Bioactive Polysaccharides from Seaweeds

Bioactive compounds with diverse chemical structures play a significant role in disease prevention and maintenance of physiological functions. Due to the increase in industrial demand for new biosourced molecules, several types of biomasses are being exploited for the identification of bioactive metabolites and techno-functional biomolecules that are suitable for the subsequent uses in cosmetic, food and pharmaceutical fields. Among the various biomasses available, macroalgae are gaining popularity because of their potential nutraceutical and health benefits. Such health effects are delivered by specific diterpenes, pigments (fucoxanthin, phycocyanin, and carotenoids), bioactive peptides and polysaccharides. Abundant and recent studies have identified valuable biological activities of native algae polysaccharides, but also of their derivatives, including oligosaccharides and (bio)chemically modified polysaccharides. However, only a few of them can be industrially developed and open up new markets of active molecules, extracts or ingredients. In this respect, the health and nutraceutical claims associated with marine algal bioactive polysaccharides are summarized and comprehensively discussed in this review.

Niche Complementarity and Resistance to Grazing Promote the Invasion Success of Sargassum horneri in North America

Invasive species are a growing threat to conservation in marine ecosystems, yet we lack a predictive understanding of ecological factors that influence the invasiveness of exotic marine species. We used surveys and manipulative experiments to investigate how an exotic seaweed, Sargassum horneri, interacts with native macroalgae and herbivores off the coast of California. We asked whether the invasion (i.e., the process by which an exotic species exhibits rapid population growth and spread in the novel environment) of S. horneri is influenced by three mechanisms known to affect the invasion of exotic plants on land: competition, niche complementarity and herbivory. We found that the removal of S. horneri over 3.5 years from experimental plots had little effect on the biomass or taxonomic richness of the native algal community. Differences between removal treatments were apparent only in spring at the end of the experiment when S. horneri biomass was substantially higher than in previous sampling periods. Surveys across a depth range of 0–30 m revealed inverse patterns in the biomass of S. horneri and native subcanopy-forming macroalgae, with S. horneri peaking at intermediate depths (5–20 m) while the aggregated biomass of native species was greatest at shallow (<5 m) and deeper (>20 m) depths. The biomass of S. horneri and native algae also displayed different seasonal trends, and removal of S. horneri from experimental plots indicated the seasonality of native algae was largely unaffected by fluctuations in S. horneri. Results from grazing assays and surveys showed that native herbivores favor native kelp over Sargassum as a food source, suggesting that reduced palatability may help promote the invasion of S. horneri. The complementary life histories of S. horneri and native algae suggest that competition between them is generally weak, and that niche complementarity and resistance to grazing are more important in promoting the invasion success of S. horneri.

Unexpected reproductive traits of Grateloupia turuturu revealed by its resistance to bleach-based biosecurity protocols

A non-indigenous alga, Grateloupia turuturu (Halymeniales, Rhodophyta), was discovered in the Damariscotta Estuary (Maine, USA) in 2017, over 200 km north of its last reported location. Because of the presence of coastal facilities (aquaculture, marine laboratories) among potential vectors, we evaluated a mandated biosecurity protocol, namely, seawater treated with bleach at 50 ppm (50 mg l−1) free chlorine for ≥2 h and measured using test strips, for lethality against G. turuturu and several native algae. We report unexpected resilience to bleach-treatment (Mastocarpus > Grateloupia > Palmaria). Holdfasts of G. turuturu and Mastocarpus stellatus survived 50 and 1000 ppm free chlorine, respectively. Cystocarps on cultured blades of G. turuturu were particularly resistant to bleach-treatment; they produced outgrowths on fragmenting blades that became fertile tetrasporophytes in culture, suggesting reproductive adaptations of cystocarps to stressful conditions that may have broader evolutionary significance. Juvenile, microscopic crusts of G. turuturu were also bleach-resistant if covered by diatoms, and developed upright axes. Free chlorine test strips were inaccurate in seawater, and their use could increase the risk of failed biosecurity as a vector for invasion. Because chlorination at economic and environmentally safe levels is insufficient, we recommend a combination of treatments for comprehensive biosecurity.

Submarine Groundwater Discharge Differentially Modifies Photosynthesis, Growth, and Morphology for Two Contrasting Species of Gracilaria (Rhodophyta)

Gracilaria coronopifolia and an invasive congener, Gracilaria salicornia, were examined across an SGD gradient in the field and laboratory. Tissue samples of both species were cultured for 16 days along an onshore-offshore SGD gradient at Wailupe, Oahu. G. salicornia tolerated the extremely variable salinity, temperature, and nutrient levels associated with SGD. In marked contrast, half of G. coronopifolia plants suffered tissue loss and even death at SGD-rich locations in the field and in laboratory treatments simulating high SGD flux. Measurements of growth, photosynthesis, and branch development via two novel metrics indicated that the 27‰ simulated-SGD treatment provided optimal conditions for the apparently less tolerant G. coronopifolia in the laboratory. Benthic community analyses revealed that G. salicornia dominated the nearshore reef exposed to SGD compared with the offshore reef, which had a greater diversity of native algae. Ultimately, SGD inputs to coastal environments likely influence benthic community structure and zonation on otherwise oligotrophic reefs.

Domestication and Proliferation of Algae Cultures for Boosting Efficiency of Waste-water Treatment through Symbiosis

Native algae strains have been domesticated and stimulated in activated sludge wastewater treatment operations. The term of domestication indicates that we did not add any selected algae to the wastewater, but made use of species existing in the system. The term of proliferation indicates a stimulation of the biological oxidation process by provision of CO2 with the air stream and illumination of the reactor. The idea of domestication of algae present in communal wastewater systems was demonstrated. Stimulation of the system with domesticated algae community did improve efficiency of the treatment process. Removal of organic components in terms of reduction of chemical and biological oxidation demands (dissolved COD, BOD) as well as nitrogen and phosphorous contents was superior to extent of removal in conventional activated sludge system. We did conclude that conventional systems lack available light and carbon resources for these microorganisms. Upon providing these, symbiotic operation can contribute to reducing greenhouse gas emissions and increase of the rate of pollutants removal kinetics. Symbiotic operation increased the production of biomass expressed in terms of total suspended solids. Biodiesel potential of the filterable biomass was in the range of 8-18%. Because of technical difficulties in manipulation of the excess sludge other than biodiesel synthesis processing scheme has been recommended for economically viable processing.