Wildfires cause rapid changes to estuarine benthic habitat

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.

Exploring spatio-temporal changes in coastal recreational fisheries and potential links to extreme weather events

Extreme weather events across coastal environments are expected to increase in frequency under predicted climate change scenarios. These events can impact coastal recreational fisheries and their supporting ecosystems by influencing the productivity of fish stocks or altering behaviours and decision-making among fishers. Using off-site telephone/diary survey data on estuarine and oceanic recreational fishing activity in eastern Australia, we analyse interannual and geographic variability in bream (Acanthopagrus spp) and snapper (Chrysophrys auratus) catch, total effort and total catch per unit effort (CPUE) through a period (2013/2014, 2017/2018 and 2019/2020) that encompassed severe drought, bushfires and flooding. Interacting spatial and temporal differences were detected for bream and may reflect spatial variation in the intensity and extent of some of the extreme weather events. The catch of snapper did not change temporally, providing little evidence that this species' catch may be influenced by the extreme weather events. Independent bioregional and temporal effects on effort were detected, while CPUE only showed significant bioregional differences. Although adverse conditions created by the extreme weather events may have dissuaded fisher participation and impacted effort, we propose that the observed temporal patterns in effort reflect the early influence of socio-economic changes brought on by the COVID-19 pandemic on coastal recreational fishing, over and above the impacts of extreme weather events. This study demonstrates how interrelated ecological, social and economic factors can shape coastal recreational fisheries and facilitates development of management strategies to address future threats to the sector.

Wildfire Ashes from the Wildland-Urban Interface Alter Vibrio vulnificus Growth and Gene Expression

Climate change-induced stressors are contributing to the emergence of infectious diseases, including those caused by marine bacterial pathogens such as Vibrio spp. These stressors alter Vibrio temporal and geographical distribution, resulting in increased spread, exposure, and infection rates, thus facilitating greater Vibrio-human interactions. Concurrently, wildfires are increasing in size, severity, frequency, and spread in the built environment due to climate change, resulting in the emission of contaminants of emerging concern. This study aimed to understand the potential effects of urban interface wildfire ashes on Vibrio vulnificus (V. vulnificus) growth and gene expression using transcriptomic approaches. V. vulnificus was exposed to structural and vegetation ashes and analyzed to identify differentially expressed genes using the HTSeq-DESeq2 strategy. Exposure to wildfire ash altered V. vulnificus growth and gene expression, depending on the trace metal composition of the ash. The high Fe content of the vegetation ash enhanced bacterial growth, while the high Cu, As, and Cr content of the structural ash suppressed growth. Additionally, the overall pattern of upregulated genes and pathways suggests increased virulence potential due to the selection of metal- and antibiotic-resistant strains. Therefore, mixed fire ashes transported and deposited into coastal zones may lead to the selection of environmental reservoirs of Vibrio strains with enhanced antibiotic resistance profiles, increasing public health risk.

Fine particle pollution during megafires contains potentially toxic elements

Wildfires that raged across Australia during the 2019-2020 'Black Summer' produced an enormous quantity of particulate matter (PM) pollution, with plumes that cloaked many urban centres and ecosystems along the eastern seaboard. This has motivated a need to understand the magnitude and nature of PM exposure, so that its impact on both built and natural environments can be more accurately assessed. Here we present the potentially toxic fingerprint of PM captured by building heating, ventilation, and air conditioning filters in Sydney, Australia during the peak of the Wildfires, and from ambient urban emissions one year later (Reference period). Atmospheric PM and meteorological monitoring data were also assessed to determine the magnitude and source of high PM exposure. The wildfires were a major source of PM pollution in Sydney, exceeding the national standards on 19 % of days between November-February. Wildfire particles were finer and more spherical compared to Reference PM, with count median diameters of 892.1 ± 23.1 versus 1484.8 ± 96.7 nm (mean ± standard error). On an equal-mass basis, differences in potentially toxic elements were predominantly due to higher SO42--S (median 20.4 vs 4.7 mg g-1) and NO3--N (2.4 vs 1.2 mg g-1) in Wildfire PM, and higher PO43--P (10.4 vs 1.4 mg g-1) in Reference PM. Concentrations of remaining elements were similar or lower than Reference PM, except for enrichments to F-, Cl-, dissolved Mn, and particulate Mn, Co and Sb. Fractional solubilities of trace elements were similar or lower than Reference PM, except for enhanced Hg (12.1 vs 1.0 %) and greater variability in Cd, Hg and Mn solubility, which displayed upper quartiles exceeding that of Reference PM. These findings contribute to our understanding of human and ecosystem exposures to the toxic components of mixed smoke plumes, especially in regions downwind of the source.

Do Freshwater and Marine Bivalves Differ in Their Response to Wildfire Ash? Effects on the Antioxidant Defense System and Metal Body Burden

Wildfires constitute a source of contamination to both freshwater and marine ecosystems. This study aimed to compare the antioxidant defense response of the freshwater clam Corbicula fluminea and the marine cockle (Cerastoderma edule) to wildfire ash exposure and the concomitant metal body burden. Organisms were exposed to different concentrations (0%, 12.5%, 25%, 50%, and 100%) of aqueous extracts of Eucalypt ash (AEAs) from a moderate-to-high severity wildfire. The activity of various enzymes, as well as lipid peroxidation, protein content, and metal body burden, were determined after 96 h of exposure. A significant increase in the protein content of soft tissues was observed for C. edule at AEA concentrations ≥ 25%, unlike for C. fluminea. Similarly, significant effects on lipid peroxidation were observed for cockles, but not for clams. For both species, a significant effect in the total glutathione peroxidase activity was observed at AEA concentrations ≥ 25%. Relative to the control, AEAs-exposed clams showed higher Cd content, whereas AEAs-exposed cockles showed higher Cu content, thus exhibiting different responses to the exposure to wildfire ash. The susceptibility of bivalves to ashes, at environmentally relevant concentrations, raises concern about the effects of post-fire runoff to bivalve species.