We depend on mangrove forests far more than we realize. Help mother nature to recover from overdevelopment by planting mangrove seedlings in deforested areas. The whole programme is 3 hours, including 60 minutes of boat ride.
Another great option is to volunteer at the Turtle Sanctuary, including beach clean-up of the area to improve the survival rate of the hatchlings. There is also signage painting, and (depending on season) release of the baby turtles to the sea.