Under which law can the Coast Guard take measures to prevent acts of terrorism against vessels?

The Maritime Transportation Security Act is the correct choice because it specifically addresses the need for security in the maritime domain, which includes preventing acts of terrorism targeting vessels and ports. This act established a comprehensive framework for maritime security, requiring the development of security plans for ships and port facilities, and it emphasizes the importance of coordinating efforts between federal, state, local, and private sector entities to enhance security against threats.

This act mandates assessments of vulnerabilities and outlines procedures for responding to and mitigating security incidents, making it a critical tool in the Coast Guard's mission to safeguard the maritime environment from terrorism. It provides the legal foundation for various security measures, including screening vessels, controlling access to facilities, and conducting drills and exercises to improve preparedness for potential terrorist threats.

The other options, while relevant to maritime regulations and safety, do not specifically focus on terrorism prevention in the same comprehensive manner as the Maritime Transportation Security Act. For instance, the Magnuson Act primarily deals with fisheries management, the Ports and Waterways Safety Act focuses on navigational safety, and the National Marine Sanctuaries Act is aimed at protecting marine environments, rather than addressing the unique security challenges posed by terrorism against maritime transportation.