I'll add a little to the good advice listed above. Whether or not you want copyright depend what you intend to with the project that you create. I released first two books with Creative Commons licenses and encourage others to take whatever they like. If you are asking the question, then you are probably concerned about predicting your intellectual property from theft. Nobody is going around stealing webcomics and making bank off them, but if it makes you feel at ease, go ahead and and file a copyright application. You've got nothing to lose but thirty bucks.
Copyrights in the U.S. are awarded automatically now at the instant of publication. Filing a copyright simply means that you are documenting your copyright. Most nations adhere to the Berne Treaty so their rules work similarly to those in the U.S. with the big exception being that copyrights last longer in the U.S. than in those other countries. China does not recognize any foreign laws regarding intellectual property.
Copyright is not to be confused with trademark. Trademark law exists to prevent others from creating counterfeit products similar your own products and tricking the consumer into thinking that they are the same thing. Apple Computers has used trademarks to stop others from using certain colors computer cases and even from using the word "pod" in website names. You could trademark the name and logo of your webcomic if you wanted. Trademarks are NOT granted automatically.