Acclimation potential and biochemical response of four temperate macroalgae to light and future seasonal temperature scenarios

Seasonal Variation in the Biochemical Composition and Fatty Acid Profiles of the Red Alga Halymenia durvillei from Ngazidja (Comoros)

The study of Comorian red alga Halymenia durvillei showed a significant biochemical composition with high ash and polysaccharide content and the presence of n-3 and n-6 essential fatty acid molecules. Seasonal monitoring showed a real change in biochemical composition depending on the harvesting period. On an annual average basis, the algae contained 35.59 ± 2.55% dw ashes, 0.7 ± 0.19% dw soluble proteins, 0.27 ± 0.02% dw total lipids, and 35.09 ± 6.14% dw polysaccharides. The pigment composition was 130 µg/g dw R-phycoerythrin, 1.49 µg/g dw chlorophyll a, and 0.09 µg/g dw carotenoids. The most abundant fatty acid identified was palmitic acid (C16:0), which accounted for almost 43.33% of total fatty acids. Oleic acid (C18:1n-9) was the most abundant unsaturated fatty acid, at 11.58%. Linoleic acid (C18:2n-6) was reported to be the most abundant polyunsaturated fatty acid in Halymenia durvillei. The fatty acid profile was also characterized by arachidonic acid (C20:4n-6) and eicosapentaenoic acid (C20:5n-3).

Ex-situ restoration of the Mediterranean forest-forming macroalga Ericaria amentacea: Optimizing growth in culture may not be the key to growth in the field

Evidence of local and regional declines in the canopy-forming alga Ericaria amentacea, a foundation species of diverse marine forest communities on exposed Mediterranean coasts, have spurred restoration efforts focused on sustainable ex-situ techniques. The need to balance the costs of culture maintenance and the susceptibility of early life stages to stressors in the native habitat, including rapid, often extreme shifts in temperature, hydrodynamics and nutrient availability, have driven current efforts to create a culture environment that primes seedlings for outplant, increasing their resilience rather than maximizing growth. We tested the effects of 1) higher culture temperature (25 °C) combined with wave simulation and 2) reduced nutrient loads (10% of standard protocol) with wave simulation on post-culture and post-outplant outcomes relative to optimal growth conditions in established protocols (20 °C, no waves, high-nutrient culture medium). While increased temperature and water motion negatively affected seedling growth in culture, and higher nutrients caused oxidative stress likely associated with enhanced epiphyte overgrowth, these effects were not clearly translated into patterns of long-term growth in the field. Instead, survival in the initial days post-outplant appeared to be the bottleneck for restoration potential, where substrates with persisting seedlings at one month were generally found with flourishing juveniles at four months. Larger clumps of seedlings, in turn, were strongly associated with both initial survival and future growth. These results underscore the importance of the zygote settlement phase to establish high seedling densities, which may be optimized by phenological monitoring of the donor population. They also suggest that less-controlled, more environmentally-realistic culture conditions involving the introduction of mild stress may enhance the survival of early life stages of E. amentacea during the transition to the native environment, providing a means to simultaneously reduce human resource costs in culture and move toward scaling up.

What does the future look like for kelp when facing multiple stressors?

As primary producers and ecosystem engineers, kelp (generally Order Laminariales) are ecologically important, and their decline could have far-reaching consequences. Kelp are valuable in forming habitats for fish and invertebrates and are crucial for adaptation to climate change by creating coastal defenses and in providing key functions, such as carbon sequestration and food provision. Kelp are threatened by multiple stressors, such as climate change, over-harvesting of predators, and pollution. In this opinion paper, we discuss how these stressors may interact to affect kelp, and how this varies under different contexts. We argue that more research that bridges kelp conservation and multiple stressor theory is needed and outline key questions that should be addressed as a priority. For instance, it is important to understand how previous exposure (either to earlier generations or life stages) determines responses to emerging stressors, and how responses in kelp scale up to alter food webs and ecosystem functioning. By increasing the temporal and biological complexity of kelp research in this way, we will improve our understanding allowing better predictions. This research is essential for the effective conservation and potential restoration of kelp in our rapidly changing world.

Resistance and recovery of benthic marine macrophyte communities to light reduction: Insights from carbon metabolism and dissolved organic carbon (DOC) fluxes, and implications for resilience

A crucial factor in the long-term survival of benthic macrophyte communities under light-reduction stress is how they balance carbon metabolism during photosynthesis and respiration. In turn, the dissolved organic carbon (DOC) released by these communities, which can be highly light-dependent, stands as a source of carbon, fuelling marine communities and playing an important role in the ocean carbon sequestration. This is the first study to evaluate light-reduction stress and recovery in the seagrass Zostera noltei and the macroalga Caulerpa prolifera. Light reduction led to a significant decrease in the production of both communities from autotrophic to heterotrophic. Results indicated that most of the DOC released by vegetated coastal communities comes from photosynthetic activity, and that the net DOC fluxes can be greatly affected by shading events. Finally, both communities showed resilience underpinned by high recovery but low resistance capacity, with C. prolifera showing the highest resilience to unfavourable light conditions.

Growth Resilience of Subarctic Rhodoliths (Lithothamnion glaciale, Rhodophyta) to Chronic Low Sea Temperature and irradiance

Rhodolith beds are pervasive marine biological systems in the subarctic North Atlantic. Limited knowledge about effects of temperature and irradiance on rhodolith growth limits the ability to anticipate the response of rhodolith beds to this ocean's chronic low, yet changing sea temperature and irradiance regimes. We carried out a 149-d laboratory experiment with Newfoundland Lithothamnion glaciale rhodoliths to test the predictions that growth (i) is inhibited at temperatures of ~0.5°C and (ii) resumes as temperature increases above 0.5°C, albeit at a higher rate under high than low irradiances. Rhodoliths were grown in experimental tanks at near-zero (~0.7°C) seawater temperatures during the first 85 d and at temperatures increasing naturally to ~6°C for the remaining 64 d. Rhodoliths in those tanks were exposed to either low (0.02 mol photons·m^-2 ·d^-1 ) or high (0.78 mol photons·m^-2 ·d^-1 ) irradiances during the entire experiment. Rhodoliths grew at a linear rate of ~281 μm·year^-1 (0.77 μm·d^-1 ) throughout the experiment under both irradiance treatments despite daily seawater temperature variation of up to 3°C. Near-zero temperatures of ~0.5 to 1.0°C did not inhibit rhodolith growth. Model selection showed that PAR-day (a cumulative irradiance index) was a better predictor of growth variation than Degree-day (a cumulative thermal index). Our findings extend to ~0.5°C the lower limit of the known temperature range (~1 to at least 16°C) over which growth in L. glaciale rhodoliths remains unaffected, while suggesting that the growth-irradiance relationship in low-light environments at temperatures below 6°C is less irradiance-driven than recently proposed.

Pigment Composition of Nine Brown Algae from the Iberian Northwestern Coastline: Influence of the Extraction Solvent

Brown algae are ubiquitously distributed in the NW coastline of the Iberian Peninsula, where they stand as an underexploited resource. In this study, five solvents were applied to the extraction of pigments from nine brown algae, followed by their determination and quantification by HPLC-DAD. A total of 13 compounds were detected: Six were identified as chlorophylls, six were classified as xanthophylls, and one compound was reported as a carotene. Fucoxanthin was reported in all extracts, which is the most prominent pigment of these algae. Among them, L. saccharina and U. pinnatifida present the highest concentration of fucoxanthin (4.5-4.7 mg∙g-1 dry weight). Ethanol and acetone were revealed as the most efficient solvents for the extraction of pigments, showing a maximal value of 11.9 mg of total pigments per gram of dry alga obtained from the ethanolic extracts of H. elongata, followed by the acetonic extracts of L. ochroleuca. Indeed, ethanol was also revealed as the most efficient solvent according to its high extraction yield along all species evaluated. Our results supply insights into the pigment composition of brown algae, opening new perspectives on their commercial exploitation by food, pharmaceutical, and cosmeceutical industries.