Remote sensing retrieval of phytoplankton group can provide important data for a comprehensive understanding of the role of phytoplankton in marine ecosystem. However, due to the complex optical characteristics, there are still great challenges in the remote sensing retrieval of phytoplankton group in offshore waters. In this study, the eastern China seas region, a complex optical class II water body, is taken as the research area. By using three modeling methods, namely band combination method, multiple linear regression method based on singular value decomposition (SVD+MLR) and XGBoost regression method based on singular value decomposition (SVD+XGBoost), the phytoplankton group is retrieved from remote sensing reflectance (R_rs) data. Verified by the in-situ measured data set, the chlorophyll a (Chl a) concentration retrieval model of eight phytoplankton groups by SVD+XGBoost has the highest accuracy, and the determination coefficient (R²) of Chl a concentration inversion model of diatoms and dinoflagellates in the validation set is greater than 0.7. In contrast, the accuracy of Chl a concentration of chlorophytes, cyanobacteria and chrysophytes estimated by the three modeling methods is low (the R² of the validation results is less than 0.45). At the same time, the applicability of three atmospheric correction methods of OLCI images (C2RCC, POLYMER and MUMM) in the eastern China seas is evaluated. The results show that compared with the other two atmospheric correction algorithms, C2RCC has better performance in each band (root mean square error is less than 0.0048 sr⁻¹). Finally, the performance of the retrieval model on satellite images is verified by the in-situ data. The validation results show that the diatoms Chl a concentration model established by SVD+MLR has better accuracy (the R² is 0.56), while the Chl a concentration inversion models of other phytoplankton groups have poor results.

The stable acquisition of large-scale and continuous coastline data through remote sensing is an important basis for the development of coastal zone research. Aiming at the problems of noise sensitivity and threshold instability in the traditional edge detection algorithm for high-resolution remote sensing images, the strected forests edge detection algorithm based on the structured random forest model is introduced to identify the sandy shoreline of the west coast of Haikou City, and proposed based on the Bruun-Dean balanced profile model, a new method of tide level correction is established to fit the profile model, and finally the fine coastline data is extracted. Based on the measured data, the precision evaluation and error analysis of the extraction results are carried out, and the prospects for method improvement and popularization and application are put forward. The research show that: (1) the result of the water edge line detected by the strected forests edge detection algorithm is clear and delicate, which is more accurate and efficient than the traditional edge detection operator methods such as Roberts operator, Canny operator, and LoG operator, and is suitable for the study of coastline extraction from high-resolution remote sensing images; (2) aiming at the tide level correction of the sandy coastline, the fitted profile model established based on the RTK measured data and the fitted profile model overcomes the large error of the traditional linear model and improves the accuracy and feasibility of the coastline correction; (3) based on actual measurement for the shoreline, the results are quantitatively analyzed using the section method, and it is verified that the positioning accuracy of the extracted shoreline is better than 2.5 m.

Accurate inversion of shallow water depth is essential for marine space management and ecological environment protection. Lingyang Reef of Xisha Islands in the South China Sea is taken as a typical study area. The single-band model, multi-band model and band-ratio model are established based on GeoEye-1 and WorldView-2 high-resolution multi-spectral remote sensing data and measured points. The results show that the correlation of the inversion model established with the participation of green band is generally high, while the multi-band model established by four bands combination has the highest accuracy and the correlation coefficient reaches 0.870 and 0.853, respectively. Comparing with the inversion accuracy of GeoEye-1 and WorldView-2 data in different depth ranges based on the above model, the conclusion is that the inversion errors of the two kinds of data in different depth ranges have the same trend, with the maximum value of the average relative errors occurring in the range of 0−5 m and the minimum value occurring in the range of 20−25 m. In general, the inversion accuracy of WorldView-2 image is higher than that of GeoEye-1 image. This study has a certain reference significance for the inversion of water depth in shallow tropical sea.

In order to investigate the tolerance of temperature and salinity of Tapes dorsatus juveniles, ecological methods with the laboratory controlled system was used in this study. The results showed that: (1) in the temperature tolerance test, juveniles maintained 90%−100% survival rate at the low-temperature groups (4℃, 6℃, 8℃ and 10℃) for 0 d, 2 d, 3 d and 7 d and at the high-temperature groups (33℃, 34℃, 35℃ and 36℃) for 5 d, 4 d, 1 d and 0 d, respectively; (2) under temperature stress, at the low-temperature groups, the semilethal temperatures at 48 h, 96 h, 144 h and 192 h were 5.02℃, 7.68℃, 9.01℃ and 9.20℃. And in the high-temperature groups, the semilethal temperatures at 48 h, 96 h, 144 h and 192 h were 35.44℃, 34.74℃, 34.43℃ and 34.25℃, respectively. In the salinity tolerance test, (1) juveniles maintained 90%−100% survival rate at low-salinity groups (13.0, 15.6, 18.2, 20.8 and 23.4) for 1 d, 1 d, ≥9 d, ≥9 d and ≥9 d while in the high-salinity groups (41.6, 44.2, 46.8, 49.4 and 52.0) followed by 9 d, 2 d, 1 d, 1 d and 1 d, respectively; (2) the semilethal salinity at 48 h, 96 h, 144 h and 192 h in the low-salinity groups were 14.46, 16.02, 16.76 and 16.91, while in the high-salinity groups were >52.0, 51.79, 50.58 and 48.88, respectively; (3) for survival, the suitable and the optimum salinities of T. dorsatus juveniles were 16.91−48.20 and 18.20−41.60, respectively. For growth, the suitable and the optimum salinities were 23.58−45.15 and 33.90, respectively. The results indicated that T. dorsatus juveniles had strong tolerance to high temperature and were suitable for cultivation with higher temperatures in the southern sea area. The suitable survival salinity range was wide, and the optimal growth salinity was basically the same as the offshore sea water. T. dorsatus juveniles suitable for breeding in the offshore sea water.

The foxl2 plays essential roles in regulating ovarian differentiation, development and functional maintenance of vertebrate. However, its function in ovarian development of the swimming crab Portunus trituberculatus remains unknown. In the present study, we firstly cloned the full-length cDNA of P. trituberculatus foxl2 (Ptfoxl2) which contained a 5′ untranslated region (UTR) of 701 bp, a 3′ UTR of 211 bp, and an open reading frame (ORF) 1590 bp. Gene expression analysis in different tissues showed that Ptfoxl2 exhibited the highest expression in ovary. There were significant differences in its expression in different stages of ovarian development, and its expression was the highest in stage V. After eyestalk ablation, Ptfoxl2 expression decreased significantly. In addition, RNAi of Ptfoxl2 resulted in a significant reduction in vitellogenin expression of ovary. Taken together, these results indicated that Ptfoxl2 played an important role in the regulation of ovarian development of P. trituberculatus by inhibiting endogenous vitellogenesis in maturation stage. In order to further analyze the post-transcriptional regulation of Ptfoxl2, the miRNAs targeting Ptfoxl2 was predicted by bioinformatics analysis and the interaction between the miRNAs and Ptfoxl2 was verified using the dual luciferase reporter assay. The results showed that the relative luciferase activity was significantly reduced after co-transfection of miR-9 mimics and pmirGLO-Ptfoxl2-3′ UTR. Expression analysis showed that miR-9 exhibited opposite pattern at ovarian maturation stage and after eyestalk ablation. Collectively, the results demonstrated that miR-9 can regulate Ptfoxl2 expression in the swimming crab.

To investigate the effect of Pseudoalteromonas marina pilZ gene knockout on the biofilm formation and its influence on the settlement and metamorphosis of Mytilus coruscus larvae, ΔpilZ was constructed by homologous recombination, and the changes in bacterial density, biofilm thickness, c-di-GMP level and extracellular polymeric substances (EPS) of ΔpilZ bacteria biofilm were analyzed, as well as the regulation of the settlement and metamorphosis of M. coruscus larvae. The results showed that compared with the wild-type strain, the biofilm formed by ΔpilZ strain significantly increased the biofilm thickness, the number of bacteria, while the contents of β-polysaccharides and proteins in EPS were decreased and the settlement and metamorphosis of M. coruscus larvae were inhibited (p<0.05). There was no significant difference in c-di-GMP level, α-polysaccharide and lipid contents (p>0.05). In conclusion, P. marina pilZ gene knockout can regulate the bacterial biofilm and the content of EPS including β-polysaccharides and proteins contents, then inhibit the settlement and metamorphosis of M. coruscus larvae.

Planktonic larvae are the necessary stages during the growth and development of many fishery species, such as shellfish, benthic fish, polychaete in the Huanghe River Estuary adjacent waters. Seasonal studies on the planktonic larvae community were carried out for biodiversity and bio-resource protection researches in the region. The larvae samples were collected from the vertical hauling of a mesh size 0.160 mm plankton net onboarding of six cruises during April 2019, June 2019, and August 2019, November 2019, January and April 2020 in the sea. Of the 16 planktonic larvae identified, 87% groups were meroplankton. The community diversity index (H') showed higher in June and August than in November and January. For the study region, the dominant organisms of planktonic larvae were bivalve larvae, nauplii, gastropoda larvae, polychaeta larvae, copepodite larvae, auricularia larvae. But the composition of dominant species varied with seasons, with the highest seasonal turnover rate (67%) from April to June, only bivalve larvae and nauplii dominated the planktonic larvae community for all seasons. Total planktonic larvae abundance reached the highest in November, the lowest in January. The planktonic larvae had their high abundance mostly near the estuaries of the Huanghe River and the Xiaoqinghe River, and in the middle part of Laizhou Bay. By cluster analysis, three assemblages of communities were differentiated based on the family compositions and their abundance at each station of six surveyed months. The representative species for monthly cluster groups were nauplii for spring (April) and winter (January) groups, bivalve larvae for summer-autumn (June to November) group. The station cluster groups overlapped geographically with the same representative species (bivalve larvae and nauplii). From statistical analysis of MANOVA and ANOSIM, biodiversity index, abundance, similarity among cluster groups presented significantly different among measured months, but stations, suggesting a seasonal variation for planktonic larvae community. Bio-environment multiple regression analysis showed that the combination of water temperature and zooplankton abundance had the most effects on the planktonic larvae community.

This research aimed to screen the best mating combinations of Litopenaeus vannamei. Five populations of L. vannamei with different genetic backgrounds were used as parents, and 12 combinations of the F₁ generation were constructed by mating. The ASReml4 software was used to estimate the general fitness (GCA) and specific fitness (SCA) for growth and tolerance to combined stress (high salt (35), low pH (6±0.1), and high ammonia nitrogen (70 mg/L) co-stress) traits of the 12 combinations of P105 in L. vannamei. The results showed that the SCA of the parents played a dominant role in the performance of offspring traits, with combinations K♀×K♂(0.35±0.25), GX♀×W♂(0.31±0.22) and GX♀×M♂(0.29±0.29) ranking high in SCA for body mass; combinations GX♀×GX♂(3.65±1.79), L♀×L♂(2.19±2.33) and W♀×GX♂(1.30±2.03) ranking high in SCA for tolerance to combined stress. The analysis of heterozygous dominance H showed that the crosses showed some heterozygous dominance for growth (body mass, body length, cephalothorax length, and full length of ventral segments) and stress tolerance traits, and the H for growth and stress tolerance traits of the six crosses GX♀×W♂, GX♀×K♂, GX♀×M♂, W♀×GX♂, K♀×GX♂ and K♀×M♂ were negative except for the combination GX♀×K♂ (0.10%−80.79% and 6.87%−42.86%), with the highest H for the combination GX♀×W♂ body mass (25.52%) and the higher H for the combination W♀×GX♂ tolerance to combined stress (41.72%). The study showed that the hybrid combination GX♀×W♂ had the highest SCA and H for body mass; the hybrid combination W♀×GX♂ had the highest SCA and higher H for tolerance to combined stress, which can be considered to enhance the application of the two combinations in matching crosses for growth and combined stress tolerance traits respectively.

To understand the species composition of the dominant fish species communities in the East China Sea and to monitor and protect their diversity, environmental DNA technology to analyze the species diversity of fish in the East China Sea was used in this study. Through the collection of seawater samples, eDNA extraction, amplification and high-throughput sequencing analysis, a total of 44 species of marine fishes in 2 classes, 23 orders, 29 families and 42 genera were detected, and most of the species were found in the traditional fishery resources survey in the East China Sea. Among them, the species with high relative abundance were red nose anchovy (Thryssa kammalensis), blue-spotted horse mackerel (Scomberomorus niphonius), Japanese mackerel (Scomber japonicus), small yellowtail (Larimichthys polyactis) and mullet (Mugil cephalus). The alpha diversity among stations was significant difference, and generally showed high biodiversity at coastal stations and high biological abundance at offshore stations. The results suggested that environmental DNA technology could quickly explore the diversity and spatial distribution of fish species in the East China Sea, as an effective supplementary to traditional fisheries resource monitoring.

In order to explore the diversity of pure cultured bacteria in the deep-sea sedimentary environment of the Indian Ocean, bacteria were isolated and identified from 12 sediment samples collected from the Indian Ocean. A total of 343 strains of bacteria were obtained by pure culture isolation method and 16S rRNA gene sequence analysis showed that these isolates belonged to Firmicutes, Proteobacteria, Actinobacteria, Bacteroidete and were divided into 5 classes, 13 orders, 26 families and 121 species under 39 genera. The dominant taxa were Streptomyces (separation rate is 16.53%) and Bacillus (separation rate is 8.26%), among which there were 12 potential new taxa. The results show that the deep-sea sedimentary environment of the Indian Ocean is rich in culturable bacteria and contains many new species; secondly, the isolation and culture methods are directly related to the bacterial species diversity obtained from marine sediments.