Research on the Synergistic Effect of the Composite System for High-Quality Development of the Marine Economy in China

: The key to achieving the high-quality development of the marine economy (HDME) is to facilitate synergy through the coordination of marine elements. By adopting a perspective concerning complex systems, this paper presents a comprehensive framework—the composite system for high-quality development of the marine economy (CSHDME)—that synergistically integrates the ﬁve dimensions of economy—technology—ecological—society—culture in the marine domain. Building upon this framework, in this paper, we construct a CSHDME synergy evaluation index system using relevant data from 11 coastal provinces in China from 2010 to 2020. We utilize the subsystem orderliness degree model and composite system synergy degree model to calculate the degree of subsystem orderliness and degree of composite system synergy for the CSHDME as well as analyze the development status of the CSHDME subsystem and the degree of CSHDME synergy. The results indicate that: (1) the ﬁve-dimensional subsystem of the CSHDME exhibits an overall trend of year-on-year growth, with signiﬁcant development disparities; (2) the degree of the synergy of the CSHDME is characterized by strong regional differences, strong ﬂuctuations, instability, and low synergy; (3) the degree of the synergy of the CSHDME demonstrates the spatial evolution characteristics of low synergy, strong differences, strong ﬂuctuations, and high agglomeration; and (4) the degree of orderliness and development speed of subsystems affect the degree of the synergy of the CSHDME. Therefore, measures such as the rational allocation of marine resources, accurate improvement of shortcomings, optimization of the spatial layout, and strengthening of regional cooperation should be considered to further promote the synergistic development of the CSHDME.


Introduction
In being a strategic point of high-quality development, the marine economy is crucial for achieving sustainability and the robust growth of the national economy. Hence, attaining HDME is an inevitable necessity [1]. Recently, the development of the marine economy has gained momentum in China. In 2021, the marine GDP exceeded CNY 9 trillion, approximately 15% of the coastal GDP and 8% of the national GDP. The marine economy tends to be considered an important engine of the national economy, and HDME has recently received heightened attention from the Party Central Committee and the State Council. In March 2018, General Secretary Xi Jinping proposed that the ocean is a strategic location for high-quality development [2]. In June 2018, General Secretary Xi Jinping stressed that efforts should be made to promote the transformation of the marine economy to quality and efficiency-oriented [3]. In recent years, coastal provinces have formulated development strategies for strong marine provinces, set up plans for HDME, and put forward clear requirements. In general, HDME has become the standard that guides the development of the marine economy in China into the near future, and has both high strategic value and practical significance.
However, along with the continuous expansion of the marine economy, some issues have gradually come to the fore, such as large differences in the development of marine regions and the serious homogenization of marine industries. Despite the complexity and diversity of marine resources and elements, it is still difficult to form development synergy through mutual collaboration, which restricts the progress of HDME. From a systemic perspective, the marine economy is an open composite system [4]; changes in internal and external factors such as economic development, technological progress, natural resources, circumstance constraints, policy interventions, and public participation affect and drive the development of other elements; thus, the CSHDME represents the high-quality, balanced, and coordinated development of various dimensional elements such as the marine economy, technology, ecology, society, and culture. Therefore, there is an urgent need to adhere to the outlined systemic concept, coordinate resources and elements of all dimensions of the marine economy, and explore the synergistic effect between the elements of the CSHDME so as to accelerate HDME. This paper adopts the subsystem orderliness degree model and the composite system synergy degree model, intending to explore the synergistic effect of the CSHDME in China, thus providing theoretical support and practical directions toward further promoting HDME. This papers contributions are summarized as follows: (1) From the perspective of complex systems, this paper takes many factors such as marine economy, technology, ecology, society, and marine culture into consideration and constructs a fivedimensional composite system of the marine environment economy-technologyecological-society-culture for HDME, which improves upon the research framework of the composite system of the marine economy (hereinafter referred to as CSME). (2) This paper uses the composite system synergy degree model to measure the degree of the synergy of the CSHDME, which greatly enriches the research content of the CSME in terms of theory and method. (3) By analyzing the synergistic effect of the CSHDME, this paper judges the level and state of synergy development of the CSHDME in 11 coastal provinces and attempts to analyze the deep-seated reasons affecting the level of synergy development of the CSHDME, which provides a reference to aid provinces in formulating marine development strategies, accelerating HDME.
The rest of this paper is structured in the following sections: Section 2 combs and summarizes the related literature; Section 3 constructs a comprehensive framework for CSHDME; Section 4 describes the research methods and data sources used in this paper; Section 5 analyzes the empirical results; and Section 6 presents the conclusions and discussion of this paper.

Literature Review
From a systematic perspective, the CSHDME emphasizes connection and coordinated development across internal elements of the composite system [5]. However, by reviewing the relevant literature, it is found that scholars research on the synergistic effects of internal factors within the CSHDME is still rare. Currently, most of the research focuses on exploring the CSME as well as the development of its coupling and coordination. This paper reviews the relevant literature by focusing on five aspects: the concept of the CSME, the composition of the CSME, the research on the correlation of the CSME, the research on the coordination of the CSME, and the research on the evaluation of the synergy level of the CSME.

The Concept of the CSME
Scholars research on the concept of the CSME began with the consideration of the economic development of the marine environment, pointing out that the marine economy is a concentrated embodiment of the interaction between human beings and the natural environment and refers to the marine industry covering marine resources, environment, industry, science and technology, and other elements, located in the geographic space with specific marine characteristics, namely those concerning resources, economy, and the social environment, as a comprehensive environment; the geographic space is an interrelated and complex open system involving many elements [6,7]. As research deepens and the underlying trends continue to change, scholars tend to pay more attention to the internal elements of the composite system when defining the concept, pointing out that the CSME is a complex, diversified, and three-dimensional network system interwoven with many elements, multiple dimensions, and multi-level structures, composed of the marine economy subsystem with different functions and attributes [8,9]. The CSME is defined as a special complex system with a certain structure and function composed of two or more subsystems interacting, interweaving, and infiltrating [10]. With the idea of high-quality development put forward, some scholars have also discussed the CSME in relation to the goal of high-quality development [11], but analysis of the connotation of HDME remains from a systematic perspective [12] without making a clear definition of its specific connotation.
At the same time, following the United Nations Conference on Sustainable Development in 2012, the blue economy, as an extension of the marine economy, has been widely regarded by scholars for its connotation of sustainable development [13]. Scholars believe that the blue economy is an ocean economy with economic, social, resource-related, and environmental sustainability with good development prospects, as well as a complex and sustainable new dynamic economic development system [14], which can comprehensively utilize favorable conditions such as science and technology and talent systems, strive to link land and sea resources, and ultimately achieve maximum dynamic economic, social, and spatial operation of complex economic systems [15] (because the blue economic system and the CSME have similar essential characteristics, in the latter part of the text, both terms are uniformly expressed as CSME); however, its internal elements and interactions are unclear [16].

The Composition of the CSME
Current research on the composition of the CSME considers that the CSME is constituted by the interactive evolution of the marine economy subsystem and its supporting subsystems [17]. Different supporting subsystems can be roughly divided into four classes. The first class only considers the marine ecosystem and asserts that the CSME is a composite system covering the marine ecosystem and the marine economy subsystem [18,19]. In the second class, the social value of the marine economy is taken further into account, and it is considered that the CSME is a composite system covering the marine economy subsystem, marine ecological environment subsystem, and marine social subsystem [20,21]; this comprises the most accepted division of the CSME at present. The third class integrates the kinetic energy of the marine economy into the CSME, asserting that marine science and technology can not only deal with energy and development efficiency in marine economic development but can also reduce pollution [22,23], and is an indispensable part of the CSME. The fourth class takes cultural awareness or system level into consideration and asserts that the CSME should also include management subsystems and cultural subsystems [24].

Research on the Correlation of the CSME
Based on different objects, the current research on the correlation of the CSME can be broadly divided into three categories. The first category includes marine economy and marine science and technology, exploring the one-way influence of marine tidal energy, wind energy, and other marine science and technology on the marine economy [25], as well as the two-way interaction between the aforementioned phenomena through vector autoregressive models [26]. The second category comprises marine economy and marine ecology, exploring the hindering effect of marine pollution and greenhouse emissions on the development of the marine economy [27], as well as portraying the interaction between the two Systems 2023, 11, 282 4 of 24 in an N or U shape through the environmental Kuznets curve [28]. The third category is composed of marine science and technology and the marine environment. Porters hypothesis is used as a primary means to analyze whether marine environmental regulation can stimulate relevant scientific and technological innovation activities [29].

Research on the Coordination of the CSME
As early as 1987, the Brundtland report proposed to adopt sustainable development as a goal and coordinate the relationship between humans and nature. With continuous research, the academic community has gradually reached a consensus to pursue the coordination of development (economic, social, etc.) and environment, and the field of the marine economy is no exception. Based on different focus points, current research on the coordination of the CSME can be roughly divided into three categories. The first category focuses on the continuity of the coordinated development of the CSME, analyzes the coupled coordination phenomenon of marine economic development and the marine ecosystem through case forms, and explores the internal contradictions of the CSME, such as marine ecological fishery culture and the state of the marine economy, the marine economy and environment, protected marine areas, and marine economic sectors [30,31]. The second category focuses on the equity of the coordinated development of the CSME and mainly uses the correlation degree model and the coupling coordination degree model to explore the coupling coordination relationship between the marine economy and social change [32]. The third category focuses on the commonality of the coordinated development of the CSME and mainly uses the spatiotemporal coordination model and the synergy model to examine the synergy within the complex marine economic system covering multiple subsystems such as economic, environmental, and social subsystems [33,34].

Research on the Evaluation of Synergy Level of the CSME
The research approach to evaluating the synergy level of the CSME is first to construct a multi-level and multi-dimensional CSME covering multiple subsystems and construct an evaluation index system; on the basis of calculating the comprehensive development level of each subsystem, the coordinated development level of the CSME and its characteristics or influencing factors are analyzed by using the correlation model, the spatiotemporal coordination model, and the coupling coordination model [35,36]. The research found that although the current level of CSME synergy development has been improved, in general, the level of synergy development is still not high, and CSME subsystems remain in a state of mutual confrontation or mutual adaptation [37].
To sum up, although scholars have analyzed the concept, composition, correlation, coordination, and synergy level of the CSME from various angles, the current research has not paid enough attention to marine society, marine technology, marine culture, and other factors, and is more focused on analyzing the coupled coordination relationship between the marine economy and ecological, resource-related, environmental, and another single subsystem (element) or one or two subsystems (elements), and lacks a systematic and holistic grasp of the CSME, as well as a profound comprehension of the HDME in the context of present-day understanding. Therefore, to some extent, the current evaluation of the level of CSME synergy development is not comprehensive enough, and it is also difficult to determine the deep-seated reasons for the low level of synergy. In view of this, this paper presents a comprehensive framework-the CSHDME-based on a perspective of complex systems. By integrating marine resources and elements, the system synergistically integrates the five dimensions of economy-technology-ecological-society-culture in the marine domain and establishes an evaluation index system of the degree of the synergy of the CSHDME. Utilizing related data from between 2010 and 2020, we measure and analyze the degree of subsystem orderliness and the degree of synergy of the CSHDME of 11 coastal provinces and attempt to determine the deep-seated reasons affecting the level of CSHDME synergy development.

Analysis of the Connotation of the CSHDME
On the one hand, from the perspective of the core meaning of high-quality development, according to the report of the 19th National Congress of the Communist Party of China, the core meaning of high-quality development is higher quality, more efficient, more equitable, and more sustainable development. Among them, higher quality focuses on the dimension of economic development, emphasizing the high quality and efficiency of economic development. More efficient focuses on the dimension of scientific and technological innovation and resource optimization, emphasizing less investment and high yield. More equitable focuses on social and livelihood dimensions, emphasizing that development should be more equitable and should be the fundamental purpose of promoting peoples well-being. More sustainable draws attention to ecological and environmental dimensions; the emphasis is on sustainable, long-term development. At the same time, the path of high-quality development may face various risks and challenges. It is necessary to use culture as a crux to promote high-quality development. Therefore, culture is also one of the core elements of high-quality development.
On the other hand, from the perspective of the requirements of the times, the Chinese government has put forward new requirements in the context of the era of high-quality development. In the report of the 20th National Congress of the Communist Party of China, it is pointed out that the construction of a new development pattern should be accelerated, focusing on promoting high-quality economic development. Furthermore, strategies promoting science and education should be implemented, strengthening the support of talents for modernization. Additionally, cultural self-confidence and self-improvement should be promoted to boost new glories of socialist culture. The well-being of peoples livelihood should also be promoted to improve their quality of life. Finally, green development should be considered, promoting the harmonious coexistence of man and nature.
It can be seen that, in the new era, high-quality development mainly involves economic development, scientific and technological innovation, cultural self-confidence, social livelihood, and ecological and environmental resources, as well as other dimensions. HDME should also represent the high-quality and efficient development of the marine economy, marine science and technology, marine culture, marine society, peoples livelihood, and the marine ecological environment.

Composite System Model Construction for HDME
Based on the above analysis, drawing on the core idea of the Attia-Singer index theorem and the expression of the Chern-Weil theory whole = superposition of parts [38], we define HDME as a composite system made up of five marine subsystems: economy, technology, ecology, society, and culture, all of which are multi-element and multi-structure complex systems.
In Equation (1), CS denotes the CSHDME; X 1 , X 2 , X 3 , X 4 , and X 5 denote the marine economy subsystem, marine technology subsystem, marine ecological subsystem, marine society subsystem, and marine culture subsystem in the CSHDME, respectively; i characterizes subsystems within the CSHDME; e j denotes the index elements of subsystem X i ; C k is the synergistic relationship, which is the set of synergistic relationships in the CSHDME, covering the mutual synergistic relationships among the subsystems and the elements within subsystems; T is time, which reflects the dynamic spatiotemporal features of the CSHDME; and R is the region, which refers to the region of the CSHDME in each province and region in the coastal area.

The Indicator Orderliness Degree Model
We set the order parameter of the subsystem X j of the CSHDME to be e j = e j1 , e j2 , e j3 , . . . , e jn , where n ≥ 1, β ji ≤ e ji ≤ α ji , and i = 1, 2, . . . , n. α ji denotes the maximum value of the ith order parameter component e ji of subsystem j, and β ji denotes the minimum value.
In addition, when e j1 , e j2 , e j3 , . . . , e jk are positive indices, the larger the value, the higher the orderliness degree of the subsystem. Conversely, when e jk+1 , e jk+2 , e jk+3 , . . . , e jn are inverse indices, the larger the value, the lower the orderliness degree of the subsystem. The equation for calculating the orderliness degree of the component e ji of order parameter e j of the subsystem X j for the CSHDME is as follows [39]: From Equation (2), we can see that µ j e ji ∈ [0, 1]. When the value of µ j e ji is larger, the contribution of the component e ji of order parameter e j to the orderliness degree of the subsystem X j is higher. Conversely, When the value of µ j e ji is smaller, the contribution of the component e ji to the orderliness degree of the subsystem X j is lower.

The Subsystem Orderliness Degree Model
In general, the overall contribution by each order parameter component e ji to the orderliness degree of the subsystem X j can be achieved by the integration of µ j e ji . This paper uses a linear weighted summation method in order to integrate each order parameter component. The formula for calculating the orderliness degree of the subsystem of the CSHDME for the order parameter e j is shown in Equation (3) [40]: where λ i is the weight coefficient representing the importance of e ji in maintaining the orderly operation of the subsystem. From Equation (3), we can see that µ j e j ∈ [0, 1]. When the value of µ j e j is larger, the contribution by the order parameter e j to the orderliness degree of the subsystem X j is higher, and the orderliness degree of the subsystem is higher. Conversely, the smaller the value of µ j e j , the lower the contribution and the lower the orderliness degree that the subsystem has.

The Composite System Synergy Degree Model
We assume that when the CSHDME is at the initial moment t 0 , u 0 , and u 0 5 (e 5 ) denote the orderliness of the marine economy subsystem, technology subsystem, ecological subsystem, society subsystem, and culture subsystem, respectively. When the CSHDME evolves into the next point t 1 , u 1 1 (e 1 ), u 1 2 (e 2 ), u 1 3 (e 3 ), u 1 4 (e 4 ), and u 1 5 (e 5 ) represent the orderliness of the marine economy subsystem, technology subsystem, ecological subsystem, society subsystem, and culture subsystem, respectively. The formula for calculating the synergy of the CSHDME is shown in Equation (4) [41].
From Equation (4), we can see that the degree of the synergy of the CSHDME is required to be determined according to the dynamic process of the five-dimensional degree of subsystem orderliness of marine dimensions economy-technology-ecological-societyculture over time. That is, we need to analyze the collaborative state of the CSHDME from Systems 2023, 11, 282 7 of 24 the dynamic change process over the time series of the five subsystems degrees of orderliness. Sig(·) represents a symbolic function, and its expression is shown in Equation (5): Equation (5) shows that the necessary and sufficient condition for the degree of synergy C to be positive is as follows: the orderliness of the five marine economy-technologyecological-society-culture subsystems at the moment t 1 is larger than their orderliness at the moment t 0 . That is, the CSHDME is in a synergistic evolutionary state with positive synergy when and only when the degree of orderliness of all five subsystems at the moment t 1 is better than that of the five subsystems at the moment t 0 .
From the analysis of Equations (4) and (5), we can see that the degree of synergy C of the CSHDME takes the value range [−1, 1], and the larger the degree of synergy C, the higher the degree of synergy development of the CSHDME; conversely, the smaller the degree of synergy C, the lower the degree of synergy development of the CSHDME. In particular, if the degree of orderliness of one (or several) of the five subsystems increases more with time, while the degree of orderliness of the other four (or several) subsystems increases less with time, the value of the synergy of the CSHDME is still positive, but the value is relatively small, indicating that the synergy of the CSHDME is at a relatively low-grade level of benign development. On the contrary, if the degree of orderliness of any subsystem at the moment t 1 is inferior to its orderliness degree at the moment t 0 , whatever the degree of orderliness of the other four subsystems is, it results in a negative degree of synergy C of the CSHDME, indicating that the CSHDME is in a non-synergistic evolutionarily inferior state. The degree of synergy of the CSHDME is classified as shown in Table 1.  (2) Data pre-processing This paper pre-processed the original data from the following three aspects: first, linear interpolation and approximation of missing values were conducted. Then, because some indicators lacked the corresponding marine statistical-caliber data, this paper adopted the method of stripping coefficients for the corresponding national economic data, based on the methods of Wang et al. [42] and Song and Ning [43]; the stripping coefficient is the ratio of marine GOP to regional GDP. Finally, to eliminate the effect of price factors, the relevant economic data were converted into prices with 2010 as the base period.

Indicator Selection and Weight Determination 4.3.1. Indicator Selection
Intending to objectively assess the synergistic impact of the CSHDME in China, we selected representative order parameters in the five-dimensional subsystem of marine economy-technology-ecological-society-culture to assess the degree of the orderliness of the CSHDME subsystems according to the principles of accessibility, relevance, and completeness of marine data, and to evaluate the synergy level of the CSHDME accordingly. The specific selection process is shown below.
(1) Marine economy subsystem as it centers on the exploitation, utilization, and protection of various marine and spatial resources. The subsystems high-quality development emphasizes the high quality, high efficiency and high level of marine economic development, which means not only the expansion of the scale of the marine economy, the improvement and optimization of the structure of the marine economy and other quality enhancement, and the efficiency of marine input and output, total factor productivity and other efficiency enhancement. It also requires the promotion of high-level openness. Therefore, the marine economy subsystem can be examined through five dimensions: marine economy scale and economic efficiency, marine economy coordination and stability, and marine economy openness. With reference to the research of Gao et al. [44], Wang et al. [45], and Li et al. [46], 11 order parameter components, such as the added value of the marine industry, are selected. (2) Marine technology subsystem. Due to the special attributes of the marine economy, its development, utilization, and protection are more dependent on the support of high technology. Innovation is a powerful driving force for the high-quality development of the marine economy. The input and output of innovation, the efficiency of innovation, and the innovation vitality inspired by new industries have become important indicators to measure innovation capability. Therefore, the marine technology subsystem pays more attention to marine technology research and output in the process of development, which can be examined through four dimensions: marine technology innovation input and output, marine technology innovation efficiency, and technology kinetic energy. With reference to the research of Wu et al. [47], Liu et al. [48], and others, six order parameter components, such as the proportion of marine scientific research investment, are selected. (3) Marine ecological subsystem. The marine ecological subsystem is centered on the resource environment and consists of marine natural environmental elements and environmental marine development elements. The construction of ecological civilization is the essence of achieving high-quality development of the marine economy. In July 2021, the Ministry of Natural Resources of China proposed that the current marine ecological environment still suffers from the problem of insufficient ecological carrying capacity and ecological pressure, and should take marine ecological and environmental protection as the core, comprehensively improve the efficiency of marine environmental resources utilization, and accelerate the green development of the ocean. It can be seen that the high quality of the marine ecological subsystem should not only focus on marine ecological resources and their carrying pressure but also on the protection and development efficiency of the marine ecological environment. Therefore, the marine ecological subsystem can be examined through four dimensions: marine ecological conditions, marine ecological efficiency, marine ecological pressure, and protection. Referring to the research of Yang and Sun [49], Li et al. [50], and others, eight order parameter components such as mariculture area are selected. (4) Marine social subsystem. This subsystem is centered on human beings and formed based on interpersonal relationships and interactions such as human-sea relations, marine-related production, and living practices. Working for peoples happiness is an essential feature of the high-quality development of the marine economy. The high-quality development of the marine social subsystem should take the protection and improvement of peoples livelihood as the starting and ending point and should be a two-way enhancement of high-quality life and high-quality consumption on the basis of equalization of public services. In this respect, there are certain elements that represent urban capital construction level, social security and public transportation protection, consumption structure and consumption level. Therefore, the marine social subsystem can be examined through four dimensions: the level of marine city construction, marine residents quality of life, marine residents consumption level, and marine residents consumption structure. Referring to the research of Di and Sun [51], Guo et al. [52], and others, seven order parameter components, such as the number of berths for production in ports above the scale, are selected. (5) Marine culture subsystem. The marine culture subsystem in this paper emphasizes the worth of marine culture and refers to cultural elements in marine activities that can be refined and developed with market value, thus excluding elements of marine culture that are only appreciated at the spiritual level or are difficult to market. In August 2018, General Secretary Xi Jinping emphasized that we should improve the modern cultural industry system and market system, cultivate new cultural industries and cultural consumption patterns, and enhance peoples sense of cultural acquisition and happiness with high-quality cultural supply, which points out the direction for promoting the marine cultural industry to achieve high-quality development. This inevitably involves government policies, material carriers and spiritual culture and other related elements in the process of high-quality development of the marine culture subsystem. Therefore, with reference to the research of Wang et al. [45], Qin et al. [53], and Xu [54], the marine culture subsystem can be examined through three dimensions: institutional culture, material culture, and spiritual culture, and seven order parameter components such as the government-market relationship index are selected.
Based on the above selection process, we finally determined the synergy degree evaluation index system of the CSHDME, including five subsystems, twenty order parameters, and thirty-nine order parameter components, all of which are listed in Table 2 (First four columns).

Weight Determination
This paper refers to the equal weight determination method of Zhang and Jin [55] and adopts a method of combining subjective and objective assignment methods (hierarchical analysis and entropy method) to identify the weights of the synergy degree evaluation indexes of the CSHDME; the calculation formula is shown in Equation (6): where λ ji is the comprehensive weight of the ith order parameter component of the jth subsystem of the CSHDME, w ji is the objective weight value identified by the entropy weight method, µ ji is the subjective weight value identified by the hierarchical analysis method, and α represents the relative importance of the objective weight (0 < α < 1). In this paper, α is 0.5. Based on Equation (6), we calculated the order parameter component weights of the CSHDME, as shown in Table 2 (Last three columns).

Analysis of Degree of Subsystem Orderliness Results
According to Equation (3), the orderliness degree of the five-dimensional subsystem of marine economy-technology-ecological-society-culture of the CSHDME is calculated, and the results can be seen in Figure 1.
As can be seen from Figure 1, the degree of the orderliness of the marine economy subsystem in the 11 coastal provinces grew year by year from 2010 to 2020, with smaller interprovincial differences and a difference of 0.23. The degree of the orderliness of the marine technology subsystem shows an increasing trend, but the difference between provinces is obvious, with a difference of 0.33. The degree of the orderliness of the marine ecological subsystem increases year by year, and the difference between provinces is relatively obvious, with a difference of 0.28. The degree of the orderliness of the marine social subsystem is high and increases year by year, with smaller inter-provincial differences; the difference is 0.21. The degree of the orderliness of the marine culture subsystem increases year by year, but the fluctuation is obvious, and the regularity is not strong; the difference between provinces is relatively significant, with a difference of 0.26.
weights of the CSHDME, as shown in Table 2 (Last three columns).

Analysis of Degree of Subsystem Orderliness Results
According to Equation (3), the orderliness degree of the five-dimensional subsystem of marine "economy-technology-ecological-society-culture" of the CSHDME is calculated, and the results can be seen in Figure 1. As can be seen from Figure 1, the degree of the orderliness of the marine economy subsystem in the 11 coastal provinces grew year by year from 2010 to 2020, with smaller inter-provincial differences and a difference of 0.23. The degree of the orderliness of the marine technology subsystem shows an increasing trend, but the difference between provinces is obvious, with a difference of 0.33. The degree of the orderliness of the marine ecological subsystem increases year by year, and the difference between provinces is relatively obvious, with a difference of 0.28. The degree of the orderliness of the marine social subsystem is high and increases year by year, with smaller inter-provincial differences; the difference is 0.21. The degree of the orderliness of the marine culture subsystem increases year by year, but the fluctuation is obvious, and the regularity is not strong; the difference between provinces is relatively significant, with a difference of 0.26.
Generally speaking, the degree of the orderliness of the five subsystems of the CSHDME shows a positive trend of year-on-year growth, but there are shortcomings in two aspects of marine science and technology and marine culture, which may hinder synergy development of the CSHDME; thus, there is an urgent need to optimize the resource allocation and coordinate the internal development of the CSHDME.

Analysis of the CSHDME's Degree of Synergy Results
According to the results obtained from the previous section on the degree of the orderliness of CSHDME's subsystems, this section applies Equations (4) and (5) to calculate the CSHDME's degree of synergy across 11 provinces and analyzes the spatial and temporal evolution of their calculated results.  Generally speaking, the degree of the orderliness of the five subsystems of the CSHDME shows a positive trend of year-on-year growth, but there are shortcomings in two aspects of marine science and technology and marine culture, which may hinder synergy development of the CSHDME; thus, there is an urgent need to optimize the resource allocation and coordinate the internal development of the CSHDME.

Analysis of the CSHDMEs Degree of Synergy Results
According to the results obtained from the previous section on the degree of the orderliness of CSHDMEs subsystems, this section applies Equations (4) and (5) to calculate the CSHDMEs degree of synergy across 11 provinces and analyzes the spatial and temporal evolution of their calculated results.

Analysis of the Time-Series Change in the CSHDME Synergy Level
The results of the degree of synergy of the CSHDME composite system in 11 coastalarea provinces are shown in Figure 2. From Figure 2, it is clear that the degree of the synergy of the CSHDME in the 11 studied coastal provinces in China presents the time-series change characteristics of strong regional differences, strong volatility, instability, and low synergy. The strong regional variability is reflected in the obvious differences in the degree of synergy of the 11 provinces. For example, the synergy development level of Zhejiang was at a moderate level during the observation period, while the synergy development level of Shanghai, which is also within the southern ocean economic zone, was at a moderate non-synergy level during most years. The strong volatility is reflected in the fact that most of the provinces had obvious and large changes during the observation period, such as Hainan, which had a trend of "moderate non-synergy-moderate synergy" in alternate years during the observation period. The instability is reflected in the fact that although some provinces were at a moderate synergy level during the observation period, their synergy development level was difficult to maintain and changed frequently and significantly. The low level of synergy is reflected by the fact that although Zhejiang and Shandong had a moderate synergy level, no provinces reached a high synergy level, and some provinces were even at a moderate non-synergy level in most observation years; in general, the composite system's synergy level in coastal areas is still at a low level.

Analysis of the Spatial Evolution of the CSHDME's Synergy Level
On the basis of the observation period of this paper (2010-2020), and combined with the previous analysis of the subsystems' degree of orderliness and the CSHDME composite system's degree of synergy, this paper divides the observation period into three stages: 2010-2013, 2013-2016, and 2016-2020, and analyzes the minimum, maximum, and average values of the composite system's degree of synergy for the 11 studied coastal provinces in each of these stages to explore the characteristic trend of the synergy level's spatial evolution (in the three periods, the value interval of the maximum value was located in the moderate synergy interval ([0.333, 0.666]), and the analysis of spatial changes was not significant, so it is excluded in the following analysis), as can be seen in Figure 3. From Figure 2, it is clear that the degree of the synergy of the CSHDME in the 11 studied coastal provinces in China presents the time-series change characteristics of strong regional differences, strong volatility, instability, and low synergy. The strong regional variability is reflected in the obvious differences in the degree of synergy of the 11 provinces. For example, the synergy development level of Zhejiang was at a moderate level during the observation period, while the synergy development level of Shanghai, which is also within the southern ocean economic zone, was at a moderate non-synergy level during most years. The strong volatility is reflected in the fact that most of the provinces had obvious and large changes during the observation period, such as Hainan, which had a trend of moderate non-synergy-moderate synergy in alternate years during the observation period. The instability is reflected in the fact that although some provinces were at a moderate synergy level during the observation period, their synergy development level was difficult to maintain and changed frequently and significantly. The low level of synergy is reflected by the fact that although Zhejiang and Shandong had a moderate synergy level, no provinces reached a high synergy level, and some provinces were even at a moderate non-synergy level in most observation years; in general, the composite systems synergy level in coastal areas is still at a low level.

Analysis of the Spatial Evolution of the CSHDMEs Synergy Level
On the basis of the observation period of this paper (2010-2020), and combined with the previous analysis of the subsystems degree of orderliness and the CSHDME composite systems degree of synergy, this paper divides the observation period into three stages: 2010-2013, 2013-2016, and 2016-2020, and analyzes the minimum, maximum, and average values of the composite systems degree of synergy for the 11 studied coastal provinces in each of these stages to explore the characteristic trend of the synergy levels spatial evolution (in the three periods, the value interval of the maximum value was located in the moderate synergy interval ([0.333, 0.666]), and the analysis of spatial changes was not significant, so it is excluded in the following analysis), as can be seen in Figure 3.  As shown in Figure 3, the CSHDME's synergy level in coastal areas of China shows the spatial characteristics of strong variability, strong volatility, and high agglomeration. The strong variability is reflected in the CSHDME's extremely unbalanced synergy level across provinces and the large gap between regions. From the spatial evolution figure of the three periods, the value range of the minimum value is (−0.666, 0.666], and 11 provinces fall in the extreme value range at both ends of the three periods, i.e., the lowest value range ((−0.666, −0.333]) and the highest value range ((0.333, 0.666]), and the gap between the value range of the minimum value and the provinces remains unchanged after the three periods. The average value interval is (−0.333, 0.666], similar to the minimum value, and after three stages, the gap between the average value interval and the province did not close.
The strong volatility is reflected in the large variation in the CSHDME's synergy level in the 11 provinces over the three periods. In terms of minimum values, the changes range across the three intervals, and the associated fluctuations are obvious. During the observation period, seven provinces, including Liaoning, Hebei, Fujian, Guangdong, Guangxi, Shandong, and Jiangsu, all showed a change from "moderate synergy state to moderate non-synergy state" or "moderate non-synergy state to moderate synergy state". In terms of the average value, the variation is slightly smaller compared to the minimum value, but the variation in some provinces also ranges across two intervals, and the volatility is also strong. During the observation period, seven provinces, including Liaoning, Hebei, Fujian, Shandong, Jiangsu, Guangdong, and Guangxi, all showed a change of "moderate synergistic state-mildly non-synergistic state" or "mildly non-synergistic state-moderate synergistic state".
The high agglomeration is reflected in the spatial characteristics of the three periods of synergy across the 11 provinces, which are similar to those of the neighboring provinces. In terms of the minimum and average values, the spatial synergy state is generally As shown in Figure 3, the CSHDMEs synergy level in coastal areas of China shows the spatial characteristics of strong variability, strong volatility, and high agglomeration. The strong variability is reflected in the CSHDMEs extremely unbalanced synergy level across provinces and the large gap between regions. From the spatial evolution figure of the three periods, the value range of the minimum value is (−0.666, 0.666], and 11 provinces fall in the extreme value range at both ends of the three periods, i.e., the lowest value range ((−0.666, −0.333]) and the highest value range ((0.333, 0.666]), and the gap between the value range of the minimum value and the provinces remains unchanged after the three periods. The average value interval is (−0.333, 0.666], similar to the minimum value, and after three stages, the gap between the average value interval and the province did not close.
The strong volatility is reflected in the large variation in the CSHDMEs synergy level in the 11 provinces over the three periods. In terms of minimum values, the changes range across the three intervals, and the associated fluctuations are obvious. During the observation period, seven provinces, including Liaoning, Hebei, Fujian, Guangdong, Guangxi, Shandong, and Jiangsu, all showed a change from moderate synergy state to moderate non-synergy state or moderate non-synergy state to moderate synergy state. In terms of the average value, the variation is slightly smaller compared to the minimum value, but the variation in some provinces also ranges across two intervals, and the volatility is also strong. During the observation period, seven provinces, including Liaoning, Hebei, Fujian, Shandong, Jiangsu, Guangdong, and Guangxi, all showed a change of moderate synergistic state-mildly non-synergistic state or mildly non-synergistic state-moderate synergistic state.
The high agglomeration is reflected in the spatial characteristics of the three periods of synergy across the 11 provinces, which are similar to those of the neighboring provinces.
In terms of the minimum and average values, the spatial synergy state is generally similar: from 2010 to 2013, the 11 provinces show the spatial synergy state of high north and low south; from 2013 to 2016, the spatial synergy state shows low at both ends and high in the middle; and from 2016 to 2020, the spatial synergy state shows high south and low north.

Trajectory Analysis of Degree of Synergy of the CSHDME
Aiming to investigate the time-series changes in the composite systems degree of synergy, time-series trajectories of the five subsystems across the 11 coastal provinces were further analyzed, which can be seen in Figure 4.
Systems 2023, 11, x FOR PEER REVIEW 17 of 24 similar: from 2010 to 2013, the 11 provinces show the spatial synergy state of "high north and low south"; from 2013 to 2016, the spatial synergy state shows "low at both ends and high in the middle"; and from 2016 to 2020, the spatial synergy state shows "high south and low north".

Trajectory Analysis of Degree of Synergy of the CSHDME
Aiming to investigate the time-series changes in the composite system's degree of synergy, time-series trajectories of the five subsystems across the 11 coastal provinces were further analyzed, which can be seen in Figure 4.  As shown in Figure 4a, within the observation period, the CSHDME's synergy development level in Tianjin shows a "几"-shaped time-series trend, maintaining a moderate synergy level in 2010-2013 and 2014-2017 but decreasing to a moderate non-synergy level in 2014-2015 and 2017-2020. Observing the time-series trajectories of the five subsystems carefully, when the CSHDME's synergy development state in Tianjin is more stable, the five subsystems show roughly the same change trend. For example, between 2010 and 2013, the five subsystems show the same change trend. On the contrary, between 2017 and 2020, the change trajectories of the five subsystems differ greatly; the marine culture subsystem and the marine economy subsystem show opposite trends of movement with other subsystems in some years (e.g., 2017-2018 and 2018-2019), leading to a decrease in synergy manifesting as a low CSHDME synergy level. This indicates that the synergy development among subsystems has a decisive role in the CSHDME's synergy development.
As shown in Figure 4b, within the observation period, the CSHDME's synergy development level in Hebei was in a moderate synergy state and relatively stable, but it dropped sharply in 2013-2014 and appeared in a moderate non-synergy state. In that year, , leading to a decrease in synergy manifesting as a low CSHDME synergy level. This indicates that the synergy development among subsystems has a decisive role in the CSHDMEs synergy development.
As shown in Figure 4b, within the observation period, the CSHDMEs synergy development level in Hebei was in a moderate synergy state and relatively stable, but it dropped sharply in 2013-2014 and appeared in a moderate non-synergy state. In that year, the marine economy subsystem showed a negative change trajectory, which was opposite to the change trajectory of the other four subsystems and hindered the steady improvement of the CSHDMEs synergy level. Therefore, it can be seen that synergy development among the five subsystems cannot be ignored.
As shown in Figure 4c, the CSHDMEs synergy development level in Liaoning shows relatively stable, moderate synergy in the earliest stage of observation, but a W-shaped time-series change trajectory in the latest stage of observation. Observing the time-series trajectories of the five subsystems carefully, the trajectories of the five subsystems are generally similar, and the magnitude of changes is relatively stable from 2010 to 2015. However, from 2015 to 2020, the change trends of the five subsystems show significant differences, such as the marine social subsystem and the ecological subsystem showing opposite trajectories of changes, and the magnitude of changes is larger. This indicates that balanced synergy development among subsystems plays a significant role in the stable development of the CSHDMEs synergy.
As shown in Figure 4e, within the observation period, the CSHDMEs synergy development level in Shanghai shows an M-shaped time-series change trajectory, and the synergy development level varies greatly and unstably. Carefully observing the timeseries trajectories of the five subsystems, the trends of the marine ecological subsystem and the cultural subsystem are roughly similar to the evolutionary trajectory of the composite systems degree of synergy. Combined with the results of the subsystems degree of orderliness in the previous section (Figure 1e), we can see that the marine culture subsystem represents the shortcomings of Shanghai, while the ecological subsystem presents itself as relatively advantageous. This indicates that the level of CSHDME synergy is not only determined by the inferior or the dominant subsystems of a province but also by balanced synergy development among subsystems, resulting in the steady improvement of CSHDME synergy development levels.
It can be seen in Figure 4d,f, during the observation period, although the CSHDME in Shandong is slightly higher than that in Jiangsu, its change trajectory is very similar to that of Jiangsu: both show a relatively stable moderate synergy state in the early period of observation but drop sharply to a moderate non-synergy state in 2018-2019. The synergy level then increases. Looking closely at the time-series change trajectories of the five subsystems, in the early period, the stable development of the CSHDMEs synergy level in Shandong and Jiangsu both benefited from the steady improvement of the marine economy, ecological, and society subsystems in the same direction, while the technology subsystem, which constitutes a shortcoming of Shandong, and the marine culture subsystem, the shortcoming of Jiangsu (as can be seen from Figure 1d,f), showed an opposite trend and although the influence was limited due to the small base, they also hindered the improvement of the CSHDMEs synergy level both in Shandong and in Jiangsu.
As shown in Figure 4g, within the observation period, the CSHDMEs synergy level in Zhejiang is moderate, and it ranks first among the 11 provinces. Careful observation of the trajectories of the five subsystems shows that the four subsystems of marine economy, technology, ecology, and society have similar development trajectories, and the trajectories of the subsystem of marine culture are different from the other four subsystems, and the magnitude of change is larger. However, as can be seen from the previous section, the culture subsystem represents a shortcoming of the CSHDMEs synergy development in Zhejiang, and its value is relatively small (as can be seen from Figure 1g), so it has a relatively small impact on the CSHDMEs overall synergy level in Zhejiang, but because of this, it is also the key to the improvement of the composite systems synergy development level in Zhejiang.
As shown in Figure 4h, within the observation period, the CSHDMEs synergy development level in Fujian shows a moderate synergy development state that changes from stable to positive. Taking a closer look at the time-series change trajectories of the five subsystems, the changes in the marine technology subsystem are not obvious, but as the shortcoming of Fujian (as can be seen from Figure 1h), its time-series change trajectory is opposite to that of the CSHDMEs synergy development trajectory, which plays a certain inhibiting effect on the level of CSHDME synergy development. Thus, improving the degree of the orderliness of the marine technology subsystem is beneficial to promoting the CSHDMEs synergy development level in Fujian.
It can be seen in Figure 4i,j that, during the observation period, the time-series trajectories of the CSHDMEs synergy development level in Guangdong and Guangxi are similar, showing a W-shaped trend at the beginning of the observation period and a steady increase at the end of the observation period. When taking a closer look at the time-series trajectories of the five subsystems, from 2010 to 2016, the CSHDMEs synergy development level changed significantly, and the overall level is relatively low. In addition, the marine culture system has a similar time-series development trajectory in Guangdong and Guangxi. From 2015 to 2020, the CSHDMEs synergy development level tends to be stable and relatively high, and the marine ecological subsystem has a similar development trajectory in both provinces, but the marine technology subsystem shows opposite development trajectories. The trajectory of synergy development of the marine social subsystem and CSHDME is similar in Guangxi, and the trajectory of the synergy development of the marine economy subsystem and CSHDME is similar in Guangdong. Therefore, it is crucial for Guangdong and Guangxi to improve the CSHDMEs synergy development level by fully utilizing the advantages of the marine economy, social, and ecological subsystems, and compensating for the shortcomings of marine culture and technology (as can be seen from Figure 1i,j).
As shown in Figure 4k, within the observation period, the CSHDMEs synergy development level in Hainan shows a W-shaped time-series change trend, and the synergy development level is extremely unstable. If we observe the time-series trajectories of the five subsystems, the marine economy subsystem has a similar trajectory from 2010 to 2016, while the marine economy, marine technology, and marine society subsystems have the opposite trajectory from 2016 to 2020. It is worth noting that, during the observation period, the marine culture subsystem has roughly the same trajectory as the CSHDMEs synergy development, while the marine culture subsystem represents a developmental shortcoming (as can be seen from Figure 1k), as well as the key to improving the synergy level of the CSHDME.
According to the analysis of the aforementioned findings, the current CSHDMEs synergy development level in China is still not high, and there are many problems, such as instability and unevenness. Promoting the CSHDMEs synergy level is inseparable from the orderly development of its subsystems. Improving the composite systems synergy level as soon as possible is crucial; this can be achieved by compensating for weaknesses associated with the development of the CSHDME, promoting coordination and steady development within subsystems, and striving toward balanced and consistent development across subsystems.

Research Conclusions
From the perspective of complex systems, this paper uses the subsystem orderliness degree model and composite system synergy degree model to measure and analyze the degree of the orderliness of five subsystems and the CSHDME composite systems degree of synergy in 11 coastal provinces of China from 2010 to 2020, respectively.
From the perspective of research content, differing from previous studies that focus on a single element or two or three elements of marine economy, society, and ecology as the focus of the marine economy, this paper is based on a perspective of complex systems, taking into account marine science and technology, society, culture, and other elements, and constructing a composite system covering marine economy-science and technologyecology-society-culture subsystems. This provides a comprehensive framework for the systematic and global study of the marine economy in other countries. In contrast to the simple calculation and analysis of the composite systems synergy, this paper attempts to identify shortcomings by analyzing the trajectory of the degree of synergy. Furthermore, it strives to analyze the deep-seated reasons that affect the CSHDMEs degree of synergy, providing a reference for improving the composite systems synergy level and predicting future development directions.
The research results of this paper show that: (1) the five-dimensional subsystem of marine economy−technology-ecological-society-culture of the CSHDME generally demonstrates a trend of annual growth, but development differences are relatively obvious, with the marine economy and marine science and technology subsystems representing shortcomings of the CSHDME; (2) the composite systems degree of synergy shows the timeseries change characteristics of strong regional differences, strong volatility, instability, and low synergy; (3) the composite systems degree of synergy shows the spatial evolution characteristics of low synergy, strong differences, strong volatility, and high agglomeration; and (4) judging from the trajectory of the CSHDMEs degree of synergy, the low-level subsystems have more influence on the CSHDME. The decrease in the degree of orderliness of any subsystem, especially those representing shortcomings, or the rapid development of some subsystems has a negative impact on the CSHDME. Only when the degree of orderliness of the five subsystems increases at the same time does it positively affect the CSHDMEs degree of synergy.

Management Enlightenment
Based on the above conclusions, we propose the following strategies to enhance the level of synergy development of composite systems: (1) Reasonable allocation of marine resources and accurate improvement of shortcomings.
In view of the great differences in the development of the five subsystems, coastal provinces should rationally allocate marine resources through forward-looking layout, policy guidance, and other measures to accurately enhance development shortcomings. In response to the low degree of orderliness in the marine science and culture subsystems, coastal provinces can enhance the development level of the marine science and technology subsystem by increasing innovation investment, supporting marine bottleneck technology projects, leveraging the synergistic effect of universities research institutes marine enterprises innovation entities, and cultivating innovative industrial clusters. Coastal provinces can improve the development level of the marine culture subsystem through measures such as increasing cultural investment, cultivating high-quality marine cultural products, and improving the added value of marine cultural brands.
(2) Optimize the spatial layout of the marine space and strengthen regional cooperation.
In view of the problems of strong differences, high aggregation, and instability in the CSHDMEs level of synergy, it is necessary for the government and other relevant departments to coordinate marine ecology, production, and living-space resources and elements, plan and optimize the spatial layout of the marine economy in general, and eliminate administrative barriers among coastal provinces as soon as possible. Coastal regional cooperation can be strengthened by forming a unified management department or association, building a dynamic networked marine information-sharing platform, strengthening marine resource sharing and industrial collaboration among provinces, and enhancing the CSHDMEs overall level of synergy in coastal areas.
(3) Narrowing the development gap and promoting balanced development.
In light of the conclusion that the development level or development speed of subsystems affects the CSHDMEs level of synergy development, it is necessary for the government and other relevant departments to strengthen macro-control, promote the convection of population, capital, resources, and other marine factors through measures such as policy inclination and increased investment, and give play to the driving effect of superior subsystems (such as the marine economy and society subsystems) on those disadvantaged subsystems, in terms of resource development and utilization, and industrial transformation and upgrading through market-led and policy-guided measures, so as to narrow the development gap between subsystems and promote the balanced development of the five subsystems, so as to form a joint force for the development of the composite system.

Limitations and Future Research Directions
Firstly, the construction of an evaluation index system for the CSHDMEs synergy level depends on the reliability and completeness of data. However, because of the special attributes of the marine economy, some data may not be available, or there may be deviations that may influence the comprehensiveness and accuracy of the evaluation index system. Secondly, the elements covered by the CSHDME are complicated, and their internal relationships and interactions are intricate; this not only increases the difficulty of constructing an evaluation index system but also may lead to the omission of elements. In summary, although this paper has endeavored to consider various factors when building the evaluation index system of the CSHDMEs synergy level, there are still some limitations requiring further improvement and optimization during subsequent research.

Data Availability Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest:
The authors declare no conflict of interest.