There is a lot of ecotourism in the Coronado area. It is not specifically in Coronado, proper, but there is ecotourism in the west beach areas in general, and it is great. There is a lot of hiking, whale watching, fishing, etc. I am sure there is a lot more but these are the major ecotourism activities that you can do around Coronado.
(Piedra pintada, or painted stone, El Valle de Anton, 27 miles away from Coronado, pictured. )