Native freshwater mussels, benthic and filter-feeding, maintain or improve water quality conditions and support diverse aquatic communities that are beneficial for salmon, lamprey and other native fish . Regrettably the freshwater mussels are some of the most imperiled species in North America. The Western Pearlshell mussel Margaritifera falcate WPS , the species of interest for our work, is listed as Near Threatened on the International Union for Conservation of Nature (IUCN) Red List. As more threatened and endangered mussels are moved into refugia it is becoming critical to be able to assess their health and physiological status.
The WPS mussels used in this study were from Abernathy Creek (Longview, WA) and consisted of mussels from three collection years, 2018, 2019 and 2020. Collection years 2018 and 2019 were held in buckets containing sand, gravel and cobble like the substrate where they were found. These buckets, with holes for water circulation, were floating in a shade covered outdoor 10 ft. circular tank supplied with creek water. The mussels from collection year 2020 were held in a trough inside that also contained sand, gravel and cobble and was supplied with creek water. Mussels still residing in Abernathy Creek were also sampled.
Hemolymph was drawn from 10 mussels in each population. The parameters checked in the hemolymph were magnesium, ammonia, alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Increased ammonia and decreased magnesium were shown in previous work at Abernathy to be stress indicators in WPS. The transaminases are considered biomarkers of general stress in aquatic invertebrates . Overall, the parameters were not significantly different between the populations held for different lengths of time in the facility and the mussels in the creek. Only the magnesium was significantly lower (P<0.05) in the mussels collected in 2020 and held in the trough inside. Although not significantly different , the other parameters for the mussels held in the inside trough also indicated that population was stressed, possibly due to no cover on the trough and more activity around it. Making the refugia environment as natural as possible will be key to maintaining captive populations.