Didymosphenia geminata, commonly referred to as didymo or “rock snot”, a species of rapidly reproducing single cell micro-algae that is capable of growing to harmful levels in freshwater rivers and streams, has been detected in the St. Marys River near Sault Ste. Marie. The St. Marys River drains Lake Superior beginning at Whitefish Bay and flows 75 miles southeast into Lake Huron. A native of cold, low nutrient freshwater rivers, streams, and less frequently, inland lakes, within northern temperate and boreal regions of Europe, Asia and parts of North America, including most of Canada, the species is capable of creating thick mats which smother the rock and pebble based habitat that is critical to supporting cold water trout populations and the macro-invertebrate insect communities which are such an important component of riverine food chains.
Although capable of sexual and asexual reproduction, nuisance level accumulations of didymo are known to result primarily from asexual reproduction. When didymo cells rapidly divide, the stalk that was attaching the cell to a rock or pebble also divides, soon creating thick mats of complex, multi-layered structures that are resistant to degradation and prone to rapid bio-accumulation. Streams and rivers possessing clear, cold, sun drenched freshwater ranging in temperature from 4°- 16° C (39° – 60° F) and low (oligotrophic) nutrient concentrations are known to provide optimal ecological conditions for asexual reproduction of the species and the formation of nuisance level didymo mats. Thick didymo colonies are capable of clogging municipal water intakes and may eventually render recreational fishing nearly impossible due to large clumps of didymo floating down stream that easily catch on fishing flies, spinners, and hooks, demanding almost constant removal each time the line is retrieved.
With the recent detection and confirmation of didymo near St. Ste. Marie, Michigan joins a rapidly growing list of states and Canadian provinces that are currently known to host the native, though sometimes invasive algae, within North America, including Alaska, Arkansas, California, Colorado, Idaho, Missouri, Montana, New Hampshire, New York, North and South Dakota, Tennessee, Utah, Vermont, West Virginia, Virginia, Washington, Wyoming as well as the provinces of Ontario, Quebec, British Columbia and Alberta. Confirmations of didymo infestations in Chile and New Zealand remain the only reports of invasive didymo in the Southern Hemisphere.
Recreation boaters, including those using kayaks and canoes, are advised to use extreme care in disinfecting their watercraft immediately upon removal from rivers and streams that are known to host active didymo colonies – didymo may be spread by transferring a single drop of water hosting the microscopic organism to unaffected water bodies possessing ecological conditions that are capable of supporting the species. In addition, recreational fisherman are advised to thoroughly dis-infect all fishing gear, including artificial lures, fishing line and waders. The Missouri Department of Conservation offers the following guidance for preventing the spread of didymo:
• Don’t wear porous-soled waders when fishing in trout parks, trout streams
• Treat your porous-soled waders to avoid spreading didymo
• Check all gear and equipment after use and remove any visible algae. If you notice algae on your equipment at a later time, do not dispose of the algae by putting it down a drain. Dispose of it in the trash.
• Clean all equipment with a 2 percent household bleach solution, 5 percent saltwater solution, or dishwashing detergent. Allow all equipment to stay in contact with the solution for at least three minutes. Soak all soft items, such as felt-soled waders and life jackets, in the solution for at least 20 minutes.
• Dry all equipment in sunlight for at least 48 hours.
• Consider replacing felt-soled waders with a new, environmentally sensitive alternative.