 They cover 71% of the planet's surface, host the majority of its biodiversity and produce more than half of its oxygen. A healthy ocean is vital for a healthy planet. But the impacts of human activities are causing widespread ocean changes. These threaten ocean life and the livelihoods of more than a billion people. Nuclear applications are helping us understand and mitigate these major environmental challenges, especially ocean acidification and pollution. Greenhouse gas emissions are increasing the acidity of our oceans and corroding fragile marine life. To better understand and measure these impacts, scientists are using the calcium-45 radioactive tracer technique. They set up experimental aquaria with seawater at different pH levels and add calcium-45 as a tracer to measure the difference in the growth of corals and shellfish. Gathering this data is vital to protecting the health of coral reefs, which are so critical to marine ecosystems and coastal communities. Today people are facing dangerous levels of contaminants in their seafood. From heavy metals, pesticides, microplastics and more. Using techniques based on mass spectrometry, scientists are able to identify the level and source of pollutants in seafood. When analyzing a sample, they remove all its organic matter, leaving only the contaminants behind, and then use specialized analytical instruments to determine contaminants present in the sample. Having this data helps coastal countries make appropriate management decisions to regulate pollution. These nuclear and nuclear-derived techniques provide a unique window into understanding the processes behind ocean change, an understanding that can help us secure a healthy ocean for the future. The IAEA, through its marine environmental laboratories and its technical cooperation program, supports member states in acquiring and efficiently using these nuclear techniques.