The impacts of climate change on the ocean ecosystem have emerged as one of the most pressing environmental challenges of the twenty-first century. Oceans cover more than 70 percent of the Earth’s surface and play a vital role in regulating the global climate, absorbing large amounts of carbon dioxide, and providing food, livelihood, and biodiversity. However, the rising concentration of greenhouse gases and associated global warming are profoundly altering marine environments. These impacts are complex and interconnected, influencing physical processes, biological communities, and human societies that depend on marine resources. One of the most visible impacts of climate change on the ocean ecosystem is ocean warming. The oceans absorb about 90 percent of the excess heat generated by greenhouse gases. This rise in sea surface temperature has multiple consequences. Warmer waters affect the physiology, behavior, and distribution of marine species. Many fish, plankton, and invertebrates are shifting their ranges towards cooler waters, typically towards the poles or into deeper layers of the ocean. This disrupts established food webs and fisheries that coastal communities rely upon. Coral reefs, which thrive in stable temperature conditions, are particularly vulnerable. When sea temperatures rise beyond their tolerance level, corals expel the symbiotic algae living in their tissues, leading to coral bleaching. If such events are prolonged or recurrent, corals die, resulting in the collapse of reef ecosystems that host thousands of species. The loss of coral reefs also reduces natural coastal protection against waves and storms. Another major impact is ocean acidification, which results from increased absorption of atmospheric carbon dioxide by seawater. When carbon dioxide dissolves in seawater, it forms carbonic acid, lowering the pH of the ocean. This process decreases the availability of carbonate ions, essential building blocks for calcifying organisms such as corals, mollusks, and some plankton species. As a result, shellfish and coral reefs find it increasingly difficult to form and maintain their calcium carbonate structures. This not only undermines the survival of individual species but also destabilizes the larger marine food web. Acidification can affect sensory behavior in fish, reducing their ability to detect predators, locate prey, and navigate. Such disruptions ripple through ecosystems and ultimately influence the availability of seafood for humans. Sea-level rise, another outcome of climate change, also has direct and indirect consequences for ocean ecosystems. Melting ice sheets and thermal expansion of seawater are causing gradual increases in sea levels. Higher sea levels can inundate coastal habitats such as mangroves, salt marshes, and estuaries, which serve as nurseries for many marine organisms. Mangroves and marshes also provide vital ecosystem services, including carbon sequestration and storm protection. Their loss exposes coastal communities to greater risks of flooding and storm surges while reducing biodiversity. Additionally, sea-level rise alters salinity gradients in estuaries, disturbing the balance of species that are adapted to specific conditions. This creates challenges for both marine and freshwater species that rely on transitional zones. Changes in ocean circulation patterns due to climate change also impact ecosystems. Ocean currents, which distribute heat, nutrients, and oxygen, are influenced by differences in temperature and salinity. Climate change disrupts these patterns, leading to shifts in nutrient availability and productivity. For example, weakening of upwelling systems reduces the supply of nutrients from deeper waters to surface waters,