You are right that the two notes are often combined because both are thought to be fresh. But to people hypersensitive to marine notes like me, they are quite different.
Marine usually refers to molecules like calone, which to most (?) people smell like a sea breeze from the ocean, but to people like me smell like decaying shellfish. Calone is variously described as fresh, slightly salty, melony or cucumber like. Citrus notes tend to be fleeting, so they are gone in no time, while marine ones are very persistent. So if a frag has both notes, typically what you smell for most of the time are the marine ones. For instance, Light blue for men is predominantly marine; the flanker Light blue Stromboli has a pleasant citrus-lemony top, but within 5 minutes it's back to the marine powerhouse.
Citruses without marine include things like Eau Sauvage, the Hermes Oranges Vertes, and the Acqua di Parma colonias. I cannot suggest a marine, since I don't like them. Probably one of the strongest I've smelled is the niche Tirrenico by I profumi del Forte.