The Agence France Presse reports that the Islamic Revolutionary Guard Corps has been given command over “naval operations” in Persian Gulf and Strait of Hormuz. A study conducted by the U.S. Office of Naval Intelligence concluded that,

the military reorganization launched in 2007 transfers responsibility for the Gulf from the regular navy to the elite Guards’ naval force, which has an arsenal of small, high-speed boats and cruise missiles.

The Islamic Republic’s regular naval forces are now responsible for the Gulf of Oman and the Caspian Sea regions.
This change in the operational theater of the IRGC navy is likely designed to allow Iran to effectively shut down shipping through the Strait of Hormuz and the Persian Gulf; something that the Iranian government has threatened in the past. Of course, as the Agence France Presse article points out, shutting down either sea lanes would have a massive deleterious effect on Iran’s economy in addition to damaging the economies of Europe and the United States.
Update:
On November 25, the Iranian Navy has detained five British nationals who accidentally sailed into Iranian waters in the Persian Gulf. The Britons were sailing a yacht, possibly named the Kingdom of Bahrain, on their way to Bahrain for a Dubai-Muscat race.
The five sailors are reported to be in good health and are being well treated.