UPDATE 1-US, China to roll out tit-for-tat port fees, threatening more turmoil at sea

* US, China begin collecting port fees on each other's vessels * China says Chinese-built ships exempted from its levies * US aims to loosen Chinese dominance in global maritime, bolster US shipbuilding * Trade spat revived as Trump announces new 100% tariffs on Chinese goods (Updates with details released by China in paragraphs 2-4) BEIJING/LOS ANGELES, Oct 14 (Reuters) – The United States and China on Tuesday will begin charging port fees on ocean shipping firms that move everything from holiday toys to crude oil, making the high seas a key front in the trade war between the world's two largest economies. China said it had started to collect the special charges on U.S.-owned, operated, built, or flagged vessels but clarified that Chinese-built ships would be exempted from the levies. In