This chapter focuses on changes to the distribution of hard-bottom habitats that are directly or indirectly attributable to human activities. We report some documentation and key examples about the past and current losses of hard-bottom habitats, particularly those of biogenic origin. We also discuss the threats related to the addition of artificial hard or rock-armoured substrata as a consequence of coastal urbanization. We discuss the significance of these changes to coastal areas and why we should be concerned about them. We also discuss how much change has already passed unrecognized, and recommend greater effort in the maintenance and restoration of what remains of valuable natural hard-bottom habitats.