Search

The damages of Mariana's mining mud in the physiology of the brown algae Sargassum cymosum and its main epiphytic, the red algae Hypnea pseudomusciformis, were evaluated by controlled essays. Seaweeds were exposed to presence or absence of mud, isolated or in biological association, for 5 and 15 days. Measured parameters were growth rates, biochemical descriptors, and the chemical investigation of concentration and metal profile of the mud dissolved in seawater. Results showed that the highest values for metals were Al > Fe > Mn > Zn in both exposure periods. The mud also affected the growth rate with lethality in both isolated and associative treatments with H. pseudomusciformis after 15 days. According to our redundancy analysis (RDA), the profile and concentration of all metallic elements can induce different physiological responses of the organisms. We were able to observe a higher physiological adaptive ability of S. cymosum against the long-term presence of metals by the synthesis of phenolic compounds, while the deviation of metabolic routes in H. pseudomusciformis can be addressed as the main responsible for its lethality. Moreover, the presence of Hypnea in associative treatments reduces Sargassum's detoxification ability. The present results reinforce the importance of biological interaction studies in a context of physiological resilience against mining mud pollution and mutual influences of species over the individual ability to avoid oxidative stress.

We herein report the physiological and cellular changes in the brown seaweed Sargassum cymosum (C. Agardh 1820) after short- (7 days) and long-term (14 days) exposure to manganese (Mn). To accomplish this, S. cymosum segments were cultivated without metal (0 mg L −1 Mn, Control) and with Mn (10, 20, 40 and 80 mg L −1 ) during 7 and 14 days under laboratory-controlled conditions. Seaweeds had high Mn biosorption capacity. Mn treatments had higher growth rates than Control at both exposure times, but reduction in cell viability after 14 days. Photosynthetic pigments (chlorophylls a and c ) increased with Mn treatments, and changes in the composition of carotenoid profile were observed. Phenolic and flavonoid compounds also showed content reductions relative to exposure time and Mn concentration. In confocal analysis, lower autofluorescence of chloroplasts and phenolic compounds was observed. Scanning Electron Microscopy analysis indicated changes on the thallus surface of Mn treated samples, with disruption of cortical cell walls after 14 days. Transmission Electron Microscopy revealed cellular damage, with organelle disruption and disorganization of cell wall fibrils. Medium to high concentrations of Mn proved to be a metabolic stressor for S. cymosum , causing damage to organelle structure and cellular organization, while, at the same time, attenuating acclimation mechanisms for resistance against toxicity. Since this metal is not recognized as a pollutant in Brazilian coastal waters, S. cymosum is at risk for both heavy metal contamination and variations in abiotic parameters, such as salinity or pH, which could, in turn, intensify the metabolic damage to S. cymosum after long-term exposure of Mn. [ABSTRACT FROM AUTHOR]