This study aims to evaluate the impact of urban spatial expansion on the landscape patterns of coastal cities in Türkiye through the use of spatio-temporal indices. To this end, temporal samples covering a period of approximately 30 years (1986–2000 and 2000–2015) were analyzed for six selected coastal cities in Türkiye. The urban spatial growth patterns in these cities were characterized using 17 geospatial indices, and Pearson’s correlation coefficient and principal component analysis were employed to assess the quantitative relationships between urban spatial development and the fragmentation of landscape networks. The results of the study demonstrated that the patterns of landscape fragmentation caused by the spatial growth patterns of the selected coastal cities can be divided into two categories: disconnected landscape connections and perforated landscape patterns. Leapfrog development was identified as a major factor in the fragmentation of landscape continuity, leading to the formation of perforated green structures. The findings of this research can serve as spatial guidelines for addressing disconnected landscapes, a crucial factor in enhancing urban sustainability in Türkiye’s coastal cities. Furthermore, the outcomes of this study may be useful for informing the national well-being strategy for urban planning and natural mitigating policies in Türkiye’s coastal regions.