Aquatic Invasive Species

Marine and Freshwater Research doi: 10.1071/MF08011 (2008)

Didymosphenia geminata, an invasive freshwater diatom, forms thick mats in riverbeds.  Riverbeds are home to trout redds, gravel nests in which eggs are laid.  According to a recent study, didymo may impede the flow of water to redds, decreasing the amount of oxygen received by eggs and causing a decline in trout populations.

A study by the Clutha Fisheries Trust, led by Drs. Tobias Bickel and Gerard Closs, investigated the effect of didymo on hydraulic conditions in trout redds.  The team collected data from rivers with varying didymo presence, measuring in each the oxygen concentration, hydraulic conductivity, substrate water flow, and surface water – groundwater exchange rate.  They found that the amount of didymo had no effect on the first three variables, but that there was significant indication that didymo diminishes surface water – groundwater exchange.  This water transfer is critical to trout egg development, and the authors recommend that further research be done.

Freshwater Biology doi:10.1111/j.1365-2427.2009.02247.x (2009)

Didymosphenia geminata, more commonly known as “rock snot”, is considered a serious invasive species. More than just decreasing an ecosystem’s aesthetic appeal, didymo may, according to a recent study, affect the biological community of the invaded territory.

Cathy Kilroy of the New Zealand National Institute of Water and Atmospheric Research Limited and her colleagues studied the effect of didymo on periphyton biomass, invertebrate community diversity and composition, and overall taxon richness. The team performed studies in three different rivers, one dammed, one unregulated but lake-fed, and one unregulated with no lakes. Statistical analysis of the results indicated that the presence of didymo led to an increase in periphyton biomass and invertebrate density, as well as a shift and homogenization of the invertebrate community. The data did not, however, indicate any decrease in overall taxon richness or species diversity. Nonetheless, the fact that didymo has clearly measurable effects suggests that it could create problems in some environments.

Emilia Rybak

Didymo is a type of invasive microscopic algae that is native to North America and Europe, but has extended into multiple western and eastern U.S. states. It is often spread unknowingly by clinging to felt-bottom fishing boots. Its growth and expansion can affect both aquatic organisms and humans. Specifically, it grows in think layers that fully cover river bottoms, which harms sport fish that feed on organisms living in river bottoms and also congests water intakes.

Didymo’s potentially drastic impact on native aquatic species and their habitats can be attributed to several factors. For example, as is the case with several other invasive species, Didymo is capable of spreading rapidly. However, it does not require specific select conditions to survive. Unlike other aquatic invasive species, Didymo can flourish not only in waters that are flowing and nutrient-rich, but also those that are still, pristine, and nutrient-poor. Additionally, there are no known strategies to manage and eliminate Didymo once it expands throughout a body of water. Thus, the combination of these factors allows Didymo to spread uncontrollably and hinders its removal from infested areas.

I think that Didymo is a particularly threatening invasive species that needs to be taken seriously by ecologists and fishermen across the U.S. It is unfortunate that Didymo cannot ever be completely eradicated once it spreads into an area, which is why prevention measures are all the more important for this invasive species. Fisherman can use simple preventive methods to substantially reduce the expansion of Didymo, and I think that if these strategies are carried out thoroughly and regularly, they can be considerably effective. Practices like using rubber-sole boots as alternatives to felt-bottom ones, and following a “check, clean and dry” technique of inspecting fishing equipment can help slow the spread of Didymo into other regions. I would like to know the extent of the effect of Didymo on the popularity of fishing spots around the U.S., since it reduces sport fish populations by harming various organisms on which they feed.

Sources:

http://www.dec.ny.gov/animals/54244.html

http://www.digitalfrontier.com/sites/greenmountaintroutfitters/untitled89/index.html