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Ulva is the dominant genus in the green tide events and is considered to have efficient CO2 concentrating mechanisms (CCMs). However, little is understood regarding the impacts of ocean acidification on the CCMs of Ulva and the consequences of thalli's acclimation to ocean acidification in terms of responding to environmental factors. Here, we grew a cosmopolitan green alga, Ulva linza at ambient (LC) and elevated (HC) CO2 levels and investigated the alteration of CCMs in U. linza grown at HC and its responses to the changed seawater carbon chemistry and light intensity. The inhibitors experiment for photosynthetic inorganic carbon utilization demonstrated that acidic compartments, extracellular carbonic anhydrase (CA) and intracellular CA worked together in the thalli grown at LC and the acquisition of exogenous carbon source in the thalli could be attributed to the collaboration of acidic compartments and extracellular CA. Contrastingly, when U. linza was grown at HC, extracellular CA was completely inhibited, acidic compartments and intracellular CA were also down-regulated to different extents and thus the acquisition of exogenous carbon source solely relied on acidic compartments. The down-regulated CCMs in U. linza did not affect its responses to changes of seawater carbon chemistry but led to a decrease of net photosynthetic rate when thalli were exposed to increased light intensity. This decrease could be attributed to photodamage caused by the combination of the saved energy due to the down-regulated CCMs and high light intensity. Our findings suggest future ocean acidification might impose depressing effects on green tide events when combined with increased light exposure.

Copper (Cu) is an essential element for macroalgae and has been extensively studied, but the interactive effects of temperature and Cu on these organisms remain less understood. In this study, we measured the photosynthetic characteristics of Ulva lactuca exposed to varying Cu concentrations and different temperatures (10 °C, 15 °C, and 20 °C). The results indicated that at the same temperature, as the concentration of Cu increased, the relative growth rate of U. lactuca showed a decreasing trend. Under three different temperatures, the photosynthetic rate and chlorophyll content of the algae significantly decreased with the increase in Cu concentration. Under the same Cu concentration conditions, as the temperature rises, the RGR of the algae gradually increases. In the case of low Cu concentration (LCu), the net photosynthetic rate at 15 °C and 20 °C increased by 103.72% and 104.97%, respectively, compared to the rate at 10 °C. Under high Cu concentration (HCu), the net photosynthetic rate at 15 °C and 20 °C increased by 192.18% and 245.67%, respectively, compared to that at 10 °C. The pigment content showed a similar trend. These results indicated that under the same temperature conditions, high concentrations of Cu inhibited the growth of algae, while under the same Cu treatment conditions, a suitable increase in temperature could alleviate the toxic effects of Cu on the algae.

Axenic gametes of the marine green macroalga Ulva mutabilis Foyn (Ria Formosa, locus typicus) exhibit abnormal development into slow-growing callus-like colonies with aberrant cell walls. Under laboratory conditions, it was previously demonstrated that all defects in growth and thallus development can be completely abolished when axenic gametes are inoculated with a combination of two specific bacterial strains originally identified as Roseo-bacter sp. strain MS2 and Cytophaga sp. strain MS6. These bacteria release diffusible morphogenetic compounds (= morphogens), which act similar to cytokinin and auxin. To investigate the ecological relevance of the waterborne bacterial morphogens, seawater samples were collected in the Ria Formosa lagoon (Algarve, Southern Portugal) at 20 sampling sites and tidal pools to assess their morphogenetic effects on the axenic gametes of U. mutabilis. Specifically the survey revealed that sterile-filtered seawater samples can completely recover growth and morphogenesis of U. mutabilis under axenic conditions. Morphogenetic activities of free-living and epiphytic bacteria isolated from the locally very abundant Ulva species (i.e., U. rigida) were screened using a multiwell-based testing system. The most represented genera isolated from U. rigida were Alteromonas, Pseudoalteromonas and Sulfitobacter followed by Psychrobacter and Polaribacter. Several naturally occurring bacterial species could emulate MS2 activity (= induction of cell divisions) regardless of taxonomic affiliation, whereas the MS6 activity (= induction of cell differentiation and cell wall formation) was species-specific and is probably a feature of difficult-to-culture bacteria. Interestingly, isolated bacteroidetes such as Algoriphagus sp. and Polaribacter sp. could individually trigger complete Ulva morphogenesis and thus provide a novel mode of action for bacterial-induced algal development. This study also highlights that the accumulation of algal growth factors in a shallow water body separated from the open ocean by barrier islands might have strong implications to, for example, the wide usage of natural coastal seawater in algal (land based) aquacultures of Ulva.

Generally unseen and infrequently measured, submarine groundwater discharge (SGD) can transport potentially large loads of nutrients and other land-based contaminants to coastal ecosystems. To examine this linkage we employed algal bioassays, benthic community analysis, and geochemical methods to examine water quality and community parameters of nearshore reefs adjacent to a variety of potential, land-based nutrient sources on Maui. Three common reef algae, Acanthophora spicifera, Hypnea musciformis, and Ulva spp. were collected and/or deployed at six locations with SGD. Algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with nutrient and δ15N-nitrate values of coastal groundwater and nearshore surface water at all locations. Benthic community composition was estimated for ten 10-m transects per location. Reefs adjacent to sugarcane farms had the greatest abundance of macroalgae, low species diversity, and the highest concentrations of N in algal tissues, coastal groundwater, and marine surface waters compared to locations with low anthropogenic impact. Based on δ15N values of algal tissues, we estimate ca. 0.31 km2 of Kahului Bay is impacted by effluent injected underground at the Kahului Wastewater Reclamation Facility (WRF); this region is barren of corals and almost entirely dominated by colonial zoanthids. Significant correlations among parameters of algal tissue N with adjacent surface and coastal groundwater N indicate that these bioassays provided a useful measure of nutrient source and loading. A conceptual model that uses Ulva spp. tissue δ15N and N % to identify potential N source(s) and relative N loading is proposed for Hawai'i. These results indicate that SGD can be a significant transport pathway for land-based nutrients with important biogeochemical and ecological implications in tropical, oceanic islands.

The pollution by heavy metals in coastal waters has gradually intensified due to industrial development. In this study, physiological responses of Ulva lactuca , one of the most common green seaweeds with important ecological and economic value in the global intertidal zone, to acute copper stress were investigated. Results showed that an increase in copper ions concentration significantly inhibited photosynthetic activity and inorganic nitrogen utilization by U. lactuca but, increased its respiration. Copper stress limited the activity and gene expression of enzymes related to carbon and nitrogen assimilation of U. lactuca . Under moderate copper stress, U. lactuca had higher soluble carbohydrate and soluble protein contents, whereas under high copper stress, these components decreased sharply. Copper stress increased malonaldehyde content, and relative electrical conductivity in U. lactuca , but changes in antioxidant enzyme activities were not significant and even slightly decreased. Moreover, the contents of 8-hydroxy-deoxyguanosine and polyADP ribose polymerase in U. lactuca increased by high Cu 2+ concentration culture, indicating that oxidative damage caused by high Cu 2+ level involved its DNA damage and interfered with DNA repair in the alga. Copper stress seemed to be more damaging to the carbon assimilation process of U. lactuca , resulting in weakened resistance to copper stress and lower growth rate. This reflected the threat of coastal high copper stress to intertidal biodiversity. This provided ecological reference for the assessment of offshore heavy metal pollution represented by copper.

Ulva intestinalis (UI) is widely available edible seaweed and has potential to be introduced as functional food items in Bangladesh. However, potential health hazards of this seaweed with biotoxicity assays and its relation to heavy metal contents were not evaluated previously. With these objectives, toxic effects of UI collected from floating raft culture in Monkhali Beach was evaluated using various organisms such as Chlorella vulgaris , Artemia salina , Daphnia magna , and Lactuca sativa . In relation to this effects, heavy metal concentrations (Fe, Cr, Ni, Cu, Zn, Pb, Cd, and As) and its potential health hazards were subsequently analyzed. The results showed that UI water extract had positive effects on the survivability and growth of the all-test organisms over different time periods, with minimal LC50 values, indicating no toxic to tested organisms. However, increased levels of total dissolved solids and electrical conductivity were observed as extract concentrations increased but considered to be safe below 5 mg kg −1 , as compared to control. Moreover, Fe, Cr, Ni, Cu and Zn (43.60, 0.10, 0.44, 0.07, 0.27 and 0.13 mg kg −1 of dry weight, respectively) in UI were found to be low levels compared to previous studies, in addition, Cd and As remained not detected. No significant health risk (HQ < 1) and target carcinogenic risk were found. Therefore, UI could be utilized as functional foods or nutraceuticals for health-conscious consumers of Bangladesh without having potential risks.

Main conclusion Benzopyrene is rapidly incorporated and metabolized, and induces oxidative stress and activation of antioxidant enzymes, and CYP450 and GST metabolizing enzymes in Ulva lactuca . To analyze absorption and metabolism of benzo[ a ]pyrene (BaP) in Ulva lactuca , the alga was cultivated with 5 µM of BaP for 72 h. In the culture medium, BaP level rapidly decreased reaching a minimal level at 12 h and, in the alga, BaP level increased until 6 h, remained stable until 24 h, and decreased until 72 h indicating that BaP is being metabolized in U. lactuca. In addition, BaP induced an initial increase in hydrogen peroxide decreasing until 24 h, superoxide anions level that remained high until 72 h, and lipoperoxides that initially increased and decreased until 72 h, showing that BaP induced oxidative stress. Activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (AP), glutathione reductase (GR) and glutathione peroxidase (GP) were increased, whereas dehydroascorbate reductase (DHAR) activity was unchanged. The level of transcripts encoding these antioxidant enzymes was increased, but transcripts encoding DHAR remained unchanged. Interestingly, the activity of glutathione-S-transferase (GST) was also increased, and inhibitors of cytochrome P450 (CYP450) and GST activities enhanced the level of BaP in algal tissue, suggesting that these enzymes participate in BaP metabolism.

To analyze the copper-induced cross talk among calcium, nitric oxide (NO), and hydrogen peroxide (H₂O₂) and the calciumdependent activation of gene expression, the marine alga Ulva compressa was treated with the inhibitors of calcium channels, ned-19, ryanodine, and xestospongin C, of chloroplasts and mitochondrial electron transport chains, 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and antimycin A, of pyruvate dehydrogenase, moniliformin, of calmodulins, N-(6-aminohexyl)-5-chloro-1-naphtalene sulfonamide, and of calcium-dependent protein kinases, staurosporine, as well as with the scavengers of NO, 2-(4-carboxypheny1)-4,4,5,5-tetramethylimidazoline-1-oxy1-3-oxide, and of H₂O₂, ascorbate, and exposed to a sublethal concentration of copper (10 µm) for 24 h. The level of NO increased at 2 and 12 h. The first peak was inhibited by ned-19 and 3-(2,3-dichloropheny1)-1, 1-dimethylurea and the second peak by ned-19 and antimycin A, indicating that NO synthesis is dependent on calcium release and occurs in organdíes. The level of H₂O₂ increased at 2, 3, and 12 h and was inhibited by ned-19, ryanodine, xestospongin C, and moniliformin, indicating that H₂O₂ accumulation is dependent on calcium release and Krebs cycle activity In addition, pyruvate dehydrogenase, 2-oxoxglutarate dehydrogenase, and isocitrate dehydrogenase activities of the Krebs cycle increased at 2, 3,12, and/or 14 h, and these increases were inhibited in vitro by EGTA, a calcium chelating agent. Calcium release at 2, 3, and 12 h was inhibited by 2-(4-carboxypheny1)-4,4,5,5-tetramethylimidazoline-1-oxy1-3-oxide and ascorbate, indicating activation by NO and H₂O₂. In addition, the level of antioxidant protein gene transcripts decreased with N-(6-aminohexyl)-5-chloro-1-naphtalene sulfonamide and staurosporine. Thus, there is a copper-induced cross talk among calcium, H₂O₂, and NO and a calcium-dependent activation of gene expression involving calmodulins and calcium-dependent protein kinases.

Background The marine alga Ulva compressa is the dominant species in copper-polluted coastal areas in northern Chile. It has been shown that the alga tolerates micromolar concentrations of copper and accumulates copper at the intracellular level. Transcriptomic analyses were performed using total RNA of the alga cultivated with 10 μ M copper for 0, 1, 3 and 5 days using RNA-seq in order to identify processes involved in copper tolerance. Results The levels of transcripts encoding proteins belonging to Light Harvesting Complex II (LHCII), photosystem II (PSII), cytochrome b6f, PSI, LHCI, ATP synthase and proteins involved in repair of PSII and protection of PSI were increased in the alga cultivated with copper. In addition, the level of transcripts encoding proteins of mitochondrial electron transport chain, ATP synthase, and enzymes involved in C, N and S assimilation were also enhanced. The higher percentages of increase in the level of transcripts were mainly observed at days 3 and 5. In contrast, transcripts involved protein synthesis and degradation, signal transduction, and replication and DNA repair, were decreased. In addition, net photosynthesis and respiration increased in the alga cultivated with copper, mainly at days 1 to 3. Furthermore, the activities of enzymes involved in C, N and S assimilation, rubisco, glutamine synthase and cysteine synthase, respectively, were also increased, mainly at days 1 and 3. Conclusions The marine alga U. compressa tolerates copper excess through a concomitant increase in expression of proteins involved in photosynthesis, respiration, and C, N and S assimilation, which represents an exceptional mechanism of copper tolerance.