On the Health Benefits vs. Risks of Seaweeds and Their Constituents: The Curious Case of the Polymer Paradigm.

To exploit the nutraceutical and biomedical potential of selected seaweed-derived polymers in an economically viable way, it is necessary to analyze and understand their quality and yield fluctuations throughout the seasons. In this study, the seasonal polysaccharide yield and respective quality were evaluated in three selected seaweeds, namely the agarophyte Gracilaria gracilis, the carrageenophyte Calliblepharis jubata (both red seaweeds) and the alginophyte Sargassum muticum (brown seaweed). It was found that the agar synthesis of G. gracilis did not significantly differ with the seasons (27.04% seaweed dry weight (DW)). In contrast, the carrageenan content in C. jubata varied seasonally, being synthesized in higher concentrations during the summer (18.73% DW). Meanwhile, the alginate synthesis of S. muticum exhibited a higher concentration (36.88% DW) during the winter. Therefore, there is a need to assess the threshold at which seaweed-derived polymers may have positive effects or negative impacts on human nutrition. Furthermore, this study highlights the three polymers, along with their known thresholds, at which they can have positive and/or negative health impacts. Such knowledge is key to recognizing the paradigm governing their successful deployment and related beneficial applications in humans.

Ocean Acidification Accelerates the Growth of Two Bloom-Forming Macroalgae.

While there is growing interest in understanding how marine life will respond to future ocean acidification, many coastal ecosystems currently experience intense acidification in response to upwelling, eutrophication, or riverine discharge. Such acidification can be inhibitory to calcifying animals, but less is known regarding how non-calcifying macroalgae may respond to elevated CO2. Here, we report on experiments performed during summer through fall with North Atlantic populations of Gracilaria and Ulva that were grown in situ within a mesotrophic estuary (Shinnecock Bay, NY, USA) or exposed to normal and elevated, but environmentally realistic, levels of pCO2 and/or nutrients (nitrogen and phosphorus). In nearly all experiments, the growth rates of Gracilaria were significantly increased by an average of 70% beyond in situ and control conditions when exposed to elevated levels of pCO2 (p<0.05), but were unaffected by nutrient enrichment. In contrast, the growth response of Ulva was more complex as this alga experienced significantly (p<0.05) increased growth rates in response to both elevated pCO2 and elevated nutrients and, in two cases, pCO2 and nutrients interacted to provide a synergistically enhanced growth rate for Ulva. Across all experiments, elevated pCO2 significantly increased Ulva growth rates by 30% (p<0.05), while the response to nutrients was smaller (p>0.05). The δ13C content of both Gracilaria and Ulva decreased two-to-three fold when grown under elevated pCO2 (p<0.001) and mixing models demonstrated these macroalgae experienced a physiological shift from near exclusive use of HCO3- to primarily CO2 use when exposed to elevated pCO2. This shift in carbon use coupled with significantly increased growth in response to elevated pCO2 suggests that photosynthesis of these algae was limited by their inorganic carbon supply. Given that eutrophication can yield elevated levels of pCO2, this study suggests that the overgrowth of macroalgae in eutrophic estuaries can be directly promoted by acidification, a process that will intensify in the coming decades.

Bioremediation using Gracilaria chouae co-cultured with Sparus macrocephalus to manage the nitrogen and phosphorous balance in an IMTA system in Xiangshan Bay, China.

A cage experiment using the red alga Gracilaria chouae co-cultured with the black seabream Sparus macrocephalus in Xiangshan Bay, China was conducted to measure the nutrient flux of the integrated multi-trophic aquaculture (IMTA) system. Results showed that trash fish were the main nutrient input contributor and adult fish were the main nutrient output contributor in the system. Contents of N and P in adult fish accounted for 54.45% and 59.48% of N and P in trash fish and fry, which suggests that 45.55% of N and 40.52% of P generated by fish farming were released into to the water. G. chouae proved to be an efficient bioremediation species in this IMTA system. To balance the excess nutrients generated by the system, 231.09 kg of seedlings should be cultured and 5315.07 kg of adult seaweed should be harvested.

Galactans of Gracilaria pudumadamensis (Gracilariales, Rhodophyta) of Indian waters.

Galactans from the Indian agarophyte Gracilaria pudumadamensis were extracted and characterized. The isolated native (GP(Native)) and alkali treated (GP(Alkali)) galactans were characterized by IR, 13C NMR, GC-MS and GPC. It was found that GP(Native) and GP(Alkali) were composed mainly of 3,6-anhydro L-galactose, 6-O-methylated D-galactose and galactose in various mole proportions (15.6:69.9:17.5 mole% for GP(Native) and 20.2:69.8:10.0 mole% for GP(Alkali)). The GP(Native) and GP(Alkali) exhibited low gel strengths (< 100 g/cm2) and high melting points (-76 degrees C), which may be due to the presence of high 6-O-Me-galactose contents. The latter, having low sulfate (2.1%), was by far the greatest 6-O-Me-galactose containing polysaccharide in a Gracilaria spp. reported in the literature. This methylated agar contained very low heavy metal ions estimated by inductively coupled plasma spectrophotometry (ICP). The results of this investigation would be useful in bioprospecting of agarophytes, especially those occurring in Indian waters and would be potentially useful in food, personal care and related domains.

UVR defense mechanisms in eurytopic and invasive Gracilaria vermiculophylla (Gracilariales, Rhodophyta).

The invasive success of Gracilaria vermiculophylla has been attributed to its wide tolerance range to different abiotic factors, but its response to ultraviolet radiation (UVR) is yet to be investigated. In the laboratory, carpospores and vegetative thalli of an Atlantic population were exposed to different radiation treatments consisting of high PAR (photosynthetically active radiation) only (P), PAR+UV-A (PA) and PAR+UV-A+UV-B (PAB). Photosynthesis of carpospores was photoinhibited under different radiation treatments but photosystem II (PSII) function was restored after 12 h under dim white light. Growth of vegetative thalli was significantly higher under radiation supplemented with UVR. Decrease in chlorophyll a (Chl a) under daily continuous 16-h exposure to 300 µmol photons m(-2) s(-1) of PAR suggests preventive accumulation of excited chlorophyll molecules within the antennae to minimize the generation of dangerous reactive oxygen species. Moreover, an increase in total carotenoids and xanthophyll cycle pigments (i.e. violaxanthin, antheraxanthin and zeaxanthin) further suggests effective photoprotection under UVR. The presence of the ketocarotenoid ß-cryptoxanthin also indicates protection against UVR and oxidative stress. The initial concentration of total mycosporine-like amino acids (MAAs) in freshly-released spores increased approximately four times after 8-h laboratory radiation treatments. On the other hand, initial specific MAAs in vegetative thalli changed in composition after 7-day exposure to laboratory radiation conditions without affecting the total concentration. The above responses suggest that G. vermiculophylla have multiple UVR defense mechanisms to cope with the dynamic variation in light quantity and quality encountered in its habitat. Beside being eurytopic, the UVR photoprotective mechanisms likely contribute to the current invasive success of the species in shallow lagoons and estuaries exposed to high solar radiation.

Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation.

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O(2)(•-) and H(2)O(2)) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 µM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ~150 kDa; Fe-SOD ~120 kDa), glutathione peroxidase (GSH-Px, ~120 and 140 kDa), glutathione reductase (GR, ~110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura.

Evaluation of Gracilaria caudata J. Agardh for bioremediation of nutrients from shrimp farming wastewater.

The accelerated development of shrimp farming in Brazil in recent decades has caused negative impacts to the environment. The most evident effects resulting from this activity is the increase in organic material, the reduction in oxygen and the excessive rise in water nutrients. Thus, there is a need for finding alternative solutions that can mitigate the negative impacts caused by this activity. A potentially viable solution is the use of macroalgae to remove nutrients from the cultivation systems. This study examined in situ (shrimp pond), the growth and storage of nitrogen and phosphorous from the macroalga Gracilaria caudata. A short-term measurement experiment was also conducted to evaluate the bioremediation potential this species. These results showed positive values for biomass and growth during the study period, except at day 45 for the tubular nets and day 75 for the cages, when they reached lower values than those of the initial weight. The results obtained indicate that G. caudata may reach annual production of 59.16 ton ha(-1) of wet weight, which corresponds to 11.83 ton dry weight. Nitrogen and phosphorous content in the algal tissues increased with time. The mean for the period was 2.61+/-0.26% and 0.20+/-0.03% for the nitrogen and phosphorous, respectively. An estimate of the data showed that 1 ha of cultivated algae has the potential to remove 0.309 ton ha(-1) year(-1) of nitrogen and 0.024 ton ha(-1) year(-1) of phosphorous. The study of the biofiltration capacity of G. caudata showed a significant reduction in nutrients. The removal of NH(4)-N was around 59.5%, NO(3)-N 49.6% and PO(4)-P 12.3% in 4 h. These results suggest that although G. caudata showed relatively modest growth rates, they can be cultivated together with shrimp and can contribute to the removal of nitrogen and phosphorous from the pond. Moreover, the capacity to efficiently remove nutrients demonstrated in laboratory experiments encourages the use of this alga as a bioremediation agent.