Abstract:The sustained growth of marine filter-feeding bivalve aquaculture in China, while instrumental for food security and coastal economies, has triggered widespread concern regarding ecosystem overloading. Intensive cultivation can lead to significant ecological pressures, including alterations in planktonic communities due to excessive grazing pressure, degradation of sediment environments, and declines in benthic biodiversity. These changes subsequently manifest as reduced growth rates, increased disease incidence, and unstable production within the cultivation industry itself. To address these challenges and steer the industry towards sustainable development, a scientific and comprehensive assessment of aquaculture carrying capacity is urgently required. This study undertakes a systematic evaluation of the carrying capacity for filter-feeding bivalves across China, encompassing national, provincial, typological, and species-specific scales, by employing the foundational theoretical framework of the Logistic population growth model. The concept of carrying capacity is intrinsically linked to population ecology, originating from the Logistic equation where the environment can support a maximum population size, denoted as K, beyond which growth ceases. Translating this to aquaculture, carrying capacity represents the maximum sustainable yield per unit water body in a specific area that does not harm the ecological environment, maintains ecosystem stability, and aligns with sustainable production goals. The Logistic model offers a robust theoretical basis for quantifying this upper limit of cultivation scale. This research leverages long-term historical data on aquaculture production and area compiled from the China Fishery Statistical Yearbooks spanning the period from 1979 to 2022. By fitting this extensive time-series data to the Logistic model, the key parameters, namely the intrinsic growth rate and the environmental carrying capacity K, were derived for different analytical dimensions. The findings reveal a critical situation at the national level. The calculated carrying capacity for filter-feeding bivalves in China is 13.37 million tonnes. Alarmingly, the current aquaculture production, recorded at 15.95 million tonnes , already exceeds this sustainable limit by 19.2 percent. This pattern of overcapacity is widespread at the provincial scale. Among the eight major coastal provinces analyzed, six provinces including Shandong, Jiangsu, Zhejiang, Fujian, Guangdong, and Guangxi have surpassed their individually estimated carrying capacities. Fujian Province stands out with the most severe overshoot, where current production exceeds its capacity by 38.9 percent. In contrast, Hebei and Liaoning provinces were found to have current production levels close to their estimated capacities. A further breakdown by aquaculture type shows that both predominant systems are operating beyond their sustainable thresholds. The shallow-sea aquaculture carrying capacity is estimated at 7.93 million tonnes, but current production reaches 9.98 million tonnes, resulting in a 25.8 percent overshoot. Similarly, for tidal flat aquaculture, the carrying capacity is 5.41 million tonnes, while production stands at 5.96 million tonnes, exceeding the limit by 10.2 percent. Analysis of major cultured species indicates that oysters and clams are particularly over-exploited. The carrying capacity for oysters is 4.67 million tonnes, but production has surged to 7.25 million tonnes, representing a substantial overshoot of 55.2 percent. Clams, with a capacity of 4.21 million tonnes, are also over-capacity by 12.6 percent. Other species like mussels, scallops, and cockles are currently near their estimated capacity limits. The reliability and applicability of the Logistic model for this large-scale assessment were strongly supported by high goodness-of-fit values, with most Pearson R2 values exceeding 0.8, indicating a robust fit to the historical data trends.The discussion contextualizes these results by emphasizing that the estimated K values represent not only the theoretical natural ecological limit but also incorporate the effects of existing management policies and technological levels. The prevalent over-capacity cultivation is identified as a primary driver for increased environmental pressure and intensified competition for food resources among cultured bivalves, potentially compromising their growth and health. The study validates its methodological approach by comparing its large-scale results with findings from localized, high-resolution studies conducted in specific bays like Sanggou Bay for oysters and Jiaozhou Bay for clams, confirming the feasibility of the Logistic model for macro-scale assessment. In conclusion, this research provides compelling evidence that over-capacity bivalve aquaculture is a pervasive issue across various spatial scales and categories in China. It underscores the critical and urgent need for implementing science-based and spatially differentiated management strategies. Key recommendations include controlling and potentially reducing the cultivation scale in over-capacity regions, especially for shallow-sea systems and in provinces like Fujian and Shandong for oyster cultivation. Furthermore, promoting technological innovations such as the development of high-quality seeds and the strategic expansion into offshore aquaculture, coupled with strengthened environmental monitoring networks, is essential. Future research should focus on integrating more complex methodologies like dynamic energy budget models or ecosystem dynamics modeling with real-time monitoring data to enhance the precision and dynamic nature of carrying capacity assessments. Ultimately, the establishment of a standardized, institutionalized, and regularly updated carrying capacity assessment system is paramount for providing a scientific foundation to guide the transformation of China's bivalve aquaculture industry from a model of extensive expansion to one prioritizing ecological health and long-term sustainability.
