Sustainable Marine Structures

Marine aquaculture siting in tropical coastal waters is usually treated as a scoring problem: criteria are weighted, cells are ranked, and constraints enter as low scores that a high score elsewhere can offset. Where the sea is already allocated to tourism, conservation, shipping and customary fishing, this treatment misrepresents the decision, because prior claims are not weak preferences. This paper formulates a screening framework built on the opposite premise. Six stages are applied in sequence, each operating only on what survives the stage above it: biophysical suitability by weighted overlay; a spatial union of non-compensatory exclusions; an operational feasibility screen; a nitrogen and phosphorus mass balance that sets a production ceiling; system-specific discounted cash-flow analysis at scales appropriate to each technology; and a composite evaluation reported under four weighting schemes. The framework is specified completely by ten governing equations, four pairwise comparison matrices with consistency ratios between 0.017 and 0.026, membership functions for every criterion, and a sixteen-parameter mass-balance set and is demonstrated through a worked example for a stipulated four-zone tropical island setting of 9,184 km2. In the demonstration, 68.6% of the evaluated area is biophysically suitable; exclusions and the operational screen remove a further 3,456 km2, and 31.0% remains developable; two-thirds of the excluded area is attributable to competing use rather than to biophysical unsuitability. Nitrogen binds in only one of the four zones, and the two-dimensional composite ranks the zones identically at first and last place under every weighting scheme tested, with only the middle two positions being weighting-dependent. The worked example uses stipulated geometry and stated parameter values throughout and is not an assessment of any actual location.