Effects of wildfire ash on the fatty acid and sugar profiles of bivalves - A comparative study of a freshwater and a marine species

Wildfires can impact both freshwater and marine ecosystems through post-fire runoff, but its effects on bivalves, particularly those living in marine habitats, remain largely overlooked. While evidence exists that wildfire ash can alter the fatty acid (FA) and sugar profiles of aquatic biota, its influence on the biochemical profiles of bivalves have not been addressed to date. This study aimed to assess the effects of ash exposure on the FA and sugar profiles of two bivalve species used for human consumption: a freshwater clam (Corbicula fluminea) and a marine bivalve (Cerastoderma edule), additionally evaluating potential effects on their nutritional value. Both species were exposed to environmentally relevant concentrations of aqueous extracts of Eucalypt ash (AEAs) for 96 h. Results showed species-specific responses to ash extracts exposure, with more pronounced effects on C. edule. This species exhibited a trend for reduced FA content, statistically significant for C17:0 but also evident for unsaturated FAs, which is relevant for human health as they represent a decrease in the nutritional value. Conversely, an increase in the sugar content of this species was observed with increasing AEA concentrations, despite only statistically significant for galactose and xylose. In contrast, the clams exhibited only minor effects, showing a trend for increased FA and decreased sugar contents, but only significant for the monounsaturated FA content. This study suggests a higher sensitivity of marine bivalves to wildfire ash compared to their freshwater counterparts. Moreover, it highlights, for the first time, the potential of post-fire runoff to alter the biochemical profiles of bivalve species, raising concerns about broader impacts on aquatic trophic webs and human health, an issue that becomes particularly relevant given the forecasted increase in wildfire's frequency and extension due to global warming.