All websites and their content are inherently copyrighted, provided they are original works. Registration is not mandatory and it is up to the creator. If the content of the website is valuable, financially or otherwise, or there is a need to protect the website and its contents for legal reasons, then taking a few minutes to register the copyright to the website is probably worthwhile.
Website publishers are often victims of copyright infringement by unknowing or unscrupulous individuals who think nothing of copying someone else's work and passing it off as their own. Unfortunately, it's almost impossible to completely prevent infringement, but marking your website material with "All Rights Reserved" or using the copyright symbol can be enough of a deterrent to prevent many potential offenders from stealing your work. You may display the copyright symbol or language claiming copyright even if you choose not to register your work.
A blog is a type of website with original content that's added by you or by others working for your business. A blog can be copyright protected in the same way and in the same category as a website.
A website's graphics, content, visual elements is copyrighted at the time of development. So putting the copyright notice on the bottom of a site states that the material displayed is not to be used without permission of the owner.