Effects of macroalgae Gracilaria lemaneiformis and Saccharina japonica on growth and gonadal development of the sea urchin Strongylocentrotus intermedius: New insights into the aquaculture management in southern China

Taking advantage of the seasonally appropriate water temperature in southern China is an important approach to expanding Strongylocentrotus intermedius aquaculture for the increasing market demand. However, appropriate diets remain largely uninvestigated and seed supply is in shortage, leaving the most serious problems of S. intermedius aquaculture in southern China unaddressed. Here, a feeding experiment was conducted for ∼6 months (from November 2018 to May 2019) to compare the somatic and gonadal growth, as well as gonadal development of S. intermedius (∼30 mm of test diameter) fed either macroalgae Gracilaria lemaneiformis or Saccharina japonica at the temperatures simulating water those off southern China coast (Fuzhou, 119°50′ E, 26°24′ N). Test size, wet body weight, specific growth rate, lantern size, wet gut weight and gonad yield of S. intermedius fed S. japonica were all significantly larger than those of sea urchins fed G. lemaneiformis. The present results indicate that long-term feeding G. lemaneiformis is unacceptable for aquacultural S. intermedius in southern China, because of the inefficiency of supporting somatic and gonadal growth. Saccharina japonica may suffice as a suitable diet for the aquaculture of S. intermedius in southern China. Further, spent gonads were observed in S. intermedius fed G. lemaneiformis in May 2019, meanwhile all gonads of individuals fed S. japonica remained in the premature stage. This suggests that G. lemaneiformis displays a promising potential for accelerating gonadal development of S. intermedius and subsequently supports the seed production of sea urchins in spring in southern China. The present study provides valuable information into the aquaculture management of S. intermedius in southern China.