The potential value of different species of benthic diatoms as food for newly metamorphosed sea urchin Strongylocentrotus intermedius

Eight benthic diatom species were isolated from coastal seawater of Dalian, Liaoning, China and their potential as food for aquaculture was evaluated based on their cell characteristics and effect on settlement, growth and survival of newly metamorphosed S. intermedius. All species were within the size range ingested by juvenile sea urchins, i.e. 6.74–35.89 μm. Cellular growth rates ranged from 0.44 divisions day− 1 (Rhaphoneis surirella) to 0.73 divisions day− 1 (Navicula seminulum). Eight monocultures of benthic diatoms, mixed diatoms (an equal mixture of the eight species), natural occurring diatoms, and a control (no diatoms) were used as substrata and food to evaluate larval settlement and juvenile growth of S. intermedius. Larval settlement rates differed significantly between experimental substrata after 24 h (p < 0.05) and 48 h (p < 0.01). A significantly higher number of larvae settled on R. surirella (53.34% ± 2.22 SE) and Nitzschia sp. (58.32% ± 5.00 SE) compared to N. corymbosa (15.00% ± 0.56 SE), A. coffeaeformis (8.34% ± 2.78 SE) and the control (5.00% ± 1.67 SE) (p < 0.05) plates. Juveniles could detach benthic diatoms with both weak and strong adhesion on the sixth day after settlement when the mouth opened and the teeth could be seen. Greatest growth (test diameter) occurred on N. corymbosa (631.64 μm ± 1.14 SE). Survival of juvenile was also greatest on N. corymbosa (95.83% ± 1.05 SE). These results indicate the effectiveness of Nitzschia sp., R. surirella, A. proteus var. oculata and N. corymbosa as single species over mixed diatoms and natural diatoms in larval settlement and juvenile growth of S. intermedius. Thus, Nitzschia sp. has the best potential diet for larval settlement and juvenile growth of S. intermedius. R. surirella can be used as cue to induce larvae settlement, and A. proteus var. oculata and N. corymbosa can be used as food for growing juveniles. Nitzschia sp., R. surirella, A. proteus var. oculata and N. corymbosa can be used as good food by sea urchin hatcheries or nurseries, which have traditionally operated with natural diatom films in China, to improve growth and survival of post-larvae, and increase the consistency of production.