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| NAS - Nonindigenous Aquatic Species |
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Common Name: starry stonewort, green alga
Taxonomy: available through 
Identification: Nitellopsis has long, uneven-length branches that look angular at each joint and may have one cream-colored bulb at the base of each cluster of branches. This macroalga displays relatively straight branches arranged in whorls, which attach at acute angles to stem nodes. Creamy white bulbils can occur at the base of the main axis just below the substrate-water interface and on branches of the main axis at nodes. Dark red gametangia can occur on branches at nodes. Plants are dioecious. Female oogonia, with bracts on either side, form at the upper nodes of branchlets. Plants can form gyrogonites, which are calcified, spiral-shaped fructifications (Bharathan 1983, 1987; Schloesser et al. 1986; Soulie-Marsche et al. 2002). Internodal cells of N. obtusa are quite large, often on the order of a few cm long (Steudle and Zimmermann 1977; Yoshioka and Takenaka 1979). Most stem and branch cells are around 1 mm in diameter, while stems themselves can reach up to 80 cm long (Hargeby 1990; Sher-Kaul et al. 1995).
Size: Main stem to 80cm
Native Range: N. obtusa is native to Eurasia, from the west coast of Europe to Japan (Mills et al. 1993; Soulie-Marsche et al. 2002).
Nonindigenous Occurrences: This plant was first discovered in the Great Lakes in the St. Lawrence River in 1978. N. obtusa was reported in 1983 from the St. Clair River, which is part of the Lake St. Clair drainage, and from the Detroit River, which is part of the Lake Erie drainage (Schloesser et al. 1986; Mills et al. 1993).
Ecology:
Nitellopsis is sometimes found in deep, slow moving water where other plants are scarce. N. obtusa is known to maintain permanent populations in freshwater or brackish water with salinity up to 5‰. It can tolerate salinity fluctuations up to 17‰ for around 1 week. It has the ability to shift cells from a high-energy state to a state of passive permeability under high salt loading or unfavorable environmental conditions. It experiences suppressed growth at water temperatures of 30°C. In such conditions apical cells no longer form and some plant cells may die (Moteyunene and Vorob’ev 1981; Marchyulenene et al. 1982; Winter et al. 1999).
N. obtusa was the 9th most common plant in the St. Clair-Detroit River system when it was first reported in 1983. Sampling indicates it occurs in relatively protected zones of this river system at water velocities of 3–11 cm/s, and on soft substrates such as silt, sand, and fine detritus. It occurs at 1–3.5 m depth and in areas with light transmittance ranging from 1–50%. In the Detroit-St. Clair River system it first appears around July and obtains highest biomass in September, gradually declining until March the following year, when it decomposes. It has been recorded in water temperatures of 0–24°C in this area. It occurs more in the Detroit River than the St. Clair River, while other Characeae occur more frequently in the latter. The environmental parameters determining Characeae distribution in these two rivers are not clear. In the St. Lawrence River, it is uncommon in early July but increases through to October. It occurs at an average depth of 4.8 m depth and 6% light transmittance. In its native habitat, it is typically found at depths of 3–8 m, preferring deeper habitats with low light transmittance but relatively high calcium and phosphorus content where other Characeae generally occur less frequently (Schloesser et al. 1986; Nicholls et al. 1988; Berger and Schagerl 2004).
In Bremen, the presence of this species may be favored by benthic fish, which feed on higher plants, thus conferring an advantage to charophytes (Trapp and Kirst 1999). In the Netherlands, many characean species, including this one, disappeared during a period of heavy eutrophication but have reappeared as water clarity has improved and eutrophication has decreased (Simons et al. 1994). Increases 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). 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). In Sweden, it typically hosts many chironomids while Chara tomentosa harbors more amphipods and isopods. The difference can likely be explained by the fact that this species experiences winter die-offs, while C. tomentosa remains green year-long. Each host species harbors invertebrates with different life history strategies suited to each plant’s life cycle (Hargeby 1990). 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). Finally, it often produces oospores in eutrophic conditions (Bharathan 1987).
Means of Introduction: N. obtusa was very likely introduced in ballast water to the Great Lakes (Schloesser et al. 1986; Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction: Unknown.
Remarks: N. obtusa was first reported from the St. Lawrence River in 1978, 850 km from the site where it was first found in the Great Lakes (Schloesser et al. 1986; Mills et al. 1993).
N. obtusa was thought to have been locally extirpated in some regions of its native range where it has been rediscovered, in, for example, parts of Germany (Golombek 1998; Raabe 2006) and Japan (Kato et al. 2005). It is considered rare in Bremen, Germany but has recently increased in abundance in some lakes (Trapp and Kirst 1999). Populations are considered somewhat vulnerable in Sweden (Blindow 1994).
References
Berger, J. and M. Schagerl. 2004. Allelopathic activity of Charceae. Biologia (Bratislava) 59(1):9-15.
Bharathan, S. 1983. Developmental morphology of Nitellopsis obtusa. Proceedings of the Indian Academy of Sciences. Plant Sciences 92(5):373-379.
Bharathan, S. 1987. Bulbils of some charophytes. Proceedings of the Indian Academy of Sciences. Plant Sciences 97(3):257-264.
Blindow, I. 1987. The composition and density of epiphyton on several species of submerged macrophytes – the neutral substrate hypothesis tested. Aquatic Botany 29:157-168.
Blindow, I. 1994. Rare and threatened charophytes in Sweden. Svensk Botanisk Tidskrift 8(2):65-73.
Golombek, P. 1998. Rediscovery of Nitellopsis obtusa in Hamburg. Floristische Rundbriefe 32(1):105-109.
Hargeby, A. 1990. Macrophyte associated invertebrates and the effect of habitat permanence. Oikos 57(3):338-346.
Kato, S., S. Higuchi, Y. Kondo, S. Kitano, H. Nozaki, and J. Tanaka. 2005. Rediscovery of the wild-extinct species Nitellopsis obtusa (Charales) in Lake Kawaguchi, Japan. Journal of Japanese Botany 80(2):84-91.
Lewandowski, K. and T. Ozimek. 1997. Relationship of Dreissena polymorpha (Pall.) to various species of submerged macrophytes. Polskie Archiwum Hydrobiologii 44(4):457-466.
Marchyulenene, D. P., R. F. Dushauskene-Duzh, E. B. Moteyunene, I. Y. Trainauskaite, and V. B. Nyanishkene. 1982. Effect of temperature conditions in a water body on hydro photocenoses. Soviet Journal of Ecology 13(2):120-125.
Mills, E. L., J. H. Leach, J. T. Carlton, and C. L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.
Moteyunene, E. B. and L. N. Vorob’ev. 1981. Ecological physiological characteristics of Charophyta algae cells. 2. Ionic permeability of cell membranes. Lietuvos TSR Mokslu Akademijos Darbai Serija C Biologijos Mokslai 1:99-114.
Nicholls, S. J., D. W. Schloesser, and J. W. Geis. 1988. Seasonal growth of the exotic submersed macrophyte Nitellopsis obtusa in the Detroit River of the Great Lakes. Canadian Journal of Botany 66:116-118.
Raabe, U. 2006. Starry stonewort (Nitellopsis obtusa) rediscovered in Berlin. Verhandlungen des Botanischen Vereins von Berlin und Brandenburg 139:181-186.
Ruiters, P. S., R. Noordhuis, and M. S. Van Den Berg. 1994. Stoneworts account for fluctuations in Red-crested Pochard Netta rufina numbers in the Netherlands. Limosa 67(4):147-158.
Schloesser, D. W., P. L. Hudson, and S. Jerrine Nichols. 1986. Distribution and habitat of Nitella obtusa (Characeae) in the Laurentian Great Lakes. Hydrobiologia 133:91-96.
Sher-Kaul, S., B. Oertli, E. Castella, and J.-B. Lachavanne. 1995. Relationship between biomass and surface area of six submerged aquatic plants species. Aquatic Botany 51:147-154.
Simons, J., M. Ohm, R. Daalder, P. Boers, and W. Rip. 1994. Restoration of Botshol (The Netherlands) by reduction of external nutrient load: recover of a characean community, dominated by Chara connivens. Hydrobiologa 275-276:243-253.
Soulie-Marsche, I., M. Benammi, and P. Gemayel. 2002. Biogeography of living and fossil Nitellopsis (Charophyta) in relationship to new finds from Morocco. Journal of Biogeography 29(12):1703-1711.
Steudle, E. and U. Zimmermann. 1977. Effect of turgor pressure and cell size on the wall elasticity of plant cells. Plant Physiology 59:285-289.
Trapp, S. and G.-0. Kirst. 1999. Nitellopsis obtusa in Bremen. Abhandlungen Naturwissenschaftlichen Verein zu Bremen 44(2-3):505-510.
Winter, U., G. O. Kirst, V. Grabowski, U. Heinemann, I. Plettner, and S. Wiese. 1999. Salinity tolerance in Nitellopsis obtusa. Australian Journal of Botany 47(3):337-346.
Yoshioka, T. and T. Takenaka. 1979. Nitellopsis obtuse cell birefringence change during action potential. Biophysics of Structure and Mechanism 5:1-10.
Other Resources:
A Field Guide to VALUABLE UNDERWATER AQUATIC PLANTS of the Great Lakes by Donald W. Schloesser.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 7/25/2007 Citation for this information:
Rebekah M. Kipp. 2009. Nitellopsis obtusa. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1688> Revision Date: 7/25/2007
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