Abstract:Algae have important strategic significance in optimizing food supply systems, promoting carbon sink fishery development, and enhancing marine economic competitiveness owing to their efficient biosynthetic capability, rich nutritional value, and ecological regulatory role. This article analyzes the current development status and main challenges faced by China's algae industry from the perspective of the "All-Encompassing Approach to Food,” and propose pathways and countermeasures to promote high-quality development of industry. Currently, China's algal industry has demonstrated steady overall growth, developing into a large-scale, intensive production system. Significant progress have been made in developing superior germplasm, expanding cultivation scales, upgrading products, and growing markets. However, some challenges still persist, such as limited innovation in stress-resistant germplasm, inadequate disease prevention and control systems, low levels of mechanization and automation in cultivation, short industrial chains, limited scientific research investment, outdated deep processing technology, and underdeveloped quality and safety supervision systems. To develop and expand the algal industry, it is necessary to strengthen policy support, accelerate breakthroughs in core and key technologies, and promote coordinated industry chains, green and low-carbon transformation, brand building, and global market integration.

Abstract:Algae, a blue resource with high nutritional value and environmental regulation functions, have cell walls and extracellular matrices rich in various functional groups. These characteristics enable algae to accumulate harmful heavy metals, such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) easily, posing potential food safety risks. In this review, we cover the sources, accumulation mechanisms, and speciation of heavy metals in algae, focusing on the principles, effects, and applicability of major removal techniques, including physical (heat treatment, ultrasound, and high pressure), chemical (acid washing, chelating agents, and natural deep eutectic solvents), biological (fermentation, enzymatic hydrolysis, and microbial conversion), and adsorption methods. In addition, the potential applications of combined multi-technique approaches are explored. Current studies face challenges such as an insufficient understanding of speciation, difficulty in balancing efficient removal and nutrient retention, and the underdevelopment of green processing routes and industrial support systems. Future research should focus on multiscale mechanistic analysis, the development of green and mild processes, and the strengthening of industrial application frameworks, aiming to enhance the food safety of algae products and promote high-quality industrial development.

Abstract:To investigate the growth dynamics and carbon sequestration effects of kelp under different cultivation densities, this study used the traditional cultivation density of 100 ropes per raft (K0) in Sanggou Bay as the control group. During the tender stage of kelp (January), the cultivation density was reduced to 67 ropes per raft (K1) and 50 ropes per raft (K2), respectively. Methods such as on-site instrument monitoring, in-situ perforation sampling, UV-Vis absorption spectroscopy, and organic carbon analysis were employed to measure the light attenuation rate, absorption spectra of colored dissolved organic matter (CDOM) in surface seawater, elongation rate, and thickening rate of kelp blades in different density areas of Sanggou Bay. Differences in kelp growth dynamics under varying densities were analyzed, and carbon sequestration under different cultivation densities were estimated. The results showed that: (1) The light attenuation rates in the 0–1 m depth layer differed significantly among the three cultivation density areas. (2) The highest blade elongation rate in all three density groups occurred during the E3 stage (January–March), while the highest thickening rate appeared during the E4 stage (March–April). By the end of the experiment (June), the wet weight per individual kelp in the K1 and K2 groups was significantly greater than that in K0, and the total wet weight of kelp cultivation in the K1 group was significantly higher than that in the other two groups. (3) The absorption coefficient a(355) of colored dissolved organic matter (CDOM) at 355 nm in the K0 and K1 cultivation areas was significantly higher than that in K2 from March to June, while the SUVA254 values at the K0 and K1 stations in March and June were significantly higher than those at K2. By the end of the experiment, the total carbon pool contribution of the K1 group increased by approximately 15.19% compared with K0. The findings indicate that reducing kelp cultivation density to a reasonable level can significantly enhance kelp growth, yield, and the carbon sequestration of the cultivation system. This provides data support and technical references for developing models to enhance carbon sinks through large macroalgae cultivation in shallow seas.

Abstract:Pyropia haitanensis accounts for approximately 75% of total dried laver production in China. In recent years, advances in cultivation technologies and increasing economic returns, the expansion of cultivation areas has created an urgent demand for high-quality cultivars. The life cycle of P. haitanensis consists of two distinct phases, a filamentous sporophytic stage (conchocelis) and a foliose gametophytic stage, corresponding to indoor seedling propagation and offshore farming, respectively. The primary objective of artificial indoor seedling production is to generate conchospores and propagules for marine cultivation. Therefore, achieving the synchronized development of mature conchosporangial branches and the efficient release of conchospores are critical for ensuring high yield and quality in the subsequent blade stage. Currently, all five nationally certified P. haitanensis cultivars are pure lines established through the transplantation of free-living conchocelis into shells. Free-living conchocelis cultivation enables substrate-independent propagation, reduces dependence on shell substrates and spatial requirements, and minimizes contamination by epiphytic algae. However, these improved cultivars still face challenges related to asynchronous conchocelis maturation and low conchospore release efficiency—commonly referred to as the "difficulty in breeding elite strains" when using free-living conchocelis. Therefore, the key to overcoming this challenge is to precisely regulate the developmental process of free-living conchocelis following transplantation onto shells (seeding), with a particular emphasis on the coordinated control of conchosporangial branch formation and conchospore release. A systematic understanding of the underlying developmental dynamics and molecular regulatory mechanisms is essential for establishing a robust theoretical foundation to enable the accurate manipulation of high-quality conchocelis development. Previous studies identified diacylglycerol kinase (PhDGK1) as a key regulatory gene involved in the maturation of free-living conchocelis. In this study, conchocelis of strain WO84-1 were treated with 1  μmol/L of the diacylglycerol kinase (DGK) inhibitor R59022. Phenotypic differences between the control and treatment groups first became apparent on day 16 of ripening induction, and were evident on day 26. Samples from both groups were collected on day 0, days 16 and 26 for integrated, widely targeted metabolomic profiling and transcriptome sequencing. Metabolomic analysis revealed a significant differential accumulation of key metabolite classes, including amino acids and their derivatives, lipids, flavonoids, alkaloids, terpenoids, and nucleotides and their derivatives. KEGG pathway enrichment analysis indicated that these metabolites were predominantly associated with the biosynthesis of various plant secondary metabolites, pantothenate and CoA biosynthesis, glucosinolate biosynthesis, tyrosine metabolism, efferocytosis, zeatin biosynthesis, and flavonoid biosynthesis. By day 26 of ripening induction, the inhibitor-treated conchocelis exhibited elevated levels of lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), and free fatty acids. Except for terpenoids, most amino acid- and nucleotide-related metabolites, along with alkaloids and flavonoids, showed decreasing trends in the treatment group at both time points. Weighted gene co-expression network analysis (WGCNA) clustered transcriptomic data into 15 modules. The turquoise and blue modules contained the largest number of genes (2,111 and 1,981, respectively), whereas the remaining modules contained 71–1,860 genes. Notably, genes within the red module exhibited low expression prior to ripening induction and were highly upregulated in the control group on days 16 and 26 but remained downregulated in the treatment group. KEGG enrichment analysis of genes in the red module revealed significant associations between DNA repair and replication pathways, including homologous recombination, base excision repair, mismatch repair, non-homologous end joining, DNA replication, and nucleotide excision repair. Integrated transcriptome–metabolome correlation analysis identified 22 annotated genes and 72 metabolites. Across both ripening induction stages, the treatment group showed significantly reduced levels of amino acids (and derivatives) and nucleotides (and derivatives), whereas LPC, LPE, and free fatty acids accumulated to substantially higher levels than in the control. DGK activity regulates the balance between phosphatidic acid (PA) and diacylglycerol (DG), thereby influencing the synthesis of LPC and LPE and modulating lipid metabolism. This regulatory function plays a crucial role in maintaining nuclear membrane integrity and ensuring stable expression of genes and transcription factors associated with conchocelis maturation. Through the metabolic intermediate acetyl-CoA, lipid metabolism intersects with amino acid metabolism, alkaloid biosynthesis, flavonoid metabolism, and nucleotide metabolism to form an interconnected metabolic network that coordinately regulates conchocelis development and maturation. Moreover, DGK inhibition disrupts the integrity of the membrane system and exacerbates oxidative stress. Treated conchocelis exhibited activation of multiple stress-related genes, including HSP20 and CAT. HSP20 is involved in abiotic stress responses in Pyropia, upregulation of CAT enhances reactive oxygen species scavenging, and glutathione S-transferase genes contribute to glutathione-mediated redox regulation. Therefore, DGK plays a significant role in conchocelis development and maturation by stabilizing membrane systems, enhancing antioxidant defenses, and maintaining cellular homeostasis under stressful conditions.

Abstract:Saccharina japonica, the most extensively farmed seaweed globally, is of great ecological and economic importance. Its applications extend far beyond food consumption, as it is widely utilized in industrial production, biofeed, and medical products, while also playing an important role in marine ecosystems. Its life cycle is characterized by an alternation of generations between haploid gametophytes and diploid sporophytes, with sporophytes typically produced through sexual reproduction. However, S. japonica also exhibits two alternative apomixis reproductive strategies, namely parthenogenesis and apogamy, which bypass fertilization. These asexual modes have attracted increasing attention, as they broaden our understanding of kelp developmental biology and provide new possibilities for germplasm innovation. Epiphytic microorganisms play critical roles in algal growth, morphogenesis, and disease resistance. However, it remains unclear whether sporophytes from different reproductive pathways harbor distinct microbial communities. To address this knowledge gap, we compared bacterial and eukaryotic epiphytic communities of five types of S. japonica sporophytes, representing different reproductive origins and growth states, to reveal differences in community composition, structure, and key biomarker taxa, and explore potential implications for asexual sporophyte development and cultivation. Sporophytes were induced from six female and 15 male gametophyte clones under controlled conditions, including normally growing and malformed parthenogenetic and apogamous sporophytes, as well as normally growing sexually reproduced sporophytes. After 75 days of culture, 39 sporophyte samples were collected. DNA was extracted from surface swabs, and the v3−v4 region of the bacterial 16S rRNA gene and the V4 region of the eukaryotic 18S rRNA gene were sequenced using Illumina NovaSeq 6000 platform. Sequencing reads were quality-filtered, merged, and clustered into operational taxonomic units at 97% similarity based on the SILVA reference database. Alpha diversity was evaluated using Chao1 and Shannon indices, and differences were tested using Student’s t-test. Beta diversity was assessed using non-metric multidimensional scaling (NMDS) based on Bray-Curtis distances and analysis of similarities (ANOSIM). Biomarkers were identified through linear discriminant analysis effect size (LEfSe) using a threshold LDA score ＞4 and P＜0.05. Alpha diversity analysis confirmed that malformed parthenogenetic sporophytes exhibited significantly higher bacterial richness and diversity than all other groups (P＜0.01). Sexual sporophytes showed the lowest alpha diversity in terms of both bacteria and eukaryotes. Apogamous sporophytes, regardless of morphology, generally had a higher diversity than sexual sporophytes, although the differences were not statistically significant. Beta diversity analysis revealed a clear separation of the five groups in the NMDS plots, with ANOSIM confirming significant dissimilarities for both bacterial (R=0.499, P=0.001) and eukaryotic communities (R=0.179, P=0.002). NMDS analysis further indicated that the five sporophyte growth types exhibited significant differences in species composition. In eukaryotic communities, normally growing sexually reproduced sporophytes exhibit the lowest richness and diversity, whereas malformed parthenogenetic sporophytes harbor the most structurally diverse epiphytic assemblages, which may be associated with their distinctive morphological and physiological statuses. Differential taxa among groups were identified using LEfSe and genus-level species composition analyses. Asexual sporophytes generally harbor more enriched bacterial taxa than sexual sporophytes. Malformed parthenogenetic sporophytes contained the highest number of biomarkers, whereas malformed apogamous sporophytes contained the lowest. At the genus level, Litorimonas emerged as the dominant bacterium across multiple groups and was particularly enriched in sexually reproduced sporophytes and malformed apogamous sporophytes. In contrast, the malformed parthenogenetic sporophytes were dominated by unclassified Cyanobacteria, with Litorimonas accounting for a small fraction of the community (3%). The consistent enrichment of Cyanobacteria, which possess an autotrophic capacity and produce antimicrobial metabolites, may partly explain their ecological success. In addition, Maribacter antarcticus was significantly enriched in malformed parthenogenetic sporophytes. Although its precise function remains unclear, its association with abnormal morphology warrants further experimental validation. Eukaryotic communities also exhibited notable variations. Most groups were dominated by Agarum clathratum, a kelp relative species capable of attaching to macroalgae and occasionally acting as a parasite under nutrient-rich conditions. However, malformed parthenogenetic sporophytes were enriched in Halomonhystera, a bacterivorous nematode-like taxon. Its occurrence coincided with higher bacterial loads in these samples, suggesting that host deformities and abundant microbial substrates provided favorable conditions for parasitic colonization. In summary, this study used high-throughput sequencing to systematically analyze the epiphytic microbial diversity of kelp sporophytes derived from sexual reproduction and apomixis. The results revealed significant differences in the microbial community structure between asexual and sexual sporophytes in both the bacterial and eukaryotic communities. Malformed parthenogenetic sporophytes exhibited the most distinct community structure. LEfSe analysis identified significantly different taxa, which enriched the understanding of microbial composition and structure in asexual sporophytes, and offered a solid foundation for future investigations into the interactions between asexual sporophytes and their epiphytic microbiota.

Abstract:Pythium porphyrae and Pythium chondricola, collectively known as red rot pathogens, pose a severe threat to nori (Pyropia/Porphyra) cultivation, causing substantial global economic losses. A critical factor underpinning their success as pathogens is their remarkable resilience and adaptability to fluctuating environmental conditions, which enable their persistent survival and infection. In our preliminary work, we annotated the key ectoine biosynthetic gene EctC, which is responsible for the synthesis of ectoine—an important stress-protective metabolite—from the Pythium porphyrae genome; notably, compared with homologs in terrestrial oomycetes, this gene shows a marked expansion Ectoine is a potent stress-protectant molecule that is well characterized in prokaryotes for its role in the osmoprotection and stabilization of macromolecules under various abiotic stresses, including high salinity, drought and oxidative stress. Its presence and potentially functional role in eukaryotic oomycetes, particularly in plant pathogens, represent a paradigm shift, as it was historically considered a prokaryotic-specific metabolite. This study aimed to functionally characterize the role of EctC from P. porphyrae (PpEctC) in oomycete growth, environmental stress tolerance, and pathogenicity. We employed a heterologous functional genomics approach using the established Phytophthora sojae transformation system. We generated a comprehensive set of transgenic strains in strain P6497 to investigate the function of EctC. Using the CRISPR/Cas9-mediated gene replacement strategy coupled with homology-directed repair (HDR), we successfully created a PsEctC knockout mutant (PsΔEctC-RFP), in which the native PsEctC gene was replaced with a red fluorescent protein (RFP) marker. We generated a heterologous complementation strain (PsΔEctC-PpEctC) by replacing PsEctC with the PpEctC gene from P. porphyrae. Additionally, we constructed a strain overexpressing PsEctC (Ps-oeEctC) and strain expressing PpEctC (Ps-hePpEctC) in the wild-type (WT) P. sojae background using a plasmid-based expression system. Successful gene editing, deletion, and altered expression levels of all transgenic strains were validated using PCR, qRT-PCR, and phenotypic screening. Phenotypic characterization under standard conditions revealed that the deletion of PsEctC significantly impaired mycelial growth, as evidenced by significantly smaller colony diameter of the PsΔEctC-RFP mutant compared with that of the wild-type and empty vector control (CK). Intriguingly, heterologous complementation of the PsΔEctC-PpEctC strain with PpEctC fully restored mycelial growth to that of the WT, demonstrating functional equivalence and cross-species compatibility of the P. porphyrae EctC in supporting basic P. sojae vegetative growth. In contrast, neither the knockout nor complementation significantly affected sporangia formation or zoospore production, except for an unexplained reduction in zoospore yield in the PsΔEctC-PpEctC strain. This suggests that EctC is primarily involved in hyphal expansion but not in the specific developmental reproductive stages under non-stress conditions. We then investigated the role of EctC in stress tolerance. Under high salinity stress (35% NaCl), the PsΔEctC-RFP knockout mutant exhibited a dramatic reduction in relative growth, highlighting its increased sensitivity to osmotic stress. The heterologous complementation strain (PsΔEctC-PpEctC) displayed a growth tolerance phenotype, which was statistically indistinguishable from that of the WT and CK, confirming that PpEctC could effectively restore osmotolerance. Strikingly, both the PsEctC overexpression (Ps-oeEctC) and PpEctC heterologous expression (Ps-hePpEctC) demonstrated superior growth under high-salt conditions, significantly outperforming the WT. This indicates that elevated EctC expression, whether from a native or heterologous source, confers a distinct advantage under osmotic stress. A similar trend was observed under alkaline pH stress (pH 9), in which the EctC knockout mutant was severely compromised, whereas the complemented and overexpression mutants maintained robust growth, underscoring the role of ectoine in pH stress mitigation. Given the critical role of reactive oxygen species in plant defense, we assessed the total antioxidant capacity of the transformants. We found that the PsΔEctC-RFP mutant showed a significant decrease in antioxidant capability. Conversely, both the Ps-oeEctC and Ps-hePpEctC mutants exhibited substantial enhancement in their antioxidant capacities, with the latter exhibiting a more potent effect. The complementation strain (PsΔEctC-PpEctC) showed a partial but significant recovery in antioxidant capacity compared to the knockout, although it did not reach that of the WT. This result shows a clear link between the EctC-mediated ectoine synthesis and pathogen’s oxidative stress defense system, which is crucial for countering host-induced oxidative bursts during infection. Pathogenicity assays on etiolated soybean hypocotyls provided compelling evidence for the role of EctC in virulence. The PsΔEctC-RFP knockout strain caused minimal lesions and showed a significantly lower relative in planta biomass than the WT, indicating severely attenuated virulence. Complementation with PpEctC (PsΔEctC-PpEctC) partially restored pathogenicity, leading to a higher biomass than the knockout although not to the WT levels. Most notably, heterologous expression of PpEctC (Ps-hePpEctC) resulted in hypervirulence, with significantly greater pathogen biomass recovered from the infected tissues than from the WT. The overexpression mutant (Ps-oeEctC) also showed enhanced virulence than the WT. These findings strongly suggest that EctC is a critical virulence factor and that its enhanced expression can potentiate pathogen infectivity and colonization ability, likely by bolstering resistance to host-imposed environmental and oxidative stresses. In conclusion, our study provides comprehensive functional evidence that the ectoine synthase gene EctC, particularly the PpEctC variant from P. porphyrae, plays a multifaceted and pivotal role in oomycete biology. It is integral for optimal mycelial growth, essential for tolerance to high salinity and alkaline pH, crucial for enhancing antioxidant capacity, and is a major determinant of pathogenicity. Successful heterologous complementation and the hypervirulent phenotype induced by heterologous expression confirmed functional potency of PpEctC. This study not only elucidates a previously uncharacterized stress adaptation mechanism in a destructive eukaryotic pathogen but also pinpoints EctC and the ectoine biosynthesis pathway as promising and novel targets for developing precise disease control strategies against red rot disease in nori aquaculture. Future work will focus on directly validating these findings in P. porphyrae upon the establishment of a robust transformation system.

Abstract:Sporeling malformation disease, characterized by abnormal cell proliferation and tissue disintegration, causes catastrophic losses in the seedling production of kelp Saccharina japonica. Previous studies have linked disease occurrence to environmental stressors (e.g., inadequate light exposure), the maturity of parental kelp (e.g., immature or overmatured), and alginate-decomposing bacteria, among others. Traditional culture-dependent approaches have failed to explain the complex pathogenesis of this disease, and its precise microbial etiology remains elusive. Recent advances in holobiont theory and our previous work suggest that dysbiosis of epiphytic microbiota, rather than individual pathogens, may drive sporeling malformation by disrupting host-microbe interactions and exacerbating disease severity. In the present study, we analyzed the diversity, structure, and functional profiles of epiphytic bacteria on sporelings with different malformation rates to obtain more data related to the relationships between epiphytic bacterial communities and the incidence of sporeling malformations using in situ sporeling samples. Through microscopic observations, in 2018, two groups of biological samples (Low and High groups) were collected from a workshop in a typical kelp seedling hatchery in Weihai, China. Epiphytic bacterial communities from low (~2%–6%) and high (~10%–12%) malformation groups were analyzed using 16S rRNA sequencing. Bioinformatic analyses (QIIME, USEARCH, LEfSe, and PICRUSt2) were used to assess community diversity, identify differential taxa, and predict functional profiles. Alpha diversity was lower in the high-malformation group. This indicated reduced bacterial richness. Community structure differed significantly between groups, with distinct shifts in dominant taxa. The low group demonstrated a higher presence of mutualistic and morphogenesis-associated bacteria. Meanwhile, the high group displayed more taxa associated with pathogenicity. The low group was more closely linked to metabolic and defense-related pathways. In contrast, the high group was associated with xenobiotic degradation and virulence-related functions. These findings highlight the importance of maintaining a healthy microbial community for sporeling growth and development and suggest potential targets for disease prevention and control. Future research should focus on changes in whole community functions using different omics methods and explore the interactions between the host, environment, and certain isolated bacterial strains in the context of disease development. This study not only enriches our understanding of the microbial ecology of kelp diseases but also has important practical implications for the kelp farming industry. Identifying key microbial taxa and functional pathways associated with disease may guide the development of microbial-based strategies for disease management, thereby contributing to the sustainable development of kelp cultivation.

Abstract:In China, the annual output of dried kelp is as high as 1.86 million tons; however, the harvesting process still relies heavily on manual labor, leading to low per capita efficiency and high labor intensity. Although foreign mechanized harvesting equipment exists, it is designed for long-line culture modes and is incompatible with the raft-type parallel culture system prevalent in China. The development of domestic semi-mechanized harvesting equipment faces challenges, such as poor raft adaptability and insufficient harvesting continuity, highlighting the need for synergistic innovation in both culture modes and equipment. To address these issues, we optimized mechanization-adapted culture modes and innovated key equipment components to develop a smaller-scale continuous harvesting system based on long seedling ropes, thus overcoming the efficiency bottleneck of traditional manual harvesting. First, a circuitous series-connected raft system for long seedling ropes was constructed by integrating 300 m continuous seedling ropes with 16 mm-wide quick-release buckles. This series structure preserves traditional culture density while facilitating reliable connections and rapid separation between the seedling ropes and rafts. Following a modular design approach, the core components (e.g., rectangular guiding devices, inclined conveyors, and low-damage stripping-cutting tools) were integrated with a hydraulic centralized control system, enabling single-person operation of continuous mechanized harvesting equipment. The stripping-cutting tool structure was innovatively optimized, with an outer blade diameter of 120 mm and inner blade diameter of 45 mm, and the allowable heave angle of the seedling ropes was increased to 55°. Dynamic simulation analysis using Ansys LS-DYNA software for emergency scenarios (e.g., hanging rope entanglement) revealed that the maximum equivalent stress was 405.04 MPa, far below the yield strength of the material, confirming structural strength reliability. Coupled with an umbrella-spoke-shaped seedling rope storage device (300 m capacity), stable and continuous mechanized harvesting of the entire raft was achieved. Trials of the equipment at a kelp harvesting site demonstrated that at a harvesting line speed of 9.36–14.82 m/min, the system achieved 100% kelp-harvesting completeness with no seedling rope breakage. Single-raft harvesting time ranged from 27‒36 min, and the per capita harvesting rate reached 2 t/(h·person), twice that of traditional manual labor. Only four workers are required to complete the entire process without heavy physical labor, addressing the issues of frequent start–stops and high manual assistance intensity associated with traditional equipment. The system enables integrated operations such as seedling rope separation, continuous dragging, stripping-cutting harvesting, and seedling rope storage. The novel harvesting system proposed in this study addresses the technical bottlenecks of poor raft adaptability and low harvesting continuity by establishing a collaborative solution for mechanization-adapted culture modes and equipment. The modular design accommodates operational needs across different scenarios, and the doubled efficiency effectively alleviates labor shortage pressures, providing equipment support for the large-scale promotion of mechanized harvesting in China's major kelp-producing regions. Beyond the kelp industry, the modular design concept and low-damage harvesting technology offer references for the mechanized harvesting of other large algae, contributing to the intelligent upgrading of marine aquaculture equipment.

Abstract:Large-scale algal cultivation plays a vital role in the aquaculture industry in China. Saccharina japonica, the predominant species, accounted for 61.4% of the national total algal aquaculture output of 3.0294 million tons in 2024. The harvest window for S. japonica is notably brief, typically lasting only to 2‒3 months. Freshly harvested kelp has a very high moisture content (approximately 90% wet basis), necessitating immediate primary processing to prevent spoilage and facilitate storage and subsequent processing. The two primary traditional pretreatment methods are sun-drying and salting. Although salting is efficient and weather-independent, making it suitable for large-scale processing, sun-drying remains a crucial cost-effective method in regions with ample sunlight owing to its near-zero energy consumption. Sun-drying is mainly categorized into hang-drying and pavement drying. The practice of hang-drying is space efficient and yields cleaner products; however, it has several disadvantages, including longer drying cycles, severe product curling, and polysaccharide leaching. Pavement drying offers a higher drying efficiency, but traditional direct sand-beach spreading leads to significant sand contamination, relegating its use primarily to chemical feedstocks or abalone feed. Improved pavement-drying techniques, such as the use of pebble beds or polyethylene nets, have demonstrated the potential to produce high-quality dried kelp but remain labor intensive. The fundamental challenges in traditional sun-drying methods include high labor intensity and low operational efficiency, which severely constrain industrial-scale production. This issue is further exacerbated by the declining fishery labor force. Consequently, mechanization of the sun-drying process has become an urgent priority. Significant research efforts have been directed towards mechanizing hanging-drying, leading to the development of various systems,