Marine ecosystems in the northwest Pacific are known for their high biodiversity, with many marine species, from tiny plankton to huge macroalgae. Marine biodiversity is affected by irreversible global warming, mainly the increase of greenhouse gas emissions from anthropogenic activities. For the past several decades, marine ecosystems in East Asia have been changing due to the increase in sea surface temperature (SST), which has changed some important environmental factors, including rainfall patterns, extreme weather, and ocean circulation. Such modifications in the environmental parameters have altered the physiology, phenology, and distribution pattern of marine organisms. The SST increase has also altered population and community structure, and the functioning of the ecosystem. Certain subtropical and tropical fauna and flora are now extending their range of distribution from the warm southern area to the temperate regions, disrupting or modifying the biotic interactions in the temperate ecosystem. Collaborative conservation projects and responsible policies are crucial to safeguard the environmental value of East Asia’s marine ecosystems for future generations and mitigate the negative effects of global warming on marine biodiversity. Conservation and management of East Asia’s marine environments hold significant implications for global biodiversity and ecological balance, making them a pivotal focus in addressing climate change challenges in marine ecosystems.