Aquatic Invasive Threats: Didymo

In honor of National Invasive Species Awareness Week...

Aquatic ecosystems across the planet, like their terrestrial neighbors, are threatened by the introduction of nonnative, invasive species.  Invasive species are organisms that are not naturally found in a given habitat that have been introduced by some human-caused means.

Many times, these introductions are the result of a deliberate act:  dumping out a bait bucket with fish from another stream, the release of an unwanted pet, the planting of an ornamental plant from another region.  Sometimes, the human responsible for an introduction is completely unaware of the act he or she is committing.  This is often the case with an aquatic invasive species known as Didymo (Didymospenia geminata).  This diatom- a kind of brown algae- is native to northern Europe and possibly northeastern Canadian streams. In its native environment, it occupies very cold, low nutrient streams with fast moving water.  It is thought to be introduced by contaminated boats, fishing waders, or felt-soled boots.

One common nickname for Didymo is "rock snot". Image from USDA

Since the 1990s, Didymo has been found outside of its native range in systems in the western U.S.  In 2005, it was discovered in Tennessee.  Once established in a stream, it covers rocky substrates with a blanket of blooms that crowd out native plant and animal communities.  Large infestations resemble a slimy, brown shag carpeting that can cover 100% of affected stream bottom.

The best way to help prevent the spread of this nuisance algae is to properly clean and sterilize fishing equipment after each use.  The algae can survive on fishing equipment for many weeks, even if the equipment seems dry.  Follow these recommendations from the US EPA to help reduce the risk of spreading Didymo:

• When leaving a watershed, check equipment for clumps of Didymo.  If any are found, remove them and leave them at the site.  If any are detected, inspect all equipment very thoroughly.
• Scrub and soak all equipment with a 2% (by volume) bleach solution.  Dish detergent is also suitable.
• If cleaning of equipment is not feasible, let equipment dry completely for at least 48 hours before transporting to another watershed.

Additional Resources:
http://www.epa.gov/Region8/water/didymosphenia/White%20Paper%20Jan%202007.pdf
http://www.invasivespeciesinfo.gov/aquatics/didymo.shtml