Under global change and intensive coastal development, species- or site-based management struggles to address nonlinear responses, cross-scale interactions, and deep uncertainty in coastal social-ecological systems. For sustainable coastal governance, a central challenge is to move beyond land-sea separation and fragmented transboundary governance, and to treat social systems as part of the evolving process of marine conservation.

Focusing on Sousa chinensis conservation in the Pearl River Estuary from 2005 to 2025, this study employs state-space universal dynamic equations (SS-UDE) to uncover nonlinear transitions among species activity, habitat conditions, human uses, and governance responses. It examines how land-sea pressures are absorbed, amplified, or delayed within the ecosystem, and how ecological feedbacks are perceived, interpreted, and reorganized through the social system. By placing ecological and governance variables within the same dynamic trajectory, the study traces feedback accumulation, threshold approach, and institutional adjustment across the land-sea continuum.

Results suggest that declines in dolphin sightings are more likely to occur in transitional zones where land-based inputs, nearshore development, and marine uses have already reshaped system conditions, while governance responses have not yet caught up. Transboundary governance can widen this lag by redistributing ecological signals across jurisdictions, standards, and policy cycles. Ecological signals therefore become actionable only when they enter policy learning and social negotiation, where they can inform adjustments to conservation boundaries, marine-use regulation, land-based pollution control, and cross-jurisdictional collaboration.

This study proposes shifting the object of governance from a single population or protected area to a social-ecological continuum that links watersheds, estuaries, nearshore waters, and transboundary institutions. Conservation boundaries should be revised iteratively as habitat conditions change; transboundary collaboration should maintain feedback channels around ecological connectivity; and land-based governance and marine-use regulation should be aligned within a shared risk framework. It offers a transferable case for adaptive governance in other highly developed estuaries.