Cost-effectiveness of tourism-led coral planting at scale on the northern Great Barrier Reef

Abstract

Stakeholder-led coral reef restoration efforts, aimed at locally retaining or rebuilding coral populations, have rapidly grown over the last two decades. However, the cost-effectiveness—and in turn viability—of coral restoration projects remains rarely reported. We therefore evaluated coral planting (often termed “outplanting”) cost-effectiveness across the first 3.5 years of the Coral Nurture Program (CNP), a coral restoration approach integrated within tourism operations on Australia's Great Barrier Reef. CNP operator activity reporting forms (63,632 corals planted, 5 tourism operators, and 23 reef sites) were used to opportunistically calculate coral planting costs (PC; US$ coral−1 trip−1) for “routine” planting versus when additional stewardship activities—that regulate planting effectiveness—were undertaken (e.g., nursery maintenance). Mean PC (±standard error) was US$2.34 ± 0.20 coral−1 trip−1 (ranging US$0.78–6.03, 5th–95th percentile), but increased 2- to -6-fold on trips where nursery propagation, site maintenance, or staff training was conducted to support planting efforts. The “realized” cost (PCR) of establishing coral biomass was subsequently determined by evaluating survivorship of planted corals across space (9 sites, single survey timepoint, n = 4,723 corals up to 3 years old) or over time (2 sites, over 9–12 months, n = 600 corals), resulting in costs increasing from PC to PCR by 25–71%. We demonstrate how integration of practices into tourism operations creates potential for cost-effective coral planting at “high-value” tourism reef sites, and discuss important steps for improving cost-accounting in stakeholder-led restoration programs that may be similarly positioned to routinely determine their cost-effectiveness.