Effects of climate change factors on marine macroalgae: A review

Macroalgae Bioplastics: A Sustainable Shift to Mitigate the Ecological Impact of Petroleum-Based Plastics

The surge in global utilization of petroleum-based plastics, which notably heightened during the COVID-19 pandemic, has substantially increased its harm to ecosystems. Considering the escalating environmental impact, a pivotal shift towards bioplastics usage is imperative. Exploring and implementing bioplastics as a viable alternative could mitigate the ecological burden posed by traditional plastics. Macroalgae is a potential feedstock for the production of bioplastics due to its abundance, fast growth, and high cellulose and sugar content. Researchers have recently explored various methods for extracting and converting macroalgae into bioplastic. Some of the key challenges in the production of macroalgae bioplastics are the high costs of large-scale production and the need to optimize the extraction and conversion processes to obtain high-quality bioplastics. However, the potential benefits of using macroalgae for bioplastic production include reducing plastic waste and greenhouse gas emissions, using healthier materials in various life practices, and developing a promising area for future research and development. Also, bioplastic provides job opportunities in free enterprise and contributes to various applications such as packaging, medical devices, electronics, textiles, and cosmetics. The presented review aims to discuss the problem of petroleum-based plastic, bioplastic extraction from macroalgae, bioplastic properties, biodegradability, its various applications, and its production challenges.

Characterization of a novel γ-type carbonic anhydrase, Sjγ-CA2, in Saccharina japonica: Insights into carbon concentration mechanism in macroalgae

Carbonic anhydrase (CA) is a crucial component of CO2-concentrating mechanism (CCM) in macroalgae. In Saccharina japonica, an important brown seaweed, 11 CAs, including 5 α-, 3 β-, and 3 γ-CAs, have been documented. Among them, one α-CA and one β-CA were localized in the periplasmic space, one α-CA was found in the chloroplast, and one γ-CA was situated in mitochondria. Notably, the known γ-CAs have predominantly been identified in mitochondria. In this study, we identified a chloroplastic γ-type CA, Sjγ-CA2, in S. japonica. Based on the reported amino acid sequence of Sjγ-CA2, the epitope peptide for monoclonal antibody production was selected as 165 Pro-305. After purification and specificity identification, anti-SjγCA2 monoclonal antibody was employed in immunogold electron microscopy. The results illustrated that Sjγ-CA2 was localized in the chloroplasts of both gametophytes and sporophytes of S. japonica. Subsequently, immunoprecipitation coupled with LC-MS/MS analysis revealed that Sjγ-CA2 mainly interacted with photosynthesis-related proteins. Moreover, the first 65 amino acids at N-terminal of Sjγ-CA2 was identified as the chloroplast transit peptide by the transient expression of GFP-SjγCA2 fused protein in tabacco. Real-time PCR results demonstrated an up-regulation of the transcription of Sjγ-CA2 gene in response to high CO2 concentration. These findings implied that Sjγ-CA2 might contribute to minimizing the leakage of CO2 from chloroplasts and help maintaining a high concentration of CO2 around Rubisco.

Acclimation of intertidal macroalgae Ulva prolifera to UVB radiation: the important role of alternative oxidase

BACKGROUND

Solar radiation is primarily composed of ultraviolet radiation (UVR, 200 - 400 nm) and photosynthetically active radiation (PAR, 400 - 700 nm). Ultraviolet-B (UVB) radiation accounts for only a small proportion of sunlight, and it is the primary cause of plant photodamage. The use of chlorofluorocarbons (CFCs) as refrigerants caused serious ozone depletion in the 1980s, and this had led to an increase in UVB. Although CFC emissions have significantly decreased in recent years, UVB radiation still remains at a high intensity. UVB radiation increase is an important factor that influences plant physiological processes. Ulva prolifera, a type of macroalga found in the intertidal zone, is intermittently exposed to UVB. Alternative oxidase (AOX) plays an important role in plants under stresses. This research examines the changes in AOX activity and the relationships among AOX, photosynthesis, and reactive oxygen species (ROS) homeostasis in U. prolifera under changes in UVB and photosynthetically active radiation (PAR).

RESULTS

UVB was the main component of solar radiation impacting the typical intertidal green macroalgae U. prolifera. AOX was found to be important during the process of photosynthesis optimization of U. prolifera due to a synergistic effect with non-photochemical quenching (NPQ) under UVB radiation. AOX and glycolate oxidase (GO) worked together to achieve NADPH homeostasis to achieve photosynthesis optimization under changes in PAR + UVB. The synergism of AOX with superoxide dismutase (SOD) and catalase (CAT) was important during the process of ROS homeostasis under PAR + UVB.

CONCLUSIONS

AOX plays an important role in the process of photosynthesis optimization and ROS homeostasis in U. prolifera under UVB radiation. This study provides further insights into the response of intertidal macroalgae to solar light changes.

Biotechnological Potential of Macroalgae during Seasonal Blooms for Sustainable Production of UV-Absorbing Compounds

Marine macroalgae (seaweeds) are important primary global producers, with a wide distribution in oceans around the world from polar to tropical regions. Most of these species are exposed to variable environmental conditions, such as abiotic (e.g., light irradiance, temperature variations, nutrient availability, salinity levels) and biotic factors (e.g., grazing and pathogen exposure). As a result, macroalgae developed numerous important strategies to increase their adaptability, including synthesizing secondary metabolites, which have promising biotechnological applications, such as UV-absorbing Mycosporine-Like Amino Acid (MAAs). MAAs are small, water-soluble, UV-absorbing compounds that are commonly found in many marine organisms and are characterized by promising antioxidative, anti-inflammatory and photoprotective properties. However, the widespread use of MAAs by humans is often restricted by their limited bioavailability, limited success in heterologous expression systems, and low quantities recovered from the natural environment. In contrast, bloom-forming macroalgal species from all three major macroalgal clades (Chlorophyta, Phaeophyceae, and Rhodophyta) occasionally form algal blooms, resulting in a rapid increase in algal abundance and high biomass production. This review focuses on the bloom-forming species capable of producing pharmacologically important compounds, including MAAs, and the application of proteomics in facilitating macroalgal use in overcoming current environmental and biotechnological challenges.

Mariculture structure adjustment to achieve China's carbon neutrality and mitigate climate change

China is responsible for the biggest shellfish and macroalgae production in the world. In this study, comprehensive methods were used to assess the CO2 release and sequestration by maricultured shellfish and macroalgae in China. Through considering CaCO3 production and CO2 release coefficient (Φ, moles of CO2 released per mole of CaCO3 formed) in different waters, we find that cultured shellfish released 0.741 ± 0.008 Tg C yr-1 through calcification based on the data of 2016-2020. In addition to calcification, maricultured shellfish released 0.580 ± 0.004 Tg C yr-1 by respiration. Meanwhile, shellfish sequestered 0.145 ± 0.001 and 0.0387 ± 0.0004 Tg C yr-1 organic carbon in sediments and shells, respectively. Therefore, the net released CO2 by maricultured shellfish was 1.136 ± 0.011 Tg C yr-1, which is about four times higher than that maricultured macroalgae could sequester (0.280 ± 0.010 Tg C yr-1). To achieve carbon neutrality within the mariculture system, shellfish culture may need to be restricted and meanwhile the expansion of macroalgae cultivation should be carried out. The mean carbon sequestration rate of seven kinds of macroalgae was 174 ± 6 g m-2 yr-1 while some cultivated macroalgae had higher CO2 sequestration rates, e.g. 356 ± 24 g C m-2 yr-1 for Gracilariopsis lemaneiformis and 331 ± 17 g C m-2 yr-1 for Undaria pinnatifida. In scenario 0.5 (CCUS (Carbon Capture, Utilization and Storage) sequesters 0.5 Gt CO2 per year), using macroalgae culture cannot achieve China's carbon neutrality by 2060 but in scenarios 1.0 and 1.5 (CCUS sequesters 1.0 and 1.5 Gt CO2 per year, respectively) it is feasible to achieve carbon neutrality using some macroalgae species with high carbon sequestration rates. This study provides important insights into how to develop mariculture in the context of carbon-neutrality and climate change mitigation.

Distribution of a canopy-forming alga along the Western Atlantic Ocean under global warming: The importance of depth range

Sargassum species are among the most important canopy-forming algae in the Western Atlantic Ocean (WAO), providing habitat for many species and contributing to carbon uptake. The future distribution of Sargassum and other canopy-forming algae has been modelled worldwide, indicating that their occurrence in many regions is threatened by increased seawater temperature. Surprisingly, despite the recognized variation in vertical distribution of macroalgae, these projections generally do not evaluate their results at different depth ranges. This study aimed to project the potential current and future distributions of the common and abundant benthic Sargassum natans in the WAO (from southern Argentina to eastern Canada), under RCP 4.5 and 8.5 climate change scenarios, through an ensemble SDM approach. Possible changes between present and future distributions were assessed within two depth ranges, namely areas up to 20 m and areas up to 100 m depth. Our models forecast different distributional trends for benthic S. natans depending on the depth range. Up to 100 m, suitable areas for the species will increase by 21% under RCP 4.5, and by 15% under RCP 8.5, when compared to the potential current distribution. On the contrary, up to 20 m, suitable areas for the species will decrease by 4% under RCP 4.5 and by 14% under RCP 8.5, when compared to the potential current distribution. Under the worst scenario, losses up to 20 m depth will affect approximately 45,000 km2 of coastal areas across several countries and regions of WAO, with likely negative consequences for the structure and dynamics of coastal ecosystems. These findings highlight the importance of considering different depth ranges when building and interpreting predictive models of the distribution of habitat-forming subtidal macroalgae under climate change.

A Sensitive Fluorescence Polarization Immunoassay for the Rapid Detection of Okadaic Acid in Environmental Waters

In this study, a homogeneous fluorescence polarization immunoassay (FPIA) for the detection of hazardous aquatic toxin okadaic acid (OA) contaminating environmental waters was for the first time developed. A conjugate of the analyte with a fluorophore based on a fluorescein derivative (tracer) was synthesized, and its interaction with specific anti-OA monoclonal antibodies (MAbs) was tested. A MAbs-tracer pair demonstrated highly affine immune binding (KD = 0.8 nM). Under optimal conditions, the limit of OA detection in the FPIA was 0.08 ng/mL (0.1 nM), and the working range of detectable concentrations was 0.4-72.5 ng/mL (0.5-90 nM). The developed FPIA was approbated for the determination of OA in real matrices: river water and seawater samples. No matrix effect of water was observed; therefore, no sample preparation was required before analysis. Due to this factor, the entire analytical procedure took less than 10 min. Using a compact portable fluorescence polarization analyzer enables the on-site testing of water samples. The developed analysis is very fast, easy to operate, and sensitive and can be extended to the determination of other aquatic toxins or low-molecular-weight water or food contaminants.

Temperature and high nutrients enhance hypo-salinity tolerance of the bloom forming green alga, Ulva prolifera

The response of seaweeds to environmental stressors can be population-specific, and be related to the regime of their habitats. To explore the growth and physiological responses of Ulva prolifera, two strains of this alga (Korean and Chinese strains) were studied under an interaction of temperature (20 and 25 °C), nutrients (low nutrients: 50 μM of nitrate and 5 μM of phosphate; high nutrients: 500 μM of nitrate and 50 μM of phosphate) and salinity (20, 30 and 40 psu). The lowest growth rates of both strains were observed at 40 psu of salinity, independent of temperature and nutrient levels. At 20 °C and low nutrients condition, the carbon: nitrogen (C: N) ratio and growth rate in the Chinese strain were increased by 31.1% and 21.1% at a salinity of 20 psu in comparison to the salinity of 30 psu, respectively. High nutrients decreased the ratio of C:N in both strains with increasing tissue N content. At the same time, high nutrients also increased soluble protein and pigments contents, as well as photosynthetic and growth rates in both strains at the same salinity levels at 20 °C. Under 20 °C and high nutrients conditions, the growth rates and C:N ratio of both strains were significantly decreased with increasing salinity. The pigment, soluble protein and tissue N showed an inverse trend with the growth rate at all conditions. Moreover, the higher temperature of 25 °C inhibited the growth in both strains regardless of nutrients levels. The temperature of 25 °C enhanced the contents of tissue N and pigments in the Chinese strain only at the low nutrients level. The interaction of high nutrients and 25 °C led to the accumulation of tissue N and pigment contents in both strains under all salinity conditions compared to the 20 °C and high nutrients level. The temperature of 25 °C and high nutrients decreased the growth rate in the Chinese strain at both salinities of 30 and 40 psu more than the 20 °C, and low nutrients level at the same salinity. These results suggest that the Ulva blooms caused by the Chinese strain were more impacted at hypo-salinity levels compared to the Korean strain. Eutrophic or high nutrients level enhanced the salinity tolerance in both strains of U. prolifera. There will be a decline of U. prolifera blooms of the Chinese strain at hyper-salinity levels.

Integrated transcriptome and metabolome analysis reveals molecular responses of spider to single and combined high temperature and drought stress

High temperature and drought are abiotic stresses restricting many arthropods' survival and growth. Wolf spiders are poikilothermic arthropods that are vital in managing insects and pests. Nonetheless, investigating changes in spiders under temperature and drought stress are limited, especially at the molecular and gene expression levels. The study found that the combined effects of high temperature and drought stress significantly reduced survival rates and raised superoxide dismutase and malondialdehyde levels in the wolf spider Pardosa pseudoannulata. An integrated transcriptome and metabolome analysis showed that differentially expressed genes and metabolites were highly enriched in pathways involved in the proteolysis and oxidation-reduction process. The gene expression profiles displayed that heat shock protein (HSP) families (i.e., small heat shock protein, HSP70, HSP90, and HSP beta protein) were up-regulated under temperature and/or drought stresses. Additionally, a conjoint analysis revealed that under the combined stress, several important enzymes, including maltase-glucoamylase, glycerol-6-phosphate transporter, alanine-glyoxylate transaminase, and prostaglandin-H2 D-isomerase, were altered, affecting the metabolism of starch, sucrose, amino acids, and arachidonic acid. The protein interaction network further confirmed that under the combined stress, metabolic processes, peptide metabolic processes, and ATP generation from ADP were up-regulated, indicating that spiders could accelerate the metabolism of carbohydrates and proteins to combat stress and maintain homeostasis. Overall, this work showed that exposure to a combination of pressures might cause distinct defensive reactions in spiders and offered novel perspectives to research the molecular underpinnings of spider adaptation to a changing climate.

Transcriptome analysis reveals the molecular mechanisms of adaptation to high temperatures in Gracilaria bailinae

Global warming causes great thermal stress to macroalgae and those species that can adapt to it are thought to be better able to cope with warmer oceans. Gracilaria bailinae, a macroalgae with high economic and ecological values, can survive through the hot summer in the South China Sea, but the molecular mechanisms underlying its adaptation to high temperatures are unclear. To address this issue, the present study analyzed the growth and transcriptome of G. bailinae after a 7-day exposure to 15°C (LT: low temperature), 25°C (MT: middle temperature), and 35°C (HT: high temperature). Growth analysis showed that the HT group had the highest relative growth rate (RGR = 2.1%) with the maximum photochemical quantum yield of PSII (F _v/F _m = 0.62) remaining within the normal range. Transcriptome analysis showed more differentially expressed genes (DEGs) in the comparison between MT and HT groups than in that between MT and LT, and most of these DEGs tended to be downregulated at higher temperatures. The KEGG pathway enrichment analysis showed that the DEGs were mainly enriched in the carbohydrate, energy, and lipid metabolisms. In addition, the genes involved in NADPH and ATP synthesis, which are associated with photosynthesis, the Calvin cycle, pyruvate metabolism, and the citrate cycle, were downregulated. Downregulation was also observed in genes that encode enzymes involved in fatty acid desaturation and alpha-linolenic acid metabolism. In summary, G. bailinae regulated the synthesis of NADPH and ATP, which are involved in the above-mentioned processes, to reduce unnecessary energy consumption, and limited the synthesis of enzymes in the metabolism of unsaturated fatty acids and alpha-linolenic acid to adapt to high environmental temperatures. The results of this study improve our understanding of the molecular mechanisms underlying the adaptation of G. bailinae to high temperatures.

Elevated CO2 modulates the physiological responses of Thalassiosira pseudonana to ultraviolet radiation

Diatoms account for a large proportion of marine primary productivity, they tend to be the predominant species in the phytoplankton communities in the surface ocean with frequent and large light fluctuations. To understand the impacts of increased CO2 on diatoms' capacity in exploitation of variable solar radiation, we cultured a model diatom Thalassiosira pseudonana with 400 or 1000ppmv CO2 and exposed it to high photosynthetically active radiation (PAR) alone or PAR plus ultraviolet radiation (UVR) to examine its physiological performances. The results showed that the maximum photochemical efficiency (Fv/fm) was significantly reduced by high PAR and PAR + UVR in T. pseudonana, UVR-induced inhibition on PSII activity was exacerbated by high CO2. PSII activity drops coincide approximately with PsbA content in the cells exposed to high PAR or PAR + UVR, which was pronounced at high CO2. The removal of PsbD in T. pseudonana cells declined under high CO2 during UVR exposure, limiting the repair capacity of PSII. In addition, high CO2 reversed the induction of energy-dependent form of NPQ by UVR to the increase of Y(No), indicating the severe damage of the photoprotective reactions. Our findings suggest that the adverse impacts of UVR on PSII function of T. pseudonana were aggravated by the elevated CO2 through modulating its capacity in repair and protection, which thereby would influence its abundance and competitiveness in phytoplankton communities.

Assessing the potential for demographic restoration and assisted evolution to build climate resilience in coral reefs

Interest is growing in developing conservation strategies to restore and maintain coral reef ecosystems in the face of mounting anthropogenic stressors, particularly climate warming and associated mass bleaching events. One such approach is to propagate coral colonies ex situ and transplant them to degraded reef areas to augment habitat for reef-dependent fauna, prevent colonization from spatial competitors, and enhance coral reproductive output. In addition to such "demographic restoration" efforts, manipulating the thermal tolerance of outplanted colonies through assisted relocation, selective breeding, or genetic engineering is being considered for enhancing rates of evolutionary adaptation to warming. Although research into such "assisted evolution" strategies has been growing, their expected performance remains unclear. We evaluated the potential outcomes of demographic restoration and assisted evolution in climate change scenarios using an eco-evolutionary simulation model. We found that supplementing reefs with pre-existing genotypes (demographic restoration) offers little climate resilience benefits unless input levels are large and maintained for centuries. Supplementation with thermally resistant colonies was successful at improving coral cover at lower input levels, but only if maintained for at least a century. Overall, we found that, although demographic restoration and assisted evolution have the potential to improve long-term coral cover, both approaches had a limited impact in preventing severe declines under climate change scenarios. Conversely, with sufficient natural genetic variance and time, corals could readily adapt to warming temperatures, suggesting that restoration approaches focused on building genetic variance may outperform those based solely on introducing heat-tolerant genotypes.

Effects of Glyphosate-Based Herbicide on Primary Production and Physiological Fitness of the Macroalgae Ulva lactuca

The use of glyphosate-based herbicides (GBHs) worldwide has increased exponentially over the last two decades increasing the environmental risk to marine and coastal habitats. The present study investigated the effects of GBHs at environmentally relevant concentrations (0, 10, 50, 100, 250, and 500 μg·L⁻¹) on the physiology and biochemistry (photosynthesis, pigment, and lipid composition, antioxidative systems and energy balance) of Ulva lactuca, a cosmopolitan marine macroalgae species. Although GBHs cause deleterious effects such as the inhibition of photosynthetic activity, particularly at 250 μg·L⁻¹, due to the impairment of the electron transport in the chloroplasts, these changes are almost completely reverted at the highest concentration (500 μg·L⁻¹). This could be related to the induction of tolerance mechanisms at a certain threshold or tipping point. While no changes occurred in the energy balance, an increase in the pigment antheraxanthin is observed jointly with an increase in ascorbate peroxidase activity. These mechanisms might have contributed to protecting thylakoids against excess radiation and the increase in reactive oxygen species, associated with stress conditions, as no increase in lipid peroxidation products was observed. Furthermore, changes in the fatty acids profile, usually attributed to the induction of plant stress response mechanisms, demonstrated the high resilience of this macroalgae. Notably, the application of bio-optical tools in ecotoxicology, such as pulse amplitude modulated (PAM) fluorometry and laser-induced fluorescence (LIF), allowed separation of the control samples and those treated by GBHs in different concentrations with a high degree of accuracy, with PAM more accurate in identifying the different treatments.

Photosynthetic Characteristics of Macroalgae Ulva fasciata and Sargassum thunbergii in the Daya Bay of the South China Sea, with Special Reference to the Effects of Light Quality

The changes in underwater light in field usually occur not only in intensity but in spectrum, affecting the photophysiology of marine photoautotrophs. In this study, we comparably examined the photosynthesis of two dominating macroalgae in the Daya Bay, Chlorophyta Ulva fasciata and Phaeophyta Sargassum thunbergii, under white light, as well as under red, green and blue light. The results showed that the net photosynthetic O2 evolution rate (Pn) of U. fasciata under field light increased from 25.2 ± 3.06 to 168 ± 1.2 µmol O2 g FW−1 h−1 from dawn to noon, then decreased to 42.4 ± 0.20 µmol O2 g FW−1 h−1 at dusk. The Pn of S. thunbergii exhibited a similar diel change pattern, but was over 50% lower than that of U. fasciata. The maximal photosynthetic rate (Pmax) of U. fasciata derived from the photosynthesis vs. irradiance curve under white light (i.e., 148 ± 15.8 µmol O2 g FW−1 h−1) was ~30% higher than that under blue light, while the Pmax of S. thunbergii under white light (i.e., 39.2 ± 3.44 µmol O2 g FW−1 h−1) was over 50% lower than that under red, green and blue light. Furthermore, the daily primary production (PP) of U. fasciata was ~20% higher under white than blue light, while that of S. thunbergii was 34% lower, indicating the varied light spectral compositions influence algal photosynthetic ability and thus their primary production in field, and such an influence is species-specific.

Increased CO2 Relevant to Future Ocean Acidification Alleviates the Sensitivity of a Red Macroalgae to Solar Ultraviolet Irradiance by Modulating the Synergy Between Photosystems II and I

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO₂ levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO₂ concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O₂-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (F _k) of Kautsky curves relative to the amplitude of F _J-F _o (W_k) and a decrease of the maximum quantum yield of PSII (F _v/F _m). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO₂ assimilation. When the algal thalli were grown under increased CO₂ and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO₂ levels and OA.

Ocean acidification exacerbates copper toxicity in both juvenile and adult stages of the green tide alga Ulva linza

The toxicity of heavy metals to coastal organisms can be modulated by changes in pH due to progressive ocean acidification (OA). We investigated the combined impacts of copper and OA on different stages of the green macroalga Ulva linza, which is widely distributed in coastal waters, by growing the alga under the addition of Cu (control, 0.125 (medium, MCu), and 0.25 (high) μM, HCu) and elevated pCO₂ of 1,000 μatm, predicted in the context of global change. The relative growth rates decreased significantly in both juvenile and adult thalli at HCu under OA conditions. The net photosynthetic and respiration rates, as well as the relative electron transfer rates for the adult thalli, also decreased under the combined impacts of HCu and OA, although no significant changes in the contents of photosynthetic pigments were detected. Our results suggest that Cu and OA act synergistically to reduce the growth and photosynthetic performance of U. linza, potentially prolonging its life cycle.