Abstract
The marine fish farming industry is growing at a significant rate, yet a number of concerns still remain with regards to environmental impacts on the surrounding coastal sea and its biota. Here, we assessed the impact of intensive farming on benthic prokaryotic communities at a Mediterranean sea bass and sea bream intensive aquaculture site over a period of 10 months, in relation to the increase in fish biomass within the cage together with the organic matter enrichment in the sediments. We report positive relationships between prokaryotic abundance and both organic matter and fish biomass, and a contextual decrease in prokaryotic diversity below the cages. A significant shift in microbial community composition occurred in fish farm sediments (FF) over time, indicating a likely impact of ongoing aquaculture activity on prokaryotic communities. Among the dominant taxa at the impacted site, we found Epsilonproteobacteria and Bacteroidetes, which showed a general increase with fish biomass. Analyses on specialist taxa underlined significant contributions of Clostridiales and Bacteroidales in the farmed sediments. Finally, sea bream and sea bass gut microbiome-related taxa were detected during the sampling period. Our results indicate that prokaryotic community composition underneath the cages is related to fish biomass and organic enrichment over the course of production, and confirms that the study of benthic microbial communities at aquaculture sites represents a useful tool to assess the impact of intensive mariculture on the surrounding environment.
Highlights
Over the last decade, fish farming has increased significantly, and it is predicted that more than half of fish consumed on a global scale will be produced by aquaculture by 2030 (FAO, 2016)
Biopolymeric carbon differed between stations (Supplementary Table S2 and Supplementary Figure S1-A), and two-way ANOVA analysis indicated that the organic enrichment was significantly different between sites (p < 0.01), but not among sampling times; the combined effect of site and time was not significant
Because prokaryotes are sensitive to environmental change, and may shift in abundance, diversity and community composition according to environmental perturbations, they have been widely studied in aquaculture, and suggested as one of the most promising tools for biomonitoring of farmed areas (Verhoeven et al, 2018)
Summary
Fish farming has increased significantly, and it is predicted that more than half of fish consumed on a global scale will be produced by aquaculture by 2030 (FAO, 2016). A number of concerns emerge from this increasing production, among which the dispersion of farming-related wastes into the surrounding waters and on the seafloor (Carroll et al, 2003) is urgent. This organic enrichment often leads to eutrophication and bottom hypoxia, and can significantly impair biogeochemical processes, energy transfer through the food web and the overall functioning of the benthic ecosystem (Mirto et al, 2012; Keeley et al, 2013), often facilitating the establishment and spread of adapted and more resilient non-indigenous species (Mangano et al, 2019). Other environmental concerns of this industry are related to the use of chemicals and their dispersal in the surrounding environment (e.g., antibiotics and antifoulants) as well to the introduction and spread of pathogens (Wu, 1995; Tamminen et al, 2011)
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