From their site:
Is your idea of the perfect day watching waves tumble to shore, peddling your bike along the harbor at sunset, reeling in the biggest catch, or ordering a fresh buttery lobster roll?
You can read the official rules (there are a lot of them, so read carefully) on their site.
Contest tip: Whenever you enter a contest with a specific theme, try running your potential entry photos past someone in your family or a few friends and ask them what theme they bring to mind. If you show a photo of someone fishing on a pier and your friends say, "Living near the ocean!" then you're absolutely on the right track. Keep things as focused on the theme as you can and you're on the right path. Also, try word associations for the theme. In this case, "coastal life" may create a list that includes: beaches, bonfires, clambakes, sunrise, sailing, sailboats, etc. Use that list to go through your files and find images the match the words.