Valorization of the Invasive Macroalgae Rugulopteryx okamurae as a Functional Ingredient in Formulated Feeds for Sea Urchin (Paracentrotus lividus) Aquaculture

Fishes

Paulo Rema, Subramanian Saravanan, Benjamin Armenjon, Constant Motte and Jorge Dias.

Rodrigo Brandão, João Araújo, Valentina Bosqueiro Martin, Jorge Dias, Gonçalo Silva, Michael Viegas, Florbela Soares and Pedro Pousão-Ferreira.

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Sea urchin (Paracentrotus lividus) echinoculture offers a promising solution to meet high gonad demand and mitigate overfishing. Concurrently, the invasive seaweed Rugulopteryx okamurae threatens coastal ecosystems. This study evaluated R. okamurae as a functional feed ingredient in P. lividus aquaculture across two consecutive trials to assess somatic growth, survival, gonadal development (GSI), and protein retention. Trial 1 tested dried macroalgae (R. okamurae vs. control Ulva spp.) against formulated diets (Ulva-based control vs. Mix Feed containing 10% R. okamurae + 10% Ulva spp.). Trial 2 assessed three formulated feeds: Ulva-based Feed (20% Ulva), Mix Feed (10% Ulva + 10% R. okamurae), and a R. okamurae-based Feed (20% R. okamurae). Raw dry R. okamurae proved ineffective, causing biomass loss (−1.65%) and negligible gonadal yield (GSI < 1%). Conversely, incorporating R. okamurae into formulated diets completely neutralized its raw anti-nutritional constraints. Formulated feeds achieved high survival (>94%) and significantly superior growth across both trials (GSI > 12%). Crucially, increasing dietary inclusion to 20% R. okamurae in Trial 2 yielded zootechnical performance and gonadal development comparable to Ulva-based controls, while demonstrating high gonadal protein retention (>50% DM). Within a Circular Economy framework, R. okamurae can be successfully upcycled into high-value aquaculture feeds (up to 20% inclusion) without compromising sea urchin performance.