Silence of the clams: health status of Mya arenaria clams in the Saguenay–St. Lawrence Marine Park

The cumulative effects of pollution of intertidal clam populations should be investigated to ensure the sustainable perennity of our resources. The purpose of this study was to examine the health status of intertidal clams and tissue levels of essential and non-essential elements at sites under anthropogenic stress. Clams were collected at two anthropized sites, a St. Lawrence Estuary (SLE) beluga high-residency area and reference site in the Saguenay–St. Lawrence Marine Park (Québec, Canada). Clam health status was determined by the condition factor (CF: wet weight/shell length ratio), growth index (GI: shell length/age), air survival time and weight loss index (WLI). Elemental analysis was also performed in soft tissues. The data revealed that clams from at least one of the harbor/marina sites had reduced CF, GI and WLI. Air survival time was not affected at the anthropized sites but was significantly higher at the St. Lawrence Estuary beluga high-residency area. The clams were contaminated by Ag, Al, Cd, Cu, Hg and V, with a decrease in essential cations (K, Ca, Mg) suggesting altered osmoregulation. Although the individual metals in tissues were not found at harmful concentrations based on reported data, the combined effects of non-essential elements could not be excluded. More research will be needed to better understand the cumulative effects of various stressors, such as low salinity, algal toxins and elemental composition, on clam health status.