Marine Protected Area Size Calculator

This calculator estimates a minimum marine protected area by comparing three independent lower bounds and taking the largest. First, it computes the area needed to sustain a minimum viable population by dividing your target population size by the species' density per km². Second, it applies a species-area relationship (S = c·A^z) with an exponent z of 0.25 — a value commonly cited for marine systems — inverted to solve for the area needed to support your target number of species. Third, it simply checks that the focal species' own home range isn't larger than either of those.

Whichever of the three is biggest becomes the "core area," on the logic that an MPA too small for its single largest requirement fails regardless of how well it satisfies the others. A connectivity buffer percentage (default 30%) is then added on top of the core area to account for larval dispersal corridors and edge effects, since protected boundaries lose effectiveness for species and larvae drifting near the edge. The result is further scaled by a protection-level multiplier: strict no-take zones use a multiplier of 1 (no penalty), while partial-use areas are inflated by 1.8× and high-protection areas by 1.3×, reflecting the real-world finding that weaker enforcement needs more total area to achieve the same conservation outcome. Perimeter and patrol cost are then derived by treating the final area as a circle, which is a simplifying assumption — real MPA boundaries are rarely circular, so this patrol-cost number is only good for a first-pass order-of-magnitude sketch, not a figure to submit to a funding agency.