Written By: Mitchell Dwyer, Brittany Williams, Cole Brodeur and John North.
Starry Stonewort, Nitellopsis obtusa, is a member of the Characae family (Escobar, Qiao, Phelps, Wagner, & Larkin, 2016) and is a heavily dispersed aquatic plant. Starry stonewort is a native species found in Eurasia, ranging in locations in Europe and Asia (Hackett, Caron, & Monfils, 2014). It is typically found in Europe, but occasionally can be found in Malaysia, Pakistan, and India (Naz, Diba, & Zaman, 2010). The populations are limited globally to locations between 24° and 65 ° N latitude, but population sizes vary among continents. The first non-indigenous occurrences began in the U.S. along the St. Lawrence River. Its present range includes the Great Lakes region, and locations have also been confirmed in Indiana, Wisconsin, New York, Michigan and Minnesota (Escobar et al, 2016). One of the most recent studies in Ontario found various locations in Presqu’ile Bay on the shore of Lake Ontario near Brighton, Ontario (Midwood, Darwin, Ho, Rokitnicki-Wojcik, & Grabas, 2016). In conclusion, starry stonewort is invasive in North America (see figure 1), native to parts of Eurasia, and on the endangered list in the United Kingdom (Escobar et al, 2016). Although some patterns are starting to show, little is known about the distribution of starry stonewort and why it is becoming such a problem in North America.
Starry Stonewort grows in a variety of conditions; higher water hardness, conductivity and nitrate levels all seem to be present in lakes containing the plant (Pullman & Crawford, 2009). Although little is known about the environmental conditions that promote starry stonewort’s growth it is believed that lakes with high dissolved calcium are crucial for survival. In Presqu’ile Bay, it was noted to be growing successfully and more often in areas with higher water hardness, higher conductivity, and higher nitrate-nitrite (Midwood et al, 2016). Nitellopsis obtusa prefers deeper (up to 9 m), less turbulent waters where it can take root on the bottom of the lake, but is also present in shallow waters growing on the surface. In their native habitats in Europe and Asia, it is can be found in freshwater lotic habitat with sandy bottoms or deep water (Naz et al, 2010). It has also been discovered that in their native habitat starry stonewort can enhance water clarity and provide habitat and food for fish, invertebrates, and waterfowl (Midwood et al, 2016). While performing an ecological niche modeling, researchers determined Nitellopsis obtusa’s suitable niche is in shallow water, less than 10m in depth, with a pH range of 3.8 – 38.4, a dissolved oxygen range of 5.72ml/l – 8.33ml/l and in locations with an annual mean temperature of 4.37°C – 15.57°C and a coldest month temperature range of -20.11°C – 9.63°C (Escobar et al, 2016). Starry Stonewort has been observed growing up to 2 meters (7 feet) in oligo-mesotrophic lakes in Michigan, exhibiting that water clarity and lake bathymetry are factors that should be considered for habitat establishment (Hackett et al, 2014). In Michigan it has been found to thrive in cooler waters in spring, winter, and fall (Pullman & Crawford, 2009). It has been known in Michigan to colonize in highly organic areas, with unconsolidated sediments, gravel, and sand. It is undetermined if it prefers full sun or shade (Pullman & Crawford, 2009).
Starry stonewort is classified as an r-strategist. Starry stonewort spreads extremely rapidly from lake to lake once established. There are typically many offspring produced, and early maturity. It produces oocytes which can be seen by the naked eye, which act as the seeds for reproduction. This species reproduces asexually via star-shaped structures called bulbils and fragments, resulting in rapid population growth in suitable conditions (Escobar et al, 2016). The bulbils have been found to be more abundant in late fall or early spring, although they are present for most of the growing season (Hackett et al, 2014). It is more common to find male (antheridium) plants in North America, although it is possible that female plants are just not being discovered during research (Escobar et al, 2016). In the case of a bottleneck, it could be argued that due to the species ability to rapidly reproduce they would recover in a short period of time. Biomass continues to grow until September where it starts to stagnate until winter comes, continuing the cycle (Hackett et al, 2014). Other key elements that support this conclusion are summarized in table 1.
Table 1: Summary of the reproductive characteristics of the Starry Stonewort, Nitellopsis obtusa. Note that is aligns best with the reproductive characteristics of r-strategists
|Mortality||Variable and unpredictable||More constant and predictable||Varies depending on conditions of Lake/body of water|
|Seedling size||Large||Small||Produces multiple oocytes that vary on nutrient levels|
|Parental Investment||Very little if any||Required||None|
|Frequency of Reproduction||Once to multiple times over short time period||Multiple times but over a prolonged period||Multiple times, most often occurring during optimal temperatures in summer|
|Additional factors||Most reproductively mature individuals reproduce successfully||Few reproductively mature individuals or only some reproduce successfully||All Starry Stonewort reproduce given the availability of nutrients for growth|
Starry Stonewort has a low percentage of survival in the beginning stages of its life cycle but once it has matured and taken root on the bottom of the lake it has a much greater chance of survival. Not all seeds that are dispersed will take root and this is the main reason that starry stonewort exhibits a Type III survivorship curve (The Nature Education, 2014).
Dispersal and Vectors:
Starry stonewort is able to spread rapidly from lake to lake through various factors. It is thought that the plant was first introduced via ballast water (liquid that is brought on board of a ship to help with draft and regulate stability) in the 1970’s (Midwood et al, 2016). Starry Stonewort has established itself in water bodies with very little to no traces of humans by means of aquatic animals. The oocytes easily stick to feathers on birds or the fur of waterfowl and often are released when the animal lands in the water, providing a new habitat for the Starry Stonewort to establish itself (Pullman & Crawford, 2009).It is also up for debate, whether or not it can spread through boats or trailers (Pullman & Crawford, 2009). When this happens, starry stonewort is easily able to establish itself in different bodies of water and quickly grow in population size. Recent studies however indicate that even lakes that contain no public access by means of public boat launch sites play host to Starry Stonewort (Pullman &Crawford, 2009). This means that waterfowl play an even bigger part in the dispersion and spread of Starry Stonewort to new bodies of water that contain no public access. During spring, summer, and fall the plant will continue to produce biomass and will only stop once it has “pillowed” the bottom of the lake or covered the entire floor of the lake (Pullman & Crawford, 2009). Although there has been little research on the main cause for seed dispersal, animals and humans are known vectors.
Nitellopsis obtusa, is a relatively new species in North America with limited information on life cycle, distribution and physiological tolerance (Escobar et al, 2016). It belongs to a complex taxonomical group, and have many similarities to native plants in the same taxa (Chara and Nitella spp.), making it challenging for non-expert researchers to identify (Escobar et al., 2016). Starry Stonewort can spread through fragmentation from wind currents or human activity. It can develop exceedingly fast, growing tall, dense and can create surface mops that interfere with recreation and displace native species withing the ecosystem. They make surrounding sediments inhospitable for plant growth (Pullman & Crawford, 2009). Due to this, other plants that contain no roots such as common bladderwort and coon’s tail thrive in aquatic communities containing Starry Stonewort (Pullman & Crawford, 2010). Starry Stonewort is also a very competitive aquatic plant which regularly outcompetes other non-native species such as Eurasian Water-milfoil, Fanwort, and Curly-leaved pondweed for resources and more often than not completely remove these other competing species from the body of water the Starry Stonewort has established itself in (Pullman & Crawford, 2009).
Escobar, L. E., Qiao, H., Phelps, N. B. D., Wagner, C. K., & Larkin, D. J. (2016). Realized niche shift associated with the Eurasian charophyte Nitellopsis obtusa becoming invasive in North America. Scientific Reports, 6.
Hackett R.A., Caron J.J., & Monfils A.K. (2014). Status and Strategy for Starry Stonewort (Nitellopsis obtusa (N.A.Desvaux) J.Groves) Management. Michigan Department of Environmental Quality, Lansing, Michigan.
Midwood, J. D., Darwin, A., Ho, Z. Y., Rokitnicki-Wojcik, D., & Grabas, G. (2016). Environmental factors associated with the distribution of non-native starry stonewort (Nitellopsis obtusa) in a Lake Ontario coastal wetland. Journal of Great Lakes Research, 42(2), 348-355.
Naz, S., Diba, N. J., & Zaman, M. (2010). Nitellopsis obtusa (Desv.) J. Groves. A new Charophytic record for Bangladesh. Bangladesh J. Plant Taxon, 17(2), 203-207.
Pullman, D., Crawford, G. (2010). A decade of starry stonewort in Michigan. LakeLine. pp. 36-42.
Sleith, R. S., Havens, A. J., Stewart, R. A., & Karol, K. G. (2015). Distribituion of Nitellopsis obtusa (Characae) in New York, U.S.A. Brittonia, 67 (2), 166-172.
U.S. Geological Survey. (2016). Starry stonewort (Nitellopsis obtusa) –FactSheet (n.d.) Retrieved January 27, 2017 from https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=1688“The Nature Education. (2014). Survivorship Curves. Retrieved from http://www.nature.com/scitable/knowledge/library/survivorship-curves-16349555