Assessing Vegetable Diets on the Growth of Reared Juvenile Paracentrotus lividus: Implications for Population Restoration Initiatives

The demand for the purple sea urchin Paracentrotus lividus has led to the decline of its wild populations, increasing interest in cultivating this species for commercial purposes and ecological restoration purposes. Consequently, there is a need to expand knowledge about the optimal conditions for sea urchin aquaculture, particularly regarding food regimes. Here, we evaluate the effects of several vegetable diets on the survival and growth of early juveniles of P. lividus. Using an outdoor experimental assay, we fed early juveniles (5–6.5 mm) various diets: fresh algae (Ulva sp.), aquaculture pellets, and vegetables (carrot, spinach, and maize) presented as individual or mixed diets (equal mass proportions). All diets were provided ad libitum in equal mass proportions. After 120 days, the pellet-fed urchins showed good growth but a high mortality rate (>40%). The Ulva sp. diet, considered the control regime mimicking wild sea urchin diet, resulted in low mortality but poor growth performance (maximum of 10.92 ± 1.94 mm in diameter and 0.68 ± 0.26 g in weight). In contrast, plant-based diets, especially those containing maize, led to the highest growth and lowest mortality rates (<5%). Notably, the triple mixed diet (carrot–spinach–maize) resulted in a threefold size increase, as the P. lividus juveniles reached 15 mm in 4 months. This study demonstrates the effectiveness of inexpensive, ready-to-use vegetable-based diets in optimizing rearing protocols for early juveniles of P. lividus. It offers preliminary insights into dietary preferences to rapidly attain an adequate release size for purple urchin aimed at restocking wild populations and balancing aquaculture and ecological restoration needs.