Green algae blooms of the genus Ulva are occurring globally and are primarily attributed to anthropogenic factors. At Los Tubos beach in Algarrobo Bay along the central Chilean coast, there have been blooms of these algae that persist almost year-round over the past 20 years, leading to environmental, economic, and social issues that affect the local government and communities. The objective of this study was to characterize the species that form these green tides based on a combination of ecological, morpho-anatomical, and molecular information. For this purpose, seasonal surveys of beached algal fronds were conducted between 2021 and 2022. Subsequently, the sampled algae were analyzed morphologically and phylogenetically using the molecular markers ITS1 and tufA, allowing for the identification of at least five taxa. Of these five taxa, three (U. stenophylloides, U. uncialis, U. australis) have laminar, foliose, and distromatic morphology, while the other two (U. compressa, U. aragoensis) have tubular, filamentous, and monostromatic fronds. Intertidal surveys showed that U. stenophylloides showed the highest relative coverage throughout the seasons and all intertidal levels, followed by U. uncialis. Therefore, we can establish that the green tides on the coast of Algarrobo in Chile are multispecific, with differences in relative abundance during different seasons and across the intertidal zone, opening opportunities for diverse future studies, ranging from ecology to algal biotechnology.

Seaweed aquaculture is affected by natural and anthropogenic stressors, which put the biomass productivity of the cultures at risk. Seaweed biomass for commercial purposes, principally in pharmaceutical and/or nutraceutical applications, needs to be free of pollutants; therefore, controlled cultures have relevance in regulating the quality of biomass. The aim of this work was to demonstrate the successful utilization of controlled outdoor cultures to remove excess heavy metal accumulation in Gracilaria chilensis, an important commercial seaweed farming model. Specifically, we designed a simple and operational heavy metal depuration protocol, utilizing seawater and tap water removal, which permitted the concentration reduction of 10 heavy metals, including As, Cu, and Cd but not Zn, from the biomass at 7 days of culture. The percentage of depuration of the heavy metals ranged from 32 to 92% at 7 days, which was maintained throughout 21 days of culture. During the culture period, the monitored physicochemical parameters (temperature, salinity, and dissolved oxygen, among others) remained stable, with an increase in the daily growth rate (DGR% d⁻¹) of the biomass recorded after 14 days of culture. Consequently, the experimental setup was successful for heavy metal depuration, which highlights the importance of controlled outdoor cultures as important tools of sustainability.

This review presents the production and use of biochar in terms of chemical structure, utilization, and current global market, with an emphasis on the biotechnological applications of seaweed biochar. For this purpose, a literature search was conducted in various databases, using keywords and algorithms in both Spanish and English. The results indicate that biochar from seaweed is an efficient alternative for the remediation of terrestrial and/or aquatic ecosystems. The capacity to capture different types of pollutants (microplastics, heavy metals, polycyclic aromatic hydrocarbons, among others) provides biochar properties that make it an appropriate material for environmental remediation, including the reduction of greenhouse gas emissions. The co-production of biochar and bioenergy is an alternative to mitigating the effects of climate change, contributing to reduce the use of fossil fuels and sequestering carbon in stable soil reserves. In addition, the use of biochar as a soil amendment and fertilizer is a significant tool for increasing food security and expanding crop areas in zones with physically and chemically degraded soils, characterized by low organic matter content, inadequate chemical fertilizer content, poor water retention and toxicity from pollutants. Therefore, the use of seaweed biochar is an environmental tool with high added value.

Marine green tides are ecological phenomena caused by the massive proliferation of green macroalgae, particularly species of the genus Ulva, whose frequency and geographic extent have increased worldwide. These events are commonly associated with interacting anthropogenic and environmental drivers, including nutrient enrichment, coastal modification, climatic variability, and hydrodynamic retention. In Chile, green tides have been reported in several coastal bays, including Coliumo Bay; however, systematic studies on their species composition have been largely restricted to Algarrobo Bay, another coastal upwelling-influenced embayment located in central Chile. In this study, we investigated the laminar Ulva species associated with recurrent summer green tides at Dichato Beach, located in Coliumo Bay, Biobío Region, Chile. Twenty specimens were collected during the 2025 green tide and analyzed using an integrative approach that combined detailed morphological characterization with molecular analyses based on the tufA and ITS1 markers. Our results revealed the presence of three laminar, foliose, and distromatic taxa: Ulva australis, Ulva stenophylloides, and an unresolved lineage designated as Ulva sp. (D4). These taxa showed consistent morphological differentiation in traits such as thallus color, frond margin morphology, and perforation patterns. Phylogenetic analyses further indicated that Ulva sp. (D4) did not cluster with any described species included in the analyses, supporting its recognition as a distinct lineage that may represent an undescribed taxon. This study expands the known distribution of U. australis and U. stenophylloides in the southeastern Pacific and highlights the relevance of integrative taxonomy for resolving green tide diversity and supporting future ecological monitoring and management strategies in Chilean coastal systems.