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Blooms of macroalgae have grown over the planet in recent decades as a possible result of eutrophication of coastal waters. Visually, a bloom forming can be identified by dominant presence of an organism at the expense of others. In mid-January 2014, a forming bloom of red algae was detected on the beach of Garopaba, Santa Catarina State, Brazil. This aroused the interest of tourists and locals as well as the scientific community. Thus, the objective of this study was to characterize and quantify the photosynthetic floating organisms contributing to this phenomenon. In addition, we qualitatively compared algal composition of the bloom to those deposited in the post-beach area and the adjacent rocky shore community. Five sampling points in random patches of floating material were defined. At each point, five replicates were taken with a cube of 32,768 cm 3 , resulting in a total of 25 samples. Samples were collected in the inner area enclosed by a PVC quadrate of about 900 cm² from the shore and the specimens found in post-beach zone (wrack). Twenty-four taxa of macroalgae were found in the bloom, with Aglaothamnion uruguayense as the dominance one. Ten taxa were found on shore. Only four taxa were found in the post-beach area. The biomass estimated for A. uruguayense in the floating material was 8.35 tons with an estimated area of 52,770 m 2 . It is possible that this huge biomass value of the bloom is related to the local nutrient intake, and our results reinforce the necessity of coastal integrative management initiatives.

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Anthropogenic impacts on water resources, especially by ​​nutrient discharge, is a worldwide problem in marine coastal areas. In this context, seaweed cultivation in aquaculture wastewater can be considered as an alternative for effluent mitigation, where the biomass becomes a source of valuable compounds. The current study examined the potential use of the seaweeds Ulva pseudorotundata and Ulva rigida to remove nutrients to treat effluents from the culture of Chelon labrosus. Two experiments were conducted under pilot-scale conditions to evaluate the nutrient uptake, photosynthetic activity, and biomass production of the seaweed species cultivated under 50 and 100% effluent concentrations. Photosynthetic parameters were determined by in vivo chlorophyll a fluorescence associated to photosystem II 3 times a day to estimate photosynthetic performance and seaweed physiology throughout the experiment: optimal quantum yield (Fv/Fm), in situ and ex situ electron transport rate (ETR), photosynthetic efficiency (αETR), saturation irradiance (Ek), and the maximum non-photochemical quenching (NPQmax). To evaluate seaweed metabolism and biomass compounds, elemental and biochemical composition were analyzed in the beginning and end of each experiment. Results regarding the nutrient source showed that both species removed more than 65% of ammonium after 3 hours of experimentation. At the end of the experiments, up to 94.8% of the initial ammonium was sequestered from the effluent. Additionally, after 5 days of cultivation under 50% fish effluent both Ulva species were able to remove more than 85% of the nitrate. Although a decrease in uptake efficiency was observed in cultures with 100% fish effluent, at the end of the experiment more than 440 µmol L-1 of nitrate was removed, considering all treatment conditions. The biomass values showed that growth rates of seaweed cultivated in 100% effluent were higher than those obtained in 50% effluent. Moreover, when cultivated in the 100% effluent concentration, a significant increment in protein content was detected in both Ulva species. Our results contribute to the understanding of biofiltration and photosynthetic performance of two different Ulva species in order to improve growth optimization, enhancement of biofiltration capacity and also to boost management practices of seaweed cultivation in aquaculture effluent treatment systems.

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Short-term N-NH4+ and N-NO3- removal by U. pseudorotundata under different initial nutrient concentrations and biomass stocking densities, monitoring in parallel photosynthetic parameters obtained by Pulse-Amplitude-Modulation (PAM) Fluorometry of chlorophyll-a and evaluating biomass characteristics (CHN, proteins, carbohydrates) was investigated. The results showed that U. pseudorotundata cultivated under solar radiation in a land-based out-door pilot scale was efficient in removing N-NH4+ and N-NO3- even in concentrations as high as 500 µmol L⁻¹ ensuring complete water remediation in a period of 24 h and in all experimental conditions tested, although differences were observed depending on the stocking density and type of N-source. Treatments with N-NH4+ showed faster N removal than those with N-NO3-, however, treatments with N-NO3- demanded more photosynthetic energy. Part of the ammonium removed in the respective treatments may have been volatilized as a combined effect of the pH increase related to photosynthesis and aeration in the tanks. The results presented here establish the fundamental parameters for the use of U. pseudorotundata as a biofiltering organism for effluents with high concentrations of N-NH4+ and N-NO3-.