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Chloroplasts are photosynthetic organelles that evolved through the endosymbiosis between cyanobacteria-like symbionts and hosts. Many studies have attempted to isolate intact chloroplasts to analyze their morphological characteristics and photosynthetic activity. Although several studies introduced isolated chloroplasts into the cells of different species, their photosynthetic activities have not been confirmed. In this study, we isolated photosynthetically active chloroplasts from the primitive red alga Cyanidioschyzon merolae and incorporated them in cultured mammalian cells via co-cultivation. The incorporated chloroplasts retained their thylakoid structure in intracellular vesicles and were maintained in the cytoplasm, surrounded by the mitochondria near the nucleus. Moreover, the incorporated chloroplasts maintained electron transport activity of photosystem II in cultured mammalian cells for at least 2 days after the incorporation. Our top-down synthetic biology-based approach may serve as a foundation for creating artificially photosynthetic animal cells.

Several invasive species can occupy the same geographic area. Interaction between species depends on several factors, and the results of such interactions can be highly diverse. Asparagopsis armata is a invasive red seaweed whose exudates contain a cocktail of toxic halogenated compounds. In this study, the impact of high and low levels of A. armata on the bivalve Ruditapes philippinarum was assessed in a laboratory experiment. Both are prominent invasive species in Europe and could share the same habitats. The effects of the algae were measured at different biological levels, framed by an integrated approach: bioturbation as a proxy for organismal activity and behaviour within the sediment, and several subcellular biomarkers related to oxidative stress and damage, energy metabolism, detoxification, and neurotransmission. While bioturbation revealed the effects of exudates on the bivalve, with a decrease in most parameters when exposed to the different amounts of algae, only marginal responses were found for biomarkers, suggesting a possible temporal decoupling between the behavioural response and the intrinsic biochemical environment. These results denote that despite the recognized potential of biomarkers to address a myriad of situations, a proxy for higher levels of biological organization, such as behaviour, for its integration of lower-level effects, is a robust tool to address complex and lesser-known mixtures of stressors., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The macrophyte Gelidium corneum (Hudson) J. V. Lamouroux, 1813 plays an important role as an ecosystem engineer on temperate rocky shores on the northeastern Atlantic coast. However, its cover and population biomass have declined in recent decades within the southern Bay of Biscay. This study aimed to identify the environmental thresholds, with respect to seawater temperature and irradiance, that influence the development capacity of newly formed individuals of G. corneum through vegetative reproduction. Therefore, an in situ experiment was conducted at two depths within the range of distribution of this species (5 and 12 m) and at two coastal sites on the north coast of Spain (east and west coasts of the Cantabria region, Spain). Our results revealed that G. corneum apical fragments undergoing vegetative propagation developed many new shoots over a period of sixteen weeks. The temperature and irradiance seemed to contribute to the length reached by the new fronds, whereas the number of recruits remained constant throughout the duration of the experiment. Given the slow growth rate characteristic of this species, the total shoot length in this study reached 2.97 cm, which confirms the gradual and restrained developmental pattern during the early stages of its life. We also quantified bite marks at the tips of the new plants, and more than three-quarters of them presented these signs by the final month of the study. Our study provides valuable insights into the growth process of the endangered species G. corneum through vegetative propagation and elucidates the impact that abiotic and biotic factors can have on its growth., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The objective of this study is to investigate the effect of nano-plastics (NPs) on the growth, photosynthesis, oxidative stress and antioxidant enzymes in Grateloupia turuturu and Chondrus ocellatus. Difference of surface characteristics between G. turuturu and C. ocellatus may affect adherence of plastics to their surface. The seaweed samples were cultivated at 5 different NP concentrations (0, 20, 200, 2000, 20000 ng/L) for 21 days. The accumulation of nano-plastics on surface of C. ocellatus was higher than that of G. turuturu. The highest concentration of NPs (20000 ng/L) inhibited the growth and photosynthesis activity of C. ocellatus. At the same concentrations, oxidative stress was caused with increase of antioxidant enzyme activities. G. turuturu was not affected by NPs at all tested concentrations. Based on these results, toxic effects of nano-plastics may be species specific. Toxicity is dependent on the capacity of macroalgae to accumulate nano-plastics on their surface., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jang Kyun Kim reports financial support was provided by National Research Foundation of Korea. Jang Kyun Kim reports financial support was provided by Ministry of Oceans and Fisheries of Korea. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Characteristics such as calcareous morphology and life cycle are used to understand the ecology of calcified rhodophytes. However, there is limited information regarding their chemical profiles and biological activities. Therefore, a systematic review (PRISMA) was conducted to assess the influence of the chemistry of calcareous rhodophytes on ecological interactions in the marine environment. The keywords used were: ["Chemical AND [Ecology OR Interaction OR Response OR Defense OR Effect OR Cue OR Mediated OR Induce]"] AND ["Red Seaweed" OR "Red Macroalgae" OR Rhodophy?] AND [Calcified OR Calcareous] in Science Direct, Scielo, PUBMED, Springer, Web of Science, and Scopus. Only English articles within the proposed theme were considered. Due to the low number of articles, another search was conducted with three classes and 16 genera. Finally, 67 articles were considered valid. Their titles, abstracts, and keywords were analyzed using IRaMuTeQ through factorial, hierarchical and similarity classification. Most of the studies used macroalgae thallus to evaluate chemical mediation while few tested crude extracts. Some substances were noted as sesquiterpene (6-hydroxy-isololiolide), fatty acid (heptadeca5,8,11-triene) and dibromomethane. The articles were divided into four classes: Herbivory, Competition, Settlement/Metamorphosis, and Epiphytism. Crustose calcareous algae were associated with studies of Settlement/Metamorphosis, while calcified algae were linked to herbivory. Thus, the importance of chemistry in the ecology of these algae is evident,and additional studies are needed to identify the substances responsible for ecological interactions. This study collected essential information on calcified red algae, whose diversity appears to be highly vulnerable to the harmful impacts of ongoing climate change., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Algal physiological ecology on submarine groundwater discharge (SGD) influenced reefs is likely shaped by intermittent, tidally-driven estuarine conditions that occur with SGD fluxes of fresh-to-brackish groundwater from the subterranean estuary to reef ecosystems. SGD is a common inconspicuous feature worldwide on reefs of basaltic high islands and continental margins. Yet, SGD-driven dynamics of algal physiology are not well understood. To understand how invasive species have physiologically outcompeted native species on many SGD-influenced reefs, physiology in tissue water potential (TWP) regulation, photosynthesis, nitrogen storage, and cellular anatomy were measured across a gradient of SGD-influence, for four Rhodophyte species. Compared with non-SGD conditions, SGD was associated with higher TWP, larger medulla cells with thinner walls, and thinner cortical cell walls for two invasives, Gracilaria salicornia and Acanthophora spicifera, higher photosynthetic rates in G. salicornia, greater nitrogen concentration for A. spicifera and G. salicornia, and increased δ 15 N ratios for A. spicifera, G. salicornia, and native Laurencia dendroidea. Distinct physiological strategies were measured for the two invasive species across the gradient of SGD-influence, and for L. dendroidea and Gracilaria perplexa offshore. This study illuminates species-specific physiological response, and how introduced opportunistic species may outcompete native species under conditions of SGD., (© 2024. The Author(s).)

Borg introduces the red algae - the largest living group of seaweeds., Competing Interests: Declaration of interests The author declares no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The Mediterranean Sea provides fertile ground for understanding the complex interplay between invasive species and native habitats, particularly within the context of climate change. This thermal tolerance study reveals the remarkable ability of Lophocladia trichoclados, a red algae species that has proven highly invasive, to adapt to varying temperatures, particularly thriving in colder Mediterranean waters, where it can withstand temperatures as low as 14 °C, a trait not observed in its native habitat. This rapid acclimation, occurring in less than a century, might entail a trade-off with high temperature resistance. Additionally, all sampled populations in the Mediterranean share the same haplotype, suggesting a common origin and the possibility that we might be facing an exceptionally acclimatable and invasive strain. This high degree of acclimatability could determine the future spread capacity in a changing scenario, highlighting the importance of considering both acclimation and adaptation in understanding the expansion of invasive species' ranges., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background and Aims: Globally, rising seawater temperatures contribute to the regression of marine macroalgal forests. Along the Istrian coastline (northern Adriatic), an isolated population of Gongolaria barbata persists in a coastal lagoon, representing one of the last marine macroalgal forests in the region. Our objective was to examine the impact of extreme temperatures on the morphology and physiology of G. barbata and test its potential for recovery after simulating marine heatwave (MHW) conditions., Methods: We explored the occurrence of marine heatwaves in southern Istria, adjacent to the study area, in addition to extreme temperatures inside the area itself. Subsequently, we performed a thermotolerance experiment, consisting of a stress and recovery phase, in which we exposed G. barbata thalli to four extreme (28, 30, 32 and 34 °C) and one favourable (18 °C) temperature. We monitored morphological and physiological responses., Key Results: Our findings indicate a significant rise in frequency, duration and intensity of MHWs over decades on the southern Istrian coast. Experimental results show that G. barbata demonstrates potential for both morphological and physiological recovery after exposure to temperatures as high as 32 °C. However, exposure to 34 °C led to thallus decay, with limited ability to regenerate., Conclusions: Our results show that G. barbata has a remarkable resilience to long-term exposure to extreme temperatures ≤32 °C and suggest that short-term exposure to temperatures beyond this, as currently recorded inside the lagoon, do not notably affect the physiology or morphology of local G. barbata. With more MHWs expected in the future, such an adapted population might represent an important donor suitable for future restoration activities along the Istrian coast. These results emphasize the resilience of this unique population, but also warn of the vulnerability of marine macroalgal forests to rising seawater temperatures in rapidly changing climatic conditions., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company.)

The present study focused on the physiological and biochemical aspects of Tricleocarpa fragilis, red seaweed belonging to the phylum Rhodophyta, along the South Andaman coast, with particular attention given to its symbiotic relationships with associated flora and fauna. The physicochemical parameters of the seawater at the sampling station, such as its temperature, pH, and salinity, were meticulously analyzed to determine the optimal harvesting period for T. fragilis. Seaweeds attach to rocks, dead corals, and shells in shallow areas exposed to moderate wave action because of its habitat preferences. Temporal variations in biomass production were estimated, revealing the highest peak in March, which was correlated with optimal seawater conditions, including a temperature of 34 ± 1.1 °C, a pH of 8 ± 0.1, and a salinity of 32 ± 0.8 psu. GC‒MS analysis revealed n-hexadecanoic acid as the dominant compound among the 36 peaks, with major bioactive compounds identified as fatty acids, diterpenes, phenolic compounds, and hydrocarbons. This research not only enhances our understanding of ecological dynamics but also provides valuable insights into the intricate biochemical processes of T. fragilis. The established antimicrobial potential and characterization of bioactive compounds from T. fragilis lay a foundation for possible applications in the pharmaceutical industry and other industries., (© 2024. The Author(s).)

Neoporphyra haitanensis, a red alga harvested for food, thrives in the intertidal zone amid dynamic and harsh environments. High irradiance represents a major stressor in this habitat, posing a threat to the alga's photosynthetic apparatus. Interestingly, N. haitanensis has adapted to excessive light despite the absence of a crucial xanthophyll cycle-dependent photoprotection pathway. Thus, it is valuable to investigate the mechanisms by which N. haitanensis copes with excessive light and to understand the photoprotective roles of carotenoids. Under high light intensities and prolonged irradiation time, N. haitanensis displayed reduction in photosynthetic efficiency and phycobiliproteins levels, as well as different responses in carotenoids. The decreased carotene contents suggested their involvement in the synthesis of xanthophylls, as evidenced by the up-regulation of lycopene-β-cyclase (lcyb) and zeaxanthin epoxidase (zep) genes. Downstream xanthophylls such as lutein, zeaxanthin, and antheraxanthin increased proportionally to light stress, potentially participating in scavenging reactive oxygen species (ROS). When accompanied by the enhanced activity of ascorbate peroxidase (APX), these factors resulted in a reduction in ROS production. The responses of intermediates α-cryptoxanthin and β-cryptoxanthin were felt somewhere between carotenes and zeaxanthin/lutein. Furthermore, these changes were ameliorated when the organism was placed in darkness. In summary, down-regulation of the organism's photosynthetic capacity, coupled with heightened xanthophylls and APX activity, activates photoinhibition quenching (qI) and antioxidant activity, helping N. haitanensis to protect the organism from the damaging effects of excessive light exposure. These findings provide insights into how red algae adapt to intertidal lifestyles., (© 2024 Phycological Society of America.)

The northward shift of Pyropia yezoensis aquaculture required the breeding of germplasms with tolerance to the oxidative stress due to the high light conditions of the North Yellow Sea area. The MPV17/PMP22 family proteins were identified as a molecule related to reactive oxygen species (ROS) metabolism. Here, one of the MPV17 homolog genes designated as PyM-LP2 was selected for functional identification by introducing the encoding sequence region/reverse complementary fragment into the Py. yezoensis genome. Although the photosynthetic activity, the respiratory rate, and the ROS level in wild type (WT) and different gene-transformed algal strains showed similar levels under normal conditions, the overexpression (OE) strain exhibited higher values of photosynthesis, respiration, and reducing equivalents pool size but lower intracellular ROS production under stress conditions compared with the WT. Conversely, all the above parameters showed opposite variation trends in RNAi strain as those in the OE strain. This implied that the PyM-LP2 protein was involved in the mitigation of the oxidative stress. Sequence analysis revealed that this PyM-LP2 protein was assorted to peroxisomes and might serve as a poring channel for transferring malate (Mal) to peroxisomes. By overexpressing PyM-LP2, the transfer of Mal from chloroplasts to peroxisomes was enhanced under stress conditions, which promoted photorespiration and ultimately alleviated excessive reduction of the photosynthetic electron chain. This research lays the groundwork for the breeding of algae with enhanced resistance to oxidative stresses., (© 2024 Phycological Society of America.)

Mechanical damage to a cell can be fatal, and the cell must reseal its membrane and restore homeostasis to survive. Plant cell repair involves additional steps such as rebuilding vacuoles, rearranging chloroplasts, and remodeling the cell wall. When we pierced a Griffithsia monilis cell with a glass needle, a large amount of intracellular contents was released, but the cell membrane resealed in less than a second. The turgor of the vacuole was quickly restored, and the punctured cell returned to its original shape within an hour. Organelles such as chloroplasts and nuclei migrated to the wound site for 12 h and then dispersed throughout the cell after the wound was covered by a new cell wall. Using fluorescent probes, high levels of reactive oxygen species (ROS) and calcium were detected at the wound site from 3 h after wounding, which disappeared when cell repair was complete. Wounding in a solution containing ROS scavengers inhibited cellular repair, and inhibiting nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity or blocking calcium influx reversibly inhibited cell repair. Oryzalin reversibly inhibited both chloroplast movement and ROS production during cell repair. Our results show that cell repair in G. monilis is regulated by calcium-mediated ROS signaling and that microtubules serve as mechanical effectors., (© 2024 The Author(s). Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Spores have crucial importance in the establishment and development of seaweed populations. When the spore release matches with the low tidal period, they experience an extreme variation in the environmental conditions including the temperature. In this study, we assess the photosynthetic responses and growth of haploid (tetraspores) and diploid (carpospores) spores of two Gigartinales species (Mazzaella laminarioides and Iridaea cordata) from sub-Antarctic populations when exposed to an increasing temperature. In the laboratory, freshly released spores were exposed to a temperature gradient (7 [control], 10, 15, and 20 °C) recreating the temperature increase experienced by these spores during typical spring tides. Germination and further growth of spores previously exposed to temperature treatments were assessed. Carpospores and tetraspores exhibited variation in their photosynthetic response (measured as effective quantum yield; Φ PSII ) to temperature increase. In Mazzaella laminarioides, only carpospores exhibited a reduction in Φ PSII (by 7-24% at 15-20 °C), while both types of spores of Iridaea cordata were sensitive to temperature increase (12-24% of Φ PSII reduction at 10-20 °C). Spores previously exposed to temperature treatments and maintained at 7 °C and low PAR germinated and developed in germlings. In general, germlings originated from carpospores pre-treated at high temperatures showed higher growth rates. The different responses to temperature increase exhibited by haploid and diploid propagules of both species highlight their ecophysiological capacity to face high-temperature variation ensuring successful recruitment survival., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Red coralline algae create abundant, spatially vast, reef ecosystems throughout our coastal oceans with significant ecosystem service provision, but our understanding of their basic physiology is lacking. In particular, the balance and linkages between carbon-producing and carbon-sequestering processes remain poorly constrained, with significant implications for understanding their role in carbon sequestration and storage. Using dual radioisotope tracing, we provide evidence for coupling between photosynthesis (which requires CO 2 ) and calcification (which releases CO 2 ) in the red coralline alga Boreolithothamnion soriferum (previously Lithothamnion soriferum )-a marine ecosystem engineer widely distributed across Atlantic mid-high latitudes. Of the sequestered HCO 3 - , 38 ± 22% was deposited as carbonate skeleton while 39 ± 14% was incorporated into organic matter via photosynthesis. Only 38 ± 2% of the sequestered HCO 3 - was transformed into CO 2 , and almost 40% of that was internally recycled as photosynthetic substrate, reducing the net release of carbon to 23 ± 3% of the total uptake. The calcification rate was strongly dependent on photosynthetic substrate production, supporting the presence of photosynthetically enhanced calcification. The efficient carbon-recycling physiology reported here suggests that calcifying algae may not contribute as much to marine CO 2 release as is currently assumed, supporting a reassessment of their role in blue carbon accounting.

This study delves into how two ecotypes of diatom affect the Pyropia haitanensis, a valuable and commercial red macroalga. We co-cultivated P. haitanensis with a planktonic diatom Skeletonema costatum and benthic diatom Navicula climacospheniae. The results showed that benthic diatom significantly hindered P. haitanensis growth, while planktonic ones had no major impact. The macroalga restrained planktonic diatom growth but did not affect benthic diatom. Photosynthetic pigments of macroalga, except chlorophyll, were higher, indicating stress when exposed to diatoms. Microscopic images revealed dense benthic diatom attachment, potentially stressing thalli due to limited light and EPS secretion. Total carbohydrate slightly decreased in both diatom treatments, while total protein significantly decreased with increasing benthic diatom densities. In summary, benthic diatom notably influenced P. haitanensis growth, pigments, and total protein levels. This study sheds light on the interaction between microalgal ecotypes and commercial macroalga P. haitanensis, which is crucial for its economic significance., Competing Interests: Declaration of competing interest None of the authors have any conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Rhodoliths built by crustose coralline algae (CCA) are ecosystem engineers of global importance. In the Arctic photic zone, their three-dimensional growth emulates the habitat complexity of coral reefs but with a far slower growth rate, growing at micrometers per year rather than millimeters. While climate change is known to exert various impacts on the CCA's calcite skeleton, including geochemical and structural alterations, field observations of net growth over decade-long timescales are lacking. Here, we use a temporally explicit model to show that rising ocean temperatures over nearly 100 years were associated with reduced rhodolith growth at different depths in the Arctic. Over the past 90 years, the median growth rate was 85 μm year -1 but each °C increase in summer seawater temperature decreased growth by a mean of 8.9 μm (95% confidence intervals = 1.32-16.60 μm °C -1 , p < .05). The decrease was expressed for rhodolith occurrences in 11 and 27 m water depth but not at 46 m, also having the shortest time series (1991-2015). Although increasing temperatures can spur plant growth, we suggest anthropogenic climate change has either exceeded the population thermal optimum for these CCA, or synergistic effects of warming, ocean acidification, and/or increasing turbidity impair rhodolith growth. Rhodoliths built by calcitic CCA are important habitat providers worldwide, so decreased growth would lead to yet another facet of anthropogenic habitat loss., (Global Change Biology© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Intraspecific and habitat-mediated responses to chemical cues play key roles in structuring populations of marine species. We investigated the behaviour of herbivorous-stage juvenile crown-of-thorns sea stars (COTS; Acanthaster sp.) in flow-through choice chambers to determine if chemical cues from their habitat influence movement and their transition to become coral predators. Juveniles at the diet transition stage were exposed to cues from their nursery habitat (coral rubble-crustose coralline algae (CCA)), live coral and adult COTS to determine if waterborne cues influence movement. In response to CCA and coral as sole cues, juveniles moved towards the cue source and when these cues were presented in combination, they exhibited a preference for coral. Juveniles moved away from adult COTS cues. Exposure to food cues (coral, CCA) in the presence of adult cues resulted in variable responses. Our results suggest a feedback mechanism whereby juvenile behaviour is mediated by adult chemical cues. Cues from the adult population may deter juveniles from the switch to corallivory. As outbreaks wane, juveniles released from competition may serve as a proximate source of outbreaks, supporting the juveniles-in-waiting hypothesis. The accumulation of juveniles within the reef infrastructure is an underappreciated potential source of COTS outbreaks that devastate coral reefs.

Canopy-forming macroalgae are facing large declines due to climate change worldwide. The foundation species Gelidium corneum (Hudson) J.V. Lamouroux has shown a long-term decline in the Southeastern Bay of Biscay. We conducted an in situ experiment to investigate the combined effect of solar radiation and nutrient availability on the photosynthetic acclimation and growth of this macrophyte, and on the species richness and diversity of the assemblages that it forms. Photochemical stress in G. corneum was found to be greater at the end of the study, probably as a result of a prolonged exposure to high irradiance (PAR and UVR) and due to high temperatures during summer. We found an acclimation of G. corneum specimens to summer light and thermal conditions through dynamic/reversible photoinhibition and a decrease in photosynthetic efficiency. Nutrients may also have had a positive effect in dealing with the negative effects of these stressors. Under ongoing global climate change and projections for the future, further research will be needed to better understand the effects not only on canopy forming species but also on the whole community and thus on the functioning of the ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Increased atmospheric CO 2 concentrations not only change the components of inorganic carbon system in seawater, resulting in ocean acidification, but also lead to decreased seawater pH, resulting in ocean acidification. Consequently, increased inorganic carbon concentrations in seawater provide a sufficient carbon source for macroalgal photosynthesis and growth. Increased domestic sewage and industrial wastewater discharge into coastal areas has led to nutrient accumulation in coastal seawaters. Combined with elevated pCO 2 (1200 ppmv), increased nutrient availability always stimulates the growth of non-calcifying macroalgae, such as red economical macroalga Gracilariopsis lemaneiformis. Here, we evaluated the interactive effects of nutrients with elevated pCO 2 on the economically important marine macroalga Kappaphycus alvarezii (Rhodophyta) in a factorial 21-day coupling experiment. The effects of increased nutrient availability on photosynthesis and photosynthetic pigments of K. alvarezii were greater than those of pCO 2 concentration. The highest F v /F m values (0.660 ± 0.019 and 0.666 ± 0.030, respectively) were obtained at 2 μmol L -1 of NO 3 -N at two pCO 2 levels. Under the elevated pCO 2 condition, the Chl-a content was lowest (0.007 ± 0.004 mg g -1 ) at 2 μmol L -1 of NO 3 -N and highest (0.024 ± 0.002 mg g -1 ) at 50 μmol L -1 of NO 3 -N. The phycocyanin content was highest (0.052 ± 0.012 mg g -1 ) at 150 μmol L -1 of NO 3 -N under elevated pCO 2 condition. The malondialdehyde content declined from 32.025 ± 4.558 nmol g -1 to 26.660 ± 3.124 nmol g -1 with the increased nutrients at under low pCO 2 . To modulate suitable adjustments, soluble biochemical components such as soluble carbohydrate, soluble protein, free amino acids, and proline were abundantly secreted and were likely to protect the integrity of cellular structures under elevated nutrient availability. Our findings can serve as a reference for cultivation and bioremediation methods under future environmental conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The crustose coralline algae (CCA) play an important role building carbonate habitats and enhancing species diversity in rocky shores, rhodolith beds and coral-algal reefs. Though worldwide distributed some taxonomic groups were proved to show light and temperature boundaries. Nevertheless, little is known about the biological limits of CCA recruits and photosynthetic responses in a climate change environment. In this way, experimental studies are essential to identify their optimal conditions development. The aim of the study was to test ideal environmental conditions for CCA recruits from an upwelling area to verify Fv/Fm response patterns as an indicator of photosynthetic performance. Artificial disks were fixed on a rocky shore to provide substrate for CCA recruitments and then moved to be tested in a flow-through system. The CCA tested were species of the Genus Lithophyllum and experiments were performed with CCA exposed to different levels of light, temperature and current flow rates. The photosystem II function, measured by chlorophyll a fluorescence (Fv/Fm), was used as an indicator of potential photosynthetic electron transport. There was an interaction between light intensity, flow rate and temperature. Low light intensity, high temperature and fast flow rate (20 μmol m -2 . s -1 ; 19 and 24 °C; 0.09 m s -1 respectively) provided optimal conditions for CCA recruits., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Invasive species have been a focus of concern in recent decades, becoming more problematic due to the cumulative impacts of climate change. Understanding the interactions among stress factors is essential to anticipate ecosystems' responses. Hereby, robust modeling frameworks must be able to identify the environmental drivers of invasion and forecast the current and future of their potential distribution. These studies are essential for the management of invasions and to be prepared for the future we are facing. Here we demonstrate that taxonomic misidentifications may lead to absolutely erroneous predictions, by using as an example one of the worst invasive species in the Mediterranean Sea (Lophocladia lallemandii), which has been misidentified for three decades and now is correctly identified. Consequently, and bearing in mind overall trends in species misidentification due to the loss of taxonomic expertise and the presence of cryptic species, among others, attempts to understand and predict species involved in invasion processes must always first consider taxonomic studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Global climate changes, such as warming and ocean acidification (OA), are likely to negatively impact calcifying marine taxa. Abundant and ecologically important coralline algae may be particularly susceptible to OA; however, multi-stressor studies and those on articulated morphotypes are lacking. Here, we use field observations and laboratory experiments to elucidate the impacts of warming and acidification on growth, calcification, mineralogy, and photophysiology of the temperate articulated coralline alga, Calliarthron tuberculosum. We conducted a 4-week fully factorial mesocosm experiment exposing individuals from a southern CA kelp forest to current and future temperature and pH/pCO 2 conditions (+2°C, -0.5 pH units). Calcification was reduced under warming (70%) and further reduced by high pCO 2 or high pCO 2 x warming (~150%). Growth (change in linear extension and surface area) was reduced by warming (40% and 50%, respectively), high pCO 2 (20% and 40%, respectively), and high pCO 2 x warming (50% and 75%, respectively). The maximum photosynthetic rate (P max ) increased by 100% under high pCO 2 conditions, but we did not detect an effect of pCO 2 or warming on photosynthetic efficiency (α). We also did not detect the effect of warming or pCO 2 on mineralogy. However, variation in Mg incorporation in cell walls of different cell types (i.e., higher mol % Mg in cortical vs. medullary) was documented for the first time in this species. These results support findings from a growing body of literature suggesting that coralline algae are often more negatively impacted by warming than OA, with the potential for antagonistic effects when factors are combined., (© 2022 The Authors. Journal of Phycology published by Wiley Periodicals LLC on behalf of Phycological Society of America.)

Background: Seaweeds in the upper intertidal zone experience extreme desiccation during low tide, followed by rapid rehydration during high tide. Porphyra sensu lato are typical upper intertidal seaweeds. Therefore, it is valuable to investigate the adaptive mechanisms of seaweed in response to dehydration-rehydration stress., Results: A reduction in photosynthetic capacity and cell shrinkage were observed when N. haitanensis was dehydrated, and such changes were ameliorated once rehydrated. And the rate and extent of rehydration were affected by the air flow speed, water content before rehydration, and storage temperature and time. Rapid dehydration at high air-flow speed and storage at - 20 °C with water content of 10% caused less damage to N. haitanensis and better-protected cell activity. Moreover, proteomic and metabolomic analyses revealed the abundance members of the differentially expressed proteins (DEPs) and differentially abundant metabolites (DAMs) mainly involved in antioxidant system and osmotic regulation. The ascorbic acid-glutathione coupled with polyamine antioxidant system was enhanced in the dehydration response of N. haitanensis. The increased soluble sugar content, the accumulated polyols, but hardly changed (iso)floridoside and insignificant amount of sucrose during dehydration indicated that polyols as energetically cheaper organic osmolytes might help resist desiccation. Interestingly, the recovery of DAMs and DEPs upon rehydration was fast., Conclusions: Our research results revealed that rapid dehydration and storage at - 20 °C were beneficial for recovery of N. haitanensis. And the strategy to resist dehydration was strongly directed toward antioxidant activation and osmotic regulation. This work provided valuable insights into physiological changes and adaptative mechanism in desiccation, which can be applied for seaweed farming., (© 2022. The Author(s).)

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., (© 2021 Phycological Society of America.)

Disease in the marine environment is predicted to increase with anthropogenic stressors and already affects major habitat-formers, such as corals and seaweeds. Solutions to address this issue are urgently needed. The seaweed Delisea pulchra is prone to a bleaching disease, which is caused by opportunistic pathogens and involves bacterial dysbiosis. Bacteria that can inhibit these pathogens and/or counteract dysbiosis are therefore hypothesised to reduce disease. This study aimed to identify such disease-protective bacteria and investigate their protective action. One strain, Phaeobacter sp. BS52, isolated from healthy D. pulchra, was antagonistic towards bleaching pathogens and significantly increased the proportion of healthy individuals when applied before the pathogen challenge (pathogen-only vs. BS52 + pathogen: 41-80%), and to a level similar to the control. However, no significant negative correlations between the relative abundances of pathogens and BS52 on D. pulchra were detected. Instead, inoculation of BS52 mitigated pathogen-induced changes in the epibacterial community. These observations suggest that the protective activity of BS52 was due to its ability to prevent dysbiosis, rather than direct pathogen inhibition. This study demonstrates the feasibility of manipulating bacterial communities in seaweeds to reduce disease and that mitigation of dysbiosis can have positive health outcomes., (© 2021. The Author(s), under exclusive licence to International Society for Microbial Ecology.)

Several species of unicellular eukaryotic algae exhibit relatively simple genomic and cellular architecture. Laboratory cultures of these algae grow faster than plants and often provide homogeneous cellular populations exposed to an almost equal environment. These characteristics are ideal for conducting experiments at the cellular and subcellular levels. Many microalgal lineages have recently become genetically tractable, which have started to evoke new streams of studies. Among such algae, the unicellular red alga Cyanidioschyzon merolae is the simplest organism; it possesses the minimum number of membranous organelles, only 4,775 protein-coding genes in the nucleus, and its cell cycle progression can be highly synchronized with the diel cycle. These properties facilitate diverse omics analyses of cellular proliferation and structural analyses of the intracellular relationship among organelles. C. merolae cells lack a rigid cell wall and are thus relatively easily disrupted, facilitating biochemical analyses. Multiple chromosomal loci can be edited by highly efficient homologous recombination. The procedures for the inducible/repressive expression of a transgene or an endogenous gene in the nucleus and for chloroplast genome modification have also been developed. Here, we summarize the features and experimental techniques of C. merolae and provide examples of studies using this alga. From these studies, it is clear that C. merolae-either alone or in comparative and combinatory studies with other photosynthetic organisms-can provide significant insights into the biology of photosynthetic eukaryotes., (© The Author(s) 2021. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.)

Phycobilisomes (PBSs) are the largest light-harvesting antenna in red algae, and feature high efficiency and rate of energy transfer even in a dim environment. To understand the influence of light on the energy transfer in PBSs, two red algae Griffithsia pacifica and Porphyridium purpureum living in different light environment were selected for this research. The energy transfer dynamics in PBSs of the two red algae were studied in time-resolved fluorescence spectroscopy in sub-picosecond resolution. The energy transfer pathways and the related transfer rates were uncovered by deconvolution of the fluorescence decay curve. Four time-components, i.e., 8 ps, 94 ps, 970 ps, and 2288 ps were recognized in the energy transfer in PBSs of G. pacifica, and 10 ps, 74 ps, 817 ps and 1292 ps in P. purpureum. In addition, comparison in energy transfer dynamics between the two red algae revealed that the energy transfer was clearly affected by lighting environment. The findings help us to understand the energy transfer mechanisms of red algae for adaptation to a natural low light environment., (© 2021. The Author(s).)

Rhodolith beds built by free-living coralline algae are important ecosystems for marine biodiversity and carbonate production. Yet, our mechanistic understanding regarding rhodolith physiology and its drivers is still limited. Using three rhodolith species with different branching morphologies, we investigated the role of morphology in species' physiology and the implications for their susceptibility to ocean acidification (OA). For this, we determined the effects of thallus topography on diffusive boundary layer (DBL) thickness, the associated microscale oxygen and pH dynamics and their relationship with species' metabolic and light and dark calcification rates, as well as species' responses to short-term OA exposure. Our results show that rhodolith branching creates low-flow microenvironments that exhibit increasing DBL thickness with increasing branch length. This, together with species' metabolic rates, determined the light-dependent pH dynamics at the algal surface, which in turn dictated species' calcification rates. While these differences did not translate in species-specific responses to short-term OA exposure, the differences in the magnitude of diurnal pH fluctuations (~ 0.1-1.2 pH units) between species suggest potential differences in phenotypic plasticity to OA that may result in different susceptibilities to long-term OA exposure, supporting the general view that species' ecomechanical characteristics must be considered for predicting OA responses.

Electrical lighting favours the development of photosynthetic biofilms in caves which can induce biodeterioration in the colonized substrates. The use of specific lights as a limiting factor for biofilm growth could be effective in their control and represents an alternative to chemical methods since they can damage the substrate. However, studies about lighting and the photosynthetic activity of organisms in caves are scarce. In order to select the most effective LED light source in reducing photosynthesis and therefore, in reducing the growth rates of microalgae and cyanobacteria, four biofilms in the Nerja Cave were illuminated by several light emitted diodes (LEDs) with different spectral compositions and the photobiological responses were measured both by empirical and theoretical methodologies. The empirical approach was based on the photosynthetic efficiency, by measuring the in vivo chlorophyll a (Chl a) fluorescence and the theoretical approach was based on the photonic assimilation performance related to the proportion of the light quality used for photosynthesis, according to the action spectra for photosynthesis available in the literature. The photobiological responses showed differences between the empirical and theoretical approach mainly in biofilms dominated by cyanobacteria and red algae, probably because the available action spectra were not useful for monitoring these Nerja Cave biofilms. However, the expected spectral responses of photosynthesis were observed in green microalgal biofilms with maximum photosynthetic efficiency in red and blue light although the green light was also unexpectedly high. The high photosynthetic efficiency in green light could be explained by the predictable high chlorophyll content due to a very dark environment. The results were not conclusive enough for all the biofilm types to be able to recommend a specific lighting system for the photocontrol of biofilm expansion. Therefore, new action spectra for photosynthesis of the extremophile organisms of the Nerja Cave are required. This approach, based on theoretical and empirical methodologies, is a useful tool to obtain information to allow the design of the most adequate lighting systems to reduce photosynthetic activity and favour the conservation of the caves., (Copyright © 2021 Elsevier B.V. All rights reserved.)

C-Phycocyanin (PC) is a protein used commercially as a natural blue pigment produced by cyanobacteria, cryptophytes, and rhodophytes. Although it is industrially synthesized from the cyanobacterium Arthrospira platensis, PC requires high levels of energy for its extraction, which involves freezing of cells. However, as a protein, PC is easily denatured at extreme temperatures. In this study, we extracted PC from the red alga Cyanidioschyzon merolae, denoted as CmPC, and found that this protein was tolerant to high temperatures and acidic pH. CmPC was extracted by suspending cells in water mixed with various salts and organic acids without freeze-drying or freeze-thaw. The stability of CmPC varied with salt concentration and was destabilized by organic acids. Our results indicate that C. merolae is a potential candidate for PC production with thermotolerant properties., (Copyright © 2020 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Cyanophyta-phycocyanin (C-PC) is the main constituent of the rod of phycobilisome (PBS), which is a highly ordered and large peripheral light-harvesting protein complex present on the cytoplasmic side of the thylakoid membrane in cyanobacteria and red algae. The C-PC monomer comprises two chains, α- and β-subunits, and aggregates to form ring-shaped trimers (αβ) 3 with rotational symmetry. The ring-shaped trimer (αβ) 3 is a structural block unit (SBU) that forms the rod of PBS. Two (αβ) 3 SBUs are arranged in a face-to-face manner to form an (αβ) 6 -hexamer. In this study, the electronic states of three phycocyanobilins, α84, β84, and β155 in C-phycocyanin, constituting the rod of the PBS, were calculated for both the trimer and hexamer models by considering the effect of the electrostatic field of protein moieties and water molecules. For the hexamer, the absorption wavelengths of α84, β84, and β155 were similar to those obtained experimentally; however, for the trimer, only the absorption wavelength of β155 shifted toward a shorter-wavelength. The nature of the hexamer structure as a hierarchical structure is revealed by considering the calculated absorption wavelength and energy transfer., (© 2020 The Authors. FEBS Open Bio published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

Photosynthesis and respiration rates, pigment contents, CO 2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O 2 and high CO 2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and β-carotene, while those in blue light had more phycocyanin. The dependence on O 2 concentration of the CO 2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

Photosynthetic organisms use different means to regulate their photosynthetic activity in respond to different light conditions under which they grow. In this study, we analyzed changes in the photosystem I (PSI) light-harvesting complex I (LHCI) supercomplex from a red alga Cyanidioschyzon merolae, upon growing under three different light intensities, low light (LL), medium light (ML), and high light (HL). The results showed that the red algal PSI-LHCI is separated into two bands on blue-native PAGE, which are designated PSI-LHCI-A and PSI-LHCI-B, respectively, from cells grown under LL and ML. The former has a higher molecular weight and binds more Lhcr subunits than the latter. They are considered to correspond to the two types of PSI-LHCI identified by cryo-electron microscopic analysis recently, namely, the former with five Lhcrs and the latter with three Lhcrs. The amount of PSI-LHCI-A is higher in the LL-grown cells than that in the ML-grown cells. In the HL-grown cells, PSI-LHCI-A completely disappeared and only PSI-LHCI-B was observed. Furthermore, PSI core complexes without Lhcr attached also appeared in the HL cells. Fluorescence decay kinetics measurement showed that Lhcrs are functionally connected with the PSI core in both PSI-LHCI-A and PSI-LHCI-B obtained from LL and ML cells; however, Lhcrs in the PSI-LHCI-B fraction from the HL cells are not coupled with the PSI core. These results indicate that the red algal PSI not only regulates its antenna size but also adjusts the functional connection of Lhcrs with the PSI core in response to different light intensities.

Pollution derived from human activities and the arrival of invasive species are common worldwide and affect coastal marine ecosystems negatively, and more especially in a semi-closed sea such as the Mediterranean Sea. The aim of the study was to evaluate oxidative stress biomarkers in the gonadal tissue of the sea urchin Paracentrotus lividus (Lamarck, 1816) sampled in different areas of Sant Antoni de Portmany (Ibiza Island, Spain) with different anthropic activities, and in an area deeply covered by the invasive red algae Lophocladia lallemandii. The densities of P. lividus were higher in the area with the greatest anthropogenic influence, while the area invaded by L. lallemandii showed the lowest density. A significant increase in the activities of the antioxidant enzymes catalase, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GRd) and the phase II detoxifying enzyme glutathione S-transferase (GST) was found in the most impacted area by the human activity. Moreover, malondialdehyde (MDA) and nitrite levels were also increased in the most impacted area. Similarly, the presence of L. lallemandii induced oxidative stress in P. lividus evidenced by a significant increase in all analysed biomarkers. In conclusion, changes in oxidative stress biomarkers are a good proxy to evaluate the impacts induced by anthropogenic activities and by the presence of invasive algae to P. lividus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Thorea hispida exclusively inhabits freshwater environments and is characterized by a triphasic life history. In this study, the organelle genomes and transcriptomes of different life history stages of T. hispida were examined using next generation sequencing. The chloroplast and mitochondrial genomes of the chantransia stage were 175,747 and 25,411 bp in length, respectively. The chantransia stage was highly similar to the gametophyte stage based on comparisons of organelle genomes and phylogenetic reconstruction. Transcriptomic comparisons of two stages found that ribosome-related genes were the most up-regulated in the gametophyte stage of T. hispida. Seven meiosis-specific genes, including SPO11 initiator of meiotic double-stranded breaks(spo11), meiotic nuclear divisions 1(mnd1), RAD51 recombinase(rad51), mutS homolog 4(msh4), mutS homolog 5(msh5), REC8 meiotic recombination protein(rec8), and DNA helicase Mer3(mer3), were differentially regulated between the two life history stages. The organelle genomes and transcriptomes from T. hispida provided in this study will be valuable for future studies of freshwater red algae., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Healthy benthic substrates that induce coral larvae to settle are necessary for coral recovery. Yet, the biochemical cues required to induce coral settlement have not been identified for many taxa. Here we tested the ability of the crustose coralline alga (CCA) Porolithon onkodes to induce attachment and metamorphosis, collectively termed settlement, of larvae from 15 ecologically important coral species from the families Acroporidae, Merulinidae, Poritidae, and Diploastreidae. Live CCA fragments, ethanol extracts, and hot aqueous extracts of P. onkodes induced settlement (> 10%) for 11, 7, and 6 coral species, respectively. Live CCA fragments were the most effective inducer, achieving over 50% settlement for nine species. The strongest settlement responses were observed in Acropora spp.; the only non-acroporid species that settled over 50% were Diploastrea heliopora, Goniastrea retiformis, and Dipsastraea pallida. Larval settlement was reduced in treatments with chemical extracts compared with live CCA, although high settlement (> 50%) was reported for six acroporid species in response to ethanol extracts of CCA. All experimental treatments failed (< 10%) to induce settlement in Montipora aequituberculata, Mycedium elephantotus, and Porites cylindrica. Individual species responded heterogeneously to all treatments, suggesting that none of the cues represent a universal settlement inducer. These results challenge the commonly-held notion that CCA ubiquitously induces coral settlement, and emphasize the critical need to assess additional cues to identify natural settlement inducers for a broad range of coral taxa.

The eucheumatoids Kappaphycus and Eucheuma are cultivated in tropical or subtropical regions for the production of carrageenan, a hydrocolloid widely used in the food and cosmetic industries. Kappaphycus alvarezii is a highly valued economic crop in the Coral Triangle, with the Philippines, Indonesia and Malaysia ranked among the largest producers. In the absence of measures to mitigate climate change, extreme events including heatwaves, typhoons, severe El Niño and La Niña, are expected to increase in frequency and magnitude. This inadvertently brings adverse effects to the seaweed cultivation industry, especially in the tropics. Temperatures are rapidly reaching the upper limit of biologically tolerable levels and an increase in reports of ice-ice and pest outbreaks is attributable to these shifts of environmental parameters. Nevertheless, few reports on the response of eucheumatoids to a changing environment, in particular global warming, are available. Understanding the responses and possible mechanisms for acclimation to warming is crucial for a sustainable seaweed cultivation industry. Here, the physiological and biochemical responses of K. alvarezii to acute warming indicated that the strain used in the current study is unlikely to survive sudden increases in temperature above 36°C. As temperature increased, the growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment content (chlorophyll-a, carotenoid and phycobiliproteins) were reduced while the production of reactive oxygen species increased indicating the occurrence of stress in the seaweeds. This study provides a basis for future work on long term acclimation to elevated temperature and mesocosm-based multivariate studies to identify heat-tolerant strains for sustainable cultivation., Competing Interests: The authors have declared that no potential competing interests exist.

Phototaxis, which is the ability to move towards or away from a light source autonomously, is a common mechanism of unicellular algae. It evolved multiple times independently in different plant lineages. As of yet, algal phototaxis has been linked mainly to the presence of cilia, the only known locomotive organelle in unicellular algae. Red algae (Rhodophyta), however, lack cilia in all stages of their life cycle. Remarkably, multiple unicellular red algae like the extremophile Cyanidioschyzon merolae ( C. merolae ) can move towards light. Remarkably, it has remained unclear how C. merolae achieves movement, and the presence of a completely new mechanism has been suggested. Here we show that the basis of this movement are novel retractable projections, termed tentacles due to their distinct morphology. These tentacles could be reproducibly induced within 20 min by increasing the salt concentration of the culture medium. Electron microscopy revealed filamentous structures inside the tentacles that we identified to be actin filaments. This is surprising as C. merolae 's single actin gene was previously published to not be expressed. Based on our findings, we propose a model for C. merolae 's actin-driven but myosin-independent motility. To our knowledge, the described tentacles represent a novel motility mechanism.

This study investigated the changes in bioaccumulation, bioabsorption, photosynthesis rate, respiration rate, and photosynthetic pigments (phycoerythrin, phycocyanin, and allophycocyanin) of Sarcodia suiae following cadmium exposure within 24 h. The bioabsorption was significantly higher than the bioaccumulation at all cadmium levels ( p < 0.05). The ratios of bioabsorption/bioaccumulation in light and dark bottles were 2.17 and 1.74, respectively, when S. suiae was exposed to 5 Cd 2+ mg/L. The chlorophyll a (Chl-a) concentration, oxygen evolution rate (photosynthetic efficiency), and oxygen consumption rate (respiratory efficiency) decreased with increasing bioaccumulation and ambient cadmium levels. The levels of bioaccumulation and bioabsorption in light environments were significantly higher than those in dark environments ( p < 0.05). In addition, the ratios of phycoerythrin (PE)/Chl-a, phycocyanin (PC)/Chl-a, and allophycocyanin (APC)/Chl-a were also higher in light bottles compared to dark bottles at all ambient cadmium levels. These results indicated that the photosynthesis of seaweed will increase bioaccumulation and bioabsorption in a cadmium environment.

Environmental conditions shape the occurrence and abundance of habitat-building organisms at global scales. Rhodolith beds structure important hard substrate habitats for a large number of marine benthic organisms. These organisms can benefit local biodiversity levels, but also compete with rhodoliths for essential resources. Therefore, understanding the factors shaping the distribution of rhodoliths and their associated communities along entire distributional ranges is of much relevance for conservational biology, particularly in the scope of future environmental changes. Here we predict suitable habitat areas and identify the main environmental drivers of rhodoliths' variability and of associated epiphytes along a large-scale latitudinal gradient. Occurrence and abundance data were collected throughout the South-western Atlantic coast (SWA) and modelled against high resolution environmental predictors extracted from Bio-Oracle. The main drivers for rhodolith occurrence were light availability and temperature at the bottom of the ocean, while abundance was explained by nitrate, temperature and current velocity. Tropical regions showed the highest abundance of rhodoliths. No latitudinal pattern was detected in the variability of epiphytes abundance. However, significant differences were found between sampled sites regarding the composition of predominant taxa. The predictors influencing such differences were temperature and nitrate. The Tropical region is abundant in species with warm-water affinities, decreasing toward warm temperate region. The expressive occurrence of tropical species not referred before for warm temperate beds indicate a plausible tropicalization event., Competing Interests: Declaration of competing interest None., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Coralline algae (Corallinophycideae) are calcifying red algae that are foundation species in euphotic marine habitats globally. In recent years, corallines have received increasing attention due to their vulnerability to global climate change, in particular ocean acidification and warming, and because of the range of ecological functions that coralline algae provide, including provisioning habitat, influencing settlement of invertebrate and other algal species, and stabilising reef structures. Many of the ecological roles corallines perform, as well as their responses to stressors, have been demonstrated to be species-specific. In order to understand the roles and responses of coralline algae, it is essential to be able to reliably distinguish individual species, which are frequently morphologically cryptic. The aim of this study was to document the diversity and distribution of coralline algae in the New Zealand region using DNA based phylogenetic methods, and examine this diversity in a broader global context, discussing the implications and direction for future coralline algal research. Using three independent species delimitation methods, a total of 122 species of coralline algae were identified across the New Zealand region with high diversity found both regionally and also when sampling at small local spatial scales. While high diversity identified using molecular methods mirrors recent global discoveries, what distinguishes the results reported here is the large number of taxa (115) that do not resolve with type material from any genus and/or species. The ability to consistently and accurately distinguish species, and the application of authoritative names, are essential to ensure reproducible science in all areas of research into ecologically important yet vulnerable coralline algae taxa., Competing Interests: The authors have declared that no competing interests exist.

The damages of Mariana's mining mud in the physiology of the brown algae Sargassum cymosum and its main epiphytic, the red algae Hypnea pseudomusciformis, were evaluated by controlled essays. Seaweeds were exposed to presence or absence of mud, isolated or in biological association, for 5 and 15 days. Measured parameters were growth rates, biochemical descriptors, and the chemical investigation of concentration and metal profile of the mud dissolved in seawater. Results showed that the highest values for metals were Al > Fe > Mn > Zn in both exposure periods. The mud also affected the growth rate with lethality in both isolated and associative treatments with H. pseudomusciformis after 15 days. According to our redundancy analysis (RDA), the profile and concentration of all metallic elements can induce different physiological responses of the organisms. We were able to observe a higher physiological adaptive ability of S. cymosum against the long-term presence of metals by the synthesis of phenolic compounds, while the deviation of metabolic routes in H. pseudomusciformis can be addressed as the main responsible for its lethality. Moreover, the presence of Hypnea in associative treatments reduces Sargassum's detoxification ability. The present results reinforce the importance of biological interaction studies in a context of physiological resilience against mining mud pollution and mutual influences of species over the individual ability to avoid oxidative stress.

Background: Intermittent dehydration caused by tidal changes is one of the most important abiotic factors that intertidal seaweeds must cope with in order to retain normal growth and reproduction. However, the underlying molecular mechanisms for the adaptation of red seaweeds to repeated dehydration-rehydration cycles remain poorly understood., Results: We chose the red seaweed Gloiopeltis furcata as a model and simulated natural tidal changes with two consecutive dehydration-rehydration cycles occurring over 24 h in order to gain insight into key molecular pathways and regulation of genes which are associated with dehydration tolerance. Transcription sequencing assembled 32,681 uni-genes (GC content = 55.32%), of which 12,813 were annotated. Weighted gene co-expression network analysis (WGCNA) divided all transcripts into 20 modules, with Coral2 identified as the key module anchoring dehydration-induced genes. Pathways enriched analysis indicated that the ubiquitin-mediated proteolysis pathway (UPP) and phosphatidylinositol (PI) signaling system were crucial for a successful response in G. furcata. Network-establishing and quantitative reverse transcription PCR (qRT-PCR) suggested that genes encoding ubiquitin-protein ligase E3 (E3-1), SUMO-activating enzyme sub-unit 2 (SAE2), calmodulin (CaM) and inositol-1,3,4-trisphosphate 5/6-kinase (ITPK) were the hub genes which responded positively to two successive dehydration treatments. Network-based interactions with hub genes indicated that transcription factor (e.g. TFIID), RNA modification (e.g. DEAH) and osmotic adjustment (e.g. MIP, ABC1, Bam1) were related to these two pathways., Conclusions: RNA sequencing-based evidence from G. furcata enriched the informational database for intertidal red seaweeds which face periodic dehydration stress during the low tide period. This provided insights into an increased understanding of how ubiquitin-mediated proteolysis and the phosphatidylinositol signaling system help seaweeds responding to dehydration-rehydration cycles.

Macroalgae play a crucial role in coastal marine ecosystems, but they are also subject to multiple challenges due to tidal and seasonal alterations. In this work, we investigated the photosynthetic response of Pyropia yezoensis to ultraviolet radiation (PAR: 400-700 nm; PAB: 280-700 nm) under changing temperatures (5, 10 and 15°C) and light intensities (200, 500 and 800 μmol photons m -2  s -1 ). Under low light intensity (200 μmol photons m -2  s -1 ), P. yezoensis showed the lowest sensitivity to ultraviolet radiation, regardless of temperature. However, higher temperatures inhibited the repair rates (r) and damage rates (k) of photosystem II (PSII) in P. yezoensis. However, under higher light intensities (500 and 800 μmol photons m -2  s -1 ), P. yezoensis showed higher sensitivity to UV radiation. Both r and the ratio of repair rate to damage rate (r:k) were significantly inhibited in P. yezoensis by PAB, regardless of temperature. In addition, higher temperatures significantly decreased the relative UV-inhibition rates, while an increased carbon fixation rate was found. Our study suggested that higher light intensities enhanced the sensitivity to UV radiation, while higher temperatures could relieve the stress caused by high light intensity and UV radiation., (© 2019 American Society for Photobiology.)

Climate change is leading to an increase of mean sea surface temperatures and extreme heat events. There is an urgent need to better understand the capabilities of marine macroalgae to adapt to these rapid changes. In this study, the responses of photosynthesis, respiration, and calcification to elevated temperature in a global warming scenario were investigated in the coralline alga Corallina officinalis. Algae were cultured for 7 weeks under 4 temperature treatments: (1) control under ambient-summer conditions (C, ~20 °C), (2) simulating a one-week heatwave of 1 °C (HW, T control +1 °C), (3) elevated temperature (+3, T control +3 °C), (4) combination of the two previous treatments (HW+3, T +3 +1 °C). After exposure at T +3 (up to a T max of ~23 °C), respiration and photosynthesis increased significantly. After 5 weeks, calcification rates were higher at elevated temperatures (T +3 and T HW+3 ) compared to T control , but at the end of the experiment (7 weeks) calcification decreased significantly at those temperatures beyond the thermal optimum (six-fold at T +3 , and three-fold at T HW+3 , respectively). The same trend was noted for all the physiological processes, suggesting that a prolonged exposure to high temperatures (7 weeks up to T +3 ) negatively affect the physiology of C. officinalis, as a possible consequence of thermal stress. A one-week heatwave of +1 °C with respect to T control (at T HW ) did not affect respiration, photosynthesis, or calcification rates. Conversely, a heatwave of 1 °C, when combined with the 3 °C increase predicted by the end of the century (at T HW+3 ), induced a reduction of physiological rates. Continued increases in both the intensity and frequency of heatwaves under anthropogenic climate change may lead to reduced growth and survival of primary producers such as C. officinalis., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

One of the most common anthropogenic impacts on river ecosystems is the effluent discharge from wastewater treatment plants. The effects of this contamination on stream biota may be intensified in Mediterranean climate regions, which comprise a drought period that leads to flow reduction, and ultimately to stagnant pools. To assess individual and combined effects of flow stagnation and sewage contamination, biofilm and gastropod grazers were used in a 5-week experiment with artificial channels to test two flow velocity treatments (stagnant flow/basal flow) and two levels of organic contamination using artificial sewage (no sewage input/sewage input). Stressors' effects were determined on biofilm total biomass and chlorophyll (Chl) content, on oxygen consumption and growth rate of the grazers (Theodoxus fluviatilis), and on the interaction grazer-biofilm given by grazer's feeding activity (i.e., biofilm consumption rate). The single effect of sewage induced an increase in biofilm biomass and Chl-a content, simultaneously increasing both grazers' oxygen consumption and their feeding activity. Diatoms showed a higher sensitivity to flow stagnation, resulting in a lower content of Chl-c. Combined stressors interacted antagonistically for biofilm total biomass, Chl-b contents, and grazers's feeding rate. The effect of sewage increasing biofilm biomass and grazing activity was reduced by the presence of flow stagnation (antagonist factor). Our findings suggest that sewage contamination has a direct effect on the functional response of primary producers and an indirect effect on primary consumers, and this effect is influenced by water flow stagnation.

Rhodolith beds, like many other marine ecosystems, are affected by climate change that is causing an increase in the magnitude and frequency of extreme high temperature events (heat waves). Unfortunately, this does not represent the sole peril for these communities, as coastal urbanization in conjunction with altered precipitation patterns can increase terrestrial-derived nutrient input. In Brazil, rhodolith beds are among the most extensive coastal benthic ecosystems, but despite their vast distribution and great ecological and economic importance, studies on the productivity of these communities and the impact of changing environmental conditions are almost non-existent. This study addressed the individual and combined effects of increases in temperature and nutrient concentration on the physiological performance of two widely distributed rhodolith species, Lithothamnion crispatum and Melyvonnea erubescens. The results showed species-specific responses in net photosynthetic performance, with no response in L. crispatum, while M. erubescens responded negatively to both increase in temperature and nutrients. In contrast, calcification in both species showed a significant decline at high temperature. No interactive effects were found between temperature and nutrients, yet their combined negative effects were additive, resulting in negative daily-integrated net productivity and a large decline in daily carbonate production in both species. This has strong implications for rhodolith bed primary productivity and carbonate production, as heat waves may potentially cause a strong decline in carbonate production (ca. 50% loss), accompanied by a severe drop in primary productivity that will be even more pronounced under high-nutrient conditions. Also, the species-specific responses to changes in temperature and nutrient concentration suggest that the magnitude of impact of these factors on rhodolith bed productivity will depend on the species dominating the community and may finally result in changes in rhodolith community composition., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: The heteroside floridoside is a primary photosynthetic product that is known to contribute to osmotic acclimation in almost all orders of Rhodophyta. However, the encoding genes and enzymes responsible for the synthesis of floridoside and its isomeric form, L- or D-isofloridoside, are poorly studied., Results: Here, four putative trehalose-6-phosphate synthase (TPS) genes, designated as PhTPS1, PhTPS2, PhTPS3, and PhTPS4, were cloned and characterized from the red alga Pyropia haitanensis (Bangiophyceae). The deduced amino acid sequence is similar to the annotated TPS proteins of other organisms, especially the UDP-galactose substrate binding sites of PhTPS1, 2, which are highly conserved. Of these, PhTPS1, 4 are involved in the biosynthesis of floridoside and isofloridoside, with isofloridoside being the main product. PhTPS3 is an isofloridoside phosphate synthase, while PhTPS2 exhibits no activity. When challenged by desiccation, high temperature, and salt stress, PhTPS members were expressed to different degrees, but the responses to thermal stress and desiccation were stronger., Conclusions: Thus, in P. haitanensis, PhTPSs encode the enzymatical activity of floridoside and isofloridoside phosphate synthase and are crucial for the abiotic stress defense response.

Continental hydrothermal systems are a dynamic component of global thermal and geochemical cycles, exerting a pronounced impact on water chemistry and heat storage. As such, these environments are commonly classified by temperature, thermal fluid ionic concentration, and pH. Terrestrial hydrothermal systems are a refuge for extremophilic organisms, as extremes in temperature, metal concentration, and pH profoundly impact microorganism assemblage composition. While numerous studies focus on Bacteria and Archaea in these environments, few focus on Eukarya-likely due to lower temperature tolerances and because they are not model organisms for understanding the evolution of early life. However, where present, eukaryotic organisms are significant members of continental hydrothermal microorganism communities. Thus, this manuscript focuses on the eukaryotic occupants of terrestrial hydrothermal systems and provides a review of the current status of research, including microbe-eukaryote interactions and suggestions for future directions.