Strategypage looks at the Chinese marines:
Until the 1980s, the Chinese didn't have a marine corps, only army units that were trained to conduct amphibious operations. China didn't start building its own large amphibious ships until the 1980s, at the same time they organized marine brigades. There are currently two Chinese marine brigades, containing a total of 10,000 troops, plus another 2,000 troops in support and training units.
The marines are equipped with amphibious armored vehicles and self-propelled artillery, anti-tank and anti-aircraft missiles. All of these marines are volunteers and undergo strenuous training. Each brigade also has a reconnaissance battalion, with several hundred men (and 30 women) trained to use scuba gear to get ashore and look around. These are actually special operations troops, and are carefully selected and trained. ...
Interestingly, the Chinese marines are not stationed where they could be used for an invasion of Taiwan, but in the south, where they can grab disputed islands in the South China Sea. While these islands, which control fishing and potential oil fields, are considered disputed, China has already laid claim to some of them by force. ...
The Chinese marines are trained and equipped for raiding, not for large scale landings against a defended shore. The latter task is apparently left to army divisions that have been drilled on how to get on, and off, amphibious ships. While the Chinese marines might play a part in a Taiwan invasion, their full time job appears to be in the South China Sea, where the Chinese stand ready to grab more islands, if the economic advantages seem high enough.
Read it all. It's quite good.
I don't look at the Chinese marines and dedicated amphibious forces and conclude China can't invade Taiwan because the forces are too small. No, I have other thoughts on how China would invade.
China remains a large "amphibious warfare" platform a mere 100 miles from the target, remember. Even helicopters could fly from the mainland.
I've thought of the Chinese marines as a force for the South China Sea. Heck, opposing the Chinese in the South China Sea is the reason I think our Marines are going to Australia, with small but excellent Australian forces able to support us.
(And Japan is building a similar capability north of Taiwan--with our forces on Okinawa able to back them--and Guam backing the northern and southern wings of the island defense forces.)
For Taiwan, the Chinese are hardly going to waste these marines, however. Unless a good portion is designated to sweep through the South China Sea while the invasion of Taiwan is going on, the marines could contribute to an invasion of Taiwan even if they aren't the core of the effort.
(If the Chinese are going to get hammered diplomatically for Taiwan, why not go for the South China Sea, too? These would also provide a consolation prize if the invasion of Taiwan goes badly and China wants to sue for peace over that fight and still get something out of it.)
The main role in such a Taiwan scenario would be to seize the Pescadores Islands. They could then be used for distracting attacks on the main island or just to threaten such attacks to freeze the Taiwanese defenders in place rather than rushing north to the main Chinese effort.
Don't define China's threat to invade Taiwan by the state of China's marine corps. Remember, we think of Marines as the core of large invasions. But that isn't how the rest of the world has worked. Heck, that's not how we worked in the European theater in World War II, where Army troops carried out every American amphibious invasion from North Africa to Normandy and the Rhine River crossings.