Sea urchin aquaculture using vegetable waste offers a nature-based solution (NbS) that addresses coral reef protection, organic waste recycling, and sustainable seafood production. In Hong Kong, overgrazing by long-spined sea urchins (Diadema setosum) and daily vegetable waste generation pose interconnected environmental challenges. This study examines the techno-economic feasibility of a sea-cage grow-out system using locally sourced vegetable waste as feed, designed for small-scale fishers.
A two-phase experiment screened nine vegetable waste types for feed acceptance, followed by a sea-cage trial testing five dietary treatments over two months. Banana peel emerged as the most cost-effective feed, delivering superior growth (+10.95 g) while being widely available as zero-cost waste. However, an unexpected "Red Spot Syndrome" outbreak revealed a critical trade-off: single-ingredient diets maximized short-term growth but led to higher disease-related mortality, while compound feed, despite poorer growth, sustained the highest post-outbreak survival (28% vs. 8–20% in single-feed groups).
We recommend a precautionary feeding protocol centered on a compound feed base to maintain nutritional adequacy as passive defense against disease, with banana peel as a supplemental cost-reduction option pending further research. Simple monitoring indicators—weight stagnation, spine condition, and water temperature—are proposed for early health detection.
Cost-benefit analysis confirms that this sea-cage model substantially reduces operational costs by eliminating energy-intensive water treatment, making it accessible to fishing cooperatives. By transforming an ecological pest into a revenue-generating resource, this Hong Kong-tested approach contributes directly to the UN Decade of Ecosystem Restoration.
Keywords: sea urchin aquaculture, vegetable waste recycling, nature-based solutions, adaptive management, fisher livelihoods, Hong Kong

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