With rapid urbanization and economic development along the coast, the impacts of land-based human activities on coastal and offshore marine ecosystems have been significantly increased. This paper presented the impacts through literature synthesis and discussions with international experts, which are mainly caused by the exploitation of marine resources, coastal urbanization, and environmental change. Over exploitation of marine biotic resources, coastal eutrophication, ocean acidification, coral reef degradation, marine litter, and increasing pollution of heavy metals and persistent organic pollutants due to intensive coastal industrialization have become the major challenges and problems for coastal and offshore ecosystems. With changes in marine biological community structure, deteriorating water quality, and declining marine biodiversity, those chanllenges and problems will change the functioning of marine ecosystem services and thus threaten the health of the marine ecosystem. Since the major issues of coastal and offshore ecosystems stem from land-based activities, land and ocean should be considered as a single system when addressing them. Therefore, scientific plans on land-ocean interactions should be integrated to conserve and to ensure the sustainable use of marine resources and the sustainable management of coastal ecosystems.