# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 4 Applications and Challenges of Blockchains in MIoT and IoUT
### Blockchain Integration and Applications in MIoT/IoIT  
As mentioned earlier in Section 2, integrating blockchain technology with the IoT in marine environments opens up new opportunities to overcome their inherent complexities. By leveraging the blockchain's decentralized nature, these systems can achieve more secure and transparent data handling, which is essential for maintaining the accuracy and integrity of information collected from underwater sensors. Furthermore, blockchains can help these networks scale more effectively by optimizing data management, providing a reliable solution adjusted to the specific demands of MIoT applications [14; 20]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Model** & **Description** & **Characteristics** \\ \hline Direct interaction with the blockchain & IoT devices interact with blockchain data stored on edge servers & Fast access to blockchain data, requires edge servers for storage and processing \\ \hline Direct interaction between IoT nodes & IoT nodes exchange partial blockchain data via device-to-device communication & Peer-to-peer communication, enables direct data exchange between IoT nodes without intermediaries \\ \hline Hybrid interaction with cloud and edge servers & IoT devices access blockchain data through cloud or edge servers & Combines cloud and edge resources, offloads storage and processing, suitable for low-power IoT devices \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Blockchain–IoT interaction models, [PERSON] et al. [43]. Figure 6: IoT–blockchain interaction models. Specifically, in the context of IoUT systems, a blockchain is essential in ensuring that smart objects are securely interconnected and authenticated during autonomous interactions, thereby preventing security breaches by malicious nodes. Given the resource constraints and security challenges in the IoUT, the blockchain's distributed and decentralized architecture is particularly valuable. This is because, unlike traditional security methods that rely on centralized authentication, the blockchain's consensus mechanism allows entities to process and validate IoUT data independently before adding them to the blockchain. This process not only ensures transparency, immutability, and resilience but also reduces energy consumption typically associated with centralized authentication [37]. Blockchain technology can also greatly improve environmental monitoring by addressing the weaknesses of traditional methods, which often lack efficiency and proper security [20]. With its strong data management capabilities, the blockchain ensures that data generated from underwater sensors--such as water quality measurements, pollution levels, and temperature changes--is both reliable and tamper-proof. This reliability is key in assessing the health of marine ecosystems, supporting sufficient environmental protection, and guiding policy decisions. In addition to environmental monitoring, blockchain integration can be beneficial in industrial MIoT applications, particularly in fisheries and aquaculture. For example, tasks such as tracking and monitoring fish in confined spaces are optimized through the use of RFID tags, which transmit information to central servers for analysis. Blockchain technology further supports these processes by warranting secure data management and enabling traceability. IoT technology in fisheries also enhances activities such as aquaculture, fishing, and processing by enabling the real-time monitoring of environmental conditions and fish behavior, thereby promoting sustainable practices in the marine industry [16; 36]. Also among these efforts, the DIGI4 ECO project [47] further explores innovative digital solutions for enhancing marine ecosystem management (discussed in detail below). Another area where the IoUT proves to be valuable is disaster management, particularly in all phases of a disaster situation (preparedness, emergency response, recovery, and mitigation).