October 16, 2009

FeatureRock Snot is Nothing to Sneeze At

Though endemic to some waterways in North America and northern Europe, the algae Didymosphenia geminata is starting to become a problem in lakes, streams, and other waterways where it has inadvertently been introduced.

Didymosphenia geminata is a single-cell alga commonly referred to as rock snot due to its grayish-brown color and clumpy appearance. This alga also goes by the name "didymo" for short. Though it looks slimy, it actually only feels like wet cotton or wool.

While many species of algae float on top of the water surface, didymo instead clings to rocks in river bottoms and other waterways. What starts as a few dots on a rock eventually turns into a massive clump of algae that remains attached to the rock’s surface by a stalk. The free ends of the alga float in the water, forming white “rat-tails” that resemble clumpy toilet paper.

One major problem with didymo is that it can form huge blooms without warning. These blooms can have deleterious consequences for native organisms by smothering them. The algal mats that form can also be a major problem for public works when they clog water intake systems.

Research indicates that didymo can be spread from one waterway to another by contaminated fishing equipment. Felt-soled waders worn by fly fisherman and other fishing enthusiasts are of particular concern. Studies indicate that Didymo can survive for a period of at least 24 hours outside of water. If they remain in a damp and cool environment, the alga can survive for up to 90 days. The use of felt-soled waders has been banned in New Zealand. Didymo was first discovered in a stream in New Zealand in 2004, and has since spread to over 120 rivers and streams in the country’s South Island. Protecting the country’s waterways from infiltration by didymo is a high-priority in New Zealand; anyone convicted of knowingly transferring didymo from one waterway to another may face up to five years in prison and/or a fine of up to $100,000.

In the United States, fishers are encouraged to use rubber-soled waders. Fishers are also encouraged to check their equipment before they leave the fishing site to remove any visible pieces of algae. Afterward, they should let their equipment dry completely before entering any other waterway with it. If this is not possible, officials with the U.S. EPA encourage sportsfishers to dip their fishing equipment into a solution made of bleach and water to sanitize their equipment and kill any didymo cells.

Thus far there is no recommended method to remove or kill didymo in affected waterways. Scientists in New Zealand tested one potential control agent but found its use was not yet warranted and required further study. It is in the best interest of fishers to ensure they do not aid in the spread of didymo, as the algae has been implicated in habitat loss for the very fish the sportsfishers aim to catch. Didymo algal blooms often choke out insects such as stoneflies and worms that species such as trout depend on as a food source. Reducing the spread of didymo will help ensure that adequate habitat is available for these species of game fish.

More to Explore

• An Unsightly Algae Extends Its Grip to a Crucial New York Stream
• Didymo: a nuisance and invasive freshwater alga
• Distribution Map of D. geminata in North America
• Didymo Species Profile
• Introduction to Didymosphenia geminata (Didymo) [video]
• Biosecurity New Zealand: Didymo

Last updated October 16, 2009 | Comments (2) | Permalink | Feature