To implement the Maritime Silk Road in the 21st century and to meet the demands of increasing maritime activity, a seamless, effective, and reliable communications coverage of relevant sea areas is necessary. In this review, we first outline state of the art marine communications networks in China and then analyze and compare several major marine communications networks, including marine radio communications, satellite communications, and shore-based mobile communications networks. Next, based on the geometric characteristics of numerous islands and reefs, a novel system architecture of marine communications networks is proposed, and the main technical challenges precluding its implementation are described, including channel modeling of marine communications, atmospheric duct effect, microwave scattering effect, and unified and effective network resource management. This work will benefit policy makers, scientific researchers, and engineers, by providing a global overview and enabling them to grasp the trends in marine communications, and thus is likely to promote the construction and development of marine communications in China. Keywords marine communications, marine radio communications, satellite communications, shore-based mobile communications, channel modeling of marine communications, atmospheric duct effect, microwave scattering effect, network resource management