Massive Ulva Green Tides Caused by Inhibition of Biomass Allocation to Sporulation

Morphological and Molecular Identification of Ulva spp. (Ulvophyceae; Chlorophyta) from Algarrobo Bay, Chile: Understanding the Composition of Green Tides

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.

Photoprotection by photoinhibitory and PSII-reaction centre quenching controls growth of Ulva rigida (Chlorophyta) and is a pre-requisite for green tide formation

MAIN CONCLUSION

The combined photoinhibitory and PSII-reaction centre quenching against light stress is an important mechanism that allows the green macroalga Ulva rigida to proliferate and form green tides in coastal ecosystems. Eutrophication of coastal ecosystems often stimulates massive and uncontrolled growth of green macroalgae, causing serious ecological problems. These green tides are frequently exposed to light intensities that can reduce their growth via the production of reactive oxygen species (ROS). To understand the physiological and biochemical mechanisms leading to the formation and maintenance of green tides, the interaction between inorganic nitrogen (Ni) and light was studied. In a bi-factorial physiological experiment simulating eutrophication under different light levels, the bloom-forming green macroalga Ulva rigida was exposed to a combination of ecologically relevant nitrate concentrations (3.8-44.7 µM) and light intensities (50-1100 µmol photons m-2 s-1) over three days. Although artificial eutrophication (≥ 21.7 µM) stimulated nitrate reductase activity, which regulated both nitrate uptake and vacuolar storage by a feedback mechanism, nitrogen assimilation remained constant. Growth was solely controlled by the light intensity because U. rigida was Ni-replete under oligotrophic conditions (3.8 µM), which requires an effective photoprotective mechanism. Fast declining Fv/Fm and non-photochemical quenching (NPQ) under excess light indicate that the combined photoinhibitory and PSII-reaction centre quenching avoided ROS production effectively. Thus, these mechanisms seem to be key to maintaining high photosynthetic activities and growth rates without producing ROS. Nevertheless, these photoprotective mechanisms allowed U. rigida to thrive under the contrasting experimental conditions with high daily growth rates (12-20%). This study helps understand the physiological mechanisms facilitating the formation and persistence of ecologically problematic green tides in coastal areas.

The extracellular matrix of green algae

Green algae display a wide range of extracellular matrix (ECM) components that include various types of cell walls (CW), scales, crystalline glycoprotein coverings, hydrophobic compounds, and complex gels or mucilage. Recently, new information derived from genomic/transcriptomic screening, advanced biochemical analyses, immunocytochemical studies, and ecophysiology has significantly enhanced and refined our understanding of the green algal ECM. In the later diverging charophyte group of green algae, the CW and other ECM components provide insight into the evolution of plants and the ways the ECM modulates during environmental stress. Chlorophytes produce diverse ECM components, many of which have been exploited for various uses in medicine, food, and biofuel production. This review highlights major advances in ECM studies of green algae.

Genome Sequence of the Edible Green Alga Ulva prolifera, Originating from the Yoshinogawa River in Japan

We report the genome sequence of Ulva prolifera, which originated from the Yoshinogawa River in Japan, using Oxford Nanopore Technologies MinION and Illumina sequencing reads. The genome assembly size is 103.8 Mbp, consisting of 142 scaffolds with an N₅₀ value of 4.11 Mbp.

Comparison of the Antioxidant Properties of Green Macroalgae from Diverse European Water Habitats by Use of Several Semi-Quantitative Assays

Nowadays, algae are becoming more and more popular as a food group rich in nutrients, cosmetic raw materials full of antioxidants or valuable dietary supplements. They are of interest for the industry because they are found almost all over the world, in all climatic zones, both in fresh and salt waters. The aim of this study was to take a broad look at green algae (Chlorophyta) and to show how large the variability of the content of active compounds may depend on the species and the place and time of sample collection. Particular attention was paid to compounds with antioxidant activity, whose simplified profiles were created on the basis of complementary, semi-quantitative methods. Additionally, time-yield extraction optimizations were performed. Three different specimens of Ulva lactuca were compared: from the coastal zone of the Baltic Sea, from the open Baltic Sea area around Bornholm and Ulva spiralis (Ulva lactuca polymorph) from the Atlantic Ocean. The studied algae of the Cladophora genera were three different species of freshwater algae from various habitats: a lake (Cladophora glomerata), a river (Cladophora rivularis) and aquarium farming (Cladophora aegagropila, syn. Aegagropila linnaei). The content of antioxidants and the extraction efficiency varied significantly depending on the species.