Pronounced effect of red seaweed (Gloiopeltis coliformis) diet on intake and growth of small sea urchin Mesocentrotus nudus

Abstract Body growth was measured for the small sea urchin Mesocentrotus nudus fed on the frozen or dried diets of three species of small red or brown seaweeds growing on intertidal reefs: Gloiopeltis coliformis (GF, frozen; or GD, dried), Mazzaella japonica (MF, frozen only) and Scytosiphon lomentaria (SlF, frozen only). The effects of these different seaweed preparations were investigated in comparison with sea urchins fed on frozen Saccharina japonica (SjF) kelp as a positive control. All diet experiments were conducted for two months during October–December. GF contained high levels of crude protein (16.2%) and carbohydrate (59.4%) which were not significantly different from MF. The sea urchins fed on GF or GD increased in weight significantly more than those fed other diets. Significantly higher diet conversion efficiencies led to the highest body increase rates. Test diameter increased by approximately 7 mm and body weight doubled. The cost effectiveness of feeding wild M. nudus juveniles can be greatly improved by using G. coliformis thalli, which remain after harvesting (when they are of no commercial value) and have a significantly high dry-weight to wet-weight ratio (facilitating air-drying for efficient diet storage).