Physiological and biochemical responses driven by different UV-visible radiation in Osmundea pinnatifida (Hudson) Stackhouse (Rhodophyta).

Light, or visible radiation, serves as a source of energy for photosynthesis of plants and most algae. In addition, light and ultraviolet radiation (UV-A and UV-B) act as a biological signal, triggering several cellular processes that are mediated by photoreceptors. The aim of this study was to evaluate the physiological and biochemical responses of Osmundea pinnatifida driven by different radiations through putative photoreceptors. For this, O. pinnatifida was grown under different radiation treatments composed by high intensity of light emitted by a low pressure sodium lamp (SOX), aiming to saturate photosynthesis, which was supplemented by low intensities of visible (red, green and blue) and ultraviolet radiation (UV-A and UV-B), in order to activate photoreceptors. Growth rates, photosynthesis, antioxidant activity, polyphenols, soluble proteins, phycobiliproteins, mycosporine-like amino acids (MAAs) and carotenoids were evaluated during the experiment. Complementary UV-A radiation positively influenced growth rates after 15 days of experiment, although the presence of a peak of blue light in this treatment can also have contributed. UV-B radiation increased the concentration of zeaxanthin and chlorophyll a. The blue light caused the accumulation of chlorophyll a, violaxanthin, phycoerythrin and polyphenols on different days of the experiment. Phycoerythrin also increased under green and red light conditions. Our results showed that some compounds can be modulated by different radiation, and the involvement of photoreceptors is suggested. In red algae, photoreceptors sensitive to red, green and blue light have been identified, however little is known about UV photoreceptors. The presence of photoreceptors sensitive to UV radiation in O. pinnatifida is discussed.

Reef-building coralline algae from the Southwest Atlantic: filling gaps with the recognition of Harveylithon (Corallinaceae, Rhodophyta) on the Brazilian coast.

The Southwest Atlantic is notable for having extensive reef areas cemented by nongeniculate coralline red algae. Based on an analysis of four genetic markers and morpho-anatomical features, we clarify the species of Harveylithon in the tropical and warm temperate Southwest Atlantic. Species delimitation methods (mBGD, ABGD, SPN, and PTP), using three markers (psbA, rbcL, and COI), support the recognition of three new species: H. catarinense sp. nov., H. maris-bahiensis sp. nov., and H. riosmenum sp. nov., previously incorrectly called Hydrolithon samoënse. Our findings highlight the importance of using an approach with several lines of evidence to solve the taxonomic status of the cryptic species.

Phytoremediation potential of Ulva ohnoi (Chlorophyta): Influence of temperature and salinity on the uptake efficiency and toxicity of cadmium.

Ulva ohnoi is a green macroalga with fast growth and high rates of nitrogen and phosphorus absorption. Recently, this species has been recorded in several places with record green tide formation in some of them. Using molecular tools, we herein report the first occurrence of this species in Brazil and demonstrate its potential for phytoremediation in typical environmental concentrations of Cd (0.625-15 µg L-1). Similarly, the effects of physicochemical parameters (salinity and temperature) on the toxicity and uptake efficiency of this species were evaluated. Molecular analysis of two sequences (1141 bp) obtained corroborates another 34 sequences for U. ohnoi obtained from GenBank. The addition of Cd in the medium affected photosynthetic parameters and reduced growth rate. U. ohnoi showed resistance to Cd when cultivated at 18 °C, S15 and 18-25 °C, S35, at concentrations between 0.625 and 2.5 µg. L-1 of Cd; yet, positive growth rate was maintained. Dose-dependent accumulation was observed in all combinations of factors used with a maximum value of 4.20 µg Cd per gram of dry seaweed at 15 µg. L-1 of Cd at 18 °C and S35. Maximum value of the concentration factor was 81.3 ±â€¯1.1% of Cd added at the concentration of 0.625 µg. L-1 to S15 and 18 °C. Our results demonstrate the potential of using U. ohnoi in the phytoremediation of Cd in saltwater or brackish water.

Modelling bioremediation of contaminated effluents by Ulva ohnoi. - A predictive perspective.

Ulva spp. are tolerant to salinity variations and exhibit easy acclimation, playing an essential role in the depollution of aquatic ecosystems precisely due to their high efficiency in absorbing and accumulating nutrients. For this reason, Ulva spp. becomes an attractive solution for recovering areas that suffer the impacts of problems such as the eutrophication of anthropogenic origin. In addition to being a promising alternative for the blue bioeconomy, it can contribute to the sustainability of economic activities in coastal areas. Therefore, the present study aimed to develop and elucidate the behavior of Ulva ohnoi using predictive surface response models. The algae were grown under different concentrations of nutrient and salinity levels, as predicted by the experimental design, and it was evaluated according to the potential of the biomass to absorb the nutrients, as well as its photosynthetic performance and biochemical parameters. Our study confirmed the high efficiency and preference of Ulva ohnoi in the absorption of nitrogen dissolved in the medium in the form of NH4+ and that salinity is an essential factor in the dynamics and speed of ammonium absorption. The absorption of orthophosphate by U. ohnoi is reverted to the culture medium when subjected to long-term cultivation. This process was more intense because of low salinity, even at conditions of availability of the compound. The 3D-models of response surfaces elucidate the behavior of Ulva ohnoi, attributing a correlation between nutrient availability and salinity and the biological behavior of the species. In view of what is exposed by these models, as well as the effects of saline distribution along the Lagoon, the following regions of the lagoon are suggested: Center-North, Center and South - as potential areas for the implementation of bioremediation projects with Ulva ohnoi.

Anti-infective potential of marine invertebrates and seaweeds from the Brazilian coast.

This manuscript describes the evaluation of anti-infective potential in vitro of organic extracts from nine sponges, one ascidian, two octocorals, one bryozoan, and 27 seaweed species collected along the Brazilian coast. Antimicrobial activity was tested against Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC 29212), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922) and Candida albicans (ATCC 10231) by the disk diffusion method. Antiprotozoal activity was evaluated against Leishmania braziliensis (MHOM/BR/96/LSC96-H3) promastigotes and Trypanosoma cruzi (MHOM/BR/00/Y) epimastigotes by MTT assay. Activity against intracellular amastigotes of T. cruzi and L. brasiliensis in murine macrophages was also evaluated. Antiviral activity was tested against Herpes Simplex Virus type 1 (HSV-1, KOS strain) by the plaque number reduction assay (IC50). Cytotoxicity on VERO cells was evaluated by the MTT assay (CC50). The results were expressed as SI = CC50/IC50. The most promising antimicrobial results were obtained against S. aureus and C. albicans with Dragmacidon reticulatum. Among the seaweeds, only Osmundaria obtusiloba showed moderate activity against P. aeruginosa. Concerning antiprotozoal activity, Bugula neritina, Carijoa riseii, Dragmaxia anomala and Haliclona (Halichoclona) sp. showed the most interesting results, mainly against extracellular promastigote forms of L. braziliensis (66, 35.9, 97.2, and 43.6% inhibition, respectively). Moreover, six species of seaweeds Anadyomene saldanhae, Caulerpa cupressoides, Canistrocarpus cervicornis, Dictyota sp., Ochtodes secundiramea, and Padina sp. showed promising results against L. braziliensis (87.9, 51.7, 85.9, 93.3, 99.7, and 80.9% inhibition, respectively), and only Dictyota sp. was effective against T. cruzi (60.4% inhibition). Finally, the antiherpes activity was also evaluated, with Haliclona (Halichoclona) sp. and Petromica citrina showing the best results (SI = 11.9 and SI > 5, respectively). All the active extracts deserve special attention in further studies to chemically characterize the bioactive compounds, and to perform more refined biological assays.

Functional redundancy and stability in a subtidal macroalgal community in the Southwestern Atlantic coast.

Functional redundancy can stabilize ecological functions as asynchronous fluctuations among functionally similar species may buffer environmental changes. We investigated the temporal dynamics of a subtidal macroalgal community in the warm temperate Southwestern Atlantic coast (SWA) to evaluate whether functional redundancy stabilize ecosystems functions through compensatory dynamics under realistic environmental scenarios. Despite temporal variations in the community structure occurred, a high stability in macroalgal coverage was found at the community-level driven by taxa asynchronous fluctuations. No relationship between functional redundancy and stability occurred, suggesting that functional compensation cannot surpass the influence of environmental fluctuations on the performance of ecological functions. Declines in Sargassum species abundance, along with its low functional redundancy, indicate that this canopy-forming algae must be prioritized in conservation efforts in the SWA. Our study adds to the comprehension and generalization of biodiversity-stability findings in natural systems across distinct geographical areas, also contributing to their operationalization in marine ecosystems.

Physiology, niche characteristics and extreme events: Current and future habitat suitability of a rhodolith-forming species in the Southwestern Atlantic.

Given the ecological and biogeochemical importance of rhodolith beds, it is necessary to investigate how future environmental conditions will affect these organisms. We investigated the impacts of increased nutrient concentrations, acidification, and marine heatwaves on the performance of the rhodolith-forming species Lithothamnion crispatum in a short-term experiment, including the recovery of individuals after stressor removal. Furthermore, we developed an ecological niche model to establish which environmental conditions determine its current distribution along the Brazilian coast and to project responses to future climate scenarios. Although L. crispatum suffered a reduction in photosynthetic performance when exposed to stressors, they returned to pre-experiment values following the return of individuals to control conditions. The model showed that the most important variables in explaining the current distribution of L. crispatum on the Brazilian coast were maximum nitrate and temperature. In future ocean conditions, the model predicted a range expansion of habitat suitability for this species of approximately 58.5% under RCP 8.5. Physiological responses to experimental future environmental conditions corroborated model predictions of the expansion of this species' habitat suitability in the future. This study, therefore, demonstrates the benefits of applying combined approaches to examine potential species responses to climate-change drivers from multiple angles.

Saxitoxins from the freshwater cyanobacterium Raphidiopsis raciborskii can contaminate marine mussels.

Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) is a freshwater cyanobacterium potentially producing saxitoxins (STX) and cylindrospermopsin. Its ecophysiological versatility enables it to form blooms in the most diverse types of environments, from tropical to temperate, and from relatively pristine to polluted. In Peri Lake, located in the subtropical south of Brazil, growing populations of STX-producing R. raciborskii have been detected since 1994, posing risks to the use of its waters that supply a population of about 100,000 inhabitants. Despite the existence of a monitoring system for the presence and toxicity of cyanobacteria in Peri Lake water, no assessment has been made in the coastal region, downstream of outflowing lake water, thereby potentially making available a toxic biomass to natural and cultivated shellfish populations in the salt water ecosystem. To address this problem, the present study evaluated environmental variables and STX concentration by profiling the outflowing waters between Peri Lake and the adjacent coastal zone. Laboratory experiments were carried out with three strains of R. raciborskii in order to confirm the effect of salinity on STX production and verify if Perna Perna mussels fed with R. raciborskii cultures would absorb and accumulate STX. Results showed that environmental concentrations of STX reach high levels (up to 6.31 µg L-1 STX eq.), especially in the warmer months, reaching the coastal zone. In laboratory tests, it was found that the strains tolerate salinities between 4 and 6 and that salinity influences the production of STX. In addition, mussels fed with R. raciborskii effectively absorb and accumulate STX, even in typically marine salinities (22 to 30), suggesting that R. raciborskii biomass remains available and toxic despite salinity shock. These results draw attention to the ecological and health risk associated with R. raciborskii blooms, both in the lake environment and in the adjacent marine environment, calling attention to the need to improve the monitoring and management systems for water and shellfish toxicity in the region of interest, as well as other places where toxic cyanobacteria of limnic origin can reach the coastal zone.

Cytotoxic halogenated metabolites from the Brazilian red alga Laurencia catarinensis.

Seven new (1-7) and seven previously reported (8-14) halogenated metabolites were isolated from the organic extract of the Brazilian red alga Laurencia catarinensis. The structure elucidation and the assignment of the relative configurations of the new natural products were based on detailed NMR and MS spectroscopic analyses, whereas the structure of metabolite 6 was confirmed by single-crystal X-ray diffraction analysis. The absolute configuration of metabolite 1 was determined using the modified Mosher's method. The in vitro cytotoxicity of compounds 1-14 was evaluated against HT29, MCF7, and A431 cell lines.

Relationship between fibropapillomatosis and environmental quality: a case study with Chelonia mydas off Brazil.

We documented the presence of fibropapillomatosis (FP), a debilitating tumor-forming disease, in marine turtles in Espirito Santo Bay (Brazil) from March 2007 to April 2008, and assessed the value of a specific environmental index for predicting the prevalence of FP. Turtles were captured monthly with entanglement nets and scored for presence and severity of FP. For the assessment of habitat quality, we used the ecological evaluation index (EEI) based on benthic macrophytes. The FP-free control area was classified as good quality (EEI = 8) and the study area, with high FP prevalence, was classified as bad quality (EEI= 2). Prevalence of FP in the study area was 58.3% with an average of 40 tumors per individual, and prevalence varied positively with curved carapace length (CCL). No FP was seen in the control area. The number of turtles heavily afflicted (tumor score category 3) was 10 times larger than those lightly affected (tumor score category 1). Most tumors were found on or near the front and rear flippers; no oral tumors or internal tumors were found. At recapture, 41% of formerly tumor-free turtles revealed FP, often increasing in severity with time, and very few turtles showed signs of disease regression. From the results of this study we concluded that FP is particularly severe in Espírito Santo Bay. Future studies should focus on evaluating how widespread FP is in Brazil, whether prevalence is increasing or decreasing, and elucidating the pathology and pathogenesis of FP in sea turtles in Brazil.

How experimental physiology and ecological niche modelling can inform the management of marine bioinvasions?

Marine bioinvasions are increasing worldwide by a number of factors related to the anthroposphere, such as higher ship traffic, climate change and biotic communities' alterations. Generating information about species with high invasive potential is necessary to inform management decisions aiming to prevent their arrival and spread. Grateloupia turuturu, one of the most harmful invasive macroalgae, is capable of damaging ecosystem functions and services, and causing biodiversity loss. Here we developed an ecological niche model using occurrence and environmental data to infer the potential global distribution of G. turuturu. In addition, ecophysiological experiments were performed with G. turuturu populations from different climatic regions to test predictions regarding invasion risk. Our model results show high suitability in temperate and warm temperate regions around the world, with special highlight to some areas where this species still doesn't occur. Thalli representing a potential temperate region origin, were held at 10, 13, 16, 20 and 24 °C, and measurements of optimal quantum field (Fv/Fm) demonstrated a decrease of photosynthetic yield in the higher temperature. Thalli from the population already established in warm temperate South Atlantic were held at 18, 24 and 30 °C with high and low nutrient conditions. This material exposed to the higher temperature demonstrated a drop in photosynthetic yield and significant reduction of growth rate. The congregation of modelling and physiological approach corroborate the invasive potential of G. turuturu and indicate higher invasion risk in temperate zones. Further discussions regarding management initiatives must be fostered to mitigate anthropogenic transport and eventually promote eradication initiatives in source areas, with special focus in the South America. We propose that this combined approach can be used to assess the potential distribution and establishment of other marine invasive species.

Apoptotic events induced by a natural plastoquinone from the marine alga Desmarestia menziesii in lymphoid neoplasms.

There exists an urgent need for the development of new drugs for the treatment of lymphoid neoplasms. The aim of this study was to evaluate the cytotoxic effect of the marine plastoquinone 9'-hydroxysargaquinone (9'-HSQ), focusing on investigation of the mechanism by which it causes death in lymphoid neoplastic cells. This particular plastoquinone reduced the cell viability of different hematological tumor cell lines in a time-dependent and concentration-dependent manner. Intrinsic apoptosis occurred with time-dependent reduction of mitochondrial membrane potential (42.3 ± 1.1% of Daudi cells and 18.6 ± 5.6% of Jurkat cells maintained mitochondrial membrane integrity) and apoptosis-inducing factor release (Daudi: 133.3 ± 8.1%, Jurkat: 125.7 ± 6.9%). Extrinsic apoptosis also occurred, as reflected by increased FasR expression (Daudi: 139.5 ± 7.1%, Jurkat: 126.0 ± 1.0%). Decreases were observed in the expression of Ki-67 proliferation marker (Daudi: 67.5 ± 2.5%, Jurkat: 84.3 ± 3.8%), survivin (Daudi: 66.0 ± 9.9%, Jurkat: 63.1 ± 6.0%), and NF-κB (0.7 ± 0.04% in Jurkat cells). Finally, 9'-HSQ was cytotoxic to neoplastic cells from patients with different lymphoid neoplasms (IC50: 4.9 ± 0.6 to 34.2 ± 0.4 µmol/L). These results provide new information on the apoptotic mechanisms of 9'-HSQ and suggest that it might be a promising alternative for the treatment of lymphoid neoplasms.

Ecophysiological implications of UV radiation in the interspecific interaction of Pyropia acanthophora and Grateloupia turuturu (Rhodophyta).

Radiation, both photosynthetic active radiation (PAR, l = 400-700 nm) and Ultraviolet (UVR, l = 280-400 nm) is one of the key factors regulating algal distribution in aquatic environments. Pyropia acanthophora and Grateloupia turuturu have been found over upper rocky shore areas in Southern Brazil, occupying the same niche space. The first species is native and the second one is exotic and considered a potential invader of South Atlantic. The aim of the present study was to evaluate the effects of radiation on physiological responses of both species and infer mechanisms that allow their niche competition in the environment. Samples were cultured in the following conditions: associated or separated, and with an addition of PAR, PAR + UVA (PA) and PAR + UVA + UVB (PAB), totalizing six factorial treatments during 5 days of exposure. Photosynthetic responses of Fv/Fm and ETR were daily evaluated. At the beginning and at the end of the experiment, samples were analyzed for pigment content (chlorophyll a and phycobiliproteins), and mycosporine-like amino acids (MAAs), while oxygen evolution was evaluated at the end of the experiment. As the main results, G. turuturu died when cultivated in PAB conditions. P. acanthophora presented higher amounts of chlorophyll a than G. turuturu during the whole experiment. Phycoerythrin and Fv/Fm remained constant in P. acanthophora but diminished for G. turuturu in UV treatments. ETR was higher for samples that were cultivated in associative treatment. The presence of G. turuturu in the same flask enhanced MAA synthesis in P. acanthophora, regardless of radiation condition. In addition, UV radiation can be a factor controlling species distribution and could counteract the spreading of invasive species, like G. turuturu, allowing P. acanthophora survival in upper rocky shore zones of the natural ecological distribution area.

Halimeda jolyana (Bryopsidales, Chlorophyta) presents higher vulnerability to metal pollution at its lower temperature limits of distribution.

Seaweeds living at their temperature limits of distribution are naturally exposed to physiological stressors, facing additional stress when exposed to coastal pollution. The physiological responses of seaweeds to environmental conditions combining natural and anthropogenic stressors provide important information on their vulnerability. We assessed the physiological effects and ultrastructural alterations of trace metals enrichment at concentrations observed in polluted regions within the temperature ranges of distribution of the endemic seaweed Halimeda jolyana, an important component of tropical southwestern Atlantic reefs. Biomass yield and photosynthetic performance declined substantially in samples exposed to metal, although photosynthesis recovered partially at the highest temperature when metal enrichment was ceased. Metal enrichment caused substantial ultrastructural alterations to chloroplasts regardless of temperatures. The lack of photosynthetic recovery at the lower temperatures indicates a higher vulnerability of the species at its temperature limits of distribution in the southwestern Atlantic.

Structural and physiological responses of Halodule wrightii to ocean acidification.

Coastal areas face high variability of seawater pH. Ocean acidification (OA) and local stressors are enhancing this variability, which poses a threat to marine life. However, these organisms present potential phenotypic plasticity that can offer physiological and structural tools to survive in these extreme conditions. In this study, we evaluated the effects of elevated CO2 levels and consequent pH reduction on the physiology, anatomy and ultrastructure of the seagrass Halodule wrightii. A mesocosm study was conducted in an open system during a 30-day experiment, where different concentrations of CO2 were simulated following the natural variability observed in coastal reef systems. This resulted in four experimental conditions simulating the (i) environmental pH (control condition, without CO2 addition) and (ii) reduced pH by - 0.3 units, (iii) - 0.6 units and (iv) - 0.9 units, in relation to the field condition. The evaluated population only suffered reduced optimum quantum yield (Y(II)), leaf width and cross-section area under the lowest CO2 addition (- 0.3 pH units) after 30 days of experiment. This fitness commitment should be related to carbon concentration mechanisms present in the evaluated species. For the highest CO2 level, H. wrightii demonstrated a capacity to compensate any negative effect of the lowest pH. Our results suggest that the physiological behaviour of this primary producer is driven by the interactions among OA and environmental factors, like irradiance and nutrient availability. The observed behaviour highlights that high-frequency pH variability and multifactorial approaches should be applied, and when investigating the impact of OA, factors like irradiance, nutrient availability and temperature must be considered as well.

UVR and PAR absorbing compounds of marine brown macroalgae along a latitudinal gradient of the Brazilian coast.

Absorption spectra are indicative of biological sample chemical composition and can be used as a basis for the construction of descriptive and predictive models for biotechnological screening or assays. In marine algae, chemical composition can vary due to species-specific differences in biochemistry, as well as intra-specific responses to unique environmental variables. Different indices (UVCi, UVB+Ai and PARi) were proposed and calculated to evaluate how photoprotective compounds vary in 18 species of Phaeophyceae. In addition, they were correlated to abiotic factors. Through this technique, seven main peaks were detected in the absorbing spectra of marine brown algal extracts. The highest photoprotective indices values were found in species collected in tropical areas, where higher solar radiation is observed compared to the southern Brazilian coast. Considering additional abiotic factors, water temperature and nitrate concentration were negatively correlated with UV indices. PARi's indices were positively affected by nitrate. All species collected on the Brazilian coast have absorption peaks in the region of phenolic compounds and carotenoids, suggesting that tropical marine brown macroalgae may have developed an effective antioxidant defense system, suggesting adaptation to environments characterized by high solar radiation. UVR/PAR indices congregated essential information to possible future biotechnological screening, facilitating selection of high priority species or sites, fostering actions to enhance alternative sustainable management strategies of coastal environments.

Structure of macroalgal communities on tropical rocky shores inside and outside a marine protected area.

The structure of marine macroalgal communities and morpho-functional groups were investigated in a poorly characterized region on the Tropical Southwestern Atlantic coast, Brazil. The survey was conducted at six rocky shores located on the mainland and on coastal islands distributed inside a marine protected area (MPA) and outside the MPA (near a densely populated area). We hypothesized that tropical rocky shores inside the MPA and islands have higher species richness, diversity, and evenness of marine macroalgae. Results confirmed that species richness, diversity and evenness were significantly higher inside the MPA than in rocky shores outside the MPA. Only species richness was higher on islands than on the mainland. The results suggest that human impacts could lead to a competitive advantage and dominance in the articulated calcareous morphotype, resulting in community differences and lower benthic biodiversity in tropical ecosystems near urbanized sites.

Effects of Ocean Acidification and Temperature Increases on the Photosynthesis of Tropical Reef Calcified Macroalgae.

Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO2-driven ocean acidification and temperature rises on the photosynthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3, -0.6, -0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.

Effects of copper and lead exposure on the ecophysiology of the brown seaweed Sargassum cymosum.

The effects of the heavy metals copper (Cu) and lead (Pb) on Sargassum cymosum were evaluated by determining uptake capacity, growth rates, photosynthetic efficiency, contents of photosynthetic pigments and phenolic compounds, 2,2-diphenyl-1-picrylhydrazyl radical-scavenging capacity, and morphological and cellular changes. S. cymosum was cultivated with Cu and Pb separately and combined at concentrations of 10, 25, and 50 µM for 7 days in laboratory-controlled conditions. Seaweeds under Cu treatment showed the highest biosorption capacity, and growth rates were significantly reduced compared to the control. The photosynthesis/irradiance curves showed alterations in kinetic patterns in the metal-treated samples. Specifically, Cu treatment alone inhibited electron transport rate (ETR) response, while Pb alone induced it. However, samples treated with both Cu and Pb (Cu + Pb) showed inhibition in ETR. The total amount of pigments increased relative to control. Light microscopy showed an increase in phenolic compounds, with physodes migrating towards cortical cells. Scanning electronic microscopy revealed alterations in the typical rough surface of thallus, when compared with control, especially for Pb treatments. Based on these results, it could be concluded that Cu and Pb are stress factors for S. cymosum, promoting alterations in seaweed metabolism and stimulating protective mechanisms against oxidative stress. However, the high bioaccumulation capacity of both heavy metals indicates a possible application for S. cymosum as a biosorbent agent for contaminated wastewater when metals are in low concentrations.

Salinity critical threshold values for photosynthesis of two cosmopolitan seaweed species: providing baselines for potential shifts on seaweed assemblages.

Climate change has increased precipitation in several South American regions leading to higher freshwater inputs into marine systems with potential to cause salinity declines along the coast. The current salinity profile on the southern coast of Brazil was surveyed during four years providing a baseline of the current salinity pattern in the region. Additionally, the effects of salinity decreases on the photosynthesis of the seaweeds Ulva lactuca and Sargassum stenophyllum were investigated in laboratory. Seaweeds were cultured at salinities 5, 15 and 34 and at the mean winter and summer temperatures. Photosynthetic performance was measured following 24 and 96 h from the beginning of experiment. U. lactuca remained practically unaltered by low salinities while S. stenophyllum presented declines of important photosynthetic parameters. This is due to the different regulation abilities of energy distribution at the PSII of the two species. These differences have potential to lead to seaweed community shifts.