reporter: this is ecological geneticist madeleine van oppen.'s investigating a range of approaches to make corals more resistant to rising temperatures. for example, selectively breeding to toughen up the polyp animals. or, alternatively, tinkering with the algae that give coral their colors. madeleine: the microalgae that live inside the coral tissues, we can take them out of the coral and most of these can be cultured in the lab. and in the lab, we can increase the rate by which these algae evolve. reporter: madeleine van oppen used this approach to create heat resistant algae, which, when put back into polyps, created more heat resistant corals. so, if we combine all these approaches, is that it? will we be able to save these unique ecosystems from climate change? lizzie: if we implemented every tool in our toolbox today, from marine protected areas, reducing pollution, using some of these more active interventions, stress hardening or manipulating the genetics of corals, it will not be enough to save coral reefs if we do not reduce emission