Are freshwater mussels at risk due to microplastics in Ontario's streams?
A gravid female wavyrayed lampmussel (Lampsilis fasciola) displaying her lure that resembles a small fish. She uses this lure to attract larger fish. Her goal is to place her babies (glochidia) on the gills of a fish. When the fish strikes the lure, she will release the glochidia into the face of the fish from the brood chamber in her gills The glochidia will encyst in the fish's gills and use nutrients from the fish to go through metamorphosis. Following metamorphosis, the baby will have developed all of the essential tissues and organs to begin it's benthic existence. It will drop off the fish's gills and starts it's life on the bottom of the river.
The greatest diversity of native freshwater mussels in Canada can be found in southern Ontario. There are 41 species of native freshwater mussel in southern Ontario, but 15 of these species are classified as species-at-risk of under the Species at Risk Act in Ontario.
A variety of factors have contributed to the decline in freshwater mussels in Ontario, including, invasive species (zebra and quagga mussels), decline in water quality due to erosion and input of contaminants, dams and other barriers that prevent the movement of their fish hosts, and over-exploitation.
Recently, greater attention has be placed on the potential impact on microplastics in our environment. A relatively large number of studies have identified that microplastics can be found in almost all of Canada's ecosystems, including the Arctic. The next important question is whether these ubiquitous small particles are plastic can have an adverse effect on the species that inhabit Canada's ecosystems.
There is concern that microplastics in river and stream ecosystems could have an adverse effects on freshwater mussels. Freshwater mussels are filter and deposit feeders. These species are omnivorous. The consume different microscopic organic particles (e.g., phytoplankton, small zooplankton, bacteria, fine organic detritus) by filtering them from the overlying water. They can also use cilia on their foot to transport these types of foods into their shell from the sediment. The concerns comes from the possibility of these amazing creates ingesting microplastics through filtration or deposit feeding, particularly microplastics less than 20 µm in size. Do these plastic particles accumulate in the mussels digestive system? Can they cause mortality by blocking their digestive tract, or through the release of hazardous chemicals, or by reducing the amount of nutrients that mussel acquire from their food? If mussels consume these microplastics, are they able to excrete them? Or perhaps, the mussels are able to differentiate between tasty microscope food particles and microplastics, which would allow them to avoid consuming these contaminants. These are all important questions that require answering. Freshwater mussels already have a number of stressors that they need to overcome due to human's activities that we need to do something about, we need to determine if microplastics should be added to that long list.
Female pocketbook mussel (Lampsilis cardium) displaying her fish-resembling lure.