Financial development, crucial for economic growth, involves enhancing financial institutions, markets, and instruments to facilitate efficient resource allocation. The concept's evolution reflects the changing dynamics and complexities of the global financial landscape. Early literature employed indicators such as the ratio of broad money to GDP or private credit to GDP to measure financial intermediation depth and bank functionality. Seminal publications by Goldsmith (1969) and Engerman and McKinnon (1974) demonstrated the links between financial development and economic growth. As financial markets matured, researchers expanded the scope of financial development to encompass stock and bond markets, as well as non-bank financial institutions. Levine (1997) introduced a comprehensive measure of financial development, incorporating aspects such as financial system size, efficiency, and stability. Contemporary research explores the multifaceted nature of financial development, including financial accessibility, regulatory quality, and legal and institutional frameworks. Levine and Beck (1999) developed a comprehensive database facilitating cross-country comparisons and empirical analyses. Recent international studies have enhanced our understanding of financial development's role in promoting economic growth. Svirydzenka (2016) developed a comprehensive Financial Development Index for the IMF, encompassing multiple dimensions of both financial institutions and markets. Sugandi (2022) further explored fintech's impact on financial development, highlighting its potential to accelerate financial inclusion while introducing new risks.

Quantifying financial development has led to various indicators and composite indices. Scholars have developed indicators based on monetary and credit factors (Acheampong, 2019; Hung, 2023) or built systems assessing financial depth, accessibility, and efficiency. Wang et al. (2021a) proposed a four-dimensional indicator system encompassing financial depth, breadth, efficiency, and ecological environment. Nguyen et al. (2023) included evaluations of financial institutions, market effectiveness and domestic credit to the private sector. Comprehensive indicator sets for measuring financial systems development across countries are provided by the IMF's Financial Development Index (Svirydzenka, 2016) and the World Bank's Global Financial Development Database.

The marine economy, or blue economy, has garnered recognition as a potential driver of sustainable economic growth. It encompasses diverse ocean-related activities, including marine fisheries, aquaculture, maritime transport, coastal tourism, and emerging industries like offshore renewable energy and marine biotechnology (Pontecorvo et al., 1980; Colgan, 2013; Park and Kildow, 2015). Quantifying the economic impact of the marine economy is challenging due to its diverse nature. Researchers have employed various methodologies, such as input-output analysis and computable general equilibrium models (Park and Kildow, 2015). Wenhai et al. (2019) reviewed blue economy practices, emphasizing the need for integrated approaches. Cisneros-Montemayor et al. (2021) highlighted the importance of equity and inclusion in blue economy strategies, particularly for coastal communities and developing nations.

High-quality economic development has become a focal point, emphasizing sustainable growth, improved quality of life, and environmental sustainability (Simms and Boyle, 2009; Stefan, 2012; Lau et al., 2014). In the marine economy context, researchers have proposed various indicators and evaluation methods to assess high-quality development, including per capita gross ocean product (GOP) (Liu et al., 2017), marine economic efficiency, and total factor productivity (Liu et al., 2021; Ren and Ji, 2021). Gao et al. (2022) used a support vector machine (SVM) model and particle swarm optimization (PSO) to evaluate the high-quality development of China's marine sector. Sun et al. (2023) created a bidirectional multi-index comprehensive evaluation framework, applying the PSO and SVM model to assess China's marine economy's high-quality development. Feng et al. (2024) established an indicator system for marine economic development based on economic, ecological, and social dimensions. While research on high-quality marine economic development evaluation has increased (Li et al., 2020a; Chen et al., 2024; Han and Cao, 2024; Zhang and Wang, 2024), some indicators show weak relevance to marine economic development. Refining these indicator systems could enhance measurement accuracy.

The intersection of financial development and the marine economy has attracted increasing attention in recent literature. As a crucial component of the national economy, the marine sector requires a well-developed financial system to support its growth and sustainability (Xu and Cui, 2020; Wang et al., 2021a). However, research findings on the relationship between financial development and marine economic growth are diverse.

A significant body of research suggests that financial development positively promotes marine economic development. An and Li (2020) argue that finance can facilitate marine industry structure optimization, fostering growth. Tian et al. (2019) propose that the financial industry can enhance equity financing support through a green approval mechanism for marine planning. Gao (2020) highlights how finance development promotes marine economic growth through various investment and financing mechanisms. Recent studies have also explored innovative financial instruments, such as blue bonds, to encourage private investment in the blue economy (Wang et al., 2021b; Shiiba et al., 2022).

International research has emphasized the critical role of innovative financing mechanisms in supporting sustainable marine economic development. Sumaila et al. (2021) analyzed ocean finance strategies, emphasizing the need for both public and private sector involvement. They identified key ocean-based industries requiring sustainable financing and proposed a combination of financing mechanisms. Virdin et al. (2021) examined transnational corporations’ role in the ocean economy, suggesting potential avenues for leveraging corporate finance for sustainable marine development.

Conversely, some scholars have identified potential limitations or negative effects of financial development on the marine economy, termed ‘financial inhibition’. Song et al. (2020) revealed a threshold effect in the relationship between financial development and Chinese marine economic growth, suggesting that financial development enhances marine economic growth only beyond a certain level of initial financial sector development. Ma (2017) found that while total deposits have a positive impact on the marine economy, the insurance market has a negative impact, although neither effect was statistically significant. Zhao and Peng (2017) observed that credit and insurance markets could promote marine economic growth, while the stock market has a negative impact.

These conflicting findings underscore the complex nature of the relationship between financial development and marine economic growth. The impact varies depending on specific aspects of financial development, financial sector maturity, and the unique characteristics of marine economic activities. The concept of ‘high-quality development’ in the marine economy introduces additional dimensions that traditional economic growth metrics may not fully capture. While our study focuses on China's marine economy, these findings contribute to the broader international discourse on the relationship between financial development and sustainable marine economic growth. The insights gained from China's experience can inform global strategies for leveraging financial development to support high-quality growth in marine economies worldwide.

In conclusion, financial development assessment mainly focuses on macro indicators and overall financial institutions and markets, rarely examining them within a unified index framework. The growth of digital inclusive finance has become a key metric for evaluating financial development. Therefore, we incorporate the digital inclusive financial development index to improve comprehensiveness. Despite contributions to financial development and the marine economy concepts, research exploring the linkages between the two domains is lacking. We address this gap by conducting a sub-regional regression analysis of three main marine economic regions and categorically classifying 11 coastal provinces’ marine economies into research-driven and industry-driven sectors. This study provides a more comprehensive depiction of marine economic development in various locations with distinct characteristics, contributing to a holistic understanding of the interplay between finance and sustainable marine economic development.

Economic development, rooted in industrial economics, encompasses not only the growth of economic aggregates and social wealth but also the optimization of internal economic structures and enhancement of efficiency (Jiang et al., 2014). It impacts aspects of societal quality, including overall well-being, living standards, personal development, and the ecological environment (Plummer et al., 2018; Pan et al., 2021). High-quality economic development can be defined through the vision of innovation, coordination, greenness, openness, and sharing (Gao et al., 2022). In the context of the marine economy, these take on specific characteristics:

Based on these considerations, we define marine economic high-quality development as a mode of development characterized by innovation-driven growth in marine science and technology, coordinated regional development, sustainable environmental practices, enhanced land-sea connectivity, and shared benefits across coastal and inland regions.

Next, we disentangle the complex relationship between financial development and high-quality marine economic development by examining four distinct mechanisms: risk resilience, innovation capacity, industrial structure transformation, and capital accumulation. While these mechanisms may all contribute positively to marine economic development, understanding their individual roles and relative importance is crucial for targeted policy-making and financial strategies in the marine sector.

The marine economy is characterized by high capital requirements, extended investment cycles, substantial initial outlays, and vulnerability to natural disasters. Financial development is significant in enhancing the sector’s resilience to various risks by fostering the growth of insurance businesses and other financial products.

In China, marine insurance primarily covers ship and cargo insurance within the maritime transportation sector, offering timely compensation for damages and mitigating operational risks. The fishery sector can benefit from specialized insurance providing compensation for productivity losses due to severe weather events. As financial development progresses, it is expected to stimulate growth in the insurance industry, leading to more marine insurance providers and product diversification. This expansion of financial services contributes to increased production capacity in marine-related businesses and offers additional hedging options, enhancing overall risk management capabilities.

According to this analysis, we advance H1. Testing this hypothesis will help understand how financial tools can mitigate the unique risks in the marine sector, potentially leading to more stable growth.

H1: Financial development positively influences the high-quality growth of the marine economy by enhancing its resilience through the expansion and diversification of insurance and other financial products.

The marine economy, particularly its emerging sectors such as seawater utilization, marine biomedicine, and marine equipment manufacturing, are technology-intensive industries requiring substantial human capital and advanced technologies. These sectors focus on leading-edge innovation but face significant financial challenges due to high initial investments and associated risks. Financial development can address these challenges and promote innovation in the marine economy by:

a) Providing financial support for R&D through venture capital and private equity;

b) Attracting talent and technology to regions with advanced financial sectors;

c) Attracting skilled professionals with specialized knowledge in relevant fields like computer science and materials engineering.

In light of the above analysis, we advance the second hypothesis, which explores how financial development can overcome the high barriers to innovation in marine industries, which is crucial for long-term competitiveness.

H2: Enhanced financial development stimulates high-quality innovation in marine science and technology, thereby elevating the marine economic development level.

To achieve high-quality development in the marine economy, China must increasingly rely on investments in technology and scientific research. Currently, traditional marine sectors, such as coastal tourism, transportation, and marine fisheries, generally have a low level of scientific and technological integration and are heavily dependent on natural marine resources. Emerging marine industries, including marine biomedicine and marine equipment manufacturing, offer higher value-added opportunities, but they need to be developed.

Enhancing financial development in coastal regions contributes significantly to the structural improvement of the marine industry (An and Li, 2020; Sheng et al., 2021). Financial institutions can play a pivotal role in this transition by:

a) Strategically allocating funds across various industries;

b) Evaluating the potential of marine businesses for informed capital allocation;

c) Supporting core research and acquiring expertise in science and technology;

d) optimizing market mechanisms to increase product value;

e) Offering preferential financing to high-tech enterprises in the maritime sector.

Based on these considerations, we propose the third hypothesis. Examining this hypothesis will shed light on the role of finance in facilitating the necessary structural changes for high-quality marine economic development.

H3: Financial development positively influences the upgrading of the marine industrial structure, thereby enhancing the quality of the marine economic high-level development.

Capital accumulation is fundamental to economic growth, with external capital infusion accelerating this process. Financial development expedites capital accumulation by offering diverse investment opportunities for enterprises. In the marine economy context, this process plays a crucial role in driving economic growth and creates a positive feedback loop where financial development and capital accumulation mutually reinforce each other.

Within the framework of the marine economy, this process of capital accumulation through financial development plays a crucial role in:

a) Efficient allocation of surplus value for marine enterprises;

b) Creating a positive feedback loop between capital accumulation and financial industry growth;

c) Accelerating marine capital accumulation through external capital injection.

Based on these considerations, we propose the fourth hypothesis, which investigates how financial development addresses the capital-intensive nature of marine industries, which is essential for their expansion and modernization.

H4: Financial development accelerates capital accumulation in marine industries, leading to higher fixed asset investment growth in the marine sector compared to other sectors.

These distinct yet interrelated hypotheses aim to provide a nuanced understanding of how financial development contributes to high-quality marine economic growth, enabling policymakers to design targeted financial strategies for sustainable marine economic development.

The growth of the marine industry and the expansion of the marine economy have led to noticeable disparities among coastal locations (Sun et al., 2018). These regional differences are significantly influenced by the uneven distribution of marine resources in China, which impacts both marine economic growth and industrial structure (Meng et al., 2024). To analyze these disparities, this paper categorizes the 11 coastal provinces into three regions based on the "Thirteenth Five-Year Plan for National Marine Economic Development" in Figure 1 , in which the Northern Marine Economic Zone includes Liaoning, Hebei, Tianjin and Shandong, the Eastern Marine Economic Zone includes Jiangsu, Shanghai and Zhejiang, and the Southern Marine Economic Zone includes Fujian, Guangdong, Guangxi and Hainan. These regions, arranged from north to south, exhibit variations in marine economic growth due to diverse factors, including marine resources, environmental conditions, and economic foundations.

To examine the impact of financial development on the high-quality growth of the marine economy, we propose the following model.

In this model, ME denotes the score of the marine economic high-quality development, which we calculated in Section 4.3.3; FD is the financial development score calculated in Section 4.2.3, which is based on the index system and weighting method described in Sections 4.2.1 and 4.2.2; RD, DPI, Lnop, and Fis serve as control variables. The index i corresponds to the province, t denotes the year, and ϵ i t is the error term, assumed to follow a normal distribution N ( 0 , σ i t 2 ) .

The financial development index (FD) serves as our key explanatory variable, hypothesized to influence the high-quality development of the marine economy (ME). Drawing from recent literature on coastal management and marine economics (Jiang et al., 2014; Sun et al., 2018; Gai et al., 2022) and potential impact on marine economic development, we identify four control variables: marine research investment (RD), per capita disposable income (DPI), level of international openness (Lnop), and financial support (Fis). Table 5 represents the explanation of the variables in the model (2) and their literature supports.

Table 6 shows the descriptive statistics of the variables. Most indicators exhibit positive skewness, suggesting a predominantly right-skewed distribution. The Jarque-Bera (JB) statistics indicate non-normal distributions for all variables. To ensure data reliability, we conduct unit root tests using LLC and ADF-Fisher methods. All variables pass both tests at the 1% significance level, confirming stationarity and mitigating spurious regression concerns ( Table A1 ).

Pearson correlation coefficients in Table 7 demonstrate positive correlations between the high-quality development score of the marine economy (ME) and all other variables, significant at the 1% level. These findings suggest that all variables are positively associated with marine economy development. A Hausman test results in Table A2 fail to accept the null hypothesis at the 1% significance level, supporting the fixed effects model's suitability for our analysis.

The regression outcomes in Table 8 reveal that financial development has a significant positive impact on the high-quality development of the marine economy. A 1% increase in financial development corresponds to a 0.253% growth in marine economy development quality (significant at a 1% level). The financial industry primarily supports marine economic growth by providing insurance and other financial instruments. The expansion of the insurance industry reduces business risks and contributes to the productive capacity of ocean-related firms. Additionally, advancements in financial development have facilitated the introduction of a wide range of financial derivatives for hedging risks, providing ocean-related enterprises with more hedging options and further enhancing their risk management capabilities, thereby supporting the steady growth of the marine economy. These findings provide initial support for H1, suggesting that financial development contributes to the high-quality growth of the marine economy by enhancing its resilience to various risks through the expansion and diversification of insurance and other financial products. The varying coefficients across different marine subsectors also lend support to H3, indicating that financial development influences the upgrading of the marine industrial structure. Among the control variables, scientific research investment, per capita disposable income, and openness positively contribute to the high-quality development of the marine economy. Notably, scientific research investment shows the most significant impact. The impact of local financial expenditure is less apparent, possibly due to insufficient allocation or resource diversion.

Regional variations are evident. The Eastern Marine Economic Zone demonstrates the most pronounced effect. These provinces offer a wide range of financial services for ocean-related firms, making it easier and more diverse for them to acquire financial support. In contrast, the Northern and Southern Marine Economic Zone, which include provinces with comparatively low financial development levels, show a limited influence on the high-quality development of the marine economy.

In the Northern Marine Economic Zone, openness significantly contributes to the advancement of high-quality development in the marine economy. Several large coastal ports make this zone a hub for international marine interaction. However, fiscal expenditure in this region may hinder high-quality marine sector growth by focusing on non-marine industries.

In the Eastern Marine Economic Zone, per capita disposable income plays a significant role in promoting high-quality development. The most economically advanced provinces and cities in China have the largest per capita disposable income, which corresponds to regional financial development levels. Thus, these regions' financial industries contribute more to the marine economy.

The Southern Marine Economic Zone shows substantial impacts from both per capita disposable income and the level of external development. This zone has remarkable ports, including Xiamen, Shenzhen, Guangzhou, and Beibu Gulf and has advanced worldwide trade. Residents' disposable money in this region supports high-quality marine economy growth by buying ocean-related services.

To explore potential heterogeneity in the effect of financial development on marine economic growth, we conducted a group analysis based on the proportion of marine scientific research and education management services in each province as of 2019. Provinces with a proportion exceeding 25.8% were classified as marine research and education promotion regions (Shanghai, Zhejiang, Guangdong, and Hainan). At the same time, those below this threshold were sorted as marine industry promotion regions (Liaoning, Tianjin, Hebei, Shandong, Jiangsu, Fujian, and Guangxi). This classification allowed us to investigate whether the nature of marine economic activities influences the relationship between financial development and economic growth.

The regression results in Table 9 reveal a striking contrast between the two groups. In marine research-driven regions, financial development exhibits a significant positive impact on the high-quality growth of the marine economy. This effect may be attributed to the higher investment in scientific research and innovation in these provinces, leading to a higher demand for specialized financial products such as venture capital funds and blue bonds. Moreover, the advanced financial industry in these regions facilitates more straightforward access to financing, further stimulating demand for such services.

In contrast, in marine industry-driven regions, the effect of financial development on marine economic growth is statistically insignificant. This disparity suggests that areas with a dominant marine industry tend to allocate a more significant portion of funds towards production expansion rather than scientific research. The enterprises in these areas rely more heavily on their capital and traditional external financing, reducing their dependence on innovative financial services.

The impact of research and development (R&D) investment also differs between the two groups. In marine research-driven regions, R&D investment has a clear positive effect on the high-quality growth of the marine economy. However, this effect is not apparent in marine industry-driven regions. This finding underscores the importance of R&D in driving innovation and growth in research-intensive marine economies.

Interestingly, per capita disposable income shows a more significant impact on fostering high-quality growth in marine industry-driven regions. This aligns with the higher demand for social capital in these areas compared to research-driven regions, suggesting that consumer spending plays a crucial role in supporting marine industry growth.

The degree of external openness has a negligible impact on fostering high-quality growth in both regions. Financial expenditure, however, demonstrates divergent effects: it positively influences high-quality growth in research-driven regions but negatively impacts industry-driven regions. This discrepancy may be due to the allocation of financial resources primarily towards scientific research and innovation, potentially leaving industries with lower research investment underserved in industry-driven regions.

To validate our findings, we conducted a robustness test using an alternative variable method which ensures the stability of results across different key variables. This method is suitable for testing findings using traditional measures of economic output and financial development. It addresses concerns about the specificity of the constructed indices by using widely recognized economic indicators, demonstrating that the findings are not artifacts of the index construction methodology. We replaced the high-quality development level of the marine economy with per capita Marine GDP (MGDP) as the dependent variable. Additionally, we substituted the score of financial development level with the added value of the financial industry (FI) as an alternative measure of financial development. The model selection process and regression method remained consistent with the benchmark regression.

The robustness tests presented in Table A3 corroborate our initial conclusions. We observe a significant positive relationship between the level of financial development and marine economic growth, as measured by Marine GDP. This result aligns with our previous findings and underscores the direct impact of financial development on financing opportunities for marine-related industries.

As financial development improves, marine enterprises benefit from increased financial backing and access to diverse financing options, facilitating their growth and expansion. The test also revealed that a 1% increase in the added value of the financial industry leads to a 0.018% increase in the high-quality development level of the marine economy. While positive, this impact appears less pronounced compared to the effect of the overall financial development level.

These results suggest that while the growth of the pure financial industry positively influences the high-quality development of the marine economy, the broader measure of financial development, which encompasses various aspects of the financial system, has a more substantial impact. This finding highlights the importance of comprehensive financial development strategies that go beyond just expanding the financial sector.

The consistency of these findings across different variable specifications lends credibility to our initial results and strengthens our overall conclusions. These robust findings have important implications for policymakers and stakeholders in the marine economy. They suggest that efforts to enhance financial development, particularly those tailored to marine-related industries, can yield substantial benefits for marine economic growth. Furthermore, the results underscore the importance of adopting a holistic approach to financial development that considers not only the size of the financial sector but also its efficiency, accessibility, and alignment with the specific needs of the marine economy.

To deepen our understanding of the mechanisms through which financial development influences the high-quality growth of the marine economy, we conducted a mediation effects analysis. This analysis focuses on two potential mediating variables: marine innovation output and the upgrading of marine industrial structure. We use the proportion of marine scientific research output in the added value of marine and related industries (Pso) and the marine industrial structure upgrading index (Str) as our mediating variables. The specific form of the intermediary models is described as follows:

where M E i t F D i t and C V i t represent high-quality marine economic development, financial development, and control variables, respectively, for province i in year t. The results of the mediation effect are shown in Table 10 .

The baseline model in column (1) confirms a significant positive effect of financial development on marine economic development (β = 0.253, p < 0.01). Also, financial development significantly promotes innovation (δ = 0.201, p < 0.01) and industrial upgrading (δ' = 0.341, p < 0.05). Both mediators contribute positively to marine economic development, with innovation showing a stronger effect (θ = 0.133, p < 0.05) compared to industrial upgrading (θ' = 0.045, p < 0.1).

The observed positive relationship between financial development and marine-related R&D expenditure or patents supports H2, confirming that financial development stimulates innovation in marine science and technology. We can draw this conclusion by examining the coefficients and significance levels in Model (5). The positive and significant coefficient of FD on Pso (δ = 0.201, p < 0.01) shows that financial development promotes marine innovation. The positive and significant coefficient of Pso on ME (θ = 0.133, p < 0.05) demonstrates that this innovation contributes to marine economic development. The indirect effect of financial development through innovation can be calculated as the product of these two coefficients (0.201 * 0.133 = 0.0267), which represents 10.57% of the total effect. This substantial mediation effect provides strong support for H2.

The second mediator, marine industrial structure upgrading (STR), demonstrates a notable positive correlation between financial development and industrial upgrading (δ' = 0.341, p < 0.05) in column (4). This suggests that financial development is essential in facilitating the transition of marine sectors. H3 indicates that financial development has a favorable impact on the upgrading of the marine industrial structure, leading to an enhancement in the quality of high-level development in the marine economy. The results of column (5) indicate that industrial structure upgrading has a positive impact on marine economic development (θ' = 0.045, p < 0.1), thus providing support for H3, albeit with a smaller coefficient compared to innovation output.

Calculating indirect effects, we find that marine innovation output mediates 10.57% of the total effect of financial development on marine economic growth, while industrial structure upgrading mediates 6.13%. These findings suggest that financial development's impact on marine economic growth is more strongly channeled through innovation rather than structural changes.

Financial development has a sustained direct effect after accounting for these mediators, suggesting further avenues of influence, such as risk management or market efficiency. These results emphasize the need for comprehensive financial policies that boost financial development, maritime innovation, and coastal industrial transformation.

To further validate our findings, we employed the Bootstrap method ( Tables A4 - A5 ). The results confirm the mediating roles of both marine innovation output (indirect effect: 0.349 [0.119, 0.632]) and industrial structure upgrading (0.272 [0.044, 0.517]). The significant indirect effects coupled with non-significant direct effects suggest that these two mediating variables do play a mediating utility between financial development and the level of high-quality development of the marine economy.

These results suggest that financial development significantly promotes marine economic growth, with innovation acting as a stronger mediator and industrial structure upgrading facilitating resource reallocation across marine industries. It emphasizes the need for comprehensive financial policies targeting marine innovation and industrial transformation in coastal regions, primarily through enhanced innovation capabilities and improved industrial structures.

Marine capital investment plays a crucial role in expanding maritime enterprises, potentially amplifying the impact of financial development on marine economic growth. Due to limitations in provincial and municipal data on marine capital investment, we use marine fixed asset investments from 11 provinces and cities (2011-2020) as a proxy, calculated by multiplying social fixed asset investment with the proportion of Gross Ocean Product (GOP) to national GDP. To construct the moderation effect model, we log-transform the data, where represents the logarithm of marine fixed asset investment for province in year. Other variables retain their previously defined meanings. The moderation effect model is constructed as follows:

where L n i n v i t denotes the logarithm of marine fixed asset investment for province i in year t.

Table 11 presents the results of our moderation analysis. Notably, the interaction term between financial development and marine capital investment shows a positive correlation at the 5% significance level. The observed positive relationship between financial development and fixed asset investment in the marine sector provides strong support for H4, confirming that financial development promotes capital accumulation in the marine economy. Financial development (FD), marine capital investment (Lninv), and their interaction (Lninv * FD) all exhibit positive and significant effects. Control variables such as R&D investment (RD), economic openness (Lnop), and income level (DPI) show positive impacts, while fiscal decentralization (Fis) demonstrates a negative effect.

This synergistic effect can be attributed to several mechanisms. Firstly, increased marine capital investment expands the pool of available funds for sea-related financial products, facilitating the growth of marine finance and enhancing the financial sector’s capacity to support marine enterprises. Secondly, growth in marine capital investment leads to an expansion in the operational scale of ocean-related enterprises, increasing the overall size of the marine economy and boosting demand for financial services. Furthermore, marine capital investment helps ocean-related enterprises by broadening their financing channels and reducing both financing thresholds and costs when accessing financial services.

The positive interaction between financial development and marine capital investment creates a conducive environment for high-quality growth in the marine economy. It strengthens the financial sector's capacity to support marine industries and enhances the ability of marine enterprises to utilize financial services effectively. This symbiotic relationship between financial development and marine capital investment ultimately drives sustainable economic growth in China's marine sector.

Our empirical analysis provides strong evidence for the significant role of financial development in promoting high-quality growth in China's marine economy. This section compares and contrasts our key findings with recent literature.

Firstly, our results demonstrate that financial development positively influences the high-quality growth of the marine economy by enhancing its resilience to risks through expanded financial products. This finding aligns with Su et al. (2021), who found that financial development significantly promotes marine economic growth in China's coastal areas. However, while Su et al. (2021) focused on the overall impact, our study extends this understanding by identifying specific mechanisms, particularly the role of insurance and financial derivatives in risk management.

Secondly, we found that financial development stimulates innovation in marine science and technology, acting as a stronger mediator than industrial structure upgrading. This result partially contrasts with Gao et al. (2022), who emphasized the importance of technological innovation in marine economic growth. While our study acknowledges the role of industrial upgrading, we found innovation to be a more potent channel for financial development to influence marine economic growth.

Thirdly, our analysis reveals that financial development facilitates the upgrading of the marine industrial structure, albeit with a smaller effect compared to innovation. This finding supports, but also refines, the work of Wang and Yang (2022), who identified industrial structure as a key factor in marine economic efficiency. Our results suggest that while industrial upgrading is important, it may not be the primary channel through which financial development promotes high-quality marine economic growth.

Lastly, we found that financial development promotes capital accumulation in the marine sector, with this effect being moderated by the level of marine capital investment. This interaction effect aligns with the findings of Sumaila et al. (2021) and Wang et al. (2023), who highlighted the importance of capital investment in marine economic development. However, our study extends this understanding by explicitly linking capital accumulation to financial development and quantifying their interactive effect.

This study aimed to investigate the relationship between financial development and high-quality growth in China's marine economy, focusing on how financial development influences the quality of marine economic growth and how this influence operates. We developed a comprehensive index system for measuring both financial development and high-quality development of the marine economy, analyzing data from 11 coastal provinces and cities from 2011 to 2020. Our analysis yielded several key findings:

(1). Financial development significantly promotes the high-quality progress of China's marine sector. This influence varies among different marine economic zones. The Eastern Marine Economic Zone demonstrates the strongest effect, followed by the Northern Marine Economic Zone, while the Southern Marine Economic Zone shows the weakest effect.

(2). We identified two key mediating factors: marine scientific research and the upgrading of marine industrial structure. Marine scientific research demonstrated a strong intermediary effect, suggesting that financial development significantly boosts marine economy quality by promoting innovation and research activities. The upgrading of marine industrial structure also serves as a mediator, albeit with a lesser effect.

(3). Marine capital investment positively moderates the link between financial development and marine economic growth, indicating that increased capital investment can amplify how financial development positively affects the marine economy.

(4). Other significant factors influencing the marine economic high-quality development include scientific research investment intensity, degree of economic openness, and per capita disposable income. Local financial expenditure showed a slight inhibitory effect, possibly due to inadequate local financial investment in the marine sector or allocation of financial resources to other industries.

(5). Provinces with a larger share of marine research and education services experienced a stronger influence of financial development on high-quality growth in the marine economy.

This research contributes to the existing literature by providing a focused analysis of China's marine sector, incorporating a multi-dimensional index system for measuring high-quality development. Our approach offers insights specific to coastal economic development, challenges one-size-fits-all models, and provides a more nuanced understanding of how financial development translates into high-quality marine economic growth.

Based on our findings, we propose several policy implications:

Although this study provides valuable information, it has limitations that pave the way for future research. Future studies could expand the scope both geographically and temporally to enhance the generalizability of findings. A deeper exploration of unexplored mechanisms through which the financial industry influences real economic growth is needed. Investigating the long-term environmental impacts of financial development-driven marine economic growth, conducting comparative studies with other coastal nations, and exploring the potential of fin-tech and green finance in promoting sustainable marine economic development could offer new perspectives for policymakers and industry stakeholders, further contributing to our understanding of the complex dynamics driving high-quality growth in marine economies.