Marine ecosystems have been affected by the gradual rise in temperature due to climate change. Warming scenarios and the intensification of extreme climate events, such as marine heatwaves (MHWs), have been negatively affecting marine organisms. In addition, they are also threatened by anthropogenic pollution. Lithium (Li) is an emerging pollutant that has become a major concern due to its increasing use in a variety of applications. Understanding its combination with warming scenarios is crucial, as very little is known about its impact on marine organisms. For this reason, this research aimed to assess how different temperature increase scenarios may affect the response of Mytilus galloprovincialis to the effects of Li. Mussel bioaccumulation levels and physiological and biochemical biomarkers were analyzed after 28 days of exposure to 250 μg/L of Li under different temperature scenarios (control – 17 ºC; warming – 21 ºC and a simulation of a marine heatwave - 23 ºC). The results indicate that Li concentration in the tissues increased only in the contaminated mussels when exposed to 17 and 21 ºC, and that temperature had no effect on the accumulation of Li. The respiration rate of mussels was higher in the contaminated mussels than in the non-contaminated ones. The metabolic rate decreased in mussels exposed to 21 ºC and MHW, while mussels exposed to the combination of Li and MHW increased their metabolic rate. The mussels exposed to MHW and Li exhibited cellular damage. It was found that Li was not neurotoxic to M. galloprovincialis. This study has shown that only the most stressful condition (MHW + Li) induced negative effects in this species which can negatively affect the growth and reproduction of an entire community as well as the structure and functioning of the ecosystem. In general, the presented results highlight the importance of future studies in which it is necessary to combine the effects of pollutants and climate change, namely extreme weather events such as MHWs.

The coastal area north of Yucatan has experienced a cooling SST trend from 1982 to 2015 during the upwelling season (May–September) that contrasts with the warming observed at the adjacent ocean area. Different drivers were analyzed to identify the possible causes of that unusual coastal cooling. Changes in coastal upwelling and in sea-atmosphere heat fluxes are not consistent with the observed coastal cooling. The eastward shift of the Yucatan Current observed over the last decades is hypothesized as the most probable cause of coastal cooling. This shift enhances the vertical transport of cold deeper water to the continental shelf from where it is pumped to the surface by upwelling favorable westerly winds.

Over the last few years, the expansion of urbanization has increased the levels of light pollution in natural aquatic ecosystems. Light pollution is caused by increased artificial light at night (ALAN), modifying natural light levels. ALAN disrupts circadian cycles, supressing the nocturnal production of the hormone melatonin. Urban freshwaters besides being exposed to light pollution are also experiencing warmer temperatures due to urban air and ground temperatures, paved surfaces, and decreased riparian vegetation (Urban heat island effect). With the presence of ALAN and warming, including effects of heat waves in urban ecosystems, it is of most importance to assess the combined effects of these two stressors and investigate if and how ALAN can modify the thermal tolerance of aquatic organisms. The aim of this work was to assess whether ALAN alters the upper thermal tolerance in the aquatic midge Chironomus riparius larvae and to investigate how ALAN interacts with heat on the development and physiology of the species. Moreover, I intended to further elucidate the physiological role of the hormone melatonin on this process. To assess the thermal tolerance, I determined the Critical thermal maximum limit (CTMax) of larvae (4th stage), after ten days of exposure to three different light intensities (0,1 and 10 lx) during nighttime with presence and absence of exogenous melatonin (0 and 1 μM). To detect the effects of these two combined stressors on the development of the species, I evaluated the emergence time of midge’s adults (female/male), body weight (female/male imagoes) and percentage of emergence after a chronic exposure (28 days) to three temperatures (20 ºC, 24 ºC and stimulated heat wave where organisms were exposed to 28 ºC for 6 days), under two ALAN treatments (0 and 10 lx during nighttime) and exogenous melatonin (1 μM), in a full factorial design. The results indicate that ALAN decreases the upper thermal tolerance of C. riparius larvae (CTMax) and that the supplementation of exogenous melatonin attenuated these effects. In chronic exposures, ALAN had no significant effect on the development of C. riparius. Increased temperatures, on the other hand, accelerated the development of the organisms (earlier emergence) but also led to lower body weight in adult insects. Exposure to the simulated heat wave increased mortality significantly. No effects of ALAN were observed for C. riparius life history traits but complex responses to exogenous melatonin were observed where effects of temperature were ameliorated (in case of emergence time) or increased (for body weight) in the presence of exogenous melatonin. I conclude that light pollution can change responses of C. riparius to thermal stress and that, as observed for many other aquatic invertebrates, short exposure to heat waves can have detrimental population level consequences. These results highlight the importance of studying the combined effects of warming and light pollution, two common and concomitant stressors in urban freshwater ecosystems. More research is needed not only to understand the physiological effects of exposure to ALAN as well as the role of melatonin in mediating the thermal tolerance of organisms. Moreover, these studies should also be validated in other invertebrate species. This and other studies will surely contribute to better predict the effects of warming and of global climatic changes in urban aquatic ecosystems.

Nowadays, it is of utmost importance to consider climate change factors, such as ocean warming, since the risk of negative impacts derived from increased surface water temperature is predicted to be high to the biodiversity. The need for renewable energy technologies, to reduce greenhouse gas emissions, has led to the increasing use of rare earth elements (REEs). Dysprosium (Dy) is widely used in magnets, motors, electrical vehicles, and nuclear reactors, being considered a critical REE to technology due to its economic importance and high supply risk. However, the increasing use of this element contributes to the enrichment of anthropogenic REEs in aquatic systems. Nevertheless, the information on the potential toxicity of Dy is limited. Moreover, the effects of pollutants can be amplified when combined with climate change factors. Thus, this study aimed to assess the effects of Dy (10 μg/L) in the species Mytilus galloprovincialis under actual (17 °C) and predicted warming conditions (21 °C). The Dy concentration in contaminated mussels was similar between temperatures, probably due to the detoxification capacity in individuals under these treatments. The combined stressors affected the redox balance, but higher impacts were caused by Dy and warming acting alone. In terms of cellular damage, although Dy acting alone was prejudicial to mussels, warming and both stressors acting together induced higher levels of LPO and PC. The histopathological effects of Dy in the digestive tubules were independent of the temperature tested. Regarding effects on sperm, only warming induced cellular damage, while both stressors, alone and together, impaired sperm movement. Overall, this study highlights that warming might influence the effects induced by Dy, but greater impacts were caused by the element. Eventually, the tested stressors may have consequences on mussels' reproduction capacity as well as their growth, abundance, and survival.

The assessment of expected changes in coastal sea surface temperature (SST) on a global scale is becoming increasingly important due to the growing pressure on coastal ecosystems caused by climate change. To achieve this objective, 17 Global Climate Models from CMIP6 were used, with data from historical and hist-1950 experiments spanning 1982-2050. This analysis highlights significant warming of coastal areas worldwide, with higher and more variable rates of warming than observed in previous decades. All basins are projected to experience an increase in coastal SST near 1 °C by mid-century, with some regions exhibiting nearshore SST anomalies exceeding 2 °C for the period 2031-2050 relative to 1995-2014. Regarding the Eastern Upwelling Boundary Systems, only the Canary upwelling system and the southern part of the Humboldt upwelling system manage to show lower-than-average SST warming rates, maintaining, to a certain extent, their ability to buffer global warming.

Interest on the effects of emerging contaminants over aquatic organisms has increased in the last years. Nonetheless, the toxic action of classical natural and anthropogenically-driven metals has also to be monitored, especially because they reflect real environmental situations. For that, in the present study we focused on the effects on the marine mussel Mytilus galloprovincialis of the personal care product Triclosan (TCS) and Lead (Pb), as toxic metal, under separate and co-exposure situations at environmentally relevant concentrations: TCS (1 μg/L) and Pb (50 μg/L). The consideration of an additional factor such as an increase in ambient temperature was also included to provide a forecasted scenario of climate change: from the ambient temperature at actual conditions (17 °C) to a predicted warming situation (22 °C). Water chemical characterization and some physical properties and bioaccumulation of TCS and Pb in mussels at the end of the experiment (28 days) was considered. The parameters followed up comprise the energy related system production (electron transport system) and glycogen and protein reserves. Antioxidant enzymatic defences towards reactive oxygen species (ROS) and the consequences of ROS damage over endogenous lipids (LPO) and proteins (PC). Overall the results suggested only particular responses to chemical exposures at 17 °C whereas at 22 °C the detoxification machinery was set up and this prevented the occurrence of LPO. Nonetheless, PC formation occurred under Pb and TCS + Pb co-exposure at the highest temperature. Due to the complexity of the study: 4 chemical conditions, 2 temperatures and 10 biomarkers considered, a principal component ordination (PCO) analysis was included. The results of this integrative analysis confirmed a clear effect of the temperature, more responsiveness to drugs at 22 °C and in all likelihood due to Pb presence.

There has been a significant increase in the literature regarding the effects of warming and acidification on the marine ecosystem. To our knowledge, there is very little information on the potential effects of both combined stressors on marine grazer-seaweed interactions. Here, we evaluated, for the first time several phenotypic responses (e.g periwinkle survival, condition index, consumption rates, seaweed photosynthetic activity and oxidative stress) of the temperate periwinkle Littorina obtusata (grazer) and the brown seaweed Ascophyllum nodosum (prey) to such climate change-related variables, for 15 days. Increased temperature (22 °C, pH 8.0) elicited a significant lethal effect on the periwinkle within a short-term period (mortality rate > 90%). Acidification condition (18 °C, pH 7.6) was the one that showed lower mortality rates (≈20%), reflected by lower impact on periwinkle fitness and consumption rates. Under a scenario of increased temperature and lowered pH the antioxidant defences of L. obtusata seemed to be supressed increasing the risk of peroxidative damage. The seaweed evidenced signs of cellular damage under such conditions. These results suggest that: i) lower pH per se seems to benefit the interaction between grazer and seaweed while, ii) a combined scenario of increased temperature and lowered pH may be negative for the interaction, due to the unbalance between periwinkle mortality rates and consumption rates. But most importantly, since grazing often plays an important role on structuring natural communities, such predator-prey disturbances can elicit cascading effects on the remaining community structure and functioning of the temperate rocky-shore ecosystems.

Cumulative and continuing human emissions of greenhouse gases to the atmosphere are causing ocean warming. Rising temperature is a major threat to aquatic organisms and may affect physiological responses, such as acid-base balance, often compromising species fitness and survival. It is also expected that warming may influence the availability and toxicological effects of pollutants, including Rare Earth Elements. These are contaminants of environmental emerging concern with great economic interest. This group comprises yttrium, scandium and lanthanides, being Lanthanum (La) one of the most common. The European eel (Anguilla anguilla) is critically endangered and constitutes a delicacy in South East Asia and Europe, being subject to an increasing demand on a global scale. Considering the vulnerability of early life stages to contaminants, we exposed glass eels to 1.5 μg L-1 of La for five days, plus five days of depuration, under a present-day temperature and warming scenarios (△T = +4 °C). The aim of this study was to assess the bioaccumulation, elimination and specific biochemical enzymatic endpoints in glass eels (Anguilla anguilla) tissues, under warming and La. Overall, our results showed that the accumulation and toxicity of La were enhanced with increasing temperature. The accumulation was higher in the viscera, followed by the head, and ultimately the body. Elimination was less effective under warming. Exposure to La did not impact acetylcholinesterase activity. Moreover, lipid peroxidation peaked after five days under the combined exposure of La and warming. The expression of heat shock proteins was majorly suppressed in glass eels exposed to La, at both tested temperatures. This result suggests that, when exposed to La, glass eels were unable to efficiently prevent cellular damage, with a particularly dramatic setup in a near-future scenario. Further studies are needed towards a better understanding of the effects of lanthanum in a changing world.

In recent decades, human activity has been known to influence Earth’s marine ecosystems in a multitude of different ways, such as through global warming, overfishing, coastal or marine construction, pollution, among others. These impacts will then produce different effects on the affected organism populations. One of these groups is the gelatinous one, which has gained a lot of scientific interest due to the increased frequency and abundance jellyfish populations worldwide. It is speculated that human activities may have an impact on the development and reproduction of these species. Therefore, the aim of this work was to evaluate the effect of temperature, and different substrates on the asexual reproduction and polyp settlement of the jellyfish species Phyllorhiza punctata (Von Lendenfeld, 1884). Polyps of P. punctata were subjected to two different experiments. In the first experiment, the polyps were exposed to four different temperatures (22, 24, 26, and 28 ºC), and provided with five different substrate types (glass, rock, shell, plastic (PVC), and fishing net). After 60 days, the total number of polyps for each substrate and temperature was observed. In the second experiment, a different group of polyps was exposed to the same five substrates at the temperature of 24 ºC, and after 60 days, the total number of polyps, and their preferred distribution were compared. The results showed significant differences between the temperatures of 22 and 26 ºC, showing that higher temperatures have a positive effect on polyp asexual reproduction. It was also verified that a lower number of polyps was obtained at 28 ºC when compared with to 26 ºC, which indicates that this temperature may be outside the optimal range for P. punctata polyps, and therefore might restrict polyp reproduction instead. This leads us to believe that slight warming may benefit polyp asexual reproduction of P. punctata, but only within the limits supported by the species. Furthermore, polyp settlement occurred in all the provided substrates, although significant differences were observed between the plastic and the glass, rock, and shell substrates, being the later three significantly preferred over the first one. It was also possible to perceive a higher preference by the polyps to positions further away from the bottom of the goblet (negative geotaxis). In conclusion, marine-bound human activities appear to influence gelatinous organisms, and as such, further studies are required to better understand their influence on these organisms.

Litter decomposition is an ecological process of key importance for forest headwater stream functioning, with repercussions for the global carbon cycle. The process is directly and indirectly mediated by microbial decomposers, mostly aquatic hyphomycetes, and infuenced by environmental and biological factors such as water temperature and litter quality. These two factors are forecasted to change globally within the next few decades, in ways that may have contrasting efects on microbial-induced litter decomposition: while warming is expected to enhance microbial performance, the reduction in litter quality due to increased atmospheric carbon dioxide and community composition alteration may have the opposite outcome. We explored this issue through a microcosm experiment focused on early microbial-mediated litter decomposition under stream oligotrophic conditions, by simultaneously manipulating water temperature (10 °C and 15 °C) and litter quality (12 broadleaf plant species classifed into 4 categories based on initial concentrations of nitrogen and tannins). We assessed potential changes in microbial-mediated litter decomposition and the performance of fungal decomposers (i.e., microbial respiration, biomass accrual, and sporulation rate) and species richness. We found stronger efects of litter quality, which enhanced the performance of microbial decomposers and decomposition rates, than temperature, which barely infuenced any of the studied variables. Our results suggest that poorer litter quality associated with global change will have a major repercussion on stream ecosystem functioning.