Antioxidant Activity of Dictyotales from Tropical Reefs of Brazil.

Macroalgae produce a large range of primary and secondary metabolites with ecological and economical importance. Studies on antioxidants from marine algae have increased notably, focusing on searching new sources of natural compounds for different applications, in which tropical species have been shown to have high potential, often improved by stressful environmental conditions during the tide cycle with periods of emersion and submersion. Therefore, in order to characterize the antioxidant activity and relate it to local environmental tide exposure, three species of brown marine algae, Canistrocarpus cervicornis, Dictyopteris delicatula, and Lobophora variegata from two beaches on the northeast coast of Brazil were studied. Dichloromethane:methanol (DCM:M) and aqueous extracts were tested for ferric reducing antioxidant power, 2,2-diphenyl-1-picrylhydrazyl, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) antioxidant assays and total phenolic compounds. Aqueous extracts of C. cervicornis showed up to 10 times major antioxidant activity and phenolic compounds than DCM:M extracts. Different characteristic of antioxidant activity were identified among the beaches, species, and extracts, in which aqueous extracts from C. cervicornis and L. variegata showed the most promising matrices for future prospection of natural antioxidants.

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.

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.

Coastal urbanization leads to remarkable seaweed species loss and community shifts along the SW Atlantic.

Coastal urbanization is rapidly expanding worldwide while its impacts on seaweed communities remain poorly understood. We assessed the impact of urbanization along an extensive latitudinal gradient encompassing three phycogeographical regions in the SW Atlantic. Human population density, number of dwellings, and terrestrial vegetation cover were determined for each survey area and correlated with diversity indices calculated from seaweed percent cover data. Urban areas had significantly lower calcareous algal cover (-38%), and there was significantly less carbonate in the sediment off urban areas than off reference areas. Seaweed richness averaged 26% less in urban areas than in areas with higher vegetation cover. We observed a remarkable decline in Phaeophyceae and a substantial increase of Chlorophyta in urban areas across a wide latitudinal gradient. Our data show that coastal urbanization is causing substantial loss of seaweed biodiversity in the SW Atlantic, and is considerably changing seaweed assemblages.