Hydrobiology

Antifouling coatings are an important source of trace metal contamination in coastal marine environments because they continuously release biocidal compounds from submerged structures. Among the metallic contaminants released from many antifouling coatings, copper (Cu) and zinc (Zn) are of particular environmental concern because of their persistence and bioavailability and may accumulate in filter-feeding organisms inhabiting aquaculture areas. The present study evaluated the effects of the leachable fraction of a commercial antifouling paint on survival and Cu and Zn accumulation in the Pacific cupped oyster Magallana gigas. Oysters were exposed for 21 days to three nominal concentrations of an aqueous antifouling paint extract (0, 0.05, and 0.25 mg/L). Copper and zinc concentrations in the exposure media were analytically verified by inductively coupled plasma mass spectrometry, while tissue metal concentrations were determined at the end of the experiment. Survival was analysed using Kaplan-Meier curves and log-rank tests. Mortality showed an increasing trend with exposure concentration, and overall survival differed significantly among treatments, with mortality concentrated in oysters exposed to the highest concentration tested. Both Cu and Zn accumulated in oyster tissues, although their accumulation patterns differed, reflecting distinct physiological regulation mechanisms. These findings demonstrate that the leachable fraction of antifouling paint represents a bioavailable source of Cu and Zn for marine bivalves under controlled exposure conditions. The study provides new experimental evidence supporting environmental risk assessment of antifouling-derived contamination and contributes to the sustainable management of shellfish farming areas.

Understanding the distribution of Emys orbicularis in Andalusia is essential for assessing its conservation status within one of the most fragmented sectors of its Iberian range. In this study, we applied a modelling framework integrating environmental favourability, spatial structure, and their intersection to identify the factors determining the species’ presence across the Andalusian territory. All presence records were obtained from field surveys and long-term monitoring programmes conducted by the authors, while environmental and spatial predictors were compiled from publicly available databases and processed following the modelling methodology developed by Santoro et al. A consistent pattern emerged across all models: E. orbicularis is strongly associated with forested riparian systems, stable aquatic habitats, and low levels of disturbance, while its distribution is constrained by a marked north–south gradient associated with the Sierra Morena mountain range. The species also shows a historical and continuous presence in Huelva province, including coastal areas, and traditionally occupied parts of the western Betic systems and the Cádiz coastline. Integrating environmental and spatial components allowed us to capture both habitat suitability and the spatial processes limiting the species’ presence. The intersection model, which synthesises the results of both analyses, provided the most reliable representation of the species’ potential distribution by reducing false positives and highlighting core areas of persistence associated with hydrological stability and landscape connectivity. We also observed a marked reduction in the area of occupancy derived from the records, consistent with the initial hypothesis regarding the species’ current status.

Srebarna Lake, a UNESCO Biosphere Reserve and Danube floodplain wetland, is characterized by pronounced hydrological fluctuations related to variations in Danube River water levels. This study compared phytoplankton functional organization between selected historical and recent years using the Reynolds–Padisák functional group (FG) approach and considering variations in Danube water levels. The descriptive comparison included phytoplankton samples collected between May and September from the central lake area in three historical (2003, 2004, 2007) and four recent sampling years (2022–2025). Single-month observations from intervening years were also considered. Partial redundancy analysis (pRDA) was used to evaluate differences in FG composition between historical and recent periods in relation to measured environmental gradients, using a balanced subset of six years. The recent period was characterized by generally lower Danube water levels, suggesting reduced opportunities for hydrological connectivity with the Danube. Recurrent dominance of FG SN, represented by Raphidiopsis raciborskii, was observed in 2022–2024, contrasting with the prominence of S1 and contribution of FGs M and H1 in the historical observations. A strong reduction or disappearance of cyanobacterial FGs, accompanied by lower total phytoplankton biomass, occurred under contrasting hydrological extremes, with diatom FGs prominent in 2007 following flooding events and a predominance of FGs X1 and G in 2025 under severe low-water conditions. The overall pRDA model significantly explained variation in FG composition; however, the historical–recent contrast was not statistically significant when Period was tested separately at the whole-plot level, indicating that the observed temporal patterns should be interpreted in the context of interannual variation and the measured environmental gradients.