## 4 Conclusions  
Since 2000, the geometric shape of the southwestern part of Laizhou Bay has changed significantly due to the influence of natural factors and human activities. The sea area in the southwestern part of the bay has been shrinking, and the coastline has continued to expand from the land to the sea. The construction of sea-reinforcement farming, port terminals, and breakwaters are the main reasons for the changes in the geometry of the southwest. During the 20 years from 2000 to 2020, most (85.3%) of the coastline in the bay area was in a growth trend of advancing toward the sea, there were dynamic stable areas (11.9%), and there was almost no erosion area (only 2.8%). The area of the southwestern part of Laizhou Bay decreased by 11.66%, the coastline of the bay increased by 63.27%, and the center of mass moved 2.22 km to the northeast.  
The tidal waves of Laizhou Bay enter from the bay mouth and propagate toward the top of the bay. The maximum possible tidal range gradually increases from the bay mouth to the inside of the bay. The reclamation of tidal flats has increased the tidal wave potential energy in the bay, causing the tidal range in Laizhou Bay to increase. The maximum possible tidal range in the southwestern part of the bay showed an increasing trend over the past 20 years, with the maximum increase reaching 22 cm, located at the top of the bay between Weifang Port and Guangli Port. The increased tidal range caused by tidal flat reclamation puts the lowlands along the bay at risk of being flooded, and will also place higher demands on coastal engineering protection and design standards.  
For Laizhou Bay with irregular semidiurnal tides, the tidal prism of two adjacent tidal cycles are significantly different, and the tidal prism of different tidal cycles are also different. Affected by the reduction in the area of the southwestern sea area of Laizhou Bay, the high tide, low tide, and average tidal prism in the southwestern part of the bay decreased by 4.79%, 3.29%, and 4.24%, respectively, in the past 20 years. The reduction in tidal prism has led to a corresponding reduction in the environmental capacity of pollutants in the bay, making it easier for pollutants to accumulate in the bay, thereby reducing the bay's self-purification capacity.  
Conceptualization, J.W. and J.Z.; methodology, J.W., J.Z. and S.Z.; software, S.Z., Z.Y. and W.S.; validation, J.W. and Z.Y.; formal analysis, W.S., J.Z. and Z.Y.; investigation, J.W. and W.S.; resources, K.H. and M.Z.; data curation, Z.Y. and K.H.; writing--original draft preparation, J.Z., J.W. and Z.Y; writing--review and editing, W.S., J.W. and M.Z.; visualization, J.Z., X.W. and Z.Y.; supervision, W.S. and J.Z.; project administration, J.Z. and W.S.; funding acquisition, J.Z. and W.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation project (No. 42176221); The Shandong Provincial Natural Science Foundation (No. ZR2023 MD039); The Science and Technology Innovation Development Program of Yantai (No. 2023 JCYJ101); and Yantai Key Laboratory of Quality Safety Control and Deep Processing of Seafood Products Open Fund (QSCDP202307).  
Not applicable.  
The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.  
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.