Molecular,biochemical and morphological data suggest an affiliation of Spongiochrysis hawaiiensis with the Trentepohliales (Ulvophyceae,Chlorophyta)

The aeroterrestrial, unicellular green alga Spongiochrysis hawaiiensis had been included in the ulvophycean order Cladophorales based on small subunit (SSU) rDNA sequence data, and represents so far the only fully terrestrial member of this order. Other characteristics of S. hawaiiensis that are atypical for Cladophorales include the presence of large amounts of carotenoids and a budding‐like mode of cell division. As the position of this terrestrial, unicellular alga in an order of aquatic, multicellular green algae is unusual, we re‐evaluated the phylogenetic relationships of this enigmatic organism based on supplementary SSU rDNA sequences as well as novel large ribosomal subunit (LSU) rDNA and internal transcribed spacer (ITS rDNA) sequences. Additionally, we examined several morphological characters of S. hawaiiensis, as well as low molecular weight carbohydrate (LMWC) patterns of S. hawaiiensis and members of the Cladophorales and Trentepohliales as potential chemotaxonomic markers. We found S. hawaiiensis to be uninucleate. The analysis of the LMWC content detected the presence of the polyol erythritol in S. hawaiiensis and in the Trentepohliales, while this compound was missing in the Cladophorales. The phylogenetic analyses of the novel sequences placed S. hawaiiensis in the terrestrial Trentepohliales. This placement is supported by the aeroterrestrial habitat, the presence of large amounts of carotenoids, the uninucleate cells, and the presence of the polyol erythritol as a protective compound against water loss.     

Ocean acidification reduces induction of coral settlement by crustose coralline algae

Crustose coralline algae (CCA) are a critical component of coral reefs as they accrete carbonate for reef structure and act as settlement substrata for many invertebrates including corals. CCA host a diversity of microorganisms that can also play a role in coral settlement and metamorphosis processes. Although the sensitivity of CCA to ocean acidification (OA) is well established, the response of their associated microbial communities to reduced pH and increased CO₂ was previously not known. Here we investigate the sensitivity of CCA‐associated microbial biofilms to OA and determine whether or not OA adversely affects the ability of CCA to induce coral larval metamorphosis. We experimentally exposed the CCA Hydrolithon onkodes to four pH/pCO₂ conditions consistent with current IPCC predictions for the next few centuries (pH: 8.1, 7.9, 7.7, 7.5, pCO₂: 464, 822, 1187, 1638 μatm). Settlement and metamorphosis of coral larvae was reduced on CCA pre‐exposed to pH 7.7 (pCO₂ = 1187 μatm) and below over a 6‐week period. Additional experiments demonstrated that low pH treatments did not directly affect the ability of larvae to settle, but instead most likely altered the biochemistry of the CCA or its microbial associates. Detailed microbial community analysis of the CCA revealed diverse bacterial assemblages that altered significantly between pH 8.1 (pCO₂ = 464 μatm) and pH 7.9 (pCO₂ = 822 μatm) with this trend continuing at lower pH/higher pCO₂ treatments. The shift in microbial community composition primarily comprised changes in the abundance of the dominant microbes between the different pH treatments and the appearance of new (but rare) microbes at pH 7.5. Microbial shifts and the concomitant reduced ability of CCA to induce coral settlement under OA conditions projected to occur by 2100 is a significant concern for the development, maintenance and recovery of reefs globally.     

Native generalist herbivores promote invasion of a chemically defended seaweed via refuge‐mediated apparent competition

Refuge‐mediated apparent competition was recently suggested as a mechanism that enables plant invasions. The refuge characteristics of introduced plants are predicted to enhance impacts of generalist herbivores on native competitors and thereby result in an increased abundance of the invader. However, this prediction has so far not been experimentally verified. This study tested if the invasion of a chemically defended seaweed is promoted by native generalist herbivores via refuge‐mediated apparent competition. The invader was shown to offer herbivores a significantly better refuge against fish predation compared with native seaweeds. Furthermore, in an experimental community, the presence of herbivores decreased the performance of neighbouring native seaweeds, but increased growth and relative abundance of the invader. These results provides the first experimental evidence that native generalist herbivores can shift a community towards a dominance of a well‐defended invader, inferior to native species in direct competitive interactions, by means of refuge‐mediated apparent competition.     

Red algae natural products for prevention of lipopolysaccharides (LPS)-induced liver and kidney inflammation and injuries

Background: The liver and kidney inflammation due to bacterial infection is one of the most common pathological problems leading to tissue damage or disease. In many liver and kidney disorders, which represent serious global health burden with a high economic cost, oxidative stress-related inflammation and apoptosis are important pathogenic components, finally resulting in acute liver and/or kidney failure. Erythropoietin and its analogues are well known to influence the interaction between apoptosis and inflammation in liver and kidney. Objective: The aim of the present study is to investigate and clarify the effect of Galaxaura oblongata (G. oblongata) red algae on lipopolysaccharides (LPS)-induced acute liver and kidney injury of mice with endotoxemia and associated molecular mechanism from inflammation, apoptosis and oxidative stress levels. Results: The current study cleared out that treatment of rats with the G. oblongata extract prior to LPS injection significantly lowered serum cytokines, including NF-κB, MPO and LPO, and improved liver apoptosis through suppressing protein tyrosine kinase signaling pathway, and that may be due to antibacterial activity as well antioxidant capacity of G. oblongata extract. Conclusion: The present study was cleared out the possibility of administration of G. oblongata red algae as a multi products source for biotechnological, medical, nutraceutical and pharmaceutical applications due to highly antioxidant and anti-inflammatory capacities even although more investigations are required for separating, purifying and characterizing these bioactive compounds.     

Assessment of littoral algal diversity from the northern Gulf of Mexico using environmental DNA metabarcoding

Traditional methods for algal biodiversity monitoring are costly and time inefficient because they rely on high‐level taxonomic expertise to address species identity problems involving phenotypic plasticity and morphological convergence. These problems are exacerbated in regions such as the Gulf of Mexico, that has a limited history of phycological exploration, but that are economically important or threatened by numerous anthropogenic stressors. Given the high pace of disturbance to natural systems, there is a critical need for expedient and cost‐effective tools for the study of benthic algal communities. Here we document the use of environmental DNA metabarcoding, using the partial LSU rDNA and 23S rDNA plastid molecular markers, to elucidate littoral algal diversity in the Northern Gulf of Mexico. We assigned 73.7% of algal OTUs to genus and 59.6% to species ranks. Our current study detected molecular signals for 35 algal/protist species with no previous reports in the Gulf of Mexico, thus providing an important, molecular‐validated, baseline of species richness for this region. We also make several bioinformatic recommendations for the efficient use of high‐throughput sequence data to assess biological communities.     

Japan's nationwide long‐term monitoring survey of seaweed communities known as the “Monitoring Sites 1000”: Ten‐year overview and future perspectives

“Monitoring Sites 1000” – Japan's long‐term monitoring survey was established in 2003, based on the Japanese Government policy for the conservation of biodiversity. Ecological surveys have been conducted on various types of ecosystems at approximately 1000 sites in Japan for 15 years now and are planned to be carried out for 100 years. Since 2008, seaweed communities had been monitored at six sites, featuring the kelp (e.g. Saccharina and Ecklonia; Laminariales) and Sargassum (Fucales) communities in the subarctic and temperate regions of Japan. Annual surveys were carried out during the season when these canopy‐forming seaweeds are most abundant. A non‐destructive quadrat sampling method, with permanent quadrats placed along transects perpendicular to the shoreline, was used to determine species composition, coverage, and vertical distribution of seaweeds at these sites; while destructive sampling was done every 5 years to determine biomass. The occurrence of canopy‐forming species Saccharina japonica (var. japonica) and Ecklonia cava have appeared to be stable at the Muroran (southwestern part of Hokkaido Island) and Shimoda (Pacific coast of middle Honshu Island) sites, respectively; whereas the coverage of Ecklonia radicosa (= Eckloniopsis radicosa) at the Satsuma‐Nagashima site in southern part of Kyushu Island was highly variable until its sudden disappearance from the habitat in 2016. Thalli of E. radicosa lost most of their blades through browsing by herbivorous fish, and thus, this may be one of the causes of the decline. A shift in the community structure related to environmental changes had also been observed at some other sites. Pre‐ and post‐disaster data revealed the impact of the 2011 earthquake and tsunami disasters, including a shift in the vertical distribution of Ecklonia bicyclis (= Eisenia bicyclis) to shallower depths at the Shizugawa site in the Pacific coast of northern Honshu Island, due to seafloor subsidence.     

Sporogenic and vegetative tissues of Saccharina latissima (Laminariales,Phaeophyceae) exhibit distinctive sensitivity to experimentally enhanced ultraviolet radiation : photosynthetically active radiation ratio

Fertile Saccharina latissima sporophytes, collected in the Kongsfjorden, Ny‐Ålesund, Spitsbergen, Norway (78°56.87′ N, 11°51.64′ E) were investigated in relation to its sensitivity to experimentally enhanced ultraviolet radiation : photosynthetically active radiation (UVR : PAR) ratios. Irradiance of UVR were 4.30 W m^?2 of UV‐A (320–400 nm) and 0.40 W m^?2 of UV‐B (280–320 nm), and PAR (400–700 nm) was ～4.30 W m^?2 (=20 µmol photons m^?2 s^?1). Excised soral (sporogenic) and non‐soral (vegetative) tissues were separately irradiated for 16 h at 7°C. Transmission electron microscopy showed abundant occurrence of physodes, electron dense particles (～300–600 nm) in the sorus. Paraphysis cells, with partly crystalline content, large mitochondria and abundant golgi bodies were towering over the sporangia. In soral tissue, cells were not visibly altered by the PAR + UVR irradiation. The chloroplasts, flagella and nucleus of unreleased meiospores inside the sporangial parent cells were visibly intact. Severe changes in the chloroplast structure of vegetative tissue occurred after PAR + UVR irradiation. These changes included wrinkling and dilatation of the thylakoid membranes, and appearance of electron translucent areas inside the chloroplasts. In vegetative cells exposed to PAR + UVR, the total amount of physodes, was slightly higher as in cells exposed to PAR only. Initial values of optimum quantum yield of photosystem II (F_v/F_m) were 0.743 ± 0.04 in non‐soral and 0.633 ± 0.04 in soral tissue. Vegetative tissue was observed to be more sensitive to radiant exposure of PAR and PAR + UVR compared to reproductive tissue. Under PAR, a 20% reduction in Fv/Fm was observed in non‐soral compared to no reduction in soral tissue, whereas under PAR + UVR, 60% and 33% reduction in Fv/Fm was observed in non‐soral and soral tissues, respectively. This can be attributed to the corresponding three times higher antiradical power (ARP) capacity in soral compared to non‐soral tissue.     

Selectivity in biomineralization of barium and strontium

The desmid green alga Closterium moniliferum belongs to a small number of organisms that form barite (BaSO₄) or celestite (SrSO₄) biominerals. The ability to sequester Sr in the presence of an excess of Ca is of considerable interest for the remediation of ⁹⁰Sr from the environment and nuclear waste. While most cells dynamically regulate the concentration of the second messenger Ca²⁺ in the cytosol and various organelles, transport proteins rarely discriminate strongly between Ca, Sr, and Ba. Herein, we investigate how these ions are trafficked in C. moniliferum and how precipitation of (Ba,Sr)SO₄ crystals occurs in the terminal vacuoles. Towards this goal, we simultaneously visualize intracellular dynamics of multiple elements using X-ray fluorescence microscopy (XFM) of cryo-fixed/freeze-dried samples. We correlate the resulting elemental maps with ultrastructural information gleaned from freeze-fracture cryo-SEM of frozen-hydrated cells and use micro X-ray absorption near edge structure (micro-XANES) to determine sulfur speciation. We find that the kinetics of Sr uptake and efflux depend on external Ca concentrations, and Sr, Ba, and Ca show similar intracellular localization. A highly ion-selective cross-membrane transport step is not evident. Based on elevated levels of sulfate detected in the terminal vacuoles, we propose a “sulfate trap” model, where the presence of dissolved barium leads to preferential precipitation of (Ba,Sr)SO₄ due to its low solubility relative to SrSO₄ and CaSO₄. Engineering the sulfate concentration in the vacuole may thus be the most direct way to increase the Sr sequestered per cell, an important consideration in using desmids for phytoremediation of ⁹⁰Sr.     

Environmental variability drives phytoplankton assemblage persistence in a subtropical reservoir

Temporal changes of assemblages may result from environmental variability and reflect seasonal dynamics of their ecosystem. In the subtropics, the hydrological regime is usually characterized by well‐defined wet and dry seasons, regulating discharge and influencing a series of environmental variables that affect phytoplankton persistence. Therefore, we may expect that dry seasons are environmentally more stable than wet seasons. We analysed interannual phytoplankton assemblage variability (or, inversely, persistence) in a subtropical reservoir sampled every austral summer and winter during 5 years. We tested (i) if phytoplankton assemblage structure differed between the dry (summer) and wet (winter) seasons; (ii) if assemblage persistence differed between the seasons; (iii) if assemblage persistence was related to environmental stability; and (iv) if assemblage dissimilarity increased over time. Phytoplankton assemblages differed between the summer and winter seasons. Winter indicator species were mostly Bacillariophyceae or Cryptophyceae, whereas Cyanophyceae and Chlorophyceae taxa were more frequent and abundant in summer. Assemblages in the dry season were more persistent among years than those occurring during rainy periods. Similarly, environmental variability tended to be lower among dry than among rainy seasons. The relation between the phytoplankton temporal cycle and the temporal patterns of environmental variability supports our prediction that high environmental stability results in more persistent assemblages. Assemblage dissimilarity increased as sampling years were farther apart, for both seasons. Additionally, assemblages in the rainy periods showed a more pronounced increase in dissimilarity, as their changes among years were less predictable. We found a clear temporal pattern and an increased dissimilarity over time in the phytoplankton assemblage structure. Unravelling these temporal patterns may improve our understanding of phytoplankton temporal dynamics, and may have implications for management and monitoring programs. High dissimilarity of assemblages among years, particularly among rainy periods, can obscure human impacts, and monitoring programs should take this into account.