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Extreme temperature events are becoming more recurrent and are more frequent with major impacts on coastal ecosystems, which are additionally impacted by increasing urbanization, resulting in high nutrient load. So far little is known about cumulative and/or interactive effects of global and local stressors on species' performance. Here, we evaluated the single and combined effects of simulated heatwaves and eutrophication on the ecophysiology of Laurencia catarinensis in a bi-factorial mesocosm experiment. The algae were exposed for 30 d to three different temperatures (208C, 248C, 288C) and nutrient concentrations (low, intermediate, high) and their nutrient uptake rates, photosynthetic performance, growth rates, pigment and phenolic compound concentrations, as well as antioxidant capacity was determined and compared between treatments. Under low nutrient concentration, physiological performance and growth decreased with increasing temperatures. In contrast, they increased with higher nutrient availability and moderate temperature increase close to the summer average temperature, but largely declined upon exposure to higher temperature (288C). This decline seemed to be related to oxidative stress, as indicated by an increase of compounds with antioxidant properties (lutein, zeaxanthin, phenols). Our data show that all measured parameters were affected by temperature and nutrient availability, with an interactive effect between these two factors, indicating that increasing temperature will influence macroalgal performance, and even more dramatically in coastal systems that are highly impacted by urbanization. However, the direction of the response will be determined by nutrient availability and will also depend on the magnitude of the temperature increase, that is, whether it surpasses the thermal threshold of the species.Marine macroalgae are dominant and essential components of coastal ecosystems around the world (Gattuso et al. 1998;Harley et al. 2012) and are currently threatened by a multitude of stressors, such as those related to global climate change (Harley et al. 2006(Harley et al. , 2012, but also locally by increasing nutrient and sediment loading, the overfishing and spread of invasive species (Worm and Lotze 2006;Schmidt and Scheibling 2007). Current changes in seawater temperature, due to climatic change, predict for the end of this century a continuous warming of near-surface air temperature, on the order of 2-78C with regional, seasonal and diurnal

Aim Mangrove wetlands span broad geographical gradients, resulting in functionally diverse tree communities. We asked whether latitudinal variation, allometric scaling relationships and species composition influence mangrove forest structure and biomass allocation across biogeographical regions and distinct coastal morphologies. Location Global. Time period Present. Major taxa studied Mangrove ecosystems. Methods We built the largest field‐based dataset on mangrove forest structure and biomass to date (c. 2,800 plots from 67 countries) to address macroecological questions pertaining to structural and functional diversity of mangroves spanning biogeographical and coastal morphology gradients. We used frequentist inference statistics and machine learning models to determine environmental drivers that control biomass allocation within and across mangrove communities globally. Results Allometric scaling relationships and forest structural complexity were consistent across biogeographical and coastal morphology gradients, suggesting that mangrove biomass is controlled by regional forcings rather than by latitude or species composition. For instance, nearly 40% of the global variation in biomass was explained by regional climate and hydroperiod, revealing nonlinear thresholds that control biomass accumulation across broad geographical gradients. Furthermore, we found that ecosystem‐level carbon stocks (average 401 ± 48 MgC/ha, covering biomass and the top 1 m of soil) varied little across diverse coastal morphologies, reflecting regional bottom‐up geomorphic controls that shape global patterns in mangrove biomass apportioning. Main conclusions Our findings reconcile views of wetland and terrestrial forest macroecology. Similarities in stand structural complexity and cross‐site size–density relationships across multiscale environmental gradients show that resource allocation in mangrove ecosystems is independent of tree size and invariant to species composition or latitude. Mangroves follow a universal fractal‐based scaling relationship that describes biomass allocation for several other terrestrial tree‐dominated communities. Understanding how mangroves adhere to these universal allometric rules can improve our ability to account for biomass apportioning and carbon stocks in response to broad geographical gradients.

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Four strains of Kappaphycus alvarezii were cultivated in the subtropical waters of Florianópolis, Santa Catarina State, Brazil (27°29′19′′ S/48°32′28′′ W), from February 2009 to February 2010. Seaweeds were cultivatedon floating raft near of mussel farms. Salinity ranged from 29 to 36 psu and temperature from 17.1 to 28.5°C. Higher growth rates (5.12-4.29% day −1 ) were measured in summer and autumn, showing a positive correlation between growth rate and water temperature. Lower growth rates (0.54-0.32% day −1 ) occurred in winter, resulted mainly by biomass loss. Significant differences were observed among the strains in spring and the brown tetrasporophytic strain was the only one which failed to recover, being excluded of the experiments. The effect of cultivation periods (36, 42, and 97 days) on carrageenan yield, gel strength, and viscosity were analyzed. Carrageenan yields were higher for plants kept 42 days in the sea (28%), against 25% for 36 and 97 days. There were no significant differences in carrageenan yield among the strains analyzed. Viscosity increased with the increase of cultivation period, while gel strength seemed to vary at random. Tetrasporangia and cystocarps were not observed, and lost fragments did not attach outside the raft. In general, dissolved inorganic nitrogen concentration decreased around the cultivation area as compared to the mussel farm. Results show that cultivation of K. alvarezii is technically feasible in subtropical waters and can be associated with local mussel farms, mitigating the eutrophication and, eventually, increasing the economic return of the farmers.

Marine heatwaves (MHWs) are a major concern worldwide due to their increasing impacts in recent years, and these extreme events may trigger deoxygenation of coastal waters affected by sewage and eutrophication. Here we investigate the combined effects of MHWs and nutrient enrichment on the water quality and biodiversity of the Bay of Santa Catarina Island (Brazil). We used historical (1994–2020) sea surface temperature data from satellites and in situ physical, chemical and biological parameters to assess temporal trends. Oxygen levels have been decreasing whilst phosphorus levels have been increasing in the bay. During the austral summer of 2020 a regional sea surface heatwave was detected by satellite, lasting for 9 days and coinciding with our research cruise. During this period, seawater temperatures reached 29.8°C and anoxia was detected for the first time in the bay. A decrease in macrobenthic and phytoplankton community richness correlated with decreases in oxygen both through time and towards more urbanized areas. Overall, poor wastewater treatment is a key stressor that combined with MHWs to degrade coastal waters. Mitigation strategies are needed to minimize the impact of MHWs, including improved sewage treatment, restoration and conservation of wetlands and the use of nature-based technologies to promote coastal ecosystem recovery.

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