The U.S. Navy's first ships were built for the purpose of combating North African pirates. The U.S. Marine Corps was likewise established to take on those pirates, primarily with boarding parties.
Since World War II, the U.S. Marines have focused their identity mostly upon preparing for D-Day style amphibious assaults. They were also security forces charged with protecting ship based nuclear weapons for much of that time period. There are now virtually no U.S. Marines on U.S. Naval ships not built primarily to transport Marine units. Most U.S. navy warships are destroyers and cruisers of just under 10,000 tons, although there are some old frigates which are smaller, that are in the process of being phased out of service. All of these ships are designed and armed for conventional naval warfare. The U.S. Coast Guard has smaller ships, more suited to small engagements, but these ships are only rarely called up for service with the U.S. Navy far from the U.S. Coast.
Recent incidents of piracy off the coast of Somolia, including one standoff involving a U.S. hostage right now, and another incident today where French forces killed pirates in a bid to save threatened hostages (with two pirates and one hostage killed and four other hostages saved) suggests that the most ancient of U.S. Navy and Marine missions is not obsolete, even though it may be forgotten.
These incidents also illustrate the limited usefulness of destroyers and other large naval ships designed to fight conventional World War II style naval warfare against unconvential foes like pirates. New Littoral Combat Ships in prototype stage now are supposed to be a better fit for this mission, although this has yet to be proven. Critics argue that LCS ships are still too large, at 3,000+ tons, for the missions they need to carry out. These missions may be better suited for U.S. Coast Guard sized ships, some of which are much smaller and very fast compared to U.S. Navy ships.
In addition to new ships, it may also make sense to have Marines as piracy response/boarding party soldiers on ships to execute small missions that naval sailors aren't trained to carry out.
The newly important piracy threat may be a godsend for the surface navy, at a time when its relevance to big conflicts is declining. Anti-piracy missions are something that the surface navy can do better than the Air Force, naval aviation or submarines. Also, small ships mean more ship captains, developing leadership and providing an incentive for good sailors to stay in the force.