The Bohai Sea is undergoing regional changes driven by both climate change and human activities, resulting in negative impacts on marine ecosystems, such as more frequent red-tide occurrences. However, the complex interplay of various factors within the Bohai Sea system makes it challenging to distinguish their coupled interactions and to measure critical behaviors in the system. Utilizing the Eigen Microstates Approach (EMA), we uncover the coupled relationships among climate change, human activities, ocean chemistry, ocean biology, and ocean ecology. Our analysis reveals that human-induced changes have dominated over the past 29 years, surpassing the influence of climate change. We employ the entropy of eigen microstates to quantify the disorder in the Bohai Sea system, identifying two peaks in 2012 and 2017. These peaks suggest potential critical behaviors in the system, corresponding with red-tide occurrences. This study not only underscores significant changes in the Bohai Sea but also highlights the potential of complexity science to characterize the evolution and critical behaviors of coastal zone systems.
 

Eigen Microstates Approach,Eigen Microstates Entropy,marine ecosystem,Critical Behavior,Bohai Sea