https://orcid.org/0009-0003-9423-6857
Figures
Abstract
The recurring outbreak of Ulva prolifera green tides in the Yellow Sea poses a serious threat to coastal ecosystems and coastal-related industries, necessitating the development of environmentally friendly control strategies. In this study, in situ experiments were conducted using two light intensity levels and five co-cultivation biomass density combinations to investigate their effects on the growth and photosynthetic physiology of Gracilariopsis lemaneiformis and U. prolifera. The results demonstrated a significant interactive effect of light intensity and biomass density on the competitive outcome between the two species. Specifically, the relative growth rate of U. prolifera significantly decreased with increasing biomass density of G. lemaneiformis–an inhibitory effect that was particularly pronounced under high light intensity. High light enhanced the competitive suppression capacity of G. lemaneiformis, likely associated with shading effect due to its growth, while reduced photosystem stability of U. prolifera under high light further exacerbated the inhibition. Under low light, U. prolifera alleviated competitive pressure by increasing its chlorophyll content. G. lemaneiformis suppressed U. prolifera through resource competition, and a biomass density ratio of 1:4–1:6 (U. prolifera: G. lemaneiformis) was found to balance effective ecological control with sustained growth of G. lemaneiformis. The research findings provide novel scientific insights and empirical data to support the advancement of G. lemaneiformis aquaculture and the development of biological control strategies for mitigating green tides.
Citation: Zhou W, Lu W, Hao Y, Zhou Y, Yan Y, Liu Q, et al. (2026) Effects of co-cultivation with Gracilariopsis lemaneiformis on the explosive growth and photosynthesis of Ulva prolifera. PLoS One 21(3): e0344202. https://doi.org/10.1371/journal.pone.0344202
Editor: Satheesh Sathianeson, King Abdulaziz University, SAUDI ARABIA
Received: December 2, 2025; Accepted: February 17, 2026; Published: March 10, 2026
Copyright: © 2026 Zhou et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting information files.
Funding: This work was supported by the Open fund project of Key Laboratory of Coastal Salt Marsh Ecosystems and Resources, Ministry of Natural Resources (KLCSMERMNR202302), the Excellent Master’s Dissertation Training Program of Jiangsu Ocean University (2021210102), the Research on Marine Ecological Integrated Technology for Nuclear Power Plant Heat Supply and Power Generation in Xuwei, Jiangsu Province (XA1FY-24012118-N00), the Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX24_2087), the College Student Innovation and Entrepreneurship Training Program of Jiangsu Province Higher Education (2024120125), the Marine Science and Technology Project of Jiangsu Marine Resources Development Technology Innovation Center (LWKJ-13), the Talent Introduction Fund Project of Jiangsu Ocean University (KQ19068), the Huaguoshan Talent Project of Lianyungang.
Competing interests: The authors have declared that no competing interests exist.
Introduction
The recurrent outbreaks of large-scale green tides has become a serious challenge for the global coastal ecosystems. Since 2007, the Yellow Sea in China has experienced annual outbreaks of green tides, predominantly dominated by Ulva prolifera [1,2]. These outbreaks not only degrade coastal landscapes and obstruct shipping channels, but also pose severe threats to coastal fisheries, aquaculture, and tourism [3,4]. The complex life history and multiple reproductive modes of U. prolifera are important reasons for its dominance in the Yellow Sea green tide region. Additionally, environmental changes such as global warming and coastal eutrophication are significant potential drivers of green tide outbreaks [5]. It is noteworthy that the formation of U. prolifera green tides is a complex ecological process resulting from the synergistic interaction between biological characteristics and environmental factors [4,6]. Features such as their extensive spatial distribution, excessive biomass accumulation, and rapid diffusion make it difficult for traditional single-approach control methods to achieve long-term management. This practical challenge places higher demands on the scientific rigor, systematic approach, and innovation required for green tide prevention and control efforts.
Current mitigation strategies for green tides formed by U. prolifera fall into three categories: physical, chemical, and biological methods [7]. Physical methods utilize satellite remote sensing to track the drift path of green tides in real-time, assisting salvage vessels in targeted removal of U. prolifera. These methods are costly and consume human and material resources [1]. Traditional chemical methods involve the application of compounds such as strong oxidants, heavy metal compounds, and acid treatments, which inevitably cause environmental pollution and other problems [8]. In contrast, biological control methods have garnered growing attention due to their environmentally friendly and potentially sustainable characteristics. However, their mechanisms of action, application conditions, and large-scale feasibility still require in-depth investigation [9]. Therefore, based on elucidating the ecological mechanisms, developing new biological control approaches grounded in biological interactions is of significant importance for enriching green-tide management strategies.
In China, G. lemaneiformis has become the second-largest cultivated seaweed. It not only holds significant aquacultural economic value but also demonstrates notable potential for nutrient absorption and ecological remediation [10,11]. Studies conducted under laboratory conditions have confirmed that economic macroalgae can not only inhibit U. prolifera growth by competing for light and nutrients, but also interfere with its photosynthesis and growth through the release of allelochemicals [12–14]. The competitive growth among macroalgae is influenced by multiple environmental factors such as light, nutrients, temperature, and water flow. Especially in complex nearshore ecosystems, changes in a single environmental variable may alter interspecific competition patterns through niche reconstruction. Therefore, it is necessary to analyze the interactive effects of multiple factors under conditions that closely resemble natural environments.
Light intensity and biomass density are key environmental factors regulating the competition among macroalgae [15]. As an opportunistic species, the growth of U. prolifera is highly dependent on light and nutrient availability [16,17]. In contrast, G. lemaneiformis exhibits broader adaptability to light conditions [18]. The outcome of competition between the two species may vary with changes in light conditions and relative biomass [19,20]. However, most existing studies have focused on single-factor experiments or laboratory simulations, resulting in a lack of systematic understanding of how light and biomass density interact to regulate the competitive dynamics and underlying physiological mechanisms of these two algae under in situ conditions. Especially in field environments, clarifying the inhibitory effect of G. lemaneiformis on the competitive growth of U. prolifera holds significant practical value for optimizing cultivation strategies of G. lemaneiformis and advancing biological control technologies for green tides.
In this study, an in situ experiment was conducted with two light gradients and five co-cultivation biomass densities to systematically investigate the effects of different light intensities and biomass densities on the growth rates, photosynthetic activity, and biochemical parameters of G. lemaneiformis and U. prolifera. The objective of this study was to elucidate the interspecific competitive dynamics among macroalgae and provide a scientific basis for optimizing G. lemaneiformis cultivation models and innovating biological control strategies for green tides.
Materials and methods
Experimental materials
G. lemaneiformis used in the experiment was collected from aquaculture rafts in Luoyuan Bay, Fujian Province (26°25'23.01" N, 119°41'32.12" E). Ulva prolifera was collected from Zaihaiyifang Park in Lianyungang City, Jiangsu Province (34°36'06" N, 119°46'12" E). The collected thalli of G. lemaneiformis and U. prolifera were placed in a portable temperature-controlled box at 4 ℃ and transported to the laboratory. Thalli were cleaned with filtered and sterilized seawater to remove epiphytes and other contaminants. Healthy thalli were selected for pre-cultivation in a smart illumination incubator (GXZ-500C, China) at a temperature of 20 ℃, a light intensity of 100 μmol photons m ⁻ ² s ⁻ ¹, and a photoperiod of 12 h light: 12 h dark, before being used in subsequent experiments.
Experimental design
The experiment investigated two environmental factors: light intensity and biomass density. Considering the optimal temperature and light intensity for the growth of G. lemaneiformis and U. prolifera, a two-week in situ experiment was conducted in April in the intertidal zone near Dongbawei, Guanyun County, Lianyungang City, Jiangsu Province, China (34°29'00.04" N, 119°46'02.23" E). Two light intensity levels were set: Low Light (LL: covered with 3 layers of shading net) and High Light (HL: covered with 2 layers of shading net). Under each light level, five growth biomass density gradients were established: Ulva prolifera monoculture (UP); Gracilariopsis lemaneiformis monoculture (GL); U. prolifera: G. lemaneiformis = 1:2 (1U2G); U. prolifera: G. lemaneiformis = 1:4 (1U4G); and U. prolifera: G. lemaneiformis = 1:6 (1U6G). The biomass density ratios were set based on chlorophyll a content, with the unit density defined as 0.5 g for U. prolifera and 0.8 g for G. lemaneiformis. UP and GL represent the monoculture treatment groups, designated as IC (individual culture). This resulted in 10 treatment groups combining light intensity and culture biomass density (LL: UP, GL, 1U2G, 1U4G, 1U6G; HL: UP, GL, 1U2G, 1U4G, 1U6G), with three replicates per combination. All experimental algae were cultured in 25 L tanks placed on a coastal embankment slope, with each tank filled with 20 L of natural seawater collected on-site. Additionally, fresh seawater was replaced every two days to meet the growth requirements of the thalli and to avoid nutrient limitation. During the experimental period, the air temperature ranged from 12.15 to 28.96 ℃; water temperature ranged from 13.77 to 23.77 ℃. The pH varied between 8.12 and 8.26, and salinity ranged from 31.2 to 32.5. The concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) were measured both at the start of the experiment and at each water exchange. Initial concentrations: DIN = 29.96 ± 1.34 µmol L-1, DIP = 1.16 ± 0.05 µmol L-1; concentrations at water exchange: DIN = 29.28 ± 2.24 µmol L-1, DIP = 1.12 ± 0.09 µmol L-1.
Environmental solar radiation measurement
A solar radiation receiver (LoggerNet CR3000, Tiannuo, Beijing, China) was used to monitor and record solar radiation (PAR, μmol photons m ⁻ ² s ⁻ ¹) in real-time every minute during the experimental period. Daily dose was calculated in kJ m ⁻ ².
Growth measurement
Fresh weight of algae was measured every two days. During measurement, the same number of layers of absorbent paper was used to gently press the thallus surface to remove water, maintaining consistent pressing time. All fresh weight of algae measurements were performed by the same operator using the same balance to minimize human and instrumental errors. Relative Growth Rate (RGR, % d ⁻ ¹) was calculated as follows:
Where: Wₜ is the fresh weight (g) of algae on day t, W₀ is the initial fresh weight (g), and t is the cultivation time in days (d).
Respiration rate measurement and net photosynthetic rate
Respiration rate (Rd) and net photosynthetic rate (Pn) of G. lemaneiformis and U. prolifera were measured using an oxygen electrode (YSI-5300A, YSI Inc., USA). Approximately 0.1 g of algae was cut into 1 cm segments and dark-adapted at 20 ℃ for 12 hours to minimize errors from mechanical damage. The instrument was zeroed by adding 8 ml of pure water to the reaction chamber while continuously purging with N2, adjusting the reading to zero. The solution was then repeatedly pipetted for 20 minutes, and the instrument reading was adjusted to 100. The temperature was controlled at 20 ℃ using a constant temperature circulator. Algae segments were placed in the reaction chamber for measurement; values were recorded once stable, at one-minute intervals. To measure respiration rate, a light-tight dark box was placed over the reaction chamber to create complete darkness, and the change in O2 concentration was recorded. To measure net photosynthetic rate, the distance between the halogen lamp and the reaction chamber was adjusted to simulate outdoor light conditions, and the change in O2 concentration was recorded.
Chlorophyll fluorescence parameter measurement
Chlorophyll fluorescence parameters of G. lemaneiformis and U. prolifera were measured using a handheld pulse amplitude modulation chlorophyll fluorometer (Aquapen AP 100, Photon Systems Instruments, Drásov, Czech Republic). The effective quantum yield of photosystem II (Yield) was measured every 1.5 hours from 8:30 AM to 5:30 PM for algae in each treatment group. Relative Electron Transport Rate (rETR) was determined at eight actinic light intensities [0, 10, 20, 50, 100, 200, 500, and 1000 μmol photons m ⁻ ² s ⁻ ¹] [21]:
Where Yield is the effective quantum yield; 0.5 is the ratio of absorbed to total incident light energy; PAR is the light intensity.
Rapid Light Curves (RLC) were fitted according to the following formula [22]:
Where rETR is the relative electron transport rate, PAR is the light intensity, and a, b, c are fitting parameters.
Maximum relative electron transport rate (rETRₘₐₓ), photosynthetic efficiency (α), and saturating irradiance (Iₖ) were calculated from a, b, c:
Photosynthetic pigment content determination
Approximately 0.05 g of G. lemaneiformis or U. prolifera thalli was cut into small pieces, placed in a centrifuge tube with 5 ml of anhydrous methanol, and kept in the dark at 4 ℃ for 24 hours. The supernatant was taken after shaking. Absorbance at wavelengths 470 nm, 653 nm, and 666 nm was measured using an ultraviolet spectrophotometer. Chlorophyll a (Chl a, mg g ⁻ ¹ FW) and carotenoid (Car., mg g ⁻ ¹ FW) contents were calculated as follows [23]:
Where Chl a is chlorophyll a content; Car. is carotenoid content (mg g ⁻ ¹ FW); A₄₇₀ nm, A₆₅₃ nm, A₆₆₆ nm are absorbance values at 470 nm, 653 nm, and 666 nm, respectively.
Approximately 0.05 g of G. lemaneiformis thalli was fully ground in a mortar. The ground sample was transferred to a centrifuge tube containing 5 ml of phosphate buffer. The sample was centrifuged at 5000 r min⁻1 for 15 min at 4 ℃, and the supernatant was collected. Absorbance at wavelengths 455 nm, 564 nm, 592 nm, 618 nm, and 645 nm was measured using an ultraviolet spectrophotometer. Phycoerythrin (PE, mg g ⁻ ¹ FW) and phycocyanin (PC, mg g ⁻ ¹ FW) contents were calculated as follows [24]:
Where PE is phycoerythrin concentration; PC is phycocyanin concentration; A645 nm, A618 nm, A592 nm, A564 nm, A455 nm are absorbance values at 645 nm, 618 nm, 592 nm, 564 nm, and 455 nm, respectively.
Soluble protein and soluble carbohydrate determination
Soluble protein (SP) content of G. lemaneiformis and U. prolifera was determined using the Bradford method [25]. Approximately 0.05 g of algae was ground in a mortar, mixed with 5 ml of phosphate buffer solution, and transferred to a centrifuge tube. The mixture was centrifuged at 5000 r min-1 for 15 min at 4 ℃. Then, 1 ml of supernatant was mixed with 4 ml of Coomassie Brilliant Blue solution. Absorbance was measured at 595 nm using an ultraviolet spectrophotometer. Soluble carbohydrate (SC) content was determined using the sulfuric acid-anthrone colorimetric method [26]. Approximately 0.05 g of algae was fully ground in a mortar, mixed with 5 ml of phosphate buffer solution, boiled for 1 hour, and centrifuged at 5000 r min-1 for 10 min. Then, 1 ml of supernatant was mixed with 4 ml of sulfuric acid-anthrone solution, placed in a boiling water bath for 10 min, and absorbance was measured at 620 nm using an ultraviolet spectrophotometer.
Data analysis
Experimental data are expressed as “mean ± standard deviation (mean ± SD)”. Graphing and statistical analyses were performed using Origin 2021 and SPSS 26.0 software, respectively. All experimental data met the assumptions of normality (P > 0.05) and homogeneity of variance (P > 0.05). Differences among treatment groups were analyzed using one-way analysis of variance (One-way ANOVA), with Tukey’s multiple comparison test used to determine statistically significant differences between groups. Two-way analysis of variance (Two-way ANOVA) was used to compare the effects of light intensity and biomass density on the relative growth rate, net photosynthetic rate, respiration rate, chlorophyll fluorescence parameters, chlorophyll a, carotenoids, phycoerythrin, phycocyanin, soluble protein, and soluble carbohydrate content of G. lemaneiformis and U. prolifera. A significance level of P < 0.05 was used for all statistical analyses.
Results
Environment solar radiation
The average daily variation of outdoor solar radiation during the experimental period is shown in Fig 1. The peak of daily solar radiation variation occurred at 11:01 AM, with an intensity of 1267 μmol m ⁻ ² s ⁻ ¹ (Fig 1A). The daily cumulative radiation ranged from 63.03 kJ m ⁻ ² to 139.88 kJ m ⁻ ², with a 15-day average daily cumulative radiation of 116.50 kJ m ⁻ ² (Fig 1B).
Growth
Changes in both light intensity and biomass density significantly affected the relative growth rate (RGR) of G. lemaneiformis and U. prolifera (P < 0.05), and their interaction also had a significant effect on the RGR of both species (P < 0.05) (S1 Table in S1 File). As shown in Fig 2A, under low light intensity, the relative growth rates of both G. lemaneiformis and U. prolifera were highest in monoculture, at 8.95% ± 0.57% d ⁻ ¹ and 12.92% ± 0.92% d ⁻ ¹, respectively. The growth rate of G. lemaneiformis in the 1U2G treatment group was not significantly different from the IC group (P > 0.05). G. lemaneiformis RGRs in the 1U4G and 1U6G groups decreased significantly by 21.90% and 29.27%, respectively, compared to the IC group. The growth rate of U. prolifera in the 1U2G, 1U4G, and 1U6G groups decreased significantly by 16.80%, 17.18%, and 36.92%, respectively, compared to the IC group. Under high light intensity (Fig 2B), the growth rates of both G. lemaneiformis and U. prolifera gradually decreased with increasing G. lemaneiformis biomass density, peaking in monoculture at 11.97% ± 0.41% d ⁻ ¹ and 15.21% ± 0.77% d ⁻ ¹, respectively. Compared to the monoculture group, the RGR of G. lemaneiformis in the respective co-culture groups decreased significantly by 13.32%, 35.37%, and 55.30% (P < 0.05), and the RGR of U. prolifera decreased significantly by 21.30%, 32.74%, and 45.10% (P < 0.05). Combining both light conditions, the relative growth rates of both algae species showed a decreasing trend with increasing G. lemaneiformis biomass density. Furthermore, under the same culture conditions, the RGR of U. prolifera was significantly higher than that of G. lemaneiformis (P < 0.05), with increases ranging from 14.62% to 36.89%.
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differencesin RGR among G. lemaneiformis treatments across different culture densities. Different uppercase letters indicate significant differences in RGR among U. prolifera treatments across different culture densities. * indicates a significant difference in RGR between G. lemaneiformis and U. prolifera at the same culture density.
Respiration rate and net photosynthetic rate
Biomass density significantly affected the dark respiration rate (Rd) of both G. lemaneiformis and U. prolifera (P < 0.05), while light intensity did not have a significant effect on Rd (P > 0.05). However, the interaction between light intensity and biomass density significantly affected Rd for both species (P < 0.05) (S2 Table in S1 File). As shown in Fig 3A, under low light intensity, Rd of G. lemaneiformis was significantly different only between the IC and 1U6G groups (P < 0.05), with the value in the 1U6G group being 31.50% lower than in the IC group. No significant differences were observed among other groups. For U. prolifera under low light, the Rd in the IC group reached its minimum (11.52 ± 0.72 μmol O₂ g ⁻ ¹ FW h ⁻ ¹) and differed significantly from all other treatment groups (P < 0.05). Compared with the IC group, the Rd values in the 1U2G, 1U4G, and 1U6G groups were 37.50%, 30.21%, and 23.96% higher, respectively. Under high light intensity (Fig 3B), Rd of both G. lemaneiformis and U. prolifera showed significant differences between the IC group and the 1U4G and 1U6G groups (P < 0.05). Rd peaked in the IC group for both species under HL: 13.56 ± 0.91 μmol O₂ g ⁻ ¹ FW h ⁻ ¹ for G. lemaneiformis and 16.92 ± 0.95 μmol O₂ g ⁻ ¹ FW h ⁻ ¹ for U. prolifera. With increasing G. lemaneiformis biomass density, Rd decreased slightly for both algae. Rd of G. lemaneiformis in the 1U4G and 1U6G groups decreased significantly by 27.43% and 25.66%, respectively, compared to IC. Rd of U. prolifera in the 1U4G and 1U6G groups decreased by 14.89% and 14.18%, respectively, compared to IC. Under the same culture conditions, the Rd of U. prolifera was significantly lower than that of G. lemaneiformis only in the low-light IC group (P < 0.05). Rd of U. prolifera was significantly higher than that of G. lemaneiformis (P < 0.05) in other treatment groups.
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same light intensity level across different culture densities. Different uppercase letters indicate significant differences among U. prolifera treatments at the same light intensity level across different culture densities. * indicates a significant difference between G. lemaneiformis and U. prolifera at the same culture density.
Two-way ANOVA (S2 Table in S1 File) indicated that the interaction between light intensity and biomass density did not significantly affect the net photosynthetic rate (Pn) of G. lemaneiformis and U. prolifera (P > 0.05), but changes in light intensity and biomass density individually had significant effects on Pn (P < 0.05). As shown in Fig 3C-D, under the same light intensity, Pn of both algae gradually decreased with increasing biomass density of G. lemaneiformis. This trend paralleled the changes in relative growth rate, suggesting that elevated G. lemaneiformis biomass density suppressed Pn in both species. Under low light conditions, Pn of G. lemaneiformis and U. prolifera in monoculture were 18.60 ± 1.50 μmol O₂ g ⁻ ¹ FW h ⁻ ¹ and 23.76 ± 1.30 μmol O₂ g ⁻ ¹ FW h ⁻ ¹, respectively. For both species, no significant difference in Pn was observed between the IC and 1U2G groups. Compared with the IC group, the Pn of G. lemaneiformis decreased by 18.06% and 32.26% in the 1U4G and 1U6G groups, respectively, while that of U. prolifera decreased by 33.33% and 35.86% (Fig 3C). Under high light intensity, Pn of G. lemaneiformis showed no significant difference between the 1U2G group and the IC or 1U4G groups (P > 0.05), but a significant difference existed between IC and 1U4G groups (P < 0.05). Pn of U. prolifera showed no significant difference between the 1U2G and 1U4G groups (P > 0.05), but significant differences existed between IC and 1U6G groups (P < 0.05). Pn of both species peaked in the IC group under HL: 21.72 ± 1.62 μmol O₂ g ⁻ ¹ FW h ⁻ ¹ for G. lemaneiformis and 25.92 ± 1.90 μmol O₂ g ⁻ ¹ FW h ⁻ ¹ for U. prolifera. Compared to IC, Pn of G. lemaneiformis decreased by 7.73%, 23.20%, and 44.20%, and Pn of U. prolifera decreased by 12.96%, 24.54%, and 38.89% in the respective co-culture groups (Fig 3D).
Chlorophyll fluorescence parameters
The diurnal variation of fluorescence quantum yield (Yield) for G. lemaneiformis and U. prolifera in various treatment groups is shown in Fig 4. Under low light intensity, the Yield of G. lemaneiformis at 8:00 AM was 0.53 ± 0.02, 0.53 ± 0.02, 0.50 ± 0.03, and 0.50 ± 0.02 for IC, 1U2G, 1U4G, and 1U6G groups, respectively. Yield decreased gradually from 8:30 AM to 1:00 PM, then showed an upward trend, peaking at 5:30 PM at 0.58 ± 0.02, 0.57 ± 0.01, 0.53 ± 0.02, and 0.56 ± 0.02 for the respective groups. For U. prolifera under LL, Yield at 8:00 AM was 0.66 ± 0.02, 0.64 ± 0.02, 0.63 ± 0.02, and 0.62 ± 0.02 for IC, 1U2G, 1U4G, and 1U6G groups. Yield in IC and 1U2G groups gradually decreased to a minimum from 8:30 AM to 1:00 PM, then increased. In 1U4G and 1U6G groups, Yield decreased to a minimum from 8:30 AM to 2:30 PM, then increased, also peaking at 5:30 PM at 0.72 ± 0.02, 0.72 ± 0.02, 0.72 ± 0.03, and 0.67 ± 0.03 for the respective groups (Fig 4A). Under high light intensity, Yield of G. lemaneiformis at 8:00 AM was 0.46 ± 0.01, 0.46 ± 0.02, 0.46 ± 0.02, and 0.46 ± 0.01 for IC, 1U2G, 1U4G, and 1U6G groups. Yield in IC, 1U2G, and 1U4G groups decreased to a minimum from 8:30 AM to 11:30 AM, then gradually increased. However, in the 1U6G group, Yield decreased gradually from 8:30 AM to 11:30 AM, increased from 11:30 AM to 1:00 PM, slightly decreased from 1:00 PM to 2:30 PM, then showed an upward trend, peaking at 5:30 PM at 0.53 ± 0.01, 0.47 ± 0.02, 0.48 ± 0.01, and 0.47 ± 0.02 for the respective groups. For U. prolifera under HL, Yield at 8:00 AM was 0.72 ± 0.02, 0.70 ± 0.01, 0.66 ± 0.02, and 0.66 ± 0.02 for IC, 1U2G, 1U4G, and 1U6G groups. Yield in all groups gradually decreased from 8:30 AM to 1:00 PM, then showed an upward trend, peaking at 5:30 PM at 0.71 ± 0.02, 0.68 ± 0.02, 0.67 ± 0.01, and 0.65 ± 0.02 for the respective groups (Fig 4B). Furthermore, under the same culture conditions, the Yield of U. prolifera was significantly higher than that of G. lemaneiformis.
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same light intensity level across different culture densities. Different uppercase letters indicate significant differences among U. prolifera treatments at the same light intensity level across different culture densities. * indicates a significant difference between G. lemaneiformis and U. prolifera at the same culture density.
The rapid light response curves (RLCs) for G. lemaneiformis and U. prolifera in various treatment groups are shown in Fig 5. Under low light intensity, the relative electron transport rate (rETR) of G. lemaneiformis in monoculture and the 1U4G group, and U. prolifera in all groups, showed a gradual upward trend with increasing light intensity. In contrast, rETR of G. lemaneiformis in the 1U2G and 1U6G groups initially increased and then decreased. Under high light intensity, rETR of G. lemaneiformis in all groups, and U. prolifera in the IC and 1U2G groups, showed a stable upward trend with increasing light intensity. However, rETR of U. prolifera in the 1U4G and 1U6G groups increased initially and then decreased with further elevation of light intensity.
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same light intensity level across different culture densities. Different uppercase letters indicate significant differences among U. prolifera treatments at the same light intensity level across different culture densities. * indicates a significant difference between G. lemaneiformis and U. prolifera at the same culture density.
According to two-way ANOVA (S3 Table in S1 File), light intensity and biomass density each exerted a significant effect on the rETRₘₐₓ, α, and Iₖ of both G. lemaneiformis and U. prolifera (P < 0.05). Their interaction also significantly affected these three photosynthetic parameters (P < 0.05) (Table 1). Under low light conditions, with increasing culture biomass density, rETRₘₐₓ and Iₖ of G. lemaneiformis showed a gradual decreasing trend. rETRₘₐₓ in the 1U4G and 1U6G groups decreased significantly by 16.92% and 20.24% compared to IC (P < 0.05). Iₖ in the 1U6G group decreased significantly by 37.26% compared to IC (P < 0.05). α showed a gradually increasing trend. For U. prolifera under LL, rETRₘₐₓ and Iₖ first decreased and then increased. rETRₘₐₓ in the 1U2G and 1U4G groups decreased significantly by 12.70% and 17.74% compared to IC (P < 0.05). α first increased and then decreased. Under high light intensity, rETRₘₐₓ and α of G. lemaneiformis remained relatively stable until biomass density increased to the 1U6G group, where they decreased significantly by 33.52% and 29.29%, respectively, compared to IC (P < 0.05). Iₖ showed a trend of first decreasing and then rising. For U. prolifera under HL, rETRₘₐₓ and α showed a gradually decreasing trend. rETRₘₐₓ in the 1U2G, 1U4G, and 1U6G groups decreased significantly by 20.79%, 30.97%, and 31.27%, respectively, compared to IC. Iₖ remained relatively stable, with no significant differences (P > 0.05).
Pigments content
Two-way ANOVA revealed that chlorophyll a (Chl a) and Carotenoid (Car.) content of the algae were significantly affected by light intensity and biomass density (P < 0.05), and their interaction also exerted a significant effect on Chl a and Car. content (P < 0.05) (S4 Table in S1 File). As shown in Fig 6A, under low light intensity, Chl a of G. lemaneiformis showed no significant difference between IC and 1U2G groups (P > 0.05), but significant differences compared to 1U4G and 1U6G groups (P < 0.05), decreasing significantly by 26.47% and 23.53% compared to IC. Chl a of U. prolifera in the 1U2G group was significantly different from that in the 1U4G and 1U6G groups (P < 0.05), decreasing by 16.22% and 21.62%, respectively, compared to the 1U2G group. Under high light intensity (Fig 6B), Chl a of G. lemaneiformis showed no significant difference among IC, 1U2G, 1U4G, and 1U6G groups (P > 0.05). Chl a in the 1U4G and 1U6G groups decreased significantly by 15.38% and 19.23% compared to the 1U2G group (P < 0.05). Chl a of U. prolifera in the 1U2G, 1U4G, and 1U6G groups decreased significantly by 12.90%, 12.90%, and 22.58%, respectively, compared to IC (P < 0.05). Under both LL and HL conditions, Chl a of U. prolifera was significantly higher than that of G. lemaneiformis only in the 1U4G group, by 19.35% and 18.52%, respectively (P < 0.05).
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same light intensity level across different culture densities. Different uppercase letters indicate significant differences among U. prolifera treatments at the same light intensity level across different culture densities. * indicates a significant difference between G. lemaneiformis and U. prolifera at the same culture density.
Under low light intensity, Car. content of G. lemaneiformis showed no significant difference among IC, 1U2G, and 1U4G groups (P > 0.05), but was significantly lower in these groups compared to the 1U6G group, with decreases of 33.33%, 22.22%, and 22.22% respectively (P < 0.05). Car. content of U. prolifera showed no significant difference between IC and 1U2G or 1U4G groups (P > 0.05), but IC and 1U4G groups were significantly lower than 1U6G by 33.33% and 41.67%, respectively (Fig 6C). Under high light intensity, Car. content of G. lemaneiformis showed no significant difference among IC, 1U2G, and 1U4G groups (P > 0.05). IC and 1U4G groups were significantly lower than 1U6G by 14.29% and 28.57% (P < 0.05). Car. content of U. prolifera in IC, 1U2G, and 1U4G groups was significantly higher than in 1U6G by 50.00%, 33.33%, and 33.33% (P < 0.05). Under low light, Car. content of U. prolifera was significantly higher than that of G. lemaneiformis in IC, 1U2G, and 1U6G groups by 33.33%, 42.86%, and 33.33% (P < 0.05) (Fig 6C). Under high light, Car. content of U. prolifera was significantly higher than that of G. lemaneiformis in IC, 1U2G, and 1U4G groups by 69.64%, 33.33%, and 60.00% (P < 0.05), but significantly lower by 14.29% in the 1U6G group (P < 0.05) (Fig 6D).
The phycoerythrin (PE) and phycocyanin (PC) content of G. lemaneiformis were significantly affected by light intensity and biomass density (P < 0.05). The interaction between light intensity and biomass density significantly affected PC content (P < 0.05), but not PE content (P > 0.05) (S5 Table in S1 File). Under low light intensity (Fig 7A-B), no significant differences in PE or PC content were detected between the IC and 1U2G groups (P > 0.05) or between the 1U4G and 1U6G groups (P > 0.05). Under high light intensity, PE content in the 1U2G and 1U6G groups differed significantly from IC (P < 0.05). PE and PC content in the 1U2G group increased significantly by 10.14% and 13.33% compared to IC, while in the 1U6G group, PE and PC content decreased significantly by 15.94% and 20.00% compared to IC. PE and PC content of G. lemaneiformis were significantly higher under low light intensity than under high light intensity.
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same density under HL. Different uppercase letters indicate significant differences among G. lemaneiformis treatments at the same density under LL. * indicates a significant difference between LL and HL treatments for the same culture density.
Soluble protein and soluble carbohydrate content
Changes in soluble protein (SP) and soluble carbohydrate (SC) content of G. lemaneiformis and U. prolifera under different treatments are shown in Fig 8. SP content was significantly affected by light intensity and biomass density (P < 0.05), but their interaction did not significantly affect SP (P > 0.05). Light intensity did not significantly affect SC content (P > 0.05), while biomass density significantly affected SC content of both species (P < 0.05). The interaction between light intensity and biomass density significantly affected both SP and SC content (P < 0.05) (S6 Table in S1 File). As shown in Fig 8A, under low light intensity, SP content of G. lemaneiformis showed no significant difference between IC and 1U2G groups (P > 0.05), but decreased significantly by 15.33% and 22.33% in the 1U4G and 1U6G groups compared to IC (P < 0.05). SP content of U. prolifera in the 1U2G group increased significantly by 30.61% compared to IC (P < 0.05). As shown in Fig 8B, under high light intensity, SP content of G. lemaneiformis showed no significant difference among IC, 1U2G, and 1U4G groups (P > 0.05), but decreased significantly by 16.58% in the 1U6G group compared to IC (P < 0.05). SP content of U. prolifera first increased and then decreased with increasing biomass density (Fig 8A-B); under high light intensity, SP in the 1U2G group increased significantly by 34.24% compared to IC (P < 0.05), while SP in the 1U4G and 1U6G groups showed no significant difference from IC (P > 0.05). Under the same treatment conditions, the SP content of G. lemaneiformis was significantly higher than that of U. prolifera (P < 0.05).
IC: Individual culture (monoculture); 1U2G, 1U4G, and 1U6G: Co-culture with G. lemaneiformis to U. prolifera biomass density ratios of 1:2, 1:4, and 1:6, respectively. Different lowercase letters indicate significant differences among G. lemaneiformis treatments at the same light intensity level across different culture densities. Different uppercase letters indicate significant differences among U. prolifera treatments at the same light intensity level across different culture densities. * indicates a significant difference between G. lemaneiformis and U. prolifera at the same culture density.
As shown in Fig 8C, under low light intensity, SC content of G. lemaneiformis reached its highest value in the IC group (25.43 ± 1.29 mg g ⁻ ¹ FW). SC content in the 1U2G, 1U4G, and 1U6G groups decreased significantly by 14.83%, 18.48%, and 36.06%, respectively, compared to IC (P < 0.05). SC content of U. prolifera in the 1U2G group increased significantly by 22.17% compared to IC (P < 0.05), while in the 1U6G group, it decreased significantly by 15.44% (P < 0.05). SC content of G. lemaneiformis was significantly higher than that of U. prolifera by 29.83% and 18.18% in the IC and 1U4G groups, respectively (P < 0.05) (Fig 8C-D). As shown in Fig 8D, under high light intensity, SC content of both G. lemaneiformis and U. prolifera decreased significantly with increasing biomass density. SC of G. lemaneiformis in the 1U4G and 1U6G groups decreased significantly by 26.87% and 39.90% compared to IC (P < 0.05). SC of U. prolifera in the 1U2G, 1U4G, and 1U6G groups decreased significantly by 20.10%, 19.66%, and 39.04%, respectively, compared to IC (P < 0.05). In all HL treatment groups, the SC content of G. lemaneiformis was significantly higher than that of U. prolifera (P < 0.05).
Discussion
The competitive relationships among macroalgae are a critical issue in coastal ecological regulation and algal bloom bioremediation. Their interspecific interactions directly shape community structure, influence nutrient cycling, light utilization efficiency, and niche partitioning, thereby determining the potential and scale of algal blooms. By analyzing how key environmental factors—such as light, temperature, nutrients, and water flow—regulate competitive dynamics, a theoretical foundation can be established for developing niche-competition-based “using algae to control algae” biocontrol technologies. In this study, the inhibitory effect of G. lemaneiformis on the growth of U. prolifera was investigated by regulating light intensity and biomass density ratios.
This study found that the relative growth rate and photosynthetic efficiency of U. prolifera significantly decreased with increasing G. lemaneiformis proportion under co-culture conditions, which can be attributed to the accumulation of allelopathic inhibitory compounds. Marine macroalgae produce various secondary metabolites, such as terpenes, sterols, polyphenols, and acetogenins, to protect themselves from herbivores or other phototrophs. Generally, allelopathy may involve interactions with proteins, inhibition of alkaline phosphatase, disruption of the electron transport chain, membrane damage, and oxidative damage caused by polyphenol auto-oxidation [27]. Previous studies have confirmed that G. lemaneiformis can inhibit Ulva growth by releasing specific allelochemicals [14]. Culture filtrate of G. lemaneiformis significantly reduces biomass accumulation and PSII effective quantum yield (Yield) of U. prolifera, with stronger inhibition at higher filtrate concentrations. In this study, the carotenoid content of U. prolifera was lower than that of G. lemaneiformis (by 14.29%) only in the high-light 1U6G group. Carotenoids are key pigments defending against photo-oxidative damage. Their reduction makes U. prolifera more susceptible to light stress under high light. Further studies suggest this may be related to hydrogen peroxide (H₂O₂) and halogenated hydrocarbons released by G. lemaneiformis, which can disrupt photosynthetic pigment synthesis and photosystem stability in U. prolifera, leading to increased susceptibility to photodamage under high light [12]. The more significant decrease in photosynthetic parameters of U. prolifera in high-biomass density G. lemaneiformis groups under high light in this study may be related to this mechanism.
Interactions among macroalgae involve complex interspecific competition mediated by both direct and indirect mechanisms. Neopyropia yezoensis can inhibit gamete germination in U. prolifera through allelopathic effects exerted by its dried powder, fresh thalli, and culture filtrates [28]. Conversely, when co-cultured, U. prolifera significantly suppresses the growth and net photosynthetic rate of N. yezoensis. Elevated CO2 concentrations reduce the growth rate of N. yezoensis while simultaneously enhancing its resistance to allelopathic stress from U. prolifera [29]. The cultivation of G. lemaneiformis can enhance plankton biodiversity through allelopathy by suppressing dominant plankton species [30]. However, in direct interactions between G. lemaneiformis and U. prolifera, the presence of U. prolifera inhibits the growth of G. lemaneiformis, whereas G. lemaneiformis promotes the growth of U. prolifera—though this promotive effect can be offset by higher biomass densities [19]. These findings reveal the nuanced roles of allelopathy, environmental factors such as CO₂, and density-dependent effects in shaping macroalgal community dynamics.
Resource competition is a fundamental driver of macroalgal growth. As a typical opportunistic alga, the rapid growth of U. prolifera depends on sustained light and nutrient supply [5]. In this study, G. lemaneiformis potentially compressed the ecological space of U. prolifera, affecting localized light conditions and nutrient availability. The shading effect induced by G. lemaneiformis led to a reduction in chlorophyll a content and light energy utilization efficiency in U. prolifera, thereby inhibiting its growth. Studies show that while the nitrogen uptake rate of U. prolifera is higher than that of G. lemaneiformis, the latter possesses stronger nitrogen storage capacity, storing nitrogen in the form of phycoerythrin, which may allow it to maintain a growth advantage in low-nutrient environments [12]. Simultaneously, the efficient absorption of nitrogen and phosphorus by G. lemaneiformis further restricts nutrient acquisition by U. prolifera, manifested as inhibition of nitrate reductase (NR) activity and soluble protein (SP) synthesis in U. prolifera [31,32]. This aligns with previous conclusions that Gracilariopsis spp. significantly inhibits Ulva spp. growth through resource competition, with the effect intensifying with increasing biomass density [19,33,34].
Light is the driving source for photosynthesis in macroalgae and an important environmental factor affecting their productivity. Light intensity is also a major abiotic factor influencing algal growth and photosynthesis; both excessively high and low intensities affect photosynthesis and consequently normal growth [35,36]. It is noteworthy that in the Yellow Sea green tide outbreak areas, although floating U. prolifera aggregations are primarily concentrated in the well-lit surface layer, the high turbidity of nearshore waters causes light to attenuate rapidly with water depth. The low-light and high-light treatments established in this experiment were designed to simulate two representative light environments that algae may experience in nearshore settings: one being light-limited conditions influenced by factors such as water turbidity or internal shading, and the other representing higher light conditions closer to the surface or under clear weather conditions. The relative growth rate and Pn of both G. lemaneiformis and U. prolifera in monoculture were higher under high light intensity than under low light intensity, indicating that appropriately increased light intensity benefits algal growth and photosynthetic physiology. This result is consistent with studies on other large seaweeds such as Undaria pinnatifida [37], Gracilaria lemaneiformis [38], and Gracilaria asiatica [39]. Under high light, rETRₘₐₓ and Iₖ of G. lemaneiformis were significantly higher than under low light, consistent with the trends in relative growth rate and Pn. A similar, though less pronounced, trend was observed for U. prolifera. Macroalgae regulate their pigment content, thallus structure, and morphology in response to long-term exposure to different light levels [40]. Enhanced pigment synthesis under low light requires more energy, leading to lower growth than under high light. However, under high light, Chl a and Car. content of both G. lemaneiformis and U. prolifera decreased compared to low light, and G. lemaneiformis downregulated the synthesis of PE and PC. This may be because high light inhibits photosynthetic pigment synthesis and promotes thallus growth, a pattern described as exhibiting “pigment economy” [41,42]. Therefore, under high-light conditions, the shading effect of G. lemaneiformis itself and its potential disruption to the photosystem of U. prolifera are amplified. This, to some extent, simulates the light competition effect that high-biomass G. lemaneiformis cultivation areas may exert on surface or subsurface U. prolifera, although it differs from the bloom scenario with unlimited light availability in open-sea surface waters.
Biomass density is a key factor regulating algal photosynthesis and growth, directly affecting critical environmental parameters such as available light intensity, nutrient concentration, dissolved oxygen, and inorganic carbon content [43]. When algae share the same ecological niche, this biomass density effect inevitably triggers interspecific resource competition. In this study, as biomass density increased, the relative growth rate and Pn of both G. lemaneiformis and U. prolifera decreased and were significantly lower than in monoculture controls (P < 0.05). This inhibition may stem from light attenuation and nutrient limitation caused by increased biomass density. Notably, increased G. lemaneiformis biomass exhibited a significant inhibitory effect on U. prolifera growth (P < 0.05), and the inhibition intensity strengthened with increasing G. lemaneiformis biomass density. This result aligns with reports of G. lemaneiformis competitively excluding dinoflagellates [44,45]. Previous studies indicate that nutrient levels in high-biomass density G. lemaneiformis cultivation are lower than in low-biomass density cultivation. Increased consumption may lead to inorganic carbon and nutrient shortages in high-biomass density G. lemaneiformis cultures, thereby inhibiting photosynthesis [46]. Similarly, due to the presence of U. prolifera, the growth rate of G. lemaneiformis also decreased with increasing biomass density, though less significantly than for U. prolifera, indicating competitive interaction. Previous studies have shown that when stocking biomass density increases, algal nitrate reductase (NR) activity significantly decreases. This suggests that high stocking biomass density reduces nitrogen metabolic capacity, which potentially explains the decrease in relative growth rate (RGR) observed in high-biomass density seaweed cultures [46]. When the two species were co-cultured, G. lemaneiformis exhibited a competitive advantage.
Previous studies have confirmed the effects of light intensity and biomass density on the growth and physiological performance of U. prolifera and G. lemaneiformis individually, but knowledge of their interaction is limited. With increasing co-culture biomass density, the relative growth rate, net photosynthetic rate, and chlorophyll fluorescence parameters of both G. lemaneiformis and U. prolifera significantly decreased compared to monoculture [46]. The inhibitory effect of G. lemaneiformis on U. prolifera under low light was weaker than under high light, possibly related to differences in their light adaptation strategies. Macroalgal growth is negatively correlated with stocking biomass density. Under low light, the RGR of U. prolifera decreased by 36.92% at high stocking biomass density, while under high light, it decreased by 45.10%. The extent to which increased culture biomass density inhibited the growth rates of both U. prolifera and G. lemaneiformis was itself mediated by light intensity [47]. However, under low light, the decreasing trend was less pronounced, possibly because G. lemaneiformis growth was lower, making the biomass density effect less significant. Under high light, the growth rate decrease of high-biomass density G. lemaneiformis was significant, and soluble protein content changed little, but the decrease was less pronounced than for U. prolifera. This indicates that high light intensity and high G. lemaneiformis culture biomass density significantly inhibited the growth of U. prolifera.
This study systematically analyzed the interactive effects of light intensity and biomass density on the competitive relationship between G. lemaneiformis and U. prolifera, revealing that G. lemaneiformis suppresses the growth of U. prolifera through shading effects and potential allelopathic interactions. These findings deepen the understanding of interspecific competition mechanisms among macroalgae and provide experimental support for near-shore ecological regulation based on the “using algae to control algae” concept. Additionally, they offer scientific guidance for optimizing the cultivation layout of G. lemaneiformis in specific nearshore waters (e.g., eutrophic bays and aquaculture areas) during green tide outbreaks.
Conclusions
In recent years, the recurrent and persistent outbreaks of U. prolifera-induced green tides in the Yellow Sea have posed severe threats to coastal ecosystem health and coastal-related industries. Although various mitigation strategies have been deployed to address this issue, they often incur high economic costs, substantial resource consumption, and potential environmental risks. This in situ study, conducted in a key U. prolifera bloom source area, demonstrates that the competitive outcome between G. lemaneiformis and U. prolifera is significantly regulated by the interactive effects of light intensity and biomass density. Specifically, increasing G. lemaneiformis biomass density reduces the relative growth rate (RGR) of U. prolifera, and this inhibitory effect is particularly pronounced under high-light conditions. The inhibitory effect is primarily achieved through mechanisms such as shading effects and potential allelopathic interactions. Notably a biomass density ratio of 1:4–1:6 (U. prolifera: G. lemaneiformis) was identified as an optimal ratio range that effectively suppresses U. prolifera growth while sustaining the cultivation of G. lemaneiformis. These findings confirm the feasibility of developing interspecific competition-based biological control strategies for green tides, while providing empirical data to support the optimizing of G. lemaneiformis cultivation and the advancement of green tide bioremediation.
References
- 1. Wang S, Zhao L, Wang Y, Zhang H, Li F, Zhang Y. Distribution characteristics of green tides and its impact on environment in the Yellow Sea. Mar Environ Res. 2022;181:105756. pmid:36206643
- 2. Zhang Q-C, Liu Q, Kang Z-J, Yu R-C, Yan T, Zhou M-J. Development of a fluorescence in situ hybridization (FISH) method for rapid detection of Ulva prolifera. Estuarine, Coastal and Shelf Science. 2015;163:103–11.
- 3. Geng X, Li H, Wang L, Sun W, Li Y. A comprehensive review of remote sensing techniques for monitoring Ulva prolifera green tides. Front Mar Sci. 2025;12.
- 4. Hu L, Hu C, Ming-Xia H. Remote estimation of biomass of Ulva prolifera macroalgae in the Yellow Sea. Remote Sensing of Environment. 2017;192:217–27.
- 5. Cai J, Ni J, Chen Z, Wu S, Wu R, He C, et al. Effects of ocean acidification and eutrophication on the growth and photosynthetic performances of a green tide alga Ulva prolifera. Front Mar Sci. 2023;10.
- 6. Zhang Y, He P, Li H, Li G, Liu J, Jiao F, et al. Ulva prolifera green-tide outbreaks and their environmental impact in the Yellow Sea, China. Natl Sci Rev. 2019;6(4):825–38. pmid:34691936
- 7. Xia Z, Liu J, Zhao S, Sun Y, Cui Q, Wu L, et al. Review of the development of the green tide and the process of control in the southern Yellow Sea in 2022. Estuarine, Coastal and Shelf Science. 2024;302:108772.
- 8. Liu J, Xia J, Zhuang M, Zhang J, Yu K, Zhao S, et al. Controlling the source of green tides in the Yellow Sea: NaClO treatment of Ulva attached on Pyropia aquaculture rafts. Aquaculture. 2021;535:736378.
- 9. Xia Z, Yuan H, Liu J, Sun Y, Tong Y, Zhao S, et al. A review of physical, chemical, and biological green tide prevention methods in the Southern Yellow Sea. Mar Pollut Bull. 2022;180:113772. pmid:35623218
- 10. Cao M, Zhang J, Li P, Wang J, Mi P, Sui Z. Review on recent advances of Gracilariopsis lemaneiformis (Rhodophyta). Algal Research. 2024;79:103453.
- 11. Hu Y, Du Q, Mi P, Shang E, Sui Z. Gene cloning and expression regulation in the pathway of agar and floridean starch synthesis of Gracilariopsis lemaneiformis (Rhodophyta). J Appl Phycol. 2018;31(3):1889–96.
- 12. Friedlander M, Gonen Y, Kashman Y, Beer S. Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed by Ulva cf. lactuca. J Appl Phycol. 1996;8(1):21–5.
- 13. McHugh DJ. Worldwide distribution of commercial resources of seaweeds including Gelidium. Hydrobiologia. 1991;221(1):19–29.
- 14. Xu D, Gao Z, Zhang X, Fan X, Wang Y, Li D, et al. Allelopathic interactions between the opportunistic species Ulva prolifera and the native macroalga Gracilaria lichvoides. PLoS One. 2012;7(4):e33648. pmid:22496758
- 15. Collén J, Guisle-Marsollier I, Léger JJ, Boyen C. Response of the transcriptome of the intertidal red seaweed Chondrus crispus to controlled and natural stresses. New Phytol. 2007;176(1):45–55. pmid:17803640
- 16. Liu B, Zhou Z, Wang L, Zhang X, Xu Z, Liu Z, et al. The heatwaves weaken the effect of light on the growth, photosynthesis, and reproductive capacity of Ulva prolifera. Mar Environ Res. 2025;209:107163. pmid:40339513
- 17. Zhang X, Wang H, Mao Y, Liang C, Zhuang Z, Wang Q, et al. Somatic cells serve as a potential propagule bank of Enteromorpha prolifera forming a green tide in the Yellow Sea, China. J Appl Phycol. 2009;22(2):173–80.
- 18. Cao X, Wang H, Zang X, Liu Z, Xu D, Jin Y, et al. Changes in the Photosynthetic Pigment Contents and Transcription Levels of Phycoerythrin-Related Genes in Three Gracilariopsis lemaneiformis Strains Under Different Light Intensities. J Ocean Univ China. 2021;20(3):661–8.
- 19. Pan Z, Yu Y, Chen Y, Yu C, Xu N, Li Y. Combined effects of biomass density and low-nighttime temperature on the competition for growth and physiological performance of Gracilariopsis lemaneiformis and Ulva prolifera. Algal Research. 2022;62:102638.
- 20. Zhao X, Gao L, Li X, Li G, Gao G. Differential responses of an economically important macroalga and a bloom-forming microalga to marine heatwaves in a coculture system. Aquaculture. 2025;599:742111.
- 21. Genty B, Briantais J-M, Baker NR. The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence. Biochimica et Biophysica Acta (BBA) - General Subjects. 1989;990(1):87–92.
- 22. Eilers PHC, Peeters JCH. A model for the relationship between light intensity and the rate of photosynthesis in phytoplankton. Ecological Modelling. 1988;42(3–4):199–215.
- 23. Wellburn AR. The Spectral Determination of Chlorophylls a and b, as well as Total Carotenoids, Using Various Solvents with Spectrophotometers of Different Resolution. Journal of Plant Physiology. 1994;144(3):307–13.
- 24. Beer S, Eshel A. Determining phycoerythrin and phycocyanin concentrations in aqueous crude extracts of red algae. Australian Journal of Marine and Freshwater Research. 1985;36(6):785–92.
- 25. Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976;72:248–54. pmid:942051
- 26. BECK DJ, BIBBY BG. A modified anthrone coloimetric technique for use in investigations related to the cariogenicity of foodstuffs. J Dent Res. 1961;40:161–70. pmid:13688382
- 27. Yang Y, Liu Q, Chai Z, Tang Y. Inhibition of marine coastal bloom-forming phytoplankton by commercially cultivated Gracilaria lemaneiformis (Rhodophyta). J Appl Phycol. 2014;27(6):2341–52.
- 28. Fu M, Cao S, Li J, Zhao S, Liu J, Zhuang M, et al. Controlling the main source of green tides in the Yellow Sea through the method of biological competition. Mar Pollut Bull. 2022;177:113561. pmid:35305372
- 29. Sun J, Bao M, Xu T, Li F, Wu H, Li X, et al. Elevated CO2 influences competition for growth, photosynthetic performance and biochemical composition in Neopyropia yezoensis and Ulva prolifera. Algal Research. 2021;56:102313.
- 30. Chai ZY, He ZL, Deng YY, Yang YF, Tang YZ. Cultivation of seaweed Gracilaria lemaneiformis enhanced biodiversity in a eukaryotic plankton community as revealed via metagenomic analyses. Mol Ecol. 2018;27(4):1081–93. pmid:29368406
- 31. Zhou W, Sui Z, Wang J, Chang L. An orthogonal design for optimization of growth conditions for all life history stages of Gracilariopsis lemaneiformis (Rhodophyta). Aquaculture. 2013;392–395:98–105.
- 32. Zhu M, Liu Z, Shao H, Jin Y. Effects of nitrogen and phosphate enrichment on the activity of nitrate reductase of Ulva prolifera in coastal zone. Acta Physiol Plant. 2016;38(7).
- 33. Friedlander M, Kashman Y, Weinberger F, Dawes CJ. Gracilaria and its epiphytes: 4. The response of two Gracilaria species to Ulva lactuca in a bacteria-limited environment. Journal of Applied Phycology. 2001;13(6):501–7.
- 34. Chen B, Zou D, Jiang H. Elevated CO2 exacerbates competition for growth and photosynthesis between Gracilaria lemaneiformis and Ulva lactuca. Aquaculture. 2015;443:49–55.
- 35. Xie X, Lu X, Wang L, He L, Wang G. High light intensity increases the concentrations of β-carotene and zeaxanthin in marine red macroalgae. Algal Research. 2020;47:101852.
- 36. Zhukova NV, Yakovleva IM. Low light acclimation strategy of the brown macroalga Undaria pinnatifida: Significance of lipid and fatty acid remodeling for photosynthetic competence. J Phycol. 2021;57(6):1792–804. pmid:34486722
- 37. Yago T, Arakawa H, Shigeto S, Ito ryo, Matsumoto A, Okumura Y. Effects of light conditions on the growth of commercial seaweed Undaria pinnatifida. Afr J Plant Sci. 2017;11(6):190–6.
- 38. Wu H, Jiang H, Liu C, Deng Y. Growth, pigment composition, chlorophyll fluorescence and antioxidant defenses in the red alga Gracilaria lemaneiformis (Gracilariales, Rhodophyta) under light stress. South African Journal of Botany. 2015;100:27–32.
- 39. Wedchaparn O, Ayisi CL, Huo Y, He P. Effects of Different Light Intensity Fluctuations on Growth Rate, Nutrient Uptake and Photosynthetic Efficiency of Gracilaria asiatica. J of Fisheries and Aquatic Science. 2015;10(6):533–42.
- 40. Machalek KM, Davison IR, Falkowski PG. Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina. Plant Cell & Environment. 1996;19(9):1005–16.
- 41. Chen Z, Shi M, Xu J, Wu R, Xu J, Wang J, et al. Synergistic effects of warming and low salinity enhanced the production of Gracilariopsis lemaneiformis in the warming drainage zone of Tianwan Nuclear Power Plant, China. Aquaculture. 2023;577:739961.
- 42. Gao G, Gao Q, Bao M, Xu J, Li X. Nitrogen availability modulates the effects of ocean acidification on biomass yield and food quality of a marine crop Pyropia yezoensis. Food Chem. 2019;271:623–9. pmid:30236725
- 43. Richards D, Hurd C, Pritchard D, Wing S, Hepburn C. Photosynthetic response of monospecific macroalgal stands to density. Aquat Biol. 2011;13(1):41–9.
- 44. Wang Y, Yu Z, Song X, Tang X, Zhang S. Effects of macroalgae Ulva pertusa (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta) on growth of four species of bloom-forming dinoflagellates. Aquatic Botany. 2007;86(2):139–47.
- 45. Wang Y, Zhou B, Tang X. Effects of two species of macroalgae—Ulva pertusa and Gracilaria lemaneiformis—on growth of Heterosigma akashiwo (Raphidophyceae). J Appl Phycol. 2008;21(4):375–85.
- 46. Jiang H, Zou D, Lou W, Ye C. Effects of stocking density and decreased carbon supply on the growth and photosynthesis in the farmed seaweed, Pyropia haitanensis (Bangiales, Rhodophyta). J Appl Phycol. 2017;29(6):3057–65.
- 47. Oca J, Cremades J, Jiménez P, Pintado J, Masaló I. Culture of the seaweed Ulva ohnoi integrated in a Solea senegalensis recirculating system: influence of light and biomass stocking density on macroalgae productivity. J Appl Phycol. 2019;31(4):2461–7.