Search Results (58)

Transitional waters—such as estuaries, lagoons, deltas, and coastal wetlands—are dynamic environments where freshwater and seawater interact, forming highly productive and biologically diverse ecosystems. Shaped by temperature and salinity gradients, tidal influence, sediment transport, and nutrient-rich conditions, these habitats support diverse ecological functions. Their structural complexity—including seagrass beds, salt marshes, mudflats, and mangroves—provides essential habitats for many fish species. These areas are crucial for fish life cycles, serving as nurseries, spawning grounds, feeding zones, and refuges from predators. Many commercially important species depend on them during early life stages before moving offshore, making them vital for both commercial and recreational fisheries. Beyond food provision, they deliver key ecosystem services, including water purification, coastal protection, and carbon storage. Research on the fish community of the Ria Formosa lagoon in Portugal since the 1980s highlights long-term changes in the fish community and the dominant role of habitat structure and temporal dynamics. Subtidal seagrass beds support higher fish abundance and diversity than unvegetated areas, acting as key nursery habitats and provide important fish provisioning services. Seasonal variation is also central, driven by recruitment pulses of marine migrants in late winter–spring. Recent pressures on this system have been driven by human activity and environmental change. Seagrass loss reduces nursery and feeding areas, while pollution degrades water quality. Overfishing (including illegal fishing), recreational activities, and aquaculture expansion add stress. Climate warming and invasive species such as Caulerpa prolifera, further disrupt ecosystem balance and threaten biodiversity. Sustainable management—such as habitat restoration, protected areas, and integrated policies—is essential to preserve the ecological and economic value of this unique lagoon. Ongoing research, monitoring, habitat restoration, and stakeholder engagement remain critical for ensuring resilience. Full article

Introduction: Marine heatwaves are increasing in frequency and intensity, posing major challenges for fishes inhabiting shallow coastal ecosystems. Short-term exposure to extreme warming can alter metabolic performance and thermal tolerance, with potential consequences for species persistence and school composition in thermally variable habitats. Understanding the capacity of coastal fishes to withstand acute warming events is therefore essential for predicting ecological responses to climate change. Objective: We aimed to determine the effects of simulated marine heatwaves on thermal tolerance and metabolic performance in juvenile grey mullets, Chelon labrosus and Chelon aurata, two abundant sympatric species inhabiting the Ria Formosa lagoon (southern Portugal). Methodology: Juvenile mullets acclimated at 17 °C were exposed to simulated heatwave treatments of 23, 27, or 33 °C and sampled either at peak temperature or after 48 h and 1-week recovery at 17 °C. Critical thermal maximum (CTmax, using a 1 °C/min thermal ramp), static oxygen consumption (MO2), and intermittent respirometry parameters were measured. Standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope (AS) were derived from intermittent respirometry. A complementary temperature-ramp (>3 h at each temperature step 17, 23, 27 and 33 °C) was performed to evaluate routine metabolic rate and estimate Q10 values across increasing temperatures. Additional plasma and tissue analyses are being conducted to assess energetic substrate mobilization and cellular responses to thermal and oxidative stress. Results: CTmax increased significantly with warming in both treatment modes, demonstrating rapid heat hardening in juvenile mullets. Fish exposed to 27 and 33 °C exhibited higher CTmax than control fish, and this elevated tolerance persisted after recovery. Chelon labrosus showed slightly higher CTmax values than C. aurata. Oxygen consumption increased with temperature, with the strongest responses occurring at 33 °C. SMR increased markedly with warming, particularly in heatwave-exposed fish, while MMR increased mainly at the highest temperature treatment. In contrast, AS showed no clear thermal optimum or decline across treatments. Routine metabolic rate increased non-linearly with temperature in the complementary ramp experiment, with a mean Q10 of 2.28, confirming strong thermal dependence of metabolism. Conclusions: Juvenile mullets possess substantial short-term thermal plasticity and can rapidly increase heat tolerance during marine heatwaves but this enhanced tolerance is accompanied by elevated metabolic costs under extreme warming, indicating potential energetic trade-offs near upper thermal limits. Differential physiological responses between species may influence school composition and ecological performance across thermal landscapes. Ongoing plasma and tissue analyses will further clarify the energetic and cellular mechanisms underlying thermal and oxidative stress resilience in coastal fishes. Full article

Introduction: Coastal fishes can adapt to water warming and hypoxia; however, acute tolerance does not necessarily predict longer-term performance and survival. This may be especially important in sedentary, site-faithful species with limited escape to escape increasingly unfavorable habitats. We assessed the climate-related stress responses of the Lusitanian toadfish, Halobatrachus didactylus, a benthic estuarine fish from the Northeast Atlantic, to water warming and hypoxia. Objectives: We aimed to determine the aerobic energy budget, thermal limits (CTmax), and critical oxygen tension (Pcrit), as well as blood indicators of metabolism, altered physiology and systemic stress, as proxies for whole-organism homeostatic state, thereby informing future ecophysiological assessments and bioindicator development in a context of environmental change. Methodology: We determined standard, routine, and maximum metabolic rates; aerobic scope; and critical thermal maximum (CTmax) and critical oxygen (Pcrit) thresholds on a set of 134 individuals ranging from 12 to 160 g in weight. On a different set of individuals (n = 48; 76.3 ± 2.6 g; 16.1 ± 0.18 cm), we simulated 30 days of seasonal scenarios combining low and high temperature with normoxia or hypoxia, followed by integrated metabolic, hematological, biochemical, and multivariate analyses. Results: Acute trials showed high short-term resilience: H. didactylus had an exceptionally low standard metabolic rate and routine metabolic rate, high CTmax (34.82 ± 0.66 °C), and strong hypoxia tolerance (Pcrit 0.59–1.97 mg O₂ L⁻¹), although smaller individuals were more sensitive. After 30 days, however, warming more than doubled standard and routine metabolic rates, while warm hypoxia reduced metabolic output relative to warm normoxia, consistent with metabolic depression under compounded stressors. This treatment also showed shifts in glucose, liver mass, red blood cell count, and hematocrit, identifying warm, oxygen-poor water as the most physiologically costly scenario for this species. Conclusions: Together, these results show that high acute tolerance does not guarantee resilience to climate change. In sedentary fishes, survival may depend less on surviving extremes than on maintaining energetic balance, oxygen transport capacity, and physiological homeostasis in increasingly warm, oxygen-poor coastal habitats. Full article

Introduction: Climate warming and drought are intensifying thermal stress in Mediterranean freshwater systems, potentially favoring invasive fish with broad physiological tolerance. Extended environmental tolerance and increased aerobic scope are indicative of the potential to sustain, perform and disseminate in challenging conditions. Objective: We aimed to determine the thermal scope of the invasive Australoheros facetus inhabiting southern Portuguese drainages using an array of physiological proxies. Methodology: We evaluated the thermal biology of the species across a wide temperature gradient to test how warming affects metabolic performance, thermal tolerance, and biochemical status. Fish collected from Algarve watercourses were exposed to 5, 10, 15, 20, 25 and 35 °C (n = 15 per condition, 10–60 g) for at least a week, and intermittent respirometry was used to determine standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS). Group Q10 was derived from metabolic rates. Plasma and tissue biomarkers of energy metabolism and oxidative stress were analyzed. Critical thermal maximum (CTmax) was assessed in fish acclimated for a week at 10, 20 and 30 °C (n = 10) using a 1 °C/min thermal ramp. Results: Intermediate temperatures (15–25 °C) supported the best overall physiological performance, combining stronger aerobic capacity with higher antioxidant protection. In contrast, 30–35 °C imposed clear physiological costs: maintenance metabolism increased disproportionately, aerobic scope declined, and cellular protection weakened, indicating the onset of heat stress. Despite this, A. facetus showed marked thermal plasticity, with CTmax increasing significantly with acclimation temperature. Fish acclimated to 30 °C had higher CTmax than fish acclimated to 20 °C and 10 °C, although the thermal safety margin decreased progressively as the acclimation temperature rose. Liver antioxidant activity also peaked at intermediate temperatures and declined at the warmest treatments, reinforcing the mismatch between acute tolerance and sustained performance. Conclusions: These results show that A. facetus is highly heat tolerant but that tolerance comes with energetic and cellular trade-offs near upper thermal limits. Despite this limitation at extreme conditions, the combination of broad tolerance and functional performance under warm intermediate conditions may help to explain its invasion success and stand as a competitive advantage in increasingly hot low-flow Iberian freshwater ecosystems. Full article

The present study describes the reproductive cycle of the razor clam (Solen marginatus) from the Ria Formosa lagoon in the Algarve region (southern Portugal), using histological preparations of gonads from samples collected monthly over an 18-month period, from January 2023 to June 2024. Simultaneously, the mean gonadal index (GI) was estimated and its relationship with fluctuations in seawater temperature and chlorophyll a concentration was examined. The reproductive cycle of S. marginatus showed a seasonal pattern, with a resting period between August and October, followed by the onset of gametogenesis in November, which lasted until March. Ripe individuals were observed between February–March and May, with the spawning period occurring primarily between May and July. The mean GI reflected the temporal variation in the gonadal cycle. Reproduction in this species was strongly influenced by fluctuations in seawater temperature, but was not significantly correlated with chlorophyll a concentration. The information gathered in this study is of utmost importance, as it enables the proposal of evidence-based management measures aimed at promoting the sustainable exploitation of this resource. According to these new findings, a closed season (June or July) prohibiting razor clam harvesting in the Ria Formosa lagoon between May and July is proposed. Full article

Most Portuguese aquaculture farms are located in estuaries and coastal lagoons, which are highly productive, nutrient-rich transition zones that are also among the most vulnerable to anthropogenic pressures and climate change. This study assesses Ria Formosa’s suitability for grooved carpet shell (Ruditapes decussatus) aquaculture, accounting for projected climate change and a potential increase in clam farming production. The methodology involved implementing a numerical modeling system to map key physico-chemical variables under historical (1995–2014) and future (2081–2100) conditions. Model outputs were then used to compute a suitability index (SI), which was converted into aquaculture suitability maps for this species. Results indicate that the hydrodynamic and transport components reproduced tidal propagation and the transport of salinity and heat effectively. In contrast, simulations of water quality variables were less accurate, reflecting the greater complexity and uncertainty in representing biochemical processes. Across both time periods, environmental conditions were generally less favorable in winter and more favorable in spring. Water temperature and chlorophyll-a concentration emerged as the dominant drivers of seasonal suitability. Projections suggest that Ria Formosa may become increasingly suitable for grooved carpet shell aquaculture by the end of the century. However, expanding production could compromise ecological balance, reduce resilience, and constrain the system’s long-term sustainable development. Full article

Extreme weather events, particularly marine heatwaves (MHWs), increasingly threaten aquaculture systems worldwide by impairing animal physiology and economical sustainability. This showcases the need to develop nutritional approaches that enhance animal performance under sub-optimal conditions. This study evaluated the effects of dietary supplementation with the brown macroalga Laminaria digitata (whole dried powder or extract) on the antioxidant status, digestive activity, and lipid metabolism of juvenile Sparus aurata exposed to a simulated MHW. Fish were fed four diets (control, 0.3% extract, and 0.3% or 1.5% powder) for 30 days before being exposed to a category III Mediterranean MHW. Under optimal temperature, macroalgae supplementation reduced oxidative status (lower catalase activity). The powder-feeds decreased lipid peroxidation, while the extract-feed elicited the opposite. All supplemented diets reduced proteolytic activity, and the extract-feed also decreased amylase activity. The MHW impaired gastrointestinal antioxidant defenses and liver lipid metabolism, decreasing catalase and glutathione S-transferase activities, as well as ΣPUFA n-6, 16:1 n-7, and 18:2 n-6 levels. The 0.3% powder-feed mitigated MHW-induced reductions in antioxidant activity, while both 0.3%-diets prevented thermal stress-related alterations on fatty acid profile. Overall, L. digitata powder at 0.3% was most effective at enhancing thermal stress resilience, supporting its value as a functional aquafeed ingredient. Full article

While improvements in the spectral and spatial resolution of satellite imagery have opened up new prospects for large-scale environmental monitoring, this potential has remained largely unrealised in dune ecogeomorphology. This is especially true for Mediterranean coastal dunes, where the highly mixed and sparse vegetation requires high resolution satellites and spectral unmixing techniques. To achieve this aim, we employed random forest regressors to predict the fractional cover of dune plant species in two of the sandy barriers of Ria Formosa (S. Portugal) from WorldView-2 imagery (June 2024). The algorithm, tested with spatially upscaled multispectral drone data and satellite imagery, detected the fractional cover of major species (most abundant classes and bushy vegetation) with reasonable to very good accuracy (coefficient of determination, CoD: 0.4 to 0.8) for the former and reasonable to good accuracy (CoD: 0.4 to 0.6) for the latter. Additional tests showed that (a) including the distance to the shoreline can increase model accuracy (CoD by ~0.1); (b) the grouping of species resulted in an insignificant increase in model skill; and (c) testing over independent dune plots showed generalisation beyond the training set and low risk of overfitting or noise. Overall, the approach showed promising results for large-scale observations in highly mixed coastal dunes. Full article

Vegetated intertidal ecosystems, such as seagrass meadows, salt marshes, and macroalgal beds, are vital for biodiversity, coastal protection, and climate regulation; however, they remain highly vulnerable to anthropogenic and climate-induced stressors. This study aims to assess interannual changes in intertidal vegetation cover along the Portuguese mainland coast from 2015 to 2024 using Sentinel-2 satellite imagery calibrated with high-resolution multispectral unoccupied aerial vehicle (UAV) data, to determine the most accurate index for mapping intertidal vegetation. Among the 16 indices tested, the Atmospherically Resilient Vegetation Index (ARVI) showed the highest predictive performance. Based on a model relating intertidal vegetation cover to this index, an ARVI value greater than or equal to 0.214 was established to estimate the area covered with intertidal vegetation. Applying this threshold to time-series data revealed considerable spatial and temporal variability in vegetation cover, with estuarine systems such as the Ria de Aveiro and the Ria Formosa showing the greatest extents and marked fluctuations. At the national level, no consistent overall trend was identified for the study period. Despite limitations related to satellite image resolution and single-site validation, the results demonstrate the feasibility and utility of combining UAV data and satellite indices for long-term, large-scale monitoring of intertidal vegetation. Full article

This study characterized saline waters from traditional and semi-industrial saltpans located in the Ria Formosa and Ria de Aveiro Portuguese coastal lagoons, aiming to evaluate their potential for thalassotherapy and dermatological applications. Five saline water samples were collected and analyzed for physicochemical parameters (pH, electrical conductivity, dissolved oxygen, and total dissolved and suspended solids) and chemical composition (major, minor, and trace elements), complemented by SEM-EDS analyses of the suspended solids. All samples exhibited salinities above 70 g/kg, classifying them as mineral-rich brines. Sodium was the dominant element, followed by Mg, K, and Ca, with concentrations significantly higher than those of seawater. Apparent geochemical differences were observed between the two lagoons, with Ria de Aveiro water enriched in Ca, while Ria Formosa showed higher Mg and K contents. Suspended solids were composed mainly of halite, gypsum, K-Mg salts, and biogenic aggregates, reflecting the interaction between evaporitic and microbial processes. These findings highlighted the high therapeutic potential of Portuguese saline waters for skin-related applications, supporting the safe use of natural saline resources in evidence-based wellness and dermatological practices. Full article

Extreme weather events, such as marine heatwaves (MHWs), pose serious threats to the aquaculture sector, facilitating the occurrence of disease outbreaks and compromising farmed animals’ welfare and survival. Hence, finding eco-innovative strategies to improve animal immunocompetence is essential to assure aquaculture’s sustainability and resilience in a rapidly changing ocean. This study evaluated the immunostimulatory potential of Laminaria digitata powder (0.3% and 1.5%) and extract (0.3%) in juvenile gilthead seabream (Sparus aurata) exposed to a Vibrio harveyi outbreak during a Category III MHW event (T = 25.7 °C). Overall, L. digitata supplementation did not significantly affect fish immunocompetence under optimal rearing conditions (T = 21.4 °C; no infection), nor did it induce any adverse effects. However, both the powder (1.5%) and extract (0.3%) forms of L. digitata supplementation effectively mitigated the negative impacts prompted by the MHW and Vibrio harveyi infection—evidenced by improvements in fish health indicators, hematological parameters, leukocyte viability, granulocyte proportions, and reductions in peroxidase activity and immunoglobulin M levels. From an economic standpoint, supplementation with 1.5% L. digitata powder emerged as the most promising strategy, offering a practical balance between effectiveness and affordability for large-scale applications. These findings highlight the potential of L. digitata as an immunostimulatory aquafeed supplement, with promising benefits for fish health and resilience under adverse rearing conditions. Full article

The replacement of ingredients from animal sources with plant-based ingredients is increasing the risk of contamination by mycotoxins in aquafeeds, potentially causing detrimental effects on fish welfare. However, limited research has been carried out so far on the impact of mycotoxins on fish health. Hence, the aim of this study was to assess the toxicological effects of the dietary emerging (enniatin B, ENNB) and regulated (fumonisin B1, FB1) mycotoxins (150 µg/kg) in different tissues of juvenile gilthead seabream (Sparus aurata) after 28 days of dietary exposure. Fitness indexes, plasma metabolites, and biomarkers of oxidative stress, metabolism, cellular, and neurotoxic damage were assessed. The exposure to each mycotoxin was sufficient to cause distinct effects in fish tissues. ENNB appears to be the most harmful mycotoxin to S. aurata, inducing changes on alkaline phosphatase and lipase activities in plasma, as well as protein and lipid degradation in liver. Increased lipid degradation was also induced in the brain by FB1 alone or combined with ENNB, whereas the exposure to the mixture inhibited acetylcholinesterase activity. Overall, this study contributes by highlighting the toxicological attributes of ENNB, thus reinforcing the need to include this mycotoxin in future legislation. Full article

This study aimed to evaluate the biochemical composition and bioactivities of biomass derived from wild (Laminaria ochroleuca and Saccorhiza polyschides) and cultivated (Macrocystis pyrifera) kelps, as well as industrially extracted residual pulp from M. pyrifera, to assess the potential production of high value bioproducts. All samples had a low lipid content, with M. pyrifera having the lowest (1.3% dw) and S. polyschides showing the highest value (3.3%). Fatty acids such as palmitic acid (C16:0), oleic acid (C18:1n-9 cis), alpha-linolenic acid (ALA, C18:3n-3), and eicosapentaenoic acid (EPA, C20:5n-3) were present, with the residual pulp having a distinctive n-6/n-3 ratio of less than one. The protein content was around 9% dry weight (dw) in all samples. The residual pulp and S. polyschides had the highest polyphenol content, with 4.86 and 4.94 mg GAE·g⁻¹ extract, respectively. Hydroethanolic extracts (30–70%) confirmed Fe³⁺ reducing activity (FRAP) in all samples. These findings offer valuable insights on the biochemical composition and bioactivity of the kelp species under study and the residual kelp biomass (pulp), underlining their significant potential for applications in the field of Blue Biotechnology. Full article

A complex composed of Pba3-Pba4 and subunits α5, α6, and α7 is identified as an early intermediate in proteasome core particle assembly in wild-type Saccharomyces cerevisiae cells. The same complex can be reconstituted from recombinantly produced components in vitro. Assembly of α6 and α7 with Pba3-Pba4 depends on the presence of the α5 subunit, the binding of which apparently initiates the formation of this intermediate. Our data suggest the following order of events: first, Pba3-Pba4 binds α5, then α6 is incorporated, and at the end α7. In the absence of the chaperones Pba1-Pba2 or Ump1, alternative Pba4-containing complexes are detected, the formation of which depends on the Blm10/PA200 protein. Overexpression of Pba1-Pba2 abolishes the formation of these complexes containing Pba4 and Blm10, suggesting that Blm10 may replace Pba1-Pba2 as an alternative assembly factor. Full article

Microalgae form the basis of marine food webs, essential in sustaining top predators including seabirds. However, certain species of microalgae synthesize biotoxins, which can accumulate in shellfish and fish and may cause harm to marine animals feeding on them. Toxins produced by dinoflagellates have been previously observed to be poisonous to seabirds. Also, in freshwater and brackish habitats, cyanobacteria have caused bird mortality events. In this work, we analyze the prevalence of six families of biotoxins (paralytic shellfish toxins (PSTs), microcystins (MCs), anatoxins, amnesic shellfish toxins (ASTs), cylindrospermopsin, and tetrodotoxins (TTXs)) in 340 samples from 193 wild birds admitted to a wildlife rehabilitation centre in south Portugal. Furthermore, we consider the clinical picture and signs of 17 birds that presented quantifiable levels of biotoxins in their tissues. The relationship between toxin burdens and the symptomatology observed, as well as possible biotoxin sources, are discussed. Based on previously published research data, we conclude that, in these birds, the biotoxins are unlikely to be the only cause of death but might contribute to some extent to a reduction in birds’ fitness. Full article