Gulfweed Sargassum horneri is an alternative diet for aquaculture of juvenile sea urchins Strongylocentrotus intermedius in summer

Food shortage of kelp Saccharina japonica is one of the most serious concerns for aquaculture of juvenile Strongylocentrotus intermedius in summer. For the first time, the present study provides a cost-effective approach to addressing this problem for field aquaculture. We found juvenile S. intermedius fed gulfweed Sargassum horneri (group S) had significantly higher food consumption and better growth than those fed S. japonica (group K). S. intermedius fed S. horneri and S. japonica (group M) showed significantly larger test diameter, test weight, body weight, and higher specific growth rate than those fed S. japonica only (group K), but not significantly larger or higher than those fed S. horneri only (group S). Further, gonad weight and index were significantly smaller in the group S than in the groups K and M, which indicates that S. horneri is not only a better diet for aquaculture of juvenile sea urchins S. intermedius, but leads a suitable energy allocation for cultured juvenile S. intermedius in summer. According to the present study, full replacement of S. japonica with S. horneri and the feeding regime of S. horneri and S. japonica are both acceptable for juvenile S. intermedius aquaculture in summer. Therefore, we suggest aqua-farmers choose suitable replacement according to the local availability and cost of S. horneri and S. japonica in summer.