet includes frogs, crayfish, small mammals, and birds — just about anything it can sink its teeth into. Pike will attack any fish in the vicinity, even other pike. Young pike have been found dead from choking on a pike of a similar size.
Pike move into the shallows, marshes and small streams to spawn after the spring ice melts, (in late March to early May). Females deposit up to 100,000 eggs at random. The adhesive eggs stick to flooded vegetation for about two weeks before hatching. During the summer the fish retreat to deep, cool waters. Sexual maturity is generally reached between three to five years of age. Pike grow to a relatively large size; average lengths of 46 to 51 cm are common, and lengths of 150 cm (59 inches) and weights of 25 kg (55 pounds) are not unheard of. Pike exceeding 30 pounds have been caught in Maine.
A northern pike may be confused with its close relative, the chain pickerel (Esox niger), a fish that is native to Maine. The two species are distinguished from one another by looking at the gills, cheeks (located just forward of the gill plate) and sensory pores along the lower jaw. On the pike, scales are present on the upper half of the gill cover, but are absent on the lower half. The cheek area is fully scaled. In comparison, the cheeks and gill covers of chain pickerel are all fully scaled. Pike usually have five pairs of sensory pores along the underside of the lower jaw where pickerel generally have only four. The upper sides of the adult northern pike vary from shades of dark green to olive green to brown, with 7 to 9 horizontally arranged rows of yellowish, bean-shaped spots. (The pattern of markings on the juvenile pike are different; juveniles have wavy, white to yellow vertical bars.) The underside of the fish is white to cream-colored. Pike can hybridize with chain pickerel, and the resulting hybrid may possess markings common to either or both species.
Unauthorized introductions of invasive, exotic fish species are particularly destructive to Maine's native brook trout populations, but they may also cause irreversible changes to entire aquatic ecosystems by restructuring plankton and forage fish communities that have evolved since the last glacial retreat. Pike are particularly voracious fish eaters, and their presence in one Maine lake is suspected of destroying one of the state's premier landlocked salmon populations. Strategies to eliminate or control invasive fish are difficult to design and implement, costly, and almost entirely ineffective. The illegal introduction of any fish into any Maine water is a Class E crime, punishable by fines up to $10,000. The Maine Department of Inland Fisheries and Wildlife offers a minimum reward of $2,000 for information leading to the apprehension of persons responsible for the illegal introduction of fish. Call Operation Game Thief at 1-800-253-7887. If you suspect that you have seen or caught a northern pike, please report your findings to the Maine Department of Inland Fisheries at 207-287-8000.
1. Illegal Fish Stockings Threaten Maine Lakes and Rivers by David Boucher, Fishery Biologist, Maine Department of Inland Fisheries and Wildlife; www.maine.gov/ifw/fishing/illegal_stocking.htm
2. Northern pike at www.maine.gov/ifw/fishing/species/identification/northernpike.htm
3. Northern pike at Wikipedia at http://en.wikipedia.org/wiki/Northern_pike.
Quagga mussels are native to the Caspian Sea, and like zebra mussels, are thought to have come to this country in the ballast water of ocean going ships. Quagga mussels were first discovered in the Great Lakes region in 1989, but were not identified as a distinct species until 1991.
These invaders prefer silty or sandy lake bottoms, but may be found in waters ranging from warm and shallow to deep and cold. Like zebra mussels, the shell is distinctly striped in dark and light bands. Adult quagga mussels are generally larger than zebras, 20 mm long (roughly the size of your thumbnail) and their shells are broader and more fan-shaped. The ventral (or hinged) side of the shell is convex, preventing the quagga mussel from being balanced, on this side, on a flat surface. (The zebra mussel will remain upright when placed on its ventral side.) Quagga mussel feed year round, even in winter when zebra mussels are dormant.
Quagga mussel infestations may clog power plant and industrial water systems, cause problems in irrigation canals and pipes, and foul boating equipment. Ecologically, they can alter benthic substrates and compete with native zooplankton, mussel and fish species for food and/or space. Quagga mussels have not yet been detected in Maine.
1. Quagga mussel;Wisconsin Department of Natural Resources website;http://www.dnr.state.wi.us/invasives/fact/quagga.htm
Maine is now home to several non-native crayfish species. Of those species known to be from "away," two are considered by state experts to pose the greatest threat to native ecosystems: rusty crayfish (Orconectes rusticus) and red swamp crayfish (Procambarus clarkii). Though some non-native crayfish populations are now well known, the statewide distribution of these species is not fully known. Rusty crayfish are believed to be native to the Ohio River Basin and the states of Ohio, Tennessee, Indiana and Illinois. This mid-western crayfish species has now spread to other regions in the United States from New Mexico to Maine. Rusty crayfish have been in Maine for several decades, and were probably first introduced by non-resident anglers who brought them here to use as fishing bait. Once invasive crayfish populations were well established, the sale of trapped crayfish by bait dealers may have increased the rate of spread within the state.
Rusty crayfish inhabit lakes, ponds and streams. They generally dig small pockets under rocks and other debris, though under some circumstances they may dig more substantial burrows. Unlike some other crayfish species that may inhabit seasonal waterbodies, O. rusticus needs permanent (year-round) water. Rusty crayfish have robust claws with black bands at the tips and an oval gap when closed. They also have dark, rusty spots on each side of their carapace as though you picked up the crayfish with rust-colored paint on your forefinger and thumb. (The spots may not always be present or well developed.) Like all crayfish, O. rusticus is an opportunistic omnivore. Rusty crayfish feed on a variety of aquatic plants, benthic invertebrates (like aquatic worms, snails, leeches, clams, aquatic insects and crustaceans), detritus (decaying plants and animals and the associated bacteria and fungi), fish eggs, and small fish.
Introductions of both O. rusticus and P. clarkii have caused serious damage to aquatic ecosystems outside of Maine; the latter being a notorious invasive globally. O. rusticus is an aggressive species, and is known to displace native crayfish in two ways: through crayfish-to-crayfish competition and by causing increased fish predation on native species. (Rusty crayfish, for example, force native species from the best daytime hiding places.) Rusty crayfish also are known to reduce plant and invertebrate diversity and abundance in the aquatic ecosystem. This may in turn negatively impact native fish and waterfowl populations. Many of these impacts occur only after crayfish populations have reached high nibble-your-toes densities. Impacts of these crayfish on Maine ecosystems have not been studied. Environmentally sound ways of controlling introduced populations have not yet been developed. The best way to prevent potential ecological damage is to prevent or slow the spread of these species into new waters. Maine Department of Inland Fisheries and Wildlife and other Maine researchers have begun collecting crayfish distribution data. Distribution data for all crayfish species found in Maine is valuable to researchers. Please report any crayfish sightings to: MVLMP/CIAP at 207-783-7733 or firstname.lastname@example.org.
1. Rusty Crayfish a Nasty Invader; Jeff Gunderson; 1995 (Revised 2002); Minnesota Sea Grant website;www.seagrant.umn.edu
2. The Crayfish of Maine; William Reid and Matthew Scott; the Water Column (the Maine Volunteer Lake Monitoring Program newsletter); Vol. 10, No. 3; Winter 2006; p. 12.
3. Editorial comments by Karen A. Wilson, William Reid and Matthew Scott
Spiny water flea is native to Great Britain and parts of northern Europe. This tiny crustacean was first found in Lake Huron in 1984, likely the result of another ballast water introduction. Populations can now be found throughout the Great Lakes and numerous other inland lakes in the northern Midwest region.
Spiny water fleas are more common in deep, cool lakes. However, they also inhabit warmer lakes where surface water temperatures exceed 25° C. The creature is small (1 to 1.5 cm long) with transparent exoskeleton, a large black eye spot on both sides of the head, and four pairs of legs. Most distinctive is the crustacean's long, barbed tail spine. Spiny water fleas are often first noticed by anglers, when they become entangled in fishing lines. When the line is pulled from the water, something resembling tiny straight pins waving about perpendicular to the line may be noticed. These are the miniscule creatures, raising and lowering their tails as they cling to the line. Impacts to aquatic ecosystems caused by the spiny water flea are not fully understood. What is known is that spiny water fleas reproduce rapidly, (both sexually and asexually) producing numerous offspring during the growing season, and "resting eggs" that overwinter in the sediments.
Once well established in the waterbody, spiny water fleas compete directly with other zooplankton feeders in the ecosystem (eating up to three times as much food as similar species). Their sharp spine prevents fish of a certain size class from eating them. It is believed that both of these impacts have the potential to trigger disturbances throughout the aquatic food web.
1. Spiny Water Flea; Ontario Federation of Anglers and Hunters website; www.invadingspecies.com/Invaders.cfm
2. Spiny Water Flea in the Great Lakes Region; Great Lakes Information Network web site; www.great-lakes.net
Zebra mussels are thought to have been introduced to this country as accidental stowaways attached to hulls, or in the ballast water of ships entering the Great Lakes from Europe. Since they were first discovered in this country in 1988, these tiny, freshwater bivalves, have become a major aquatic pest throughout much of the Midwest. Spreading to New England, primarily by way of boating activity, they have now impacted waters in Vermont and are known to be on the move elsewhere in New England. (Indeed, in 2006 a Courtesy Boat Inspector on Lake Winnipesaukee in New Hampshire detected-and successfully averted some zebra mussels that were hitching a ride on a boat from New York.)
Zebra mussels begin life as tiny free-swimming larvae, called veligers. It is during this stage that they are most readily transported from one waterbody to another (attached to boating gear, in bilgewater, bait buckets, etc.) and also most difficult to detect. After two or three weeks, the veligers "settle out" in the waterbody, attaching by way of strong, threadlike filaments to just about any hard surface they encounter. Rocks, sediment, wood, intake pipes, moorings, boat hulls, native mussel beds, are all at risk of colonization. Zebra mussels are small (adults are about 15 mm long) but they are voracious filter feeders, straining out major portions of the phytoplankton population and effectively starving out many native zooplankton species. The gap created in the food web may cascade through the entire ecosystem.
Zebra mussel infestations may clog power plant and industrial water systems, cause problems in irrigation canals and pipes, and foul boating equipment. Ecologically, they can alter benthic substrates and compete with native zooplankton, mussel and fish species for food and/or space. Zebra mussels have not yet been detected in Maine.
1. Frequently asked Questions about the Zebra Mussel. United States Geological Survey. Florida Integrated Science Center, Gainsville. http://cars.er.usgs.gov/Nonindigenous_Species/Zebra_mussel_FAQs/zebra_mussel_faqs.html
This low-growing, mat-forming invasive aquatic plant is a relative newcomer to North America. Glossostigma was first identified in the United States in 1992, in a single location in southern Connecticut. It has since (as of 2005) spread to nineteen known locations in Connecticut, New Jersey, Rhode Island, and Pennsylvania. It is believed that Glossostigma may even be more widely occurring,but its diminutive size and peoples' lack of familiarity with the plant have allowed it to remain largely under the radar. Pairs of leaves, resembling tiny green rabbit ears, occur along dense networks of slender rhizomes. Leaf size varies depending upon growing conditions; most are 1 to 4 cm long. Glossostigma, once established, can form a dense monoculture (averaging 10,000 to 25,000 plants per square meter) on the lake floor, carpeting the bottom from the shoreline to depths greater than two meters. Where exposed at the waters edge, Glossostigma behaves as an annual-- flowering, fruiting, and then dying back each winter. Submersed, it is a hardy perennial, remaining green and growing year round.
Because of its short stature, this invader is not considered to pose much of a threat to recreational activity (boating, swimming, etc.). However, the ability of the plant to form dense, monotypic mats makes it an ecological threat to native plant and animal communities. Glossostigma has not yet been detected in Maine. If you suspect that you have found this plant, please notify MCIAP or Maine DEP immediately.
1. Glossostigma cleistanthum: a new invasive in North America. Microsoft PowerPoint presentation by Robert S. Capers, Connecticut Agricultural Experiment Station and Donald H. Les, University of Connecticut. With edits and additions by Robert Capers.
The current distribution of common reed includes Europe, Asia, America, and Australia. The origin of the plant is unclear. Though Phragmites rhizomes have been found in North American peat cores dated 3,000 years old, the plant was not common in New England marshes at that time. The recent explosion of this plant in New England in the last 100 years, however, has led researchers to take a closer look at the origin of this now-aggressive species. Recent genetic evidence has confirmed that a more aggressive genotype from Europe was introduced some time in the late 1800's along the Atlantic coast, where problems associated with the non-indigenous genotype are currently most severe.
The European form of common reed is very aggressive, robust, densely growing wetland grass species that thrives in freshwater and brackish tidal wetlands. The hollow woody stems of this plant can grow up to five meters in height. Flowers develop by mid-summer and are arranged in tawny spikes among tufts of silky, hair-like fibers. Pollen is carried from plant to plant by the wind, and seed set is highly variable. The large purple flower heads turn gray and fluffy in late summer as they go to seed, and remain on the plant throughout the winter. Seeds germinate on exposed moist soils in the spring. Vegetative spread by below-ground rhizomes can result in dense stands.
When Phragmities invades a wetland, it alters the structure and function of the ecosystem by changing nutrient cycles and hydrological regimes. Dense Phragmities stands decrease native biodiversity and quality of wetland habitat for migrating wading birds and waterfowl. Rare and threatened bird species are particularly vulnerable to exclusion. Research to find appropriate biological controls for this species is underway, but incomplete at this time.
1. Common Reed; Blossey, Schwarzlander, Hafliger, Casagrande and Tewksbury; Invasive Plants of the Eastern U.S. website; www.invasive.org
2. Common Reed; Maine Invasive Plants; University of Maine Cooperative Extension; Bulletin #2532
Purple loosestrife is native to Europe and Asia, and was introduced into North America about 200 years ago. This plant now occurs in wetlands across the United States; with some of the largest infestations occurring in the northeast states, including Maine. Purple loose-strife is a wetland perennial that prefers open sunny areas and wet soils.
Plants may be found in wet meadows, floodplains, disturbed areas such as roadside ditches, along stream banks and around the edges of ponds, lakes and marshes. When mature (at three to five years) a single plant may be over three meters tall and produce as many as fifty stems. Leaves are blade-shaped, entire and oppositely arranged on the stems. The stems are usually square in cross-section, but may be five or six-sided. Leaves and stems may be (but are not always) covered with soft hairs. Plants form dense, woody rootballs (up to 50 cm in diameter) with a strong taproot. Purple loosestrife blooms during the summer. Its reddish-purple flowers, each with five to seven petals, are closely arranged on tall flower spikes. A mature plant may produce up to 2.5 million seeds per year. Seeds, which remain viable in the ground for at least five years, are as small as a grain of sand and are easily carried by wind, water, and passing animals, and may go undetected on muddy boots.
When purple loosestrife moves into wetlands, it displaces native plants such as cattails, sedges, bulrush and ferns. Wetlands infested with purple loosestrife have decreased native biodiversity and quality of wetland habitat for migrating wading birds and waterfowl. Rare and threatened bird species are particularly vulnerable to exclusion.
As with virtually all invasive species, control is problematic. Young purple loosestrife plants may be removed by hand or with a garden fork. It is very important that the entire plant and root system is removed, as roots broken off in the ground during the process of removal will likely sprout new plants. Removing larger plants by hand is more difficult, and may need to be repeated several times each year until the desired control is achieved. Ideally plants are removed before they flower (to prevent the possibility of seed release). In cases where flowers are present, the flowers should be carefully bagged, removed and properly disposed of prior to removing the rest of the plant. Simply removing flower spikes early in their development (by cutting or mowing) will help to reduce seed spread. However, as the plants themselves will easily regenerate, this is at best a temporary and limited means of control.
Biological control is widely recommended as a cost-effective, long term means of controlling purple loosestrife. The goal with biological control is to reduce, not eliminate, this wetland invader. Several species of insects have been approved by the United States Department of Agriculture for biological control of purple loosestrife. The Maine Department of Transportation and The Maine Department of Agriculture have recently launched an experimental program in which Galerucella beetles are being introduced into several severely infested areas.
Contrary to popular belief (that claims some ornamental cultivars of this plant are sterile), all purple loosestrife cultivars have been shown to be fertile, and capable of serving as pollen or seed sources for invasive loosestrife populations. Gardeners are advised to seek native-friendly alternatives. For more information contact MCIAP.
1. Purple Loosestrife: Beauty or Beast; a brochure by University of Connecticut Department of Plant Science Cooperative Extension Service Research Foundation
Flowering rush is native to Eurasia. Populations in the United States have now been recorded in numerous Midwestern states and parts of New England, including Maine. Flowering rush was first observed in North America in1897 in LaPrairie, Quebec. The first collection in New England was in Vermont in 1929. By the 1950s the plant was well established along the St. Lawrence River.
This hardy aquatic perennial will grow in the shallow waters of ponds, lakes and streams in water several meters deep. Its flowering stem, when present, may rise up to 1 meter above the water surface. It may also occur in forested floodplains. This species is intolerant of salt or brackish waters. The leaves are 0.6 to 0.9 meters long, fleshy, triangular in cross-section and twisted at the ends, and can be erect or floating on the surface. The plants flower from summer to fall depending upon conditions, and some populations rarely flower. The small three-petal flowers are white to deep pink to purplish brown in color, and occur on long slender stalks, arranged in an umbel-like spray of up to 30 flowers. The inflorescence is said to resemble an inverted umbrella frame.
Butomus umbellatus can displace native riparian vegetation, decrease biodiversity, alter ecosystem function and change hydrologic regimes.
1. Butomus umbellatus; Invasive Plant Atlas of New England website; http://nbii-nin.ciesin.columbia.edu/ipane/
Didymo, widely referred to as "rock snot," has historically been found in the cool, oligotrophic waters of the far northern regions of Europe and North America. Since the mid-1980s, it has begun to take on the characteristics of an invasive species in its original range, and has also been expanding its range to warmer, more nutrient rich waters. The mechanism by which this organism has become more invasive is not well understood, but some researchers believe that climate change may be playing a significant role. In the past several years, didymo has expanded its range in the Western United States and has infested rivers and streams in several southeastern states, including Virginia, West Virginia, Tennessee and North Carolina. In 2007, didymo was found in the northern reaches of the Connecticut River in Vermont, marking the first official report of Didymosphenia geminata in the Northeastern United States. Blooms have since been detected in New York and New Hampshire. To date there have been no sightings in Maine.
Didymo is a freshwater diatom that produces stalks on which it attaches itself to rocks and vegetation. This species generally lives in clear, cool streams and rivers, especially those with moderate, year-round flows and good light. (Rarely, it may occur along the rocky shores of lakes and ponds.) It may exist for a time as small (relatively benign) bubbly colonies on submerged rocks, boulders and gravel, and then suddenly "bloom" into a thick yellowy-brown layer, capable of covering large areas. Didymo mats are distinctive from other algal species that attach to rocks being neither green nor slimy. They feel more like wet cotton or thick wet felt. In a more advanced stage, didymo forms long streaming filamentous carpets, each streamer up to several centimeters long. The streamers eventually turn white at their ends and fragments (resembling clumps of tissue paper) break away and float downstream.
Prolonged severe blooms can negatively impact the habitat for beneficial macroinvertebrates (such as stoneflies, mayflies and caddisflies). These stream dwelling invertebrates are a critical food source for brook trout, river dwelling birds and other native species, so an infestation will negatively affect these natives as well. In advanced stages, a didymo bloom may restrict water flows, deplete dissolved oxygen levels (a result of the decomposition of the algal mats) and smother native mussel beds. Intense blooms make angling difficult and less appealing.
There are currently no known methods for controlling or eradicating didymo once it infests a water body. Preventing its spread is seen as the best (and currently only) defense against the harmful affects of this species. Anglers, kayakers and canoeists, boaters and jet skiers can all unknowingly spread didymo. The microscopic (and virtually invisible) algal cells cling to fishing gear, waders, boots and boats, and remain viable for several weeks under even slightly moist conditions. Decontamination requires soaking clothing and equipment in hot water containing a liberal amount of detergent. Thoroughly drying clothing and equipment for a minimum of 48 hours can also be effective, but only if completely dry conditions are maintained.
1. Didymosphenia geminata; Global Invasive Species Database website;www.issg.org/database
2. Didymo Alga . . . a New Intruder? fact sheet ; MDDEP-MRNF Scientific Advisory Committee on Didymosphenia geminata (2007); Ministere du Developpement durable, de l'Environnement et des Parcs, Ministere des Ressources naturelles et de la Faune website; www.mddep.gouv.qc.ca/biodiversite/eae/factsheet.pdf
3. Didymo: What Anglers Can Do About It; Department of Conservation Te Papa Atawhai (New Zeland); www.doc.govt.nz.
Starry stonewort is a green macroalga (a complex, multicellular algae that resembles a higher plant). Native to Eurasia, and believed to have been introduced to this continent through ballast water contamination, starry stonewort was first recorded in North America in 1978, growing in the St. Lawrence River. It has since spread to many sites along the St. Lawrence, and to portions of the Great Lakes region, (especially around Lake Ontario, parts of Michigan and New York). Though not yet known to be present in New England, Maine's proximity to infestations in the St. Lawrence River valley warrant putting this invader on our radar screen.
Like Maine's native stoneworts, Nitella and Chara, starry stonewort forms dense colonies of upright, plant-like stems sprouting whorls of slender, tentacle-like branches. The tiny, cream-colored, star-shaped reproductive structures called "bulbils" that occur at the base of branch clusters are distinctive. Even before they are evident to the naked eye the bulbils can be detected by feel, by gently squeezing the stems at the whorls. The tiny bulbils are distinctly "firm" relative to the soft gelatinous feel of the rest of the algae. If you suspect that you have found this invader, please notify MCIAP or Maine DEP immediately.
1. Mills, E.L., J.H. Leach, J.T. Carlton, and C.L. Secor. 1993. Exotic species in the Great Lakes: A history of biotic crises and anthropogenic introductions. J. Great Lakes Res. 19: 1-54
2. Geis. J. W., G. J. Schumacher, D.J. Raynal and N.P Hyduke. I981. Distribution of Nitellopsis obtusa (Charophyceae, Characeae) in the St. Lawrence River: a new record for North America. Phycologia 20(2):211-214, 1981
3. Nitellopsis obtusa: Macroalga. Fact sheet by Paul Lord, Cornell University. 2006
4. www.kranswieren.n./afbeeldingen.html. Translation support: T. Horvath and www.worldlingo.com/wl/translate
If you are interested in obtaining a more comprehensive listing of aquatic invaders on Maine's radar screen, please see the "advisory list" published in Maine's Action Plan for Managing Invasive Aquatic Species, available on line at: www.maine.gov/dep/blwq/topic/invasive/invplan.htm
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