Gouqi Island Research Articles

Use of Environmental DNA to Evaluate the Spatial Distribution of False Kelpfish (Sebastiscus marmoratus) in Nearshore Areas of Gouqi Island

This study aims to explore the spatial distribution of false kelpfish (Sebastiscus marmoratus) in the mussel farming area, artificial reef areas of Gouqi Island (Shengsi, China), and natural areas using eDNA detection methods. Surface and bottom water samples were collected at 12 stations in November 2022 and April 2023, totaling 52 samples. We used species-specific primers and probes for quantitative PCR (qPCR) detection of Sebastiscus marmoratus eDNA. The eDNA concentrations differed seasonally (p < 0.05) and did not differ (p > 0.05) among the three sampling areas and two water layers. The greatest eDNA concentrations occurred in the surface layer during the spring. Higher concentrations of Sebastiscus marmoratus eDNA were also found in the mussel aquaculture area. Temperature exhibited a significant positive correlation with Sebastiscus marmoratus eDNA concentration (p < 0.05). Additionally, we developed linear equations predicting the relationship between environmental factors and environmental factors, providing a reference for future fishery resource surveys.

Microeukaryotic communities varied along the gradient in the seaweed habitats: A case study in a typical reef island in the East China Sea

Seaweeds are ecologically important primary producers, forming unique habitats. Microeukaryotes are pivotal in ecological functioning of seaweeds, but their ecological role and processes in seaweed habitats remain poorly understood due to a lack of field data. Here we presented an innovative insights into the microeukaryotic communities along the seaweed habitat gradients using 18S rDNA sequencing around a typical reef island, Gouqi Island. We set and verified habitat gradients of brown (HB, mainly Sargassum) and green algae (HG, mainly Ulva), and the control site between them (M), with detritus samples collected from collectors by SCUBA (Self-Contained Underwater Breathing Apparatus). Along the seaweed habitats, microeukaryotic biodiversity decreased from the detritus close to the seaweed habitats to surface water with increasing distance from detritus. For the dominant ecological function, clear distinction was also found in detritus and water samples along the seaweed habitat gradient, where phototrophs, mixotrophs and phagotrophs dominated in the detritus of brown algae dominated site, medium site, and green algae dominated site, respectively, responding differently to the environmental factors and seaweeds by Mantel analysis. Furthermore, we found that stochastic processes dominated in microeukaryotic community assembly in the brown seaweed habitat whereas deterministic processes dominated in green algae habitat. Highly varied occupancy was revealed in the green algae habitat by Specificity-Occupancy (SPEC-OCCU) analysis. Our result contributed to a better understanding of the ecological functioning of microeukaryotic communities in seaweed habitats, and further provided data for the bioassessment and conservation of seaweed habitats within marine ecosystems.

Vulnerability analysis of socio-ecological systems on small islands from the perspective of fisheries and tourism: A case study of Zhoushan Gouqi Island

Small island social-ecological systems are increasingly vulnerable to the combined impacts of human activities and environmental changes, making focused vulnerability analyses critical for sustainable governance. In this study, Gouqi Island, a remote island, was selected as the research site to establish a comprehensive vulnerability assessment framework based on the Vulnerability-Sensitivity-Danger (VSD) model. To account for potential interdependencies among indicators, a fuzzy integration method was employed to quantitatively assess vulnerability trends from 2016 to 2022. The analysis revealed that vulnerability reached its lowest point in 2018, peaked at 0.876 in 2020, and remained above 2016 levels through 2022, despite a slight decline. Additionally, machine learning techniques were used to identify key factors influencing vulnerability, highlighting indicators such as D24 (proportion of fisheries and tourism output), D41 (number of tourists), and D52 (aquaculture production) as particularly significant, though distinct from traditional sensitivity indicators. These findings inform the identification of critical factors affecting the island's sustainable development and lead to the proposal of adaptive governance strategies. The insights from this study provide valuable guidance for promoting sustainable development in similar remote islands.

Changes in biomass and organic carbon content during the growth period of dominant seaweed in the intertidal zone of Gouqi Island, China

Changes in biomass and organic carbon content during the growth period of dominant seaweed in the intertidal zone of Gouqi Island, China

Peteryoungia algae sp. nov. isolated from seaweeds of Gouqi Island, China, and its unique genetic features among Peteryoungia strains.

A Gram-stain-negative, light khaki, strictly aerobic, rod-shaped, motile via multiple flagella, and catalase- and oxidase-positive bacterium, designated as SSM4.3T, was isolated from the seaweed of Gouqi Island in the East China Sea. The novel isolate grows at 0-5.0% NaCl concentrations (w/v) (optimum 1%), pH 5.0-9.0 (optimum pH 7.0), and 15-37°C (optimum 30°C). The 16S rRNA gene sequences-based phylogeny indicates that the novel marine isolate belongs to the family Rhizobiaceae and that it shared the greatest sequence similarity (98.9%) with Peteryoungia rhizophila CGMCC 1.15691T. This classification was also supported by phylogenetic analysis using core genes. The predominant fatty acids (≥ 10%) of the strain were identified as C18:1 ω7c/C18:1 ω6c. Q-10 was identified as the major isoprenoid quinone, with trace levels of Q-9 present. The major polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The complete genome size of strain SSM4.3T is 4.39Mb with a DNA G+C content of 61.3%. The average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values between the genomes of strain SSM4.3T and its closely related representatives were 74.80-86.93%, 20.00-32.30%, and 70.30-91.52%, respectively. Phylogenetic analysis, grounded on the core genes, reveals the evolutionary relationship between SSM4.3T and other Peteryoungia strains. Pan-genomics analysis of 8 previously classified Peteryoungia species and SSM4.3T revealed their unique genetic features and functions. Overall, strain SSM4.3T was considered to be a new species of the Peteryoungia genus; the name Peteryoungia algae sp. nov. has been proposed, with type strain SSM4.3T (= LMG 32561 = MCCC 1K07170).

Characterization and Genomic Analysis of Affinirhizobium gouqiense sp. nov. Isolated from Seawater of Gouqi Island Located in the East China Sea and Reclassification of Rhizobium lemnae to the Genus Affinirhizobium as Affinirhizobium lemnae comb. nov.

A novel bacterium designated as SSA5.23T was isolated from seawater. Cells of SSA5.23T are Gram-stain-negative, short, rod-shaped, and exhibit motility via numerous peritrichous flagella. The strain could grow at temperatures ranging from 15 to 35 °C (optimum at 25 °C), in a salinity range of 0-5.0% (w/v) NaCl, and within a pH range of 6.0-9.0 (optimum at pH 7.0). The predominant cellular fatty acid of SSA5.23T was C18:1 ω7c/C18:1 ω6c, and the major respiratory quinones were Q-9 and Q-10. Diphosphatidylglycerol, phosphatidylethanolamine, and phosphatidylglycerol were identified as the primary polar lipids. The complete genome (5.47 Mb) of SSA5.23T comprises of a circular chromosome of 3.64 Mb and three plasmids, specifically sized at 59.73 kb, 227.82 kb, and 1.54 Mb, respectively. Certain genes located on the plasmids play roles in denitrification, oxidative stress resistance, and osmotic tolerance, which likely contribute to the adaptability of this strain in marine conditions. Core-proteome average amino acid identity analysis effectively identified the strain's affiliation with the genus Affinirhizobium, showing the highest value (89.9%) with Affinirhizobium pseudoryzae DSM 19479T. This classification was further supported by the phylogenetic analysis of concatenated alignment of 170 single-copy orthologous proteins. When compared to related reference strains, SSA5.23T displayed an average nucleotide identity ranging from 74.9 to 80.3% and digital DNA-DNA hybridization values ranging from 19.9 to 23.9%. Our findings confirmed that strain SSA5.23T represents a novel species of the genus Affinirhizobium, for which the name Affinirhizobium gouqiense sp. nov. (type strain SSA5.23T = LMG 32560T = MCCC 1K07165T) was suggested.

Mussel Culture Activities Facilitate the Export and Burial of Particulate Organic Carbon

The recent expansion of shellfish mariculture could significantly impact the ocean carbon cycle and its associated biogeochemical processes. To understand the source and fate of particulate organic carbon (POC), a summer cruise was conducted from September 8 to 10, 2022, at a mussel farm on Gouqi Island and its adjacent areas located in the East China Sea. Parameters included in situ temperature and salinity, contents of dissolved oxygen (DO), suspended particulate matter (SPM), POC, and chlorophyll a (Chl a), as well as the stable carbon isotopic composition (δ13C) of organic matter in particle and sediment samples, which were analyzed to facilitate a comparative assessment of the areas inside and outside the mussel farm. The POM was much fresher (POC/Chl a < 150) inside the farm with little impact from sediment resuspension (lower SPM content, 11.6 ± 6.6 mg/L), while a significant influence of sediment resuspension was found outside the farm (SPM > 20 mg/L, POC/Chl a > 150). A two end-member mixing model showed that 82.0 ± 6.0% of POC originated from marine algae within the farm, much higher than that outside the farming area (66.1 ± 7.8%). Moreover, elevated DO saturation but relatively low Chl a concentration within the farm suggested continuous algae consumption following potential high productivity. The averaged δ13C values were similar among suspended POC, sinking POC, and sedimentary organic carbon within the farm, implying the fast export and burial of POC. This is likely due to the filter-feeding habits of mussels, who ingest fresh POC and then pack it as fecal pellets that rapidly settle into the sediment. This study sheds light on the distribution and sources of POM inside and outside the mussel farm on Gouqi Island, enhancing our understanding of the marine carbon cycle on shellfish farms and providing insights into the underlying biogeochemical processes.

Satellite Imagery-Estimated Intertidal Seaweed Biomass Using UAV as an Intermediary

The aim of this study was to use unmanned aerial vehicles (UAVs) as a supplement to satellite remote sensing to accurately assess benthic seaweed biomass in intertidal zones, in order to improve inversion accuracy results and investigate the spatial distribution patterns of seaweed. By adopting non-multicollinearity vegetation indices (feature sets) from PlanetScope and Sentinel-2, and using benthic seaweed biomass inverted from multispectral UAV imagery as the label set for satellite pixel biomass values, machine learning methods (Gradient boosting decision tree, GBDT) can effectively improve the accuracy of biomass estimation results for Ulva pertusa and Sargassum thunbergii species (Ulva pertusa, RSentinel22 = 0.74, RPlanetScope2 = 0.8; Sargassum thunbergii, RSentinel22 = 0.88, RPlanetScope2 = 0.69). The average biomasses of Ulva pertusa and Sargassum thunbergii in the intertidal zone of Gouqi Island are 456.84 g/m2 and 2606.60 g/m2, respectively, and the total resources are 3.5 × 108 g and 1.4 × 109 g, respectively. In addition, based on the hyperspectral data, it was revealed that a major source of error is the patchy distribution of seaweed.

Functional redundancy as an indicator for evaluating functional diversity of macrobenthos under the mussel raft farm near Gouqi Island

Biological traits analysis (BTA) helps to evaluate the effects of different environmental variables on the traits-based functional composition of macrobenthos. However, research on functional traits of macrobenthos under mussel farming is limited. We investigated the spatial and temporal response of the benthic system in terms of taxonomic and functional diversity to environmental variables of farming and natural stressors resulting from suspended mussel farming near Gouqi Island of eastern China Sea. The functional traits of macrobenthic assemblages under mussel farming were characterized by “medium adult body size”, “vermiform body form”, “high flexibility”, “infauna”, “semi-motile”, “gonochoristic”, “surface deposit-feeders”, “carnivores”, “semi-motile burrowers”, and “tube-dwellers”. Functional redundancy was stable in response to mussel farming stresses among seasons, whereas species diversity showed efficient to evaluate natural variables. Functional diversity was significantly affected by farming stressors rather than natural variables, Further analysis using multivariate methods together with continuous monitoring were highlighted to evaluate the impacts of mussel farming. Our results reinforce the importance of macrobenthic species and functional traits analysis to evaluate human stresses driven impacts in offshore ecosystems. By analysing the environmental variables with different sources, independently, we concluded the main effects of human pressures on macrobenthic community. Such distinction could be particularly effective to isolate variable environmental descriptors and evaluate their effects on functional diversity, making the current approach promising for the evaluation of ecological effects of anthropogenic stressors in aquaculture areas.

Siting and evaluation of offshore suspended mussel farms through nutritional restriction approach

An individual-based model based on mussel feeding on algae was developed for the first time, and the model was introduced to a three-dimensional water quality model based on nitrogen, phosphorus, phytoplankton cycling and dissolved oxygen balance, describing the ecological influence of mussel feeding. The drag of aquaculture facilities on suspended farms was introduced to a three-dimensional hydrodynamic model. The water quality model was coupled with the three-dimensional hydrodynamic model to simulate the hydrodynamic environment field of a large offshore suspended mussel farm in Gouqi Island throughout a year. The simulation results agree well with observations. Based on the nutritional restriction approach, the cause of mussel mortality in Gouqi Island is insufficient algal concentration and insufficient filtration rate. Accordingly, an optimized site selection of the suspended mussel farms was proposed, and its feasibility was validated in hydrology and water quality by using the model. Furthermore, hydrodynamic and ecological effects of aquaculture facilities and site selection were quantified. Aquaculture facilities in Gouqi Island reduces surface current speed by 86% and increases half-time of water exchange by 64%. P is the limiting nutrient in the suspended mussel farms of Gouqi Island. The siting of offshore suspended mussel farms only changes the local distribution of nutrients, causing minimal changes in nutrient concentrations and having limited ecological influence.

High genetic diversity revealed in the native populations of Undaria pinnatifida from China by mitochondrial sequences and nuclear microsatellites

According to historical documents, China has its own native Undaria pinnatifida populations in Zhejiang and Fujian provinces, and they are potentially valuable breeding materials for this economically important kelp. However, their distribution range has been declining northward and we cannot find it now in Fujian province and southern Zhejiang province. They are currently confirmed to be distributed only on some small islands distant from the mainland, likely facing the anthropogenic threats such as habitat deterioration and marine heatwave. Thus, they are of conservation concern. Herein, we used the mitochondrial sequences of cox3 and tatC–tLeu regions, and 10 nuclear microsatellites to analyze the genetic diversity and genetic structure of three temporal populations from Gouqi Island and one population from Yushan Island. A total of eight haplotypes of the combined cox3 and tatC–tLeu sequences were identified with five of them being unique in these populations. Based on microsatellites, we estimated a minimum expected heterozygosity of 0.671 and a minimum effective number of alleles of 5.3 within each population, and revealed shallow genetic structure among populations by Bayesian model-based STRUCTURE analysis and low Fst values. We did not detect signs of recent bottleneck in all populations. The high genetic diversity identified in the southern native populations will provide an advantageous basis for them to adapt to the future environmental changes. A thorough field survey about the detailed distribution of the native populations is needed in order to estimate their population size and better protect the natural resources of this important alga.

Diversity and Carbon Sequestration of Seaweed in the Ma’an Archipelago, China

Seaweed communities perform a variety of ecological services, including primary productivity supply, biological habitat construction, water purification, and acting as marine carbon sinks. The abundance of seaweed is the basis for the assessment of ecological services in communities. The Ma’an Archipelago, adjacent to the Yangtze River estuary in China, is an important and typical island group. In this study, the abundance of seaweed in the typical coastal islands of the Ma’an Archipelago, Zhejiang Province, was evaluated by means of sonar detection and scuba diving sampling methods. The organic carbon content of six dominant seaweed species was measured to estimate the carbon sequestration capacity of the dominant species in the Ma’an Archipelago. The results show that 27 species of Rhodophyta, 10 species of Ochrophyta, and two species of Chlorophyta were found in the Ma’an Archipelago. Seaweed was distributed in the coastal areas of the islands, with a distribution width of 2–60 m. Gouqi Island had the longest shoreline, and there, the distribution depth of the seaweed reached 15 m and the area of the seaweed community was the largest. The slope of the rocks in the Sanheng survey area was large and the width of the seaweed community was small. The distribution area of seaweed in the Ma’an Archipelago was 6.51–13.43 km2 and the organic carbon content of the seaweed was 33.16 ± 3.26%. The biomass of Ochrophyta in the Ma’an Archipelago was the largest, followed by Chlorophyta and Rhodophyta. Among the six dominant species, the carbon sequestration of Sargassum thunbergii was the largest, at 277.91–848.74 t per year, and that of Undaria pinnatifida was the smallest. This study provides scientific guidance for the assessment of the primary productivity supply, carbon sink, and conservation capacity of seaweeds in China.

Effects of Global Warming on the Growth and Proliferation of Attached Sargassum horneri in the Aquaculture Area near Gouqi Island, China

With global warming, in recent years, golden tides have frequently occurred off the coasts of China. Sargassum horneri, which attach to aquaculture rafts, can float and form small-scale golden tides after falling off. Temperature will affect the growth and reproduction of algae. In order to explore whether the temperature is the potential influence factor of the golden tide outbreak, in this study, the effects of global warming on the growth and proliferation of S. horneri in the mussel aquaculture area of Gouqi Island will be discussed. Samples of the macroalgae were collected monthly from August 2021 to July 2022 at various stages of its life cycle, and the relationship between algal growth and temperature was analyzed based on the concept of effective accumulated temperature, combined with the parameters of sea surface temperature, photosynthetic rate, growth rate, and growth cycle. Based on the continuous temperature variation observed, the growth cycle could be divided into five stages: the decreasing temperature period (October to November), the low-temperature adaptation period (December), the second suitable low-temperature period (January to February), and the high-temperature decay period (February to May). The effective accumulated temperature stored by S. horneri from 2021 to 2022 was 2772.4 °C·d; compared with previous studies, it decreased by about 800 °C·d. The winter temperature in 2022 was higher than the average temperature in the previous 5 years, allowing the macroalgae to enter the reproductive period in advance. This had a significant impact on the blooming time of golden tides and led to an earlier outbreak and extinction. Therefore, in the future, we can set up a monitoring system for the early warning of golden tides according to the change of SST in winter.

The Influence of Host Specificity and Temperature on Bacterial Communities Associated with Sargassum (Phaeophyceae) Species.

Host-related microbiota are critically important for the adaptation/acclimation of hosts to changing environments, but how environmental factors andhost characteristics shape the microbial communities remains largely unknown. We investigated the effects of temperature on habitat-forming macroalgae and their associated bacterial communities. Three Sargassum species (S. horneri, S.fusiforme, and S. thunbergii) and seawater samples were sampled in Gouqi Island, China, and these macroalgal samples were incubated at different temperatures (10, 20, and 27°C) for 7 d. Bacterial communities were identified from the 16S rRNA gene V3-V4 regions. The algae-associated bacterial communities of the field samples were significantly different from seawater, implying host specificity. During laboratory incubation, decreased physiological status (photosynthetic rate and oxidative stress response) was detected for all the species at 10°C, especially with regard to S. horneri and S. fusiforme. For each host, associated bacterial communities at 20 and 27°C clustered closely, and these were separated from samples at 10°C based on constrained PCoA analyses. Permutational multivariate analysis of variance revealed that algae-associated bacterial communities were more affected by host species (23.3%) than by temperature (2.48%) during laboratory incubation. The changes in bacterial community composition may be influenced by algae metabolites, which should be tested in a future study. These results further contribute to our understanding of algal microbiome changes in response to environmental changes.

Differences in Light Attenuation Patterns of Sargassum horneri Beds and Their Influences on Sebastiscus marmoratus Juveniles: A Case Study of Gouqi Island, Ma’an Archipelago, China

Sargassum beds ensure sustainable environmental, social, and economic benefits in the coastal areas around the world. They can provide shelter ground to different species of fish juveniles. To investigate these, we conducted field surveys in a peaking growth period of Sargassum horneri from May to June 2010 to evaluate them on Gouqi Island, Ma’an archipelago, China. The study indicated that the light attenuation rate inside the S. horneri beds was higher than that in the surrounding areas. The light attenuation rate was highest in Ganxie, the second highest in Huangshidong, and the lowest in Houtouwan. We found that the average length of Sebastiscus marmoratus corresponded to the average height of S. horneri. This study improves our understanding of the function of sheltering grounds provided by Sargassum beds. Additionally, this study is relevant to the development of the regulations and directives to ensure the sustainable exploitations and protection of wild seaweeds and the accompanying organisms resources.

Hydrodynamic effects of large-scale suspended mussel farms: Field observations and numerical simulations

The hydrodynamic effects of the largest suspended mussel farms in the East China Sea near Gouqi Island, was investigated using a high-resolution 3D ocean model and field observations. To capture the 3D farm effects on hydrodynamics, an additional depth dependent momentum sink term was introduced in the model. The model results compared well with the field observations. The present model and observational results indicate that the presence of farms reduces the flow by more than 79%, 55%, and 34% in the upper, middle, and bottom layers at the farm center, respectively. According to the harmonic analysis of predicted current, mussel farms reduce the magnitude of the semidiurnal tidal current and also alter the magnitude and direction of the diurnal tidal current. The blockage by the farm weakens the Eulerian residual tidal current within the farm in the NE-SW direction, while strengthens that at the edge of the farm in the SE-NW direction. Cross sections, Sec1 and Sec2 are perpendicular to these two major residual currents and intercept with the center of the farm from SE to NW and from NE to SW respectively. The farm effect on the total water flux over a month through the Sec2 displays a semi-lunar periodic oscillation and is one order of magnitude smaller than that at Sec1. An asymmetry tidal current was observed in the farm north of Gouqi Island. The field observation of vertical profiles of current suggests that the thickness of surface canopy boundary layer can reach 5 m upstream from the farm during flood tide, increases gradually downstream up to 10 m under the cumulative influences of the farm. And a wake zone was observed downstream from the farm during flood tide. Better understanding of farm-induced hydrodynamic effects provides insight into how to optimize farm layouts based on local hydrodynamics, to maximize farm productivity and minimize environmental impacts.

Surface Upwelling off the Zhoushan Islands, East China Sea, from Himawari-8 AHI Data

The summer upwelling around the Zhoushan Islands is well-known. The previous concise review of (mostly) observational studies reveals that the present knowledge of the Zhoushan upwelling is unsatisfactory and has focused on seasonal variations. In this study, a sea surface temperature (SST) gradient-based upwelling detection algorithm was used. The Level 3 daily and hourly SST data from the geostationary satellite Himawari-8 were used to explore statistical features, seasonal variations, and short-term variations of the Zhoushan upwelling. Despite the duration period being like in previous studies, there is a new finding that the location of the upwelling center has a significant monthly migration. The statistical results show that the potential upwelling spots are clustered in the location with large topographic gradients and can be divided into four aggregation areas: between Gouqi Island and Lvhua Island, off Shengsi Island, around the Zhongjieshan Islands, and off the Taohua-Liuheng Islands. The core area of the Zhoushan upwelling is located at 122°E–123°E, 29.5°N–31.15°N with an irregular ellipse extending from southwest to northeast. The continuous cloud-free satellite images display that the lifecycle of the short-term variations was about 24 h and included two stages: intensification and decay. Meanwhile, the surface upwelling center has onshore–offshore movement under the advective transport of local tidal currents. A preliminary discussion suggests that the quasi-24 h periodic variations may be caused by the competing effect between tidal mixing and the stratification in the water column.

Variable Optimization of Seaweed Spectral Response Characteristics and Species Identification in Gouqi Island.

Probing the coverage and biomass of seaweed is necessary for achieving the sustainable utilization of nearshore seaweed resources. Remote sensing can realize dynamic monitoring on a large scale and the spectral characteristics of objects are the basis of remote sensing applications. In this paper, we measured the spectral data of six dominant seaweed species in different dry and wet conditions from the intertidal zone of Gouqi Island: Ulva pertusa, Sargassum thunbergii, Chondrus ocellatus, Chondria crassiaulis Harv., Grateloupia filicina C. Ag., and Sargassum fusifarme. The different seaweed spectra were identified and analyzed using a combination of one-way analysis of variance (ANOVA), support vector machines (SVM), and a fusion model comprising extreme gradient boosting (XGBoost) and SVM. In total, 14 common spectral variables were used as input variables, and the input variables were filtered by one-way ANOVA. The samples were divided into a training set (266 samples) and a test set (116 samples) at a ratio of 3:1 for input into the SVM and fusion model. The results showed that when the input variables were the normalized difference vegetation index (NDVI), ratio vegetation index (RVI), Vre, Abe, Rg, Lre, Lg, and Lr and the model parameters were g = 1.30 and c = 2.85, the maximum discrimination rate of the six different wet and dry states of seaweed was 74.99%, and the highest accuracy was 93.94% when distinguishing between the different seaweed phyla (g = 6.85 and c = 2.55). The classification of the fusion model also shows similar results: The overall accuracy is 73.98%, and the mean score of the different seaweed phyla is 97.211%. In this study, the spectral data of intertidal seaweed with different dry and wet states were classified to provide technical support for the monitoring of coastal zones via remote sensing and seaweed resource statistics.

Genetic diversity of Undaria pinnatifida populations from China and their genetic relationship with those from Japan and Korea as revealed by mitochondrial and nuclear DNA sequences

Abstract Large-scale farming of Undaria pinnatifida is conducted in northern China. Conspicuous natural populations of this alga are distributed on rocky shores in this region. However, the genetic relationship between U. pinnatifida from China and native populations in other countries remains largely uncertain. We obtained sequences for the mitochondrial cox3 and tatC–tLeu regions and the internal transcribed spacer one of nuclear ribosomal DNA from representative natural and farmed populations of U. pinnatifida in China. We analyzed genetic diversity, and evaluated the genetic relationship between Chinese populations and Japanese and Korean populations. The mitochondrial and nuclear DNA sequences revealed high genetic diversity in most Chinese populations. Unique mitochondrial haplotypes were detected in the Gouqi Island population consistent with historical records of a native population on the island. Phylogenetic analyses derived from the mitochondrial DNA sequences revealed that the Chinese samples were classifiable as the Continental and Northern Japan types. All natural populations from rocky reefs in northern China were grouped with the Continental type and all farmed populations with the Northern Japan type. Mitochondrial and nuclear DNA sequences revealed significant genetic differentiation between the farmed populations and adjacent natural populations from rocky reefs, in agreement with previous results obtained using microsatellites.

Estimation of Seaweed Biomass Based on Multispectral UAV in the Intertidal Zone of Gouqi Island

UAV remote sensing inversion is an efficient and accurate method for obtaining information on vegetation coverage, biomass and other parameters. It is widely used on forest, grassland and other terrestrial vegetation. However, it is rarely used on aquatic vegetation, especially in intertidal zones and other complex environments. Additionally, it is mainly used for inversion of coverage, and there have been few studies thus far on biomass assessment. In this paper, we applied multispectral UAV aerial photography data to evaluate the biomass of seaweed in an intertidal zone. During the ebb tide, UAV aerial photography and in situ sampling data were collected in the study area. After optimizing the spectral index and performing a multiple linearity test, the spectral parameters were selected as the input of the evaluation model. Combined with two machine learning algorithms, namely random forest (RF) and gradient boosting decision tree (GBDT), the biomasses of three species of seaweed (Ulva pertusa, Sargassum thunbergii and Sargassum fusiforme) in the intertidal zone were assessed. In addition, the input parameters of the machine learning algorithms were optimized by one-way ANOVA and Pearson’s correlation analysis. We propose a method to assess the biomass of intertidal seaweed based on multispectral UAV data combined with statistics and machine learning. The results show that the two machine learning algorithms have different accuracies in terms of biomass evaluation using multispectral images; the gradient boosting decision tree can evaluate the biomass of seaweed in the intertidal zone more accurately.