The sea urchin Diadema antillarum is an ecologically vital herbivore with a critical role of consuming competitive macroalgae in Western Atlantic and Caribbean reef systems. With limited numbers due to a species-wide die off in the 1980s, the urchin is a prime candidate for restoration aquaculture. However, gaps in rearing knowledge, specifically with newly settled juveniles, obfuscate protocols for restoration-scale production. By examining the weaning point at which juvenile urchins shift from eating micro- to macroalgae, using both D. antillarum and a sympatric Caribbean sea urchin with noted differences in development, Lytechinus variegatus, we have clarified complexities in diet, survival, and developmental milestones.
A factorially designed experiment with juvenile D. antillarum used two feeding classes (micro and macro) and two size classes of juveniles (> 1.5 mm and < 1.5 mm test diameter (TD)). Two additional experiments involved the same two feeding classes at two different size classes of L. variegatus (< 1.0 mm and between 1.0 and 1.5 mm TD). The resulting data indicate juvenile D. antillarum shift to larger diets after reaching 1.5 mm in TD and are unable to eat larger food items prior to this point. Juvenile L. variegatus shift to larger diets by 1.0 mm TD and face high juvenile mortality, which stabilizes once juveniles reach that size threshold. By illuminating the intricacies in rearing early juvenile sea urchins, making the leap to increased production for species like D. antillarum becomes more feasible. These experimental methodologies and findings are broadly applicable to rearing juveniles through the difficult early life stages across sea urchin aquaculture.