China's marines, traditionally associated with South China Sea missions, has been expanded from 2 combined arms brigades to six (by incorporating 4 army brigades without amphibious training) plus a new helicopter and new special forces brigade.
The expanded force appears to be fully engaged with increased needs in the South China Sea due to Chinese island building and encroachment on territory; plus new distant missions (see China's new Djibouti base):
The expanded Marine Corps, supported by Navy long-range sealift, likely will become the core of the PLA’s future expeditionary force. Training that began in 2014 further indicates that the eventual objective for the Marine Corps is to be capable of conducting operations in many types of terrain and climates – ranging beyond the PLANMC’s former, and continuing, focus on islands and reefs in the South China Sea. The manner by which the force has expanded, however, suggests that the PLA leadership was not motivated by an immediate need for a larger amphibious capability; rather, it appears to be consistent with several new missions undertaken by the Chinese military over past decade that have provided impetus for the addition of new Marine units.
To be clear, despite Taiwan recovery (invasion) being a focus of China's military modernization (that scenario is the "primary driver" of Chinese modernization according to our DIA), the Chinese don't see any need for an expanded marine force for existing missions. Rather, with distant missions and new missions in the South China Sea, the new marine units will have plenty to keep them busy without looking at Taiwan. And the main army has kept its amphibious units even during the marine expansion.
This is consistent with my long-held belief that focus on the limitations of China's marine force when it comes to judging whether China can pull off an invasion of Taiwan is a red herring.
China doesn't require the marine combined arms brigades to invade Taiwan, although the Pescadores Islands might find a use for the marines. And as combat-ready forces they could be pulled in anyway, of course, to supplement the primary army role.
The marine special forces and helicopter units are another matter. They could easily be considered core capabilities for an invasion force.
We'll see if the Chinese combined arms marines get deployed west of the Malacca Strait anytime soon.