The world's oceans play a key role in regulating Earth's global climate, absorbing over 90% of the excess heat generated by anthropogenic greenhouse gas emissions and approximately a third of all carbon dioxide. However, this barrier function comes at a colossal environmental cost. Today, ocean ecosystems are undergoing an unprecedented transformation caused by three interrelated factors: thermal expansion and warming of water, acidification, and deoxygenation—a decline in dissolved oxygen levels. These processes threaten the planet's biodiversity and the food security of billions of people.