Written by: Brittany Williams, Mitch Dwyer, John North, Cole Brodeur
Historical Context: Starry stonewort is immensely different in North America compared to where it is historically found in Europe and Asia. The first known observation of starry stonewort in North America was in 1978 along the St. Lawrence River. Although it had been discovered 39 years ago, very little was done for roughly 30 years. It is thought that Starry stonewort was brought over to North America by ballast waters from ships (Hackett RA, 2014). This then led to the infestation of many inland lakes in Southern Ontario and Michigan. In North America the plant is hardy and grows very aggressively, but in Europe it is on the endangered list and is under general protection (Pullman and Crawford, 2009). Starry stonewort has both environmental and socio-economic effects on lake ecosystems. Initial studies suggested that starry stonewort would outcompete native plant species and negatively affect fish spawning because of its tendencies to grow dense mats on the lake bottom (Pullman & Crawford, 2010). The research regarding the effects on plant species is unclear, although some interesting observations have been made in recent years. In recent observations, it has been noted that bladderworts and coontail can actually thrive in starry stonewort infested waters. Whereas, invasive plants such as curly leaf pondweed, water milfoils, and fanwort get outcompeted by starry stonewort (Pullman & Crawford, 2010). Although the research with the effects on flora is inconclusive, the effects on fauna seem to be consistent among studies. Starry stonewort has been thought to affect waterfowl, as these species rely on native plants for nesting, foraging, and shelter. In addition, fish are losing potential spawning, and foraging habitat (Midwood et al, 2016). Another factor to starry stonewort research, is that zebra mussels seem to favour it as a substrate (Pullman & Crawford, 2010). Therefore, areas with zebra mussels and starry stonewort will have increased water clarity, which also may affect the ecology of the bodies of water. The socio-economic impacts range from impacts on fisheries to property damage and reduced recreational appeal. (Midwood et al, 2010).
Considering research and monitoring of starry stonewort is fairly new, it is no surprise that there is no highly effective removal method. Potential removal techniques are chemical methods or manual removal. An issue with starry stonewort, is the difficulty of identifying the plant properly as it looks similar to muskgrass species and native stonewort species (Escobar et al, 2016). In order to have a more successful removal and proper identification of starry stonewort, further education and awareness must be completed for future researchers. It is quite possible that starry stonewort has been occupying lakes in the past, but was misidentified. Thus giving it time to exponentially grow in abundance and spread among lakes. Due to the complicated biology of Starry stonewort and how different it is in North America compared to Europe and Asia, it is hard to implement a practical and effective management strategy (Pullman and Crawford, 2009). In the past the biggest concern was the protection and conservation of Nitellopsis obtusa. Now that it is becoming a growing concern in North America, research on controlling the invasive species is being conducted with the hope to better understand why it is so invasive in compared to why it is so endangered in different parts of the world.
Ecological Connections: Since starry stonewort is a r-strategist, its populations can be abundant and it can re-establish quickly from only a few individuals. It can spread extremely quickly, so although it may not seem like an issue one year, the next it may have completely taken over an area. It is believed to have spread rapidly throughout bodies of water through human activity. It is possible that it may have been unintentionally spread via boats going between different bodies of water (Escobar et al, 2016). Another theory of dispersal is through the feathers or feet of waterfowl, and/or the fur of aquatic mammals (Midwood et al, 2016). With the ability of starry stonewort to transform to changing environments and rapid growth abilities it becomes clear how the Great Lakes landscapes are suitable habitat conditions. Limited research has been done to determine how quickly starry stonewort will recover after removal (through chemical or manual). As there is no biological control yet for starry stonewort, there are no known natural predators or significant ways native plants can outcompete starry stonewort. This may allow the plants to grow into available habitat space, especially since it can grow in a variety of habitats rapidly.
Critical Assessment of Management Options: Based on our knowledge of the realized niche shift that Starry Stonewort has displayed in its invasion of North American waters, we have a model of the suitable habitats in which this species can exist in (Escobar et al., 2016). In terms of controlling the spread of all invasive species, preventative measures are always the best option, and using this niche model for Starry Stonewort could be a useful tool in preventing it from entering these suitable habitats. For areas already invaded by this species, there are several methods of managing its effect on the ecosystem, these methods include doing nothing, herbicide or algaecide treatment, and physical or mechanical control (Pullman and Crawford, 2010).
In many scenarios, it is best for ecosystem managers to allow invasive species to take their course and not intervene. Doing nothing may also be the most logical and beneficial way of dealing with species such as Starry Stonewort. In some lakes where there is an established population of Stonewort, it naturally mitigates other aquatic invasive species such as Eurasian water-milfoil by out competing them. This can reduce the effects on and even prevent issues involving human recreational activities. In relation to Eurasian water-milfoil, Stonewort grows at lesser depths in the water, opening up space in the littoral zone and making waters more accessible to recreation (Pullman and Crawford, 2010). An important strategy in leaving nuisance species in their non-native territories is public awareness. To avoid further dispersion, it is crucial to have active public outreach and educational programs in order to decrease the amount of human vectors. Although tolerable at this level, under different circumstances, if provided with the proper resources and space, managers are more likely to use a more progressive method to control the plant due to its ability of rapid and dense growth.
In circumstances where Starry Stonewort becomes too dense, lake managers in the past have taken the approach of using herbicides, algaecides and chemical intervention. Due to its ability to grow unattached to the substrate, Starry Stonewort is known to form dense mats floating just below and sometimes at surface of the water (Pullman and Crawford, 2010, Escobar et al., 2016). In using herbicides or algaecides, the top few inches of the mat layers will be killed off. In situations where the mats are too thick for just the herbicide to penetrate through, chemicals such as copper and endothall can be added to the treatment to remove more layers as Starry Stonewort is extremely sensitive to them (Pullman and Crawford, 2010). Another method of controlling Starry Stonewort is physical or mechanical removal. This control can be difficult to successfully accomplish due to rapid reproductive strategy of this species and recolonization is swift if nearby populations are still present (Pullman and Crawford, 2010). However, in previous studies mechanical removal using weed rollers was successful in fish breeding grounds of Lake Waumega, Michigan (Pullman and Crawford, 2010). After considering the management strategies for Starry Stonewort, it has been determined that in order to control this invasive species all three methods need to be integrated. The options used would depend on the severity and likelihood of it spreading to suitable areas. If there are low chances of it spreading, risk managers should do nothing and educate the public. If there are high chances of it spreading, herbicidal treatment or physical/mechanical removal should be done.
Table 1: Comparison of doing nothing, no removal but increased education and awareness, chemical removal and manual removal. Doing nothing is extremely costly and dangerous as the problem will increase exponentially in existing and future sites. Chemical removal may only remove the juvenile plants (Escobar et al, 2016), and manual removal will increase the chances of fragmentation. The most important thing overall is to increase education and awareness.
No Fragmentation/ Spread of Bulbils in existing infested areas
|(Increase of spreading to other bodies of water)|
|No removal, increased education and awareness||
|Increase of proper identification, Decrease of spreading from boats, Early Detection, Rapid Response||(Potential to spread among existing infested areas, but can decrease future areas)|
May quickly kill off existing plants and allow native plants to grow to overshadow it
|(Eliminating some juvenile plants, whereas may have no effect on mature plants)|
|May give native plants chance to grow up/Cleans up infested areas||(Decreasing density of mats, while fragmentation may be increased)|
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.
Pullman, D., Crawford, G. (2010). A decade of starry stonewort in Michigan. LakeLine. pp. 36-42.