It is important to "think globally but act locally".  Solving world-wide problems like coral bleaching or ocean acidification can be daunting, but that shouldn't discourage you from acting in your community.  For example, organizing a community garden at your school, creating buffer zones to prevent pollutant runoff, or organizing a campaign to reduce waste in your school can have far reaching impacts to help reefs and ocean ecosystems.

Additionally, the Sunrise Movement is a nation-wide youth organization dedicated to taking action to promote sustainability.  Forming a local hub can be a great way to act locally while being part of a wide network of students concerned about the health of the environment.