Studies of genotoxicity in fish caused by cyanobacterial microcystins can be useful both in determining the sensitivity of native species, as well as comparing exposure routes. The genotoxicity caused by the microcystins LR and LA from a bloom collected in a eutrophic lake, was revealed in the fish Astyanaxbimaculatus, a native species from South America. LC50 (72 h) was determined as 242.81 μg L -1 and LD50 (72 h) as 49.19 μg kg -1 bw. There was a significant increase of DNA damage in peripheral erythrocytes, following intraperitoneal injection (ip) with tested concentrations of 24.58 μg kg -1 bw and 36.88 μg kg -1 bw, as well as through body exposure to a concentration of 103.72 μg L -1 . Micronucleus (MN) induction was observed after ip injections of 24.58 μg kg -1 bw and 36.88 μg kg -1 bw for 72 h, as well as following body exposure for 72 at 103.72 μg L -1 . Thus, both exposure routes resulted in MN induction and DNA damage. Apoptosis-necrosis testing was carried out only by ip injection with concentrations of 24.58 μg kg -1 bw and 36.88 μg kg- 1 bw. Exposure to microcystins at lower concentrations induced more apoptosis than necrosis in peripheral erythrocytes, whereas exposure at higher concentrations gave rise to both conditions. Thus, Astyanax bimaculatus can be considered as a species sensitive to the genotoxic effects caused by microcystins.
Microbial communities are important elements in the marine environment, contributing to nutrient cycling and biogeochemical processes. Estuaries comprise environments exhibiting characteristics from freshwater to marine, leading to distinct microbial communities across this environmental gradient. Here, we examine the spatial dynamics of microbial communities in Macquarie Harbour, an estuarine system on the West coast of Tasmania, Australia. Water was sampled along the estuary to explore the structure and composition of the microbial communities using 16S/18S rRNA gene amplicon sequencing. Multivariate analyses showed environmental variables and community compositions varying along a longitudinal (river to adjacent ocean) gradient at the surface. In the harbour, differences in the microbial community were observed between surface (0-1 m) and intermediate depths (4.5-11 m depth). The results of differential abundance, network and Partial Least Square analyses suggest that Macquarie Harbour is a mixing zone, where the distributions of archaeal, bacterial and eukaryotic communities are influenced by oceanic and riverine inputs. Coupled with the natural characteristics of the Harbour, the heterotrophic component of this microbial communities inhabiting the surface and intermediate waters may play important roles in the nutrient cycle in the studied area. These results provide critical insights into the Macquarie Harbour environment and the importance of understanding the role of microbial communities for similar systems elsewhere.
Finfish aquaculture is one of the fastest-growing primary industries globally and is increasingly common in coastal ecosystems demanding effective impact monitoring tools. Bacterioplankton is ubiquitous in marine environment and its rapid response to environmental change makes them a potential bioindicator for environmental impacts. This study aims to verify the use of the taxonomic and functional profiles of bacterioplankton using high-throughput amplicon sequencing. Water was sampled along a distance gradient in three different depths from two lease areas and three control sites in a low-oxygen, highly stratified marine embayment. Our results revealed a vertical variation in bacterioplankton community strongly associated to NOx, conductivity, salinity, temperature and PO4. The overall shift in the taxonomic profile (ASVs) were more noticeable than in the functional profile. Despite depth stratification, ASVs and functional annotations were detected as potential bioindicators for aquaculture activity. Differentially abundant bacteria found in lease areas were associated with nutrient enrichment (e.g., Desulfovibrionaceae, Psychromonadaceae, and Fusibacter) or are known as potential pathogens (e.g., Pseudomonas, Vibrio and Aliivibrio) and members of the fish gut microbiome (e.g., Leptotrichiaceae, Enterobacterales and Pseudomonadales). Differences in the predicted functional profile were strongest in the bottom waters near leases, where pathways assigned to organic compounds and vitamin degradation, fermentation, methanogenesis and antibiotic resistance were detected. Overall, our findings indicated that the use of 16S rRNA sequencing of bacterioplankton communities are a promising and alternative method for detecting variations along an aquaculture gradient in the water column.
Coastal aquaculture operations for feed additive species results in the release of waste into the surrounding environment, with the potential for adverse environmental change. Ubiquitous pelagic protists are sensitive to environmental changes making them potential sentinels for detecting and monitoring impacts. This study used 18S rRNA high-throughput amplicon sequencing as a molecular tool to study the pelagic protist community, with the aim of evaluating their potential as bioindicators of aquaculture activity in a low-oxygen, highly stratified marine embayment. Sampling occurred at three different depths along a distance gradient from two leases and at three control sites. Our results showed that the diversity and composition of both phytoplankton and other protist communities were more strongly influenced by depth stratification than the aquaculture activity. Nonetheless, differential abundance and machine learning analyses revealed a suite of potential bioindicators for aquaculture activity; this included the phytoplankton taxa Chrysophyceae, Gymnodiniphycidae (Gyrodinium), Cryptomonadales and Ciliophora (Philasterides armatalis, Plagiopylida, and Strombidium). Among the other protists, ciliates were also more abundant in closer proximity to the leases in both surface and bottom samples. Overall, our findings indicated that the use of 18S rRNA sequencing of protist communities is a promising tool for identifying environmental changes from aquaculture in the water column.
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