Heavy metals (HMs) have the characteristics of high toxicity, long residual time, and difficult degradation, which pose a potential threat to aquatic ecosystems. The distribution and migration of HMs in different media can reflect their potential impact on aquatic ecosystem health. In this study, we analyzed the distribution characteristics of seven HMs (Zn, Cu, Cr, Ni, Hg, As, and Pb) in the water and sediment and five groups of organisms (fish, Crustacean, cephalopod, bivalvia, and gastropoda) in the sea ranching area of Haizhou Bay and explored the regularity of HM accumulation from water and sediments to organisms. The results showed that in the water, Zn and Hg had the smallest concentrations in the nearshore area, Cr had the lowest concentrations in the offshore area, and As, Cu, Pb, and Ni had the lowest concentrations in the central area. In the sediment, Hg had the smallest concentrations in the nearshore area and As, Pb, Cr, Cu, Ni, and Zn had the lowest concentrations in the offshore area; the average contents of seven heavy metals all meet the Class I standard of sediments in China. The concentrations of Cu and Zn in crustaceans were significantly higher than those in fishes (p < 0.05), and As showed a higher enrichment effect in cephalopods. Under the influence of feeding habits and habitat environment, the BAF value of benthic crustaceans and bivalvia accumulated HMs from sediments is high, and the BAF value of fish accumulated HMs from water and sediments is low. Overall, the concentration of HMs in water is high, and HMs in sediments are in good condition, crustaceans and bivalviaa have a strong ability to accumulate HMs from water and sediments, while fish are weak. Therefore, in order to ensure the safety of biological quality, it is necessary to focus on the discharge of heavy metal pollutants near the coast in the future.

Artificial reefs are widely recognized for their role in improving the ecological environment and creating protected habitats for marine organisms, ultimately enhancing biodiversity within the food web and fisheries resources. This study utilizes stable isotopes to analyze fish samples ranging from 3.4 to 1067 g in body mass, collected within the artificial reef area of Haizhou Bay. The objective is to determine if the δ¹⁵N-based fish body mass acts as a driving factor in shaping the food web structure. The results showed a certain level of overlap among all trophic guilds, suggesting that most trophic guilds within this region share similar living environments and feeding habits. The multiple linear regression showed a slight increasing trend between δ¹⁵N values and body mass. Furthermore, the predator–prey mass ratio (PPMR) was calculated to be 430:1 based on the δ¹⁵N–body mass relationship. This implies that larger reef fish within this artificial reef ecosystem tend to have higher δ¹⁵N values compared to smaller fish, indicating a shorter food chain in this ecosystem. In summary, this analysis provides valuable insights into the fish community structure within artificial reef ecosystems. Therefore, it is recommended that future studies focus on further characterizing the fish community structure using body mass information.

In highly variable estuarine environments, short-lived fishes must balance immediate reproduction against future growth, yet the reproductive role of maternal size remains poorly resolved. Here, we analyzed biological surveys of the yellowfin goby Acanthogobius flavimanus from Haizhou Bay, Yellow Sea, collected between 2023 and 2025, combining fecundity estimation, egg morphometry, histology, and size-structured reproductive-output modeling. Absolute fecundity scaled hyperallometrically with total length (β = 3.18, 95% CI: 3.05–3.31, R² = 0.71, p < 0.001), while mean egg diameter increased significantly with maternal size (R² = 0.65, p < 0.001), yielding an approximately 3.15-fold increase in estimated egg volume across the observed size range. Histology revealed contrasting ovarian developmental phenotypes within the same spring cohort: a precocious phenotype with active vitellogenesis and a delayed-development phenotype with structurally intact early-stage oocytes and higher condition factor. Relative Reproductive Output (RRO) modeling showed that females > 180 mm total length represented only 4.8% of abundance but contributed 18.5% of total standardized egg-production output under the assumptions of the model. Inter-annual monitoring further indicated a decline in mean body size and in the proportion of large individuals from 2023 to 2025, a pattern consistent with size truncation but requiring longer-term monitoring for causal attribution. These findings suggest that large females can contribute disproportionately to reproductive output even in a short-lived estuarine fish and support the inclusion of size structure in fisheries assessment and management.