It’s one treasure per ship per turn, so if you have multiple ships nearby, you could use it once for each. They do not all have to occur at the same time.
Thanks, I have an idea for a fleet involving Intermediaro and ships that can submerge. 😀
I think it could be pretty neat to have some MI effects that would only function while a fort was present. There’s a lot you could do, from simple boosts to cannon rolls/ranges and defensive bonuses, to more complex things like making it more costly to build there, or having ongoing negative effects that have to be dealt with to keep a fort in a prime location.
They haven’t been released yet but I have made a “mysterious island” that does something like this. I suspect that the wording might need to be cleared up however.