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New Invader
Didymo Makes Its Appearance in the Northeast
By Susy King, NEIWPCC
Invasive species come in many different sizes, shapes, and colors, but few have a nickname as disgustingly descriptive as “rock snot.” That is what some people call the species known more commonly as didymo, and the assumption can be made from its nickname alone that it is undesirable in a water body. But what exactly is didymo (or rock snot) and why is its presence in the Northeast of serious concern?
Didymo’s full and formal name is Didymosphenia geminata. It is a freshwater diatom, which is a type of single-celled algae. While the species earned its nickname from its slimy appearance, calling it rock snot is somewhat misleading because it actually has a rough texture similar to wet wool or cotton balls. Didymo uses stalks to attach to rocks and plants in a river system. It can form blooms on the bottom of river beds that can smother aquatic life such as macroinvertebrates, native algae, and other organisms. In addition, the flowing masses of stalk structures, which can resemble toilet paper, are unattractive (to say the least) and make recreation in affected water bodies much less inviting.
The first sighting of didymo in the Northeast came in the summer of 2006 when it was identified in the New York section of the Batten Kill. The following summer it was found in the New York and Vermont sections of the Batten Kill, as well as in the Connecticut River in New Hampshire and Vermont, the White River in Vermont, and the Delaware River system in New York and Pennsylvania. In 2008, didymo was discovered in the Gunpowder River in Maryland and the Mad River in Vermont.
While it is believed that the didymo found in the Northeast was transported to the region by contaminated fishing or wading gear, its origins are harder to discern. Didymo prefers colder, low-nutrient, high-clarity streams, and is believed to be native to far northern Europe and Asia. But in recent years it has been expanding its geographic range and is now being found in warmer, more nutrient-rich waters. Didymo may be expanding its range due to water quality changes, climate change, and genetic variation. In addition to the outbreaks in Northeast waters, didymo infestations have been reported in a number of states west of the Mississippi, as well as in Quebec, British Columbia, and central Europe.
The infestation that has most vividly revealed the threat posed by didymo occurred in New Zealand, where didymo was discovered in October 2004. Despite attempts by New Zealand’s government to contain the invasion, didymo spread into 12 rivers on the South Island within 18 months and formed excessive blooms in multiple locations. Amid concerns over the effects on commercial eel fisheries, water supplies, tourism, and biodiversity values, New Zealand passed a law making the intentional spread of didymo punishable by up to five years in prison and a fine of $62,000 (U.S. dollars). The serious response came as economists were warning of didymo’s potential impact: one report said the cost to New Zealand’s economy could be as high as $176 million (USD).
The Right Response
Given didymo’s rapid expansion in New Zealand, officials in Vermont and New Hampshire knew they had to act quickly when didymo turned up in the Connecticut River in June 2007. The initial response was an aggressive public outreach campaign. The states’ environmental agencies developed a joint informational website, posted signs at water bodies, developed public service announcements, identified best management practices to prevent spread, and issued a protocol for reporting suspected didymo sightings.
Because there are no known methods for eradicating didymo, management of this species must focus on spread prevention. That is a challenge since individual cells of didymo are microscopic, making it impossible to tell with the naked eye if they have attached to recreational equipment such as felt-soled waders, life jackets, bait buckets, diving gear, water shoes, canoes, and kayaks. Consequently, much responsibility falls on users of waters. The most effective way to prevent spread is to restrict recreational equipment to use in a single waterway. If this is not feasible, users are asked to follow the “check, clean, dry” approach.
Check: Before leaving a water body, look for clumps of algae or sediment attached to gear, remove them, and leave them at the site.
Clean: Non-absorbent items should be soaked and scrubbed for at least one minute in a 5 percent solution of dishwashing detergent, soaked and sprayed for at least one minute in a 2 percent solution of household bleach, or soaked for at least one minute in very hot water (140°F or above) or at least 20 minutes in hot water (120°F or above). Absorbent items should be soaked in very hot water (140°F) for at least 40 minutes or soaked for 30 minutes in a hot (120°F) 5 percent solution of dishwashing detergent. Bleach is not recommended for absorbent materials.
Dry: If cleaning is not practical, after an item is dry to the touch, it should be left dry for at least another 48 hours before being used in another water body.
To help residents who suspect they have found didymo in a waterway, Vermont and New Hampshire have developed an identification guide that is available from the states’ didymo websites (listed at the end of this article.) If the guide indicates a positive identification, a sample should be sent to the environmental agency in the respective state. GPS coordinates or a clearly marked map showing the location should be included so state staff can visit the site to confirm didymo’s presence.
On a regional level, the Northeast Aquatic Nuisance Species (NEANS) Panel allows states to have an ongoing dialogue to share experiences with didymo. NEIWPCC staff actively participate in the panel, which held a workshop in November 2007 to bring together invasive species experts in the region to discuss didymo. States with confirmed sightings provided information about their plans for response while currently unaffected states shared strategies for keeping didymo out of their waters. Following the workshop, the NEANS Panel developed a regional didymo fact sheet that contains background and spread prevention information that has been agreed upon by all states, allowing a consistent message to be disseminated throughout the region (www.northeastans.org/resources.htm).
Nationally, EPA’s response to didymo has been conducted primarily by its Region 8 office, which covers Colorado, Montana, North Dakota, South Dakota, Utah, and Wyoming. The office has developed an informational website and an international fact sheet (www.epa.gov/region8/water/didymosphenia). In addition, EPA and the Federation of Fly Fishers co-wrote a white paper on didymo in January 2007. The paper contains details on didymo’s biology, geographic distribution, and ecological relationships, as well as recommendations for response. The recommendations include developing an aggressive education and outreach program, determining the degree to which the spread of didymo is aided by specific human vectors, developing strategies to mitigate existing blooms, and verifying the direct and indirect impacts of didymo and its stalks on aquatic macroinvertebrates and fish.
The Future of Didymo
While state agencies are putting tremendous effort into addressing didymo, many questions remain unanswered. There is widespread concern that didymo will affect trout populations, but studies conducted around the world have not conclusively shown that the algae have significant impacts on trout fisheries. There is also uncertainty surrounding the factors that limit or support bloom activity. Why is it that so many rivers that contain viable didymo cells do not experience nuisance blooms? As research continues, the answers to these and other questions will help scientists and managers better understand this species and how to address its presence and prevent further spread.
In the meantime, states will continue to monitor waters to observe existing populations and detect new invasions. It is imperative that the public do its part by following practices that will prevent didymo from becoming further established in the Northeast. While we do not yet know how seriously didymo will impact Northeast waters, it is far better to take precaution now than to wait until the situation escalates and is much more difficult to control.
Susy King (sking@neiwpcc.org) is a NEIWPCC environmental analyst. She is currently serving as co-chair of the NEANS Panel.
Vermont DEC: http://www.vtwaterquality.org/lakes/htm/ans/lp_didymo.htm
New Hampshire DES: http://des.nh.gov/organization/divisions/water/wmb/exoticspecies/didymo/index.htm