NB Naturalist Feature: Improving our Understanding of Freshwater Mussels in New Brunswick
By Kerstyn Dobbs and Sarah Cusack
Freshwater mussels are bivalves that inhabit the benthic zone of freshwater ecosystems, but they are most commonly found in rivers and lakes. New Brunswick historically had 11 different species found all throughout the province, but unfortunately one species (Dwarf Wedgemussel; Alasmidonta heterodon) has been extirpated so it is no longer found anywhere in Canada (COSEWIC, 2000). Figure 1 displays the 10 extant species you can currently find throughout New Brunswick. These mussels are very important ecologically to freshwater systems as they are crucial to nutrient cycling, they stabilize substrates, are an important food source, and their shells provide habitat for smaller organisms (Vaughn, 2017).
Although freshwater mussels are very important to a healthy ecosystem, they are in big trouble. They are one of the most imperiled animals in North America with ~65% of the species endangered or already extinct (Haag and Williams, 2014; Smith and Johnson, 2020). Here in New Brunswick, we have already seen the Dwarf Wedgemussel disappear and we currently have two species (Yellow Lampmussel; Lampsilis cariosa and Brook Floater; Alasmidonta varicosa) listed as special concern (COSEWIC 2009; COSEWIC 2013). On top of this, the Triangle Floater (Alasmidonta undulata)and Tidewater Mucket (Atlanticoncha ochracea) are considered to be vulnerable in New Brunswick (NatureServe 2023). One species, Creeper (Strophitus undulatus), does not have enough data collected to have a status within New Brunswick (NatureServe 2023), but it is not very commonly found in the province.So, this means that only five of the historic eleven species that occur here are considered secure. However, it should be noted that New Brunswick has one of the only secure populations of Alewife Floater (Utterbackiana implicata) in North America (NatureServe 2023)!
When most people think of mussels, they think of them in their adult stage as free-living and found at the bottom of the river or they may even think of all the shells they have seen washed up on the shore of a river. Would you be surprised to find out that they are actually considered parasites for part of their life? Freshwater mussels have a very interesting life cycle and as larvae they are parasites of fishes (Figure 2).
Their lifecycle begins with males releasing sperm into the water and since mussels are filter feeders, females have the ability to filter the sperm out of the water and use it to fertilize their eggs. Once the eggs are fertilized, they are brooded in the gills of the female mussel until the larvae have developed enough to be released into the water. Most species of mussels just release their larvae into the water and hope they encounter a fish, while others actually create a lure that will draw in fish. Once fish bite the lure, the mussel releases the larvae into the face of the fish. The mussel larvae then need to attach to either the gills or fins of a fish to develop into juveniles. After they attach to a fish, they are called glochidia (Figure 3). They use the fish not only to develop on, but to move and distribute throughout the river/lake. Once the glochidia have developed into juveniles they release from the host fish and settle into the substrate where they will continue to grow in the substrate for up to four years (Nile et al., 2020). After the juveniles have grown enough, they will emerge from the substrate and mature into adults.
Currently, at the University of New Brunswick (Fredericton) there are two research labs working on freshwater mussels. The Duffy Lab (Dr. Michael Duffy, Department of Biology) studies glochidia (parasitic larval stage) and the DNA of the mussels, whereas the Watershed and Aquatic Research and Monitoring lab (Dr. Michelle Gray, Faculty of Forestry and Environmental Management) is focused on adult mussels and the habitats they live in. This summer the two labs have teamed up to get a better understanding of freshwater mussels throughout the Wolastoq/Saint John River system (W/SJR) with a focus specifically on Yellow Lampmussel.
Kerstyn Dobbs is a PhD student in the Duffy Lab who is studying the glochidia and DNA of freshwater mussels throughout the province. She has sequenced the mitochondrial genomes of all the mussel species found throughout the province to develop molecular tools that can be used to determine the species of mussels that are infesting the fishes she catches. She has already identified the mussel species that are using Gaspereau (Alewife; Alosa pseudoharengus, and Blueback herring; Alosa aestivalis), and American Eel (Anguilla rostrata) as host fish. The species of glochidia were identified using the molecular tool she developed, and so this tool shows great promise for future applications of identifying both glochidia and adult mussels.
Sarah Cusack is a MSc of Environmental Management (MScEM) student in the Watershed and Aquatic Research and Monitoring (WARM) lab, studying the distribution of available habitats to mussel species, with a special focus on Yellow Lampmussel as well as the species that co-occur. She has developed habitat models from existing historical mussel datasets, and used the models to predict where different species of freshwater mussels are more likely to occur. She has related mussel occurrence to topographical features that influence aquatic habitat differences (at a regional scale). Her research project combines emerging modelling techniques with traditional mussel snorkel surveys to provide a holistic approach to improving the understanding of freshwater mussels in New Brunswick. This research will give us a better idea of what habitat each species occupies, and what landscape features are important in creating key habitat characteristics in rivers and streams in this region.
This summer they are putting their heads together to get a better understanding of the life cycles of these important yet imperilled animals. The WARM lab is conducting mussel surveys throughout the river system to further our understanding of where certain species are located (Figure 4A). The Duffy Lab is collecting fish species from the same sites to determine which of the mussel species they have encountered are releasing glochidia at that time of year and which fish they are relying on (Figure 4B). This work is critical to determine where our at-risk species are, their population status, and what fish they are relying on to complete their life cycle. This work is also necessary to assess the populations of the other mussel species to determine if they should be of interest in future conservation initiatives. Additionally, the data being collected will be critical baseline data before the inevitable invasion of Zebra Mussels (Dreissena polymorpha), which are notorious for destroying healthy populations of endemic mussel species let alone species that are at risk (Strayer & Malcom, 2018). Zebra Mussels and their impacts have been observed in the upper Wolastoq (Lac Témiscouata, Quebec) so in the coming years they may begin to invade the lower parts of the Wolastoq.
We would like to thank all of our supervisors Dr. Michael Duffy, Dr. Michelle Gray, and Dr. Meghann Bruce for their continued support and guidance. We would also like to thank our summer research assistants/field technicians for their hard work and perseverance this summer (Abby Lemmon, Allysia Murphy, Anna Varty, Andrew Smith and Prahalad Vathsan). Finally, we would like to thank our wonderful lab mates for all of the support and assistance they have provided (Darren Greeley, Megan Fraser, Stephanie Scott, Tyler Lynn, and Hannah Lazaris-Decken).
- COSEWIC. 2000. COSEWIC assessment and update status report on the Dwarf Wedgemussel Alasmidonta heterodon in Canada. Committee on the Status of Endangered Wildlife in Canada Ottawa. vi + 18 pp. (http://www.sararegistry.gc.ca/status/status_e.cfm).
- COSEWIC. 2009. COSEWIC assessment and status report on the Brook Floater Alasmidonta varicose in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 79 pp. http://www.sararegistry.gc.ca/status/status_e.cfm
- COSEWIC. 2013. COSEWIC status appraisal summary on the Yellow Lampmussel Lampsilis cariosa in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xxiii pp. http://www.sararegistry.gc.ca/status/status_e.cfm
- Haag, W. R., and J. D. Williams. 2014. Biodiversity on the Brink: An Assessment of Conservation Strategies for North American Freshwater Mussels. Hydrobiologia 735(1): 45–60. https://doi.org/10.1007/s10750-013-1524-7.
- Modesto, V., M. Ilarri, A. T. Souza, M. Lopes-Lima, K. Douda, M. Clavero, and R. Sousa. 2018. Fish and Mussels: Importance of Fish for Freshwater Mussel Conservation. Fish and Fisheries 19(2): 244–59. https://doi.org/10.1111/faf.12252.
- Nile, K., E., J., M., Besser, J., Steevens and J., P., Hughes. 2020. Assessment of burrowing behavior of freshwater juvenile mussels in sediment. Freshwater Mollusk Biology and Conservation. 23(1): 68-81. https://doi.org/10.31931/fmbc.v23i2.2020.69-81.
- Smith, C. H., and N. A. Johnson. 2020. A Comparative Phylogeographic Approach to Facilitate Recovery of an Imperiled Freshwater Mussel (Bivalvia: Unionida: Potamilus Inflatus). Diversity 12 (7): 281. https://doi.org/10.3390/d12070281.
- Strayer, D. L., and H. M. Malcom. 2018. Long-Term Responses of Native Bivalves (Unionidae and Sphaeriidae) to a Dreissena Invasion.” Freshwater Science 37(4): 697–711. https://doi.org/10.1086/700571.
- Vaughn, C. C. 2018. Ecosystem Services Provided by Freshwater Mussels. Hydrobiologia 810 (1): 15–27. https://doi.org/10.1007/s10750-017-3139-x.