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Dried nori “superior diet” for long-spined sea urchin: U.S. study

A chokepoint  in the production of long-spined sea urchin (Diadema antillarum) has been removed, clearing initial steps toward the holistic approach to improving the long-term sustainability of Caribbean reefs. The study identified dried nori, a Japanese food staple, as a “superior diet” for juvenile culture. 

“Coral cover and D. antillarum population recovery are interdependent as corals provide habitat for D. antillarum shelter, and in turn, D. antillarum graze upon macroalgae and reduce competitive interactions that inhibit coral recruitment,” wrote Hassan et al. in the study, “Growth and foraging behavior of hatchery propagated long-spined sea urchins, Diadema antillarum: Implications for aquaculture and restocking.” It was published in Aquaculture Reports. 

Stocking hatchery-propagated, long-spined sea urchins is a priority option. Scant information on captive culture of the sea urchin from gametes, however, has hampered restoration efforts.

During the study conducted in Florida, hatchery-propagated D. antillarum juveniles were cultured using two diets, commercially available herbivore pellets and dried nori, with the presence/absence of stony coral (Acropora cervicornis) skeleton to understand how diet and habitat complexity affect growth and behavior of juveniles. 

The 99 per cent survival rate at the end of the experiment showed that diet or supplemental structure did not affect survival. The effect of the diet was demonstrated in growth and behaviour in juvenile.

Juveniles fed with dried nori gained more live weight and test diameter than cohorts on herbivore pellets after six weeks. The daily growth of juveniles fed dried nori was numerically faster than herbivore pellet.

Results showed that while juveniles can be cultured in captivity using both herbivore pellets and dried nori, macroalgae should be considered as the main ingredient of an optimal feed.

“We have observed a bottleneck in culture shortly after settlement when juveniles are yet to develop hardened mouthparts and appear to feed on benthic bacterial or algal biofilms,” they said.

There was no significant difference in live weight or test diameter in juveniles cultured with the presence or absence of supplemental coral structure.

“The presence of supplemental coral structure did not affect growth or behaviour but modulated habitat usage patterns.”