Governance of dietary microplastic exposure risk in marine ranching in the context of climate change.

Aquaculture facilities in marine ranches continuously fragment and release microplastics, which accumulate in filter-feeding shellfish and enter residents' diets. Climate change intensifies this pathway. Warming and ultraviolet exposure accelerate the fragmentation of aquaculture plastics, while typhoons damage facilities and release microplastics in pulses and raise the health expenditure at stake for the government, enterprises, and households. This study constructs a tripartite evolutionary game model of the government, marine ranching enterprises, and consumers. Numerical simulation is used to examine how each actor's strategies shape the system's convergence path and speed and long-term residual exposure. The findings are as follows. Whether the government can sustain regulation depends solely on whether the process-based assessment payoff covers the cost of regulation, because the outcome-based performance payoff can be free-ridden and cancels out in the payoff differential. Once subsidies exceed this government-side ceiling, they crowd out regulation and cause exposure to rebound. Enterprises' tolerance for plastic-reduction costs follows a tiered threshold structure, and the simultaneous phase-down of regulation and subsidies readily triggers a governance relapse, so a mature market premium mechanism must be in place first. Consumer participation is subject to a self-undermining mechanism whereby governance success erodes the incentive to participate. Sustaining it requires lowering information and oversight costs rather than heightening risk perception. Information disclosure relaxes the consumer participation constraint in all configurations without fiscal expenditure, making it the most cost-effective instrument. When none of the equilibrium conditions holds, the system oscillates periodically, and population-average exposure underestimates both the cumulative health cost and the risk borne by highly exposed subgroups. The results lock in the government's presence through process-based assessment, cultivate market premiums before phasing down regulation, and integrate microplastic source control into climate adaptation planning for marine ranching.