The cruise ship floats up a couple of times a day, giving you opportunities to choose whether or not you want one of several possible intrusions to occur on your island. As the game mentions, there are upsides and downsides to each.
The conch can be found on the beach, given to you as a daily reward, or purchased for 20 gems from the store. It gives you a chance to accept one of the options that the cruise ship normally offers or to call the work ship to recycle some trash. You can cycle through those options using the arrows.