Physiological responses of the invasive blue crabs Callinectes sapidus to salinity variations: Implications for adaptability and invasive success.

This study provides a comprehensive analysis of the eco-physiological responses of the blue crab (Callinectes sapidus) to variations in salinity, shedding light on its adaptability and invasive success in aquatic environments. Gender-specific differences in osmoregulation and Electron Transport System (ETS) activity highlight the importance of considering sex-specific aspects when understanding the physiological responses of invasive species. Females exhibited increased ETS activity at lower salinities, potentially indicative of metabolic stress, while males displayed constant ETS activity across a range of salinities. Osmoregulatory capacity which depended on gender and salinity, was efficient within meso-polyhaline waters but decreased at higher salinities, particularly in males. These findings provide valuable understandings into how C. sapidus specimens in an invaded area responds to salinity changes, important for considerate its distribution through saline pathways during tidal cycle fluctuations. This study shows the importance of interdisciplinary research for effective management of invasive species and conservation of affected aquatic ecosystems.

Microplastic ingestion and plastic additive detection in pelagic squid and fish: Implications for bioindicators and plastic tracers in open oceanic food webs.

The ubiquitous presence of microplastics (MPs) in the ocean represents a potential threat to marine organisms, with poorly understood long-term adverse effects, including exposure to plastic additives. The present study investigated the ingestion of MPs in two epipelagic fish species (Trachurus picturatus and Scomber colias) and three pelagic squid species (Loligo vulgaris, Ommastrephes caroli and Sthenoteuthis pteropus) from an open oceanic region of the Northeast Atlantic. Seven phthalate esters (PAEs) were also analysed in the organisms' tissue, and the potential correlation between PAEs concentrations and ingested MPs was investigated. Seventy-two fish and 20 squid specimens were collected and analysed. MPs were found in the digestive tract of all species and in the squid species' gills and ink sacs. The highest occurrence of MPs was in the stomach of S. colias (85 %) and the lowest in the stomach and ink sac of O. caroli and L. vulgaris (12 %). Most of the particles identified (>90 %) were fibres. Among all the ecological and biological factors considered (dietary preferences, season, body size, total weight, liver weight, hepatosomatic index and gastrosomatic index), only gastrosomatic index (GSI) and season were significant predictors of MPs ingestion in fish species, with a greater likelihood of ingestion in the cold season and in specimens with higher GSI values (i.e. higher feeding intensity). Four PAEs (DEP, DIBP, BBP, DEHP) were detected in all the species analysed, with average ∑PAEs concentrations ranging between 10.31 and 30.86 ng/g (wet weight). DIBP was positively correlated with ingested MPs, suggesting this compound might represent a "plastic tracer". This study looks into the problem of MPs ingestion for pelagic species in an open oceanic region, highlighting the most suitable bioindicators and providing essential insights into the factors that may influence ingestion rates. Additionally, the detection of PAEs in all species indicates the need for further research on the contamination sources, the effects of these chemicals on marine organisms, and the potential risks to human health through seafood consumption.

Seasonal variation in microplastics and zooplankton abundances and characteristics: The ecological vulnerability of an oceanic island system.

The ingestion of microplastics (MPs - plastic particles <5 mm) by planktivorous organisms represents a significant threat to marine food webs. To investigate how seasonality might affect plastic intake in oceanic islands' ecosystems, relative abundances and composition of MPs and mesozooplankton samples collected off Madeira Island (NE Atlantic) between February 2019 and January 2020 were analysed. MPs were found in all samples, with fibres accounting for 89 % of the particles. MPs and zooplankton mean abundance was 0.262 items/m3 and 18.137 individuals/m3, respectively. Their monthly variations follow the seasonal fluctuation of environmental parameters, such as currents, chlorophyll-a concentration, sea surface temperature and precipitation intensity. A higher MPs/zooplankton ratio was recorded in the warm season (May-Oct), reaching 0.068 items/individual when considering large-sized particles (1000-5000 µm). This is the first study to assess the seasonal variability of MPs in an oceanic island system providing essential information respecting its ecological impact in pelagic environments.

Shifts in the protist community associated with an anticyclonic gyre in the Alboran Sea (Mediterranean Sea).

The diversity of protists was researched in the Alboran Sea (SW Mediterranean Sea) by means of high-throughput sequencing technologies based on the amplification of the V9 region of 18S rRNA. Samples were collected at different depths in seven stations following an environmental gradient from a coastal upwelling zone to the core of an oligotrophic anticyclonic gyre (AG). Sampling was performed during summer, when the water column was stratified. The superphyla Alveolata, Stramenopila and Rhizaria accounted for 84% of the total operational taxonomic units (OTUs). The most diverse groups were Dinophyceae (21% of OTUs), Marine Alveolates-II (MALV-II; 20%), Ciliophora (9%) and MALV-I (6%). In terms of read abundance, the predominant groups were Dinophyceae (29%), Bacillariophyta (14%), MALV-II (11%) and Ciliophora (11%). Samples were clustered into three groups according to the sampling depth and position. The shallow community in coastal stations presented distinguishable patterns of diatoms and ciliates compared with AG stations. These results indicate that there was a strong horizontal coupling between phytoplankton and ciliate communities. Abundance of Radiolaria and Syndiniales increased with depth. Our analyses demonstrate that the stratification disruption produced by the AG caused shifts in the trophic ecology of the plankton assemblages inducing a transition from bottom-up to top-down control.