Environmental regulation, industrial agglomeration, and marine green development efficiency: an empirical analysis from China’s coastal provinces

Environmental regulation (ER) and industrial agglomeration (IA) are important factors that affect green development efficiency (GDE). However, there is a lack of studies on their relation in the context of the marine economy. This paper integrates ER, IA, and marine GDE (MGDE) into a unified analytical framework and uses balanced panel data from China’s 11 coastal provinces during 2008–2019 to quantify the linear, nonlinear, and spatial spillover effects between the three using the spatial Durbin model (SDM) and threshold effect model. The results show that ER has a negative impact on local and surrounding MGDE through the direct and spatial spillover effects. IA has a positive impact on local and surrounding MGDE through direct and spatial spillover effects. The synergistic impact of ER and IA can significantly boost local and surrounding MGDE. When ER surpasses a certain threshold, it amplifies the positive impact of IA on MGDE. These findings offer theoretical and practical references for the Chinese government to formulate marine environmental governance and industrial development policies.