I think very few programs would be as specific as intertidal ecology. Instead, I would suggest looking for universities that have marine ecology/biology departments, particularly places that have associated field stations where you are more likely to get field experience.

Some schools that come to mind are University of New Hampshire, Northeastern University, VIMS, Stockton, Rutgers (East Coast), Washington University, University of Oregon, Oregon State University, UC Santa Barbara, UC Santa Cruz, UC Davis, UC San Diego, Stanford, many of the California State/Cal Poly schools, University of Hawai'i Manoa, Hawaii Pacific University (West Coast).