Underwater Wireless Sensor Networks (UWSNs) are garnering significant interest for their broad potential in critical applications, including environmental monitoring, resource exploration, and disaster prevention. These networks, however, face unique challenges due to the complexities of underwater acoustic communication, such as extended propagation delays and environmental disturbances. These issues necessitate the development of sophisticated Medium Access Control (MAC) protocols specifically designed for UWSNs, distinct from those used in Terrestrial Wireless Sensor Networks (TWSNs). This paper provides a comprehensive review of MAC protocols tailored for various task-oriented scenarios in UWSNs, beginning with an in-depth exploration of the challenges specific to designing MAC protocols for these networks. The discussion emphasizes the importance of minimizing transmission latency and maximizing reliability, crucial for effective application-specific operations. This survey categorizes existing protocols based on these critical performance metrics, while also addressing the imperative of energy efficiency. Furthermore, it details the adaptive strategies these protocols employ to cope with the dynamic and challenging underwater acoustic channels. In addition to presenting a comparative analysis of the protocols, this work identifies pressing research gaps and poses open questions, establishing itself as an indispensable resource for researchers seeking to advance the field of MAC protocols in UWSNs.