Phycology, Volume 5, Issue 1 (March 2025) – 5 articles

Laminaria hyperborea, a key species in marine forest ecosystems, is experiencing pressure at its southern distribution limit in northern Portugal due to climate change and human-induced stressors. The ongoing degradation of marine forests highlights the need for effective restoration strategies to protect biodiversity and maintain the essential services provided by these habitats. Cultivation of juvenile kelps in laboratory settings is a common approach shared across multiple strategies aimed at supporting reforestation efforts; however, the specific cultivation process for L. hyperborea remains largely underexplored. In this study, we tested two seeding densities to optimize the production of L. hyperborea recruits for reforestation initiatives. We assessed the effects of seeding density on juvenile development by measuring both area coverage and length. Our findings revealed that higher seeding density initially promoted greater area coverage (e.g., 8.69 ± 0.38 cm² vs. 3.35 ± 0.27 cm²) but reduced the length of individual recruits over time (e.g., 0.26 ± 0.0026 cm vs. 0.39 ± 0.003 cm at T3). This suggests that increased competition for resources at high densities limits individual growth. In contrast, lower densities produced larger, more robust individuals (e.g., 0.50 ± 0.004 cm vs. 0.262 ± 0.003 cm at T4), which may enhance post-transplantation survival in challenging environmental conditions. This suggests that utilizing lower seeding densities may improve individual growth while decreasing overall resource use and maintenance needs, promoting a more sustainable cultivation process and minimizing impacts on donor populations. However, further research is essential to refine the cultivation protocols and fully understand the variables influencing juvenile kelp development. Improving all phases of the restoration process, from laboratory cultivation to field deployment, will be critical for reducing costs, streamlining logistics, and ensuring the scalability of future kelp restoration efforts. Full article

Ascophyllum nodosum is an ecologically and economically important species forming marine forests in temperate regions. In Europe, this brown seaweed reaches its southern distribution limit in the north of Portugal, where populations are under climatic pressure. Conservation and restoration actions are essential to preserve the important ecological roles of these populations, including biodiversity enhancement. In this study, we assessed the effect of temperature and light on the development of the early life stages of A. nodosum, from gamete germination and rhizoid development to germling growth, in order to support the establishment of nursery protocols for producing seedlings that can be used in reforestation actions. We found that for this population, temperature around 12 °C and low-light conditions (40 μmol m⁻² s⁻¹) favor gamete germination, rhizoid development, and initial germling growth during the first month, after which higher light supply (>80 μmol m⁻² s⁻¹) is needed to sustain further growth stages. The results obtained in this study are relevant for the establishment of nursery methods for A. nodosum and should be complemented by further studies to determine more precisely the light and nutrient requirements to optimize growth in the germlings’ later growth stages. Full article

As global water scarcity intensifies, the desalination of brackish groundwater and surface water plays a critical role in augmenting water supplies. However, managing reverse osmosis concentrate (ROC) from brackish water desalination remains challenging due to silica and calcium accumulation and precipitation, which cause membrane scaling and reduce freshwater recovery. This study employed the brackish diatom Gedaniella flavovirens Psetr3 in a photobiological treatment to remove dissolved silica and calcium, offering a natural, sustainable solution to improve freshwater recovery. Optimal treatment conditions were identified, with a light intensity of 200 µmol m⁻² s⁻¹ and incubation temperatures between 23 °C and 30 °C maximizing silica uptake (up to 46 ± 3 mg/L/day) while minimizing diatom mortality. This study reports, for the first time, the silica, organic, and calcite content in diatom biomass and their production rates during the photobiological treatment of ROC using G. flavovirens Psetr3. The photobiological treatment of one million gallons (3785 m³) per day of ROC would produce 174 kg of silica, 163 kg of organics, and 314 kg of calcite daily. These findings provide valuable insights into the potential for utilizing these bioresources to offset the costs of photobiological treatment and subsequent desalination processes. Full article

Since 2011, countries across the tropical Atlantic have experienced severe influxes of the seaweed species Sargassum natans and Sargassum fluitans (henceforth, “sargassum”), with nearshore and onshore ecological, economic and social impacts locally and regionally. Not all affected countries have had the same response to this emergent environmental challenge. Here, we explore the first ten years of policies produced in response to sargassum influx risk across islands in the Wider Caribbean Region, considering the variation in form, content and aim of sargassum adaptation policies. This assessment of the variation in Caribbean adaptation policies allows lessons to be identified for rapid adaptation to emergent environmental challenges. We find that several countries have no national policy for sargassum adaptation, and many subnational island jurisdictions have no island-specific policies. Whilst there is increasing anecdotal evidence of private and local adaptations taking place to address sargassum influx events, there remains significant scope for government leadership and resource support in adapting to this emergent threat. The lesson is that private adaptations to emergent threats may be quicker to develop and execute than policy adaptation, but longer-term, larger-scale adaptations depend on evidence-based, widely supported government policies with clear avenues of funding. Full article

Marine habitats are increasingly facing human-induced stressors, posing significant threats to global marine biodiversity. Understanding the ecological, economic, and social importance of marine ecosystems is paramount. This study conducts a comprehensive bibliometric analysis of seaweed biodiversity from 1992 to 2023, aiming to (i) quantify the literature productivity, (ii) identify the active countries, (iii) determine the prolific authors, (iv) highlight the highly cited publications, and (v) enumerate the influential journals. The average annual number of publications was 37. Australia and the USA ranked highest based on the total number of citations, with 7559 and 5273, respectively. The University of Western Australia led in terms of the total number of citations, with 3688 citations from 40 publications, while the Australian Research Council emerged as the top funder. Journals such as the Journal of Experimental Marine Biology and Ecology, Ecology, and Botanica Marina were identified as the top contributors. The keyword ‘biodiversity’ appeared 146 times, with a total link strength of 425. A similar analysis was presented for endemic seaweeds and their conservation. Among the seven major and four emerging drivers, climate change was the most researched driver, accounting for 45.80%, with 120 articles. This study anticipates that in the genomic era, seaweed biodiversity will receive increased attention for its potential in regard to the development of coherent conservation plans and innovative bioprospecting strategies that are beneficial to humankind. Full article