For those who might not be familiar with the tromba marina, the string is not stopped as on violin etc. Rather, it is played entirely using the overtone sequence on the string - i.e. "harmonics". Hence the connection in the name to the trumpet, which (assuming it's a pure horn with no valves) can only play the notes in the overtone sequence.

Apologies for offering redundant information to those who were not ignorant about this historical/musical oddity.