Learn English – What does it mean “to port over”

The original meaning was that Mr Romney was brought folders containing women's dossiers/resumes. So "a cover for holding magazines or loose sheets of paper together" was the meaning for this word.

At the current time the meaning of the meme is rapidly evolving, as most political situations do.

None, maritime means "of the sea" and when sea is used as a noun adjunct it means "of the sea", so maritime port, sea port and the closed compound seaport all mean a port that has direct access to the sea (coast, inlet, natural harbour). You may or may not decide to include a fluvial port on a river, but that goes equally for either word. You normally would not include dry ports (a terminal with a direct overland connection to a seaport), in either.

The original proposal says:

1. Member States shall ensure that publicly accessible LNG refuelling points for maritime and inland waterway transport are provided in all maritime ports of the Trans-European Transport (TEN-T) Core Network by 31 December 2020 at the latest.
2. Member States shall ensure that publicly accessible LNG refuelling points for inland waterway transport are provided in all inland ports of the TEN-T Core Network, by 31 December 2025 at the latest.

(Emphasis mine).

In rewriting from the proposal to produce the article the author made a mistake. My guess is they were trying to decide between keeping the term and writing "maritime and inland ports" or changing it to "sea and inland ports" on the basis that sea is a better known word than maritime and some readers might not understand maritime, and in trying to pick between the two they accidentally wrote sea and maritime ports

It's clearly not a matter of their using sea to mean something other than maritime because the time for the "sea ports" in the article matches the time for the "maritime ports" in the original.