Phytoplankton serve as crucial producers in marine ecosystems, and their community composition and populations’ dispersion directly or indirectly influence the productivity of marine waters via the trophic cascade effect within the food chain. A survey was undertaken in September 2021 and March, April, and November 2022 to examine the phytoplankton structure and the environmental variables influencing ecological niche differentiation in the waters of Tahe Bay in Lushun, Dalian city, China. The findings indicated that there are 83 species representing forty-one genera and six phyla, with an annual mean abundance of 22.13 × 10⁴ ind·m⁻³, predominantly represented by Bacillariophyta (65 species, constituting 78.31% of the total species). The phytoplankton richness indices varied from 0.83 to 4.99, diversity indices ranged from 2.03 to 2.80, and evenness indices spanned from 0.28 to 0.84. Pearson’s correlation between phytoplankton abundance and community diversity with environmental parameters, including water temperature, salinity, pH, DO, NH₃-N, and NO₃-N, was substantial in Tahe Bay’s waters. The dominant species, comprising 20 species across three phyla, primarily include broad-niche species, with Paralia sulcata being the most prevalent species, except during summer. The extent of ecological niche overlap among the dominant species varied by season, exhibiting 40.0% severe overlap in September 2021, 100.0% severe overlap in March 2022, 93.0% severe overlap in April 2022, and 58.0% severe overlap in November 2022. The findings of redundancy analysis (RDA) and canonical correspondence analysis (CCA) revealed that COD, water temperature, NO₃-N, DIP, NO₂-N, and NH₃-N are the primary environmental variables influencing the ecological niche differentiation of dominant species of phytoplankton. The results of the study elucidate the alteration rules of dominant species and the stability of the community structure of the phytoplankton community in this sea area, thereby offering a theoretical foundation for the scientific assessment of the ecological health of the area and the sustainable utilization of marine biological resources.

This study investigated the population dynamics of Cynoglossus gracilis in the offshore waters of Liaoning Province, China, to support sustainable fisheries management. Biological samples were collected from five major fishing ports between March and November 2024. Population dynamics were assessed based on growth, mortality, and exploitation parameters, and four seasonal fishing closure scenarios were evaluated using egg production per recruit (EPR) and spawning biomass per recruit (SBR) models. The estimated exploitation rate (E = 0.53) indicated that the stock was experiencing relatively high fishing pressure but remained close to the sustainable exploitation reference level. Yield-per-recruit analysis suggested that increasing the minimum catchable size could improve resource utilization efficiency. Among the evaluated closure scenarios, the April–September closure provided the greatest conservation benefit by enhancing reproductive potential and protecting spawning stock biomass. These findings provide valuable insights for optimizing harvest regulations and seasonal closure strategies, contributing to the sustainable management of Cynoglossus gracilis resources in the offshore waters of Liaoning Province.

Sebastes schlegelii is a commercially significant species in the northern Yellow Sea. Recently, Sebastes schlegelii has shown a reduced stock density and a shift toward smaller body sizes in the northern Yellow Sea area off Liaoning Province. To comprehend the population dynamics and to formulate management tactics, we established a mathematical formula describing the length–weight relationship, as well as the corresponding growth equations for the body length and body weight. The biomass of Sebastes schlegelii in the northern Yellow Sea area off Liaoning Province was evaluated using biological survey data from 2019 to 2022. The findings reveal that the length–weight formula is expressed as W = 4.98 × 10⁻⁵L^2.8878 (R² = 0.9108), with L_∞ = 407.6 mm, W_∞ = 1717.04 g, K = 0.21 a⁻¹, and t₀ = −0.65 a. The critical age was 3.34 years, and the stock biomass was 13,141.35 tonnes. The current exploitation rate of this resource is below the maximum yield, indicating sustainable utilization. A fishing closure period from April to June is considered suitable. A minimum landing size of 240.48 mm is recommended for Sebastes schlegelii.