The effects of environmental parameters on biomass, growth and pigment content of the red seaweed Gracilaria bursa-pastoris (S.G. Gmel.) P.C. Silva was investigated under field conditions in Thau Lagoon (France). The seaweed was cultivated in cages placed at three depths (1.0, 2.0 and 4.0 m) over a one-year period. The results showed elevated biomass and growth values in the spring and autumn, when temperature, light and photoperiod values were similar. The highest specific growth rates (SGR) were obtained at 1.0 m (4.95±0.29% day-1) and 2.0 m (4.45±0.33% day-1). At a depth of 4.0 m, the seaweed never exceeded 2% day-1 and obtained null values in the summer. The concentrations of phycoerythrin (RPE) and chlorophyll (CHL a) showed maximum values in the winter and minimum values in the summer. This evolution was related to water temperature, light intensity and nitrogen content in the algal tissue. The results obtained in this study show that the water depth influenced the growth and pigment composition of G. bursa-pastoris.

This study was designed to select potential areas for cultivation of the seaweed Gracilaria birdiae Plastino & E.C. Oliveira (Gracilariales, Rhodophyta) on the coast of Rio Grande do Norte state, Brazil. The Geographic Information System (GIS) and multi-criteria evaluation (MCE) were used to identify the most suitable areas. The Analytical Hierarchical Process (AHP) was applied to establish MCE weights, thereby generating viable areas for species cultivation. From a total of 3316.82 ha, around 53.67% (1780.06 ha) were indicated as highly suitable areas, 40.93% (1357.58 ha) as moderately suitable and 5.40% (179.18 ha) as scarcely suitable for seaweed cultivation. Seven areas (1084.62 ha) are located on the northern coast and 20 (2232.20 ha) on the eastern coast. The results show that GIS can be used as an effective instrument for selecting seaweed cultivation areas.

The worldwide increase in recreational activities and marine tourism is reason for concern due to its impact on reef environments. In order to assess the effect of tourism on the reef area in Maracajaú (Northeast Brazil), a study was conducted based on the presence of different seaweed species. A region of intense tourist activity was chosen, and another where tourism is prohibited. Result comparison used richness (S), biomass, diversity (H), and dominance (D), as well as an analysis of similarity between samples. Both areas exhibited differences in specific composition, biomass, diversity, richness and seaweed dominance. The highest values for biomass, richness and diversity were recorded in the tourism-free region, while the greatest dominance rates were found in the area of intense tourist activity. The latter was characterized by the dominant presence of Caulerpa racemosa (Forsskål) J. Agardh (Chlorophyta) and turf algae. These characteristics are a clear indication that the reef area subject to heavy tourist activity is undergoing degradation.

The concentrations of phycobiliproteins (phycoerythrin and phycocyanin), chlorophyll-a and total soluble proteins were determined monthly in three strains (red, green and brown) of Gracilaria domingensis (Kützing) Sonder ex Dickie, collected from natural populations on the coast of Rio Grande do Norte, Brazil. In all the strains, pigment and protein concentrations were higher in the months of less sunlight and greater nitrogen availability and decreased gradually with increased sunlight and decreased nutrient concentration. The red strain showed higher concentrations of phycoerythrin and total soluble proteins. The difference in the concentration of biochemical components over the course of the year indicates species acclimation to different environmental conditions.

Gracilaria domingensis (Kützing) Sonder ex Dickie and Gracilaria birdiae (Plastino & Oliveira) (Gracilariales, Rhodophyta) are seaweeds that occur on the Brazilian coast. Based on their economic and pharmaceutical importance, we investigated the antioxidant activity of the methanolic, ethyl acetate and hexane extracts of both species. The hexane extracts display a high antioxidant activity and comparative analyses indicated G. birdiae as the most active species. Chemical investigation of these fractions showed several carotenoids and fatty acids, as well as cholesterol and sitosterol derivatives. HPLC-DAD analysis of G. birdiae showed violaxanthin (0.04 μg.mg-1 of dry material), antheraxanthin (5.31 μg.mg-1), aloxanthin (0.09 μg.mg-1), zeaxanthin (0.45 μg.mg-1) and β-carotene (0.37 μg.mg-1) as the major carotenoids. G. domingensis showed a similar carotenoid profile, however, with much lower concentration than G. birdiae. Gas chromatography coupled to mass spectrometry was used to determine other nonpolar compounds of these seaweeds. The main compounds detected in both studied species were the fatty acids 16:0; 18:1 Δ9; 20:3 Δ6,9,12, 20:4 Δ5,8,11,14. We found no specificity of compounds in either species. However, G. birdiae, presented higher contents of carotenoids and arachidonic acid than G. domingensis.

The coral reefs of Pirangi beach have suffered the impact of anthropic actions, mainly those related to tourism. To evaluate these effects, algal samples were collected at nine stations, distributed along the reef fringe. The macrobenthic community (algae/coral) was identified through photographic methods. A total of thirty species of algae, five species of coral, and one species of mollusk were identified. In areas of intense tourist activity, small algae were predominant, while in areas without human interference, foliose algae were predominant. Cluster analysis of the organisms revealed a pattern in spatial distribution into five zones: (1) a submerged zone with very diverse flora, (2) a zone with a predominance of Caulerpa racemosa, (3) a zone with high coverage of Sargassum vulgare, (4) a trampled zone with bare spaces, small algae and Zoanthus sociatus, and (5) a zone with predominance of Palythoa caribaeroum. The results show that human disturbances of the natural order can result in a different distribution model for benthic organisms in reefs. Moreover, these results allow us to infer that the area studied has undergone changes resulting from human activities and that the differences in biological composition can be used as an important indicator of the health of the Pirangi reef.

The reproductive phenology and thallus length of Gracilaria birdiae were studied over a period of 12 months in a natural bed in Northeastern Brazil. Fertile specimens of G. birdiae were observed during the entire study period. Tetrasporophytes were the most common with an annual mean of 80.1±5.6%, followed by cystocarpic plants (9.3±3.4%), male gametophytes (8.3±3.6%) and infertile plants (2.2±3.4%). Only male gametophytes and infertile plants showed a variation in occurrence frequency during the year (p<0.05). With respect to thallus length, a distinct seasonal variation was observed for all reproductive stages (p<0.05), with the highest values recorded during the rainy season (March to August) and the lowest in the dry season (September to February). The results demonstrate that the size of individuals in this population is significantly affected by the periodic changes in the environment caused by rainfall regimes and hydrodynamism.

Qualitative and quantitative studies of mycosporine-like amino acids (MAAs) in three species of the genus Gracilaria Greville (G. birdiae, G. domingensis and G. tenuistipitata) were performed. A simple and efficient extraction procedure based on ethanol was described. HPLC, UV and mass spectrometry experiments revealed different profiles between extracts obtained from one species cultivated in the laboratory (G. tenuistipitata) and two species collected in their natural environment (G. birdiae and G. domingensis). The levels detected in the latter two species were approximately 150 times higher than in the species cultivated in vitro. This study revealed that G. birdiae and G. domingensis present a potential source for economical exploration of MAAs.

The absorption efficiency and kinetic parameters (Vmax, Ks and Vmax:Ks) of the seaweed Gracilaria cervicornis for the nutrients NH4+, NO3- and PO4(3-) were evaluated. Absorption efficiency was measured by monitoring nutrient concentrations for 5 h in culture media with initial concentrations of 5, 10, 20 and 30µM. Kinetic parameters were determined by using the Michaelis-Menten formula. Absorption efficiencies for this algae were greater in treatments with lower concentrations, as evidenced by a reduction of 85.3, 97.5 and 81.2% for NH4+, NO3- and PO4(3-), respectively. Kinetic parameters show that G. cervicornis exhibits greater ability to take up high concentrations of NH4+ (Vmax=158.5µM g dw-1 h-1) and low concentrations of PO4(3-) (Ks=5µM and Vmax:Ks=10.3). These results suggest that this algal species has good absorption capacity for the nutrients tested and may be a promising candidate as a bioremediator of eutrophized environments.