Climate change has emerged as one of the greatest environmental challenges of the 21st century, and its impacts are not limited to the terrestrial environment alone. Oceans, which cover about 71 percent of the Earth’s surface and play a crucial role in regulating global climate, are experiencing profound transformations due to rising greenhouse gas emissions and global warming. The ocean ecosystem, which provides vital resources, biodiversity, and regulates climate by absorbing carbon dioxide and heat, is increasingly threatened by human-induced climate change. The impacts on oceans are multi-dimensional, affecting physical, chemical, and biological processes, and in turn altering marine life, habitats, and human livelihoods that depend on these systems. One of the most critical impacts of climate change on the ocean ecosystem is the rise in sea surface temperatures. As atmospheric greenhouse gases trap more heat, oceans absorb over 90 percent of the excess warming. This warming alters ocean circulation patterns and directly affects marine organisms. Many species are highly sensitive to temperature thresholds, and even small increases can disrupt their reproductive cycles, migration patterns, and survival rates. Coral reefs, which thrive in narrow temperature ranges, are especially vulnerable. The phenomenon of coral bleaching occurs when corals expel their symbiotic algae under heat stress, leaving them weak and often unable to recover. Widespread coral bleaching events in regions such as the Great Barrier Reef demonstrate the magnitude of this problem. The decline of coral reefs not only threatens biodiversity but also undermines coastal protection and fisheries that millions of people depend on. Another major consequence of climate change is ocean acidification, which results from increased absorption of atmospheric carbon dioxide by seawater. When CO₂ dissolves in water, it forms carbonic acid, lowering the pH of the ocean. This process reduces the availability of carbonate ions, which are essential for calcifying organisms such as corals, mollusks, and certain plankton to build their shells and skeletons. The weakening of these organisms undermines the base of the marine food web. For example, the decline of pteropods, small planktonic snails sensitive to acidification, has cascading effects on fish species and larger predators. Moreover, coral reef structures become more fragile and less resilient to storms, eroding marine biodiversity and ecosystem services. Acidification also disrupts sensory and behavioral functions in fish, affecting their ability to detect predators or find suitable habitats. Climate change also contributes to sea level rise, primarily due to the melting of glaciers, ice sheets, and the thermal expansion of seawater. Rising sea levels inundate coastal habitats such as mangroves, salt marshes, and seagrass meadows, which are critical nurseries for fish and serve as carbon sinks. The loss of these ecosystems reduces biodiversity and weakens natural defenses against storm surges and erosion.