Recreational fishing is a multi-million dollar industry and a popular recreational pastime for many Americans. This tradition, however, may be threatened by the introduction of didymo (Didymosphenia geminata) to trout spawning areas. Tom Atwood is spearheading an effort to learn more about the effects of this species on trout eggs. Didymo, “an aquatic nuisance species” forms thick mats on the bottoms of rivers and other waterways. This species attaches itself to rocks and plants along the bed of the waterway, “making its presence ubiquitous on river bottoms” says Atwood.
The spawning habits of trout involve laying nests of eggs called redds on the bottom of riverbeds. The success of these eggs depends on the water hydraulics surrounding them. Atwood believes that the growing presence of didymo in streams will interfere with these hydraulics, leading to inhibited egg growth. This is an example of a trophic cascade or when the primary producer in a system disrupts a food chain so that the top-level predator is affected. Atwood explains that in this case, the top-level consumer being affected is the adult trout. He intends to test his hypothesis and has submitted a research proposal addressing with the issue.
Atwood’s research would involve the establishment of several experimental troughs. These would be created to simulate the environment of a typical river and redd. Trout eggs of the genus Salvelinus and Oncorhynchus will be added to the troughs. Each collection of troughs will also have a certain amount of didyo ranging from none at all to a heavy cover. Aspects of the water such as initial water velocity, oxygen concentration, fine sediment level and surface water-groundwater exchange would be continuously monitored in each trough. At the end of the study, egg mortality and successful hatches will be counted and compared to the presence of didymo. With this information, Atwood hopes to answer basic questions about the influence of didymo on water hydraulics and how it affects trout redds in nature.
The results of this study will be of prominent concern to recreational trout fishermen throughout the United States. It will educate these citizens about the threat that didymo poses to their game fish and compel them to be more cautious about unintentional invasive species transfer. The study will also elucidate the effects of didymo on the various trophic levels present in a stream ecosystem.