Boarding at sea, helping protect shipping, and fighting piracy were the reasons that Marines (in both England and America) were established as a branch separate from the Army.

The way I see it, this mission is a far better use for the Marine Corps, as compared to the current use of treating it like a faster, lighter version of the Army. The Marines have a specialization in inshore operations requiring both land and naval elements that's uniquely suited to combating piracy, and I'm encouraged to see them beginning to better develop this capability.