Global warming is an increasingly pressing issue, with significant impacts on marine ecosystems. Rising global temperatures are causing profound changes in the oceans, affecting biodiversity, ecosystem structure, and the lives of marine creatures. The following is a breakdown of the impact of global warming on marine ecosystems. First, rising sea temperatures cause coral reef bleaching. Corals are very susceptible to temperature changes; When the water temperature exceeds the threshold, the symbiotic algae that provide color and nutrition to the coral will disappear. Coral bleaching results in the mass death of coral reefs, which are habitats for many marine species. This not only harms the living creatures that depend on coral, but also impacts the fishing and tourism industries. Second, rising temperatures cause ocean acidification. When carbon dioxide (CO2) is absorbed by the ocean, it changes the pH of the seawater to become more acidic. This condition has a negative impact on organisms that have hard shells, such as molluscs and plankton. Increased acidity can disrupt the shell formation process, thereby threatening their survival and the food chains that depend on them. Third, global warming expands the area of ​​ocean temperature anomalies, which changes species migration patterns. Many fish and marine mammals, including tuna and whales, migrate to colder regions in search of more comfortable temperatures. These changes can cause conflict with fishing communities that depend on these species, and can disrupt existing ecosystems. Fourth, global warming contributes to an increase in the frequency and intensity of tropical storms. These storms not only threaten human life on the coast, but also destroy marine habitats. Coral reefs and coastal ecosystems, such as mangroves, are greatly affected by physical damage from large waves and strong currents produced by storms. Furthermore, the impact of global warming is also seen in a decrease in dissolved oxygen in the sea, which is known as hypoxia. Higher temperatures slow the process of oxygen dissolution in water, while eutrophication resulting from agricultural waste adds to the nutrient load, causing toxic algal blooms. Hypoxic conditions threaten the lives of fish and other species, creating dead zones where living things cannot survive. In addition, the impact of global warming can spread through the food chain. For example, if plankton—the base of the marine food chain—is affected—this can impact the entire ecosystem. A decrease in plankton can cause starvation for the fish and marine animals that depend on them. Changes in the El Niño phenomenon are also related to global warming. This phenomenon can cause extreme ocean temperature fluctuations as well as a major impact on global weather patterns. Coastal communities and the fishing industry often suffer major losses due to these unexpected changes. Reduction of biodiversity is another impact of global warming. Species that are unable to adapt quickly to environmental changes risk extinction. Reducing biodiversity reduces the resilience of ecosystems to further change, which can create a downward spiral that is difficult to stop. Given the harmful effects of global warming on marine ecosystems, it is important to implement effective mitigation measures. Stricter environmental protection policies and global efforts to reduce greenhouse gas emissions are urgently needed to maintain the health of our oceans and the survival of the living creatures within them.