The marine gastropod Semicassis bisulcatum, valued for its ornamental shell and edible soft tissue, lacks essential biological data for selective breeding. This study was conducted on 100 wild individuals collected from the Beibu Gulf to identify key morphological traits influencing body mass (BM) and soft body mass (SBM). Both mass traits showed high variability (SBM CV = 41.04%; BM CV = 23.88%), indicating strong breeding potential. Path analysis revealed that shell thickness (ST) exhibited the strongest direct association with body mass (path coefficient = 0.509), while shell width (SW) was most closely linked to soft body mass (path coefficient = 0.482). The combined coefficient of determination confirmed that shell thickness (ST) and shell height (SH) together were the strongest predictors for body mass. Similarly, Shell width (SW) and aperture height (AH) together had the strongest combined effect on soft body mass. These findings provide a critical morphological basis for future selective breeding programs.

Based on multi-seasonal surveys (2020–2022) in Beihai Silver Beach, this study examined phytoplankton community dynamics and environmental drivers. Results showed persistent diatom dominance, with Skeletonema costatum as the predominant species and a major bloom in autumn 2021. Species richness peaked in summer and was lowest in winter, while abundance hotspots were associated with the Fengjia River estuary. Generalized Additive Models identified reactive phosphate as the primary driver, exhibiting nonlinear relationships with species richness (R² = 0.91) and diversity (R² = 0.436). Dissolved oxygen also had significant nonlinear effects. A counterintuitive positive correlation between lead concentration and species richness highlighted complex stressor interactions. This study emphasizes phosphorus control for eutrophication mitigation and demonstrates GAMs’ utility in detecting nonlinear ecological responses, supporting science-based management of coastal ecosystems.