BACKGROUND AND OBJECTIVES: Sustainability assessments of multi-activity coastal areas generally evaluate each utilisation activity independently, leaving interdependencies unaccommodated and risking biased contribution estimates under conventional hierarchical weighting. This limitation is consequential where activities compete for shared ecological space and resources, as in tropical coastal zones of developing countries. The study objectives were to develop an activity-based sustainability assessment framework integrating hierarchical and network-based multi-criteria weighting to estimate the relative contribution of three activities: small-scale capture fisheries, vannamei shrimp ponds, and coastal tourism, in the coastal area of Pariaman City, Indonesia.METHODS: Assessments covered ۳۶ indicators across four sustainability dimensions: ecological, social, economic, and governance, with a ۱۷-node interdependence network built from ۱۴ indicators showing cross-activity dependencies through shared resources and identified causal pathways. Fifteen experts across three sectoral panels provided hierarchical weighting for each activity independently, and a subset of five experts with cross-sectoral competence provided network-based weighting to capture inter-activity influence; all paired-comparison matrices met the required consistency threshold. The resilience of the regional index to weighting uncertainty was tested through sensitivity analysis.FINDINGS: Network-based weights ranked vannamei shrimp ponds above small-scale capture fisheries and coastal tourism, but far less dominantly than under hierarchical weighting, which treated ponds as an extreme outlier by ignoring their negative influence on shared water quality and spatial resources. Each activity's contribution to the regional index, valued at ۰.۵۵۴, was nearly equal across the three activities, showing that intervention priority cannot be set from individual activity performance alone but must account for interdependent cross-activity contributions. The moderately sustainable category held consistently across sensitivity scenarios, although activity contribution order proved more sensitive to weighting uncertainty.CONCLUSION: Accounting for interdependence corrects the hierarchical approach's over-estimation of vannamei shrimp ponds and reveals a greater contribution from small-scale capture fisheries and coastal tourism than independent estimates suggest. An activity's sustainability contribution to the region cannot be accurately assessed without considering its interdependence with other activities, the main value of this activity-based framework as a decision-support approach for coastal sustainability assessment.