Nitellopsis obtusa has a moderate environmental impact in the Great Lakes.
Realized:
When it was first reported, N. obtusa was the ninth most frequently collected macrophyte in the St. Clair-Detroit River system (Mills et al. 1993, Nicholls et al. 1988). It was recorded at a peak biomass of 259 g m-2 in September, when many other macrophytes were declining, giving it a competitive advantage (Nicholls et al. 1988, Schloesser et al. 1986). Once established in inland lakes, N. obtusa forms dense mats of vegetation that completely cover the lake bottom. Mats of N. obtusa can act like a commercial benthic barrier and lead to the accumulation of phytotoxins that could create redox conditions; these conditions have a reduced impact on the rootless N. obtusa as compared to native species (Pullman and Crawford 2010).
Mats of N. obtusa also correspond with a dramatic decrease in the biomass of competing species. Although specific surveys have not been conducted yet, there is serious concern for inland lake populations of native species that are dependent on lake bottom habitat, including minnows, logperch, darters, clams, and other invertebrates (Pullman and Crawford 2010). Dense mats of N. obtusa directly impact the habitat used by native fish for spawning. Bass and sunfish are known to regularly spawn in dense growths of native Chara species, but these spawning behaviors did not occur in correspondingly dense growths of N. obtusa (Pullman and Crawford 2010).
Nitellopsis obtusa has been associated with increased water clarity in inland lakes, which could in part be due to their association with zebra mussels (Dreissena polymorpha) as a favored substrate. In spite of increased water clarity from the mussels, the dense growth of N. obtusa actually reduces light availability for other submersed flora (Pullman and Crawford 2010).
Potential:
There is also research indicating that macrophyte species have a strong influence on phytoplankton through allelopathic interactions (Hilt et al. 2010, Mulderij et al. 2007, Pullman and Crawford 2010). In Sweden, N. obtusa dies off in the winter, which reduces the ability of slow colonizers like the isopod Asellus and amphipod Gammarus to establish significant populations in this habitat. As a result, it typically hosts many chironomids, while Chara tomentosa harbors more amphipods and isopods (Hargeby 1990).
In Lake Majcz Wielki, Poland, zebra mussels settle at densities of 1000 per m2 on N. obtusa and Stratiotes aloides, and at much lower densities on other plants (Lewandowski and Ozimek 1997).
There is no indication that N. obtusa is affecting Great Lakes native populations genetically, but it has been proposed that the population of N. obtusa in the Great Lakes represents a unique phenotype from its native population in Europe (Pullman and Crawford 2010).
Nitellopsis obtusa has a high socio-economic impact in the Great Lakes.
Realized:
There is a large economic investment from inland lake communities to manage and control invasions of N. obtusa. This is both to protect boat owners from potential damage to their vessels, as well as to maintain economically important recreational fishing and swimming areas (Pullman and Crawford 2010). Moreover, N. obtusa poses a risk of entanglement to swimmers, who also are displeased with this alga’s rough texture (R. Sturtevant , pers. comm.).
As one of the filamentous algae that frequently detaches from the bottom to form a floating mat, N. obtusa contributes both to lake “scum” and mats that wash up on beaches (R. Sturtevant, pers. comm.).
Potential:
While N. obtusa negatively affects water quality for other macrophyte and phytoplankton species, there is no evidence to suggest that the quality of drinking water is significantly affected. However, there have been no studies conducted to specifically address this issue.
Nitellopsis obtusa is a relatively new invasion, particularly to the inland lakes. The long term impacts on the economic value lake property cannot yet be properly assessed.
There is little or no evidence to support that Nitellopsis obtusa has significant beneficial effects in the Great Lakes.
Potential:
Nitellopsis obtusa is becoming regarded as the most aggressive invasive species in inland lakes and has been recorded replacing other nonnative and nuisance species, including Eurasian watermilfoil (Myriophyllum spicatum), fanwort (Cabomba caroliniana), and curly leaf pond weed (Potamogeton crispus) (Pullman and Crawford 2010). Hilt et al. (2010) suggested that N. obtusa could be an effective means of restoration for deep lakes in its native range.
Nitellopsis obtusa has a significant stratigraphical account that extends back to the early Quaternary and can be useful in biogeographical research, and well as in tracing evolutionary lineages (Soulie-Marsche et al. 2002).
In European regions, this species can be a good substrate for epiphytes, even though it is frequently covered in marl, which is a byproduct of photosynthesis formed when bicarbonate is used (Brindow 1987). It is known to have allelopathic properties towards cyanobacteria (Berger and Schagerl 2004). Nitellopsis obtusa increases in the Netherlands have been associated with increases in populations of red-crested pochards (Netta rufina), which feed preferentially on this species, possibly because it is a good source of calcium and sulfur (Ruiters et al. 1994).