Coastal waters provide an important spawning and nursery ground for offshore marine organisms. To understand the suitable habitat and distribution of Harpadon nehereus, a key nearshore species, this study assessed the survey data of fishery resources and environment in Zhejiang’s nearshore fishery in Spring of 2017 to 2020. We used the generalized additive model (GAM) and random forests model (RF) to analyze the environmental factors affecting the selection of spawning habitats by H. nehereus and analyzed the suitable habitat characteristics of H. nehereus in nearshore fisheries. Our results indicate that H. nehereus is widely distributed in Zhejiang’s nearshore and that its density is higher in waters near islands and reefs. Among the relative importance scores of predictors calculated based on RF, seawater salinity is an important environmental factor affecting the distribution of H. nehereus in April (surface seawater salinity was 38.67% and bottom seawater salinity was 34.5%), followed by depth (34.19%), whereas the change in water temperature had no obvious effect on H. nehereus distribution. The suitable habitat characteristics of H. nehereus mainly include high salinity near a water depth of 40 m and a water area with sea bottom dissolved oxygen levels < 6 mg/L. The prediction results of the model indicate that the suitable habitat of H. nehereus is mainly located in the region near Zhoushan Islands in the north of the fishing grounds. Overall, these results may serve as a basis for determining the protection strategies of key nearshore species and enhancing fishery management units.

Larimichthys crocea (also known as the large yellow croaker) is one of the most economically important marine fishes in China, and research on the ecology and genetics of this species is of immense significance. In this study, we performed restriction site-associated DNA sequencing (RAD-seq) of 54 individuals collected from four sites in China to analyze the genetic structure and diversity of large yellow croaker at the genome level. It revealed that the large yellow croaker populations in the Ningde and Zhoushan coastal waters can be clearly distinguished. Different genetic diversity indices were used to analyze the genetic diversity of the large yellow croaker, which showed that there was a differentiation trend between the wild and farmed populations in Ningde. Moreover, we identified genetically differentiated genomic regions between the populations. GO gene enrichment analysis identified genes that are related to fatty acid metabolism and growth. These findings enhance our understanding of genetic differentiation and adaptation to different living environments, providing a theoretical basis for the preservation and restoration of the genetic resources of the large yellow croaker.

Beta diversity is an important way to analyze community assembly mechanisms in different habitats or along environmental gradients. However, research on marine fish assemblages around islands has lagged, especially for functional beta diversity. In this study, we evaluated taxonomic and functional beta diversity change of island fish assemblages along the coast in two seasons and revealed its relationship with environmental factors and geographical distance. Taxonomic and functional beta diversity were both dominated by turnover (over 80% and 60%), while the contribution of nestedness on functional beta diversity was significantly increased. Environmental factors such as temperature and dissolved oxygen were important drivers of beta diversity rather than geographical distance. Fish assemblages around islands that are far away from mainlands or affected greatly by anthropogenic activities usually have higher beta diversity. These results indicated that environmental filtration is the primary factor driving the mechanism of fish community assembly. Our study revealed the importance of the integrated application of two facets of biodiversity to investigate beta diversity. The findings can provide theoretical support for the protection of marine fish and the planning of marine protected areas in the future.

Introduction: Like pelagic fishes, cephalopods represent fishery resources with high worldwide potential and an important evolutionary node animal group. Thus, exploring the spatial and seasonal variations in cephalopod distribution and their associations with environmental factors is important for elucidating cephalopod diversity and the distribution of cephalopods under changing environmental conditions and for developing reasonable resource management and conservation measures.Methods: On the basis of trawl survey data from 123 stations in the coastal waters of Zhejiang, China, in the spring and autumn of 2021, the relationships among the cephalopod species composition and diversity characteristics and the spatial and seasonal changes and environmental factors were investigated via the relative importance index (IRI), the alpha diversity index, and the GAM.Results: The results revealed that the cephalopods in the coastal waters of Zhejiang belonged to three orders, six families, and 10 genera and that the dominant species were gradually replaced by species of minor economic importance and endemic small-scale fishery species. In spring, Uroteuthis duvaucelii was the dominant species, the resource density in the southern coastal waters of Zhejiang was relatively high, and the overall distribution increased from northeast to southwest. In autumn, U. duvaucelii and Abralia multihamata were the dominant species, and the coastal waters of Zhejiang presented two high-density distribution areas in the northern and central waters, with lower resource density in the southern waters. Analysis of the alpha diversity index revealed relatively low cephalopod community diversity, with significant differences in spatial and seasonal distributions. The GAM revealed that, in spring, surface dissolved oxygen and sea bottom temperature led to significant changes in cephalopod resource density (p<0.05), and water depth significantly affected cephalopod resource density (p<0.01); in autumn, only water depth significantly affected cephalopod resource density (p<0.01).Discussion: The cephalopod resources in the coastal waters of Zhejiang are under the dual stresses of fishing and environmental changes. The protection and restoration of traditional economic cephalopod resources are needed to ensure their sustainable development and utilization.

Due to overfishing and marine pollution, the status of fishery resources and the ecological environment in the sea areas have considerably changed. The proliferation and release of fishery resources have become the main means of human intervention to maintain and conserve the resource populations. The annual output of Sepiella japonica (S. japonica), once one of the four major seafood species in the East China Sea, has now recovered to a level of 4000 t. However, do the traditional spawning grounds of S. japonica still exist? Have the spawning grounds shifted? These scientific questions are worthy of attention. Based on the survey data of fishery resources and environment at 120 stations in coastal Zhejiang waters from 2015 to 2022, the spatial and temporal distribution and resource center of gravity of S. japonica in springtime were analyzed. Random forest (RF) was used to explain the importance of six environmental variables, including water depth, sea surface temperature, sea surface salinity, chlorophyll a, pH, and dissolved oxygen. The generalized additive model (GAM) nonparametric smoothing function was used to analyze the relationship between environmental factors and the distribution of S. japonica inhabiting the offshore areas of Zhejiang province, and the effects of environmental factors on spawning habitat selection of S. japonica were revealed. This study found that there was a significant interannual variation in S. japonica resources, with an overall increasing trend in the resource. The spawning grounds were mainly distributed in the Jiushan Islands Marine Reserve, the Dachen Islands Marine Reserve, and their nearby sea areas. The resource peaked at latitude 28.3° N. Additionally, the most important variables affecting the distribution of S. japonica were depth of water, followed by sea surface salinity, pH, dissolved oxygen, sea surface temperature, and chlorophyll a. S. japonica mainly inhabited sea areas with a depth of 15~25 m and a sea surface salinity of 26~32. When the pH ranged from 7.6 to 8.3, dissolved oxygen ranged from 6 to 9 mg/L, sea surface temperature ranged from 14 to 17 °C, and chlorophyll a ranged from 2.5 to 5 µg/L, S. japonica was more likely to be present. This study provides insights into the spatial distribution of S. japonica in offshore Zhejiang province, offering a reference for the rational utilization and scientific protection of this resource.