Grey mullets comprise different species which represent the most ubiquitous teleost families in the planet coastal waters. They represent an important proportion of the Mediterranean lagoons production and have been recently considered a cultivated marine fish. This study aimed to explore the intestinal bacterial communities of 34 wild-caught grey mullets in order to study their composition and the variation during different seasons. Thirty four healthy wild-caught fish were sampled and the V3-V4 hypervariable regions of 16S rRNA were sequenced. Sixty prokaryotic phyla were identified and the most abundant ones were: Proteobacteria (mean relative abundance 35.4%±17.9), Actinobacteriota (mean relative abundance 16.4%±9.9) and Firmicutes (mean relative abundance 10.1%±10.9). Bacteria belonging to the phylum Chloroflexi were rele-vant in autumn, Spirochaetota, Verrucomicrobiota, Fusobacteriota and Cyanobacteria were particularly abundant in winter while Bacteroidota characterized summer fish. A total of three hundred thirty-two prokaryotic families were identified and the twenty-six most abundant ones were: Rhodociclaceae (Proteobacteria), Brevinemataceae (Spirocheaetota) and Fusobacteriaceae (Fusobacteriota) and the Staphylococcaceae (Firmicutes). This study sheds light on the ecology and high variation in the complex gut microbial community structure of Mediterranean grey mullets, the potential biotechnological role for fish nutrition and health and for preserving the aquatic habitat, a prerequisite for a sustainable aquaculture.

The present study identifies and quantifies the dinoflagellate resting cysts along an annual cycle from a shallow Mediterranean lagoon. Sediment samples were collected and analyzed for the determination of the dinoflagellate cyst density and composition at four sampling stations in Santa Giusta Lagoon (Oristano Gulf) from March 2015 to February 2016. At the same time, selected physicochemical variables and the cell densities of the dinoflagellate species in the water column were measured and determined. The group of Peridiniales dominated the cyst assemblages at spatial and temporal scales, with an almost total prevalence of the autotrophic–mixotrophic taxa. Heterotrophic Peridiniales showed occasional importance, especially in the stations closest to the sea connections, as well as the group of Gonyaulacales and Gymnodiniales. The composition in morphotypes revealed the dominance of Ensiculifera tyrrhenica and Scrippsiella kirschiae in correspondence with the maximum cyst densities in the inner sampling stations. Cysts of Margalefidinium cf polykrikoides reached high density values following an intense summer bloom. Salinity, ammonia, and total nitrogen were the environmental variables more strongly correlated with the multivariate cyst assemblage structure. The monthly time-scale offered a more accurate focus on cyst assemblages changes in respect to the usual single seasonal sampling in Santa Giusta Lagoon. The obtained data provided further knowledge on the relation among cyst assemblage variability, environmental conditions, and dinoflagellate motile stages in the water column relevant for comparisons with similar ecosystems in the Mediterranean and worldwide.

Eutrophication is a pervasive issue in Mediterranean reservoirs, where external nutrient inputs and internal sediment releases interact to impair water quality and ecological stability. This study assessed the trophic condition of the artificial lake Cuga in Sardinia (Italy), mainly used for irrigation and providing potable water, by integrating watershed nutrient load estimates, inter-lake transfers, and internal phosphorus release. Field campaigns between July 2022 and May 2023 provided bi-monthly measurements of physical, chemical, and biological parameters, complemented by GIS-based land cover analysis and export coefficient modeling to quantify spatial nutrient sources. Additional phosphorus inputs from water transfers with a nearby reservoir were calculated, while internal sediment release was estimated using a calibrated mass balance model. Results revealed high nutrient concentrations, with mean total phosphorus of 128 mg P m⁻³, chlorophyll a averaging 9.9 mg m⁻³, and Secchi depth below 1 m, classifying the reservoir as eutrophic to hypertrophic under OECD and Carlson indices. Spatial loads were dominated by agricultural areas, while inter-lake transfers and internal sediment release contributed substantially to the overall phosphorus budget. The predictive Vollenweider model closely matched the observed conditions, confirming the robustness of the combined approach. Maintaining good ecological status in Mediterranean reservoirs is essential for safeguarding human well-being, as eutrophication degrades drinking-water quality, increases treatment costs, and can promote toxin-producing algal blooms with direct implications for public health. These findings highlight the need for integrated management strategies addressing both external and internal nutrient sources to mitigate eutrophication in Mediterranean reservoirs, which affects the ecosystem functioning and the related human needs and well-being.