Larval development and metamorphosis in the sea urchin Loxechinus albus (Echinodermata: Echinoidea): Effects of diet type and feeding frequency

Techniques presently used in the mass production of larvae and juveniles of the sea urchin Loxechinus albus require optimization of methods related to their feeding. For this reason, the present research evaluated the effects of the type of diet and the frequency of feeding on morphological development and larval survival, as well as on the success of larval metamorphosis. The effect of the diet type was assessed in an experiment with three microalgal diets (Chaetoceros calcitrans = C, C. calcitrans and Isochrysis galbana = CI and C. calcitrans, I. galbana, and Tetraselmis suecica = CIT). The effect of feeding frequency was assessed in a second experiment with three feeding regimes (daily feeding at normal ration-DN, feeding every second day at normal ration-SN, and feeding every second day at double ration-SD). Total larval growth and the growth of larval structures were affected by the type of food and by the feeding frequency. Larvae fed diets C and CI showed no significant difference in survival of competent larvae (mean ± SD: 48.8 ± 16.9 and 58.3 ± 14.4%) and in percent metamorphosis (59.3 ± 13.5 and 56.7 ± 10.3%). The size of the postmetamorphic sea urchins was significantly greater for the CI treatment (419.6 ± 35.4 μm) than for the C treatment (403.3 ± 31.6 μm). Larvae fed with CIT diet did not reach competence. Larvae fed at the DN regime reached competence in significantly greater numbers (46.0 ± 3.7%) than those fed with the SN regime (29.8 ± 5.5%) or the SD regime (31.4 ± 7.5%). There was no significant difference in the numbers of larvae achieving metamorphosis between regimes DN (49.3 ± 8.6%) and SD (57.3 ± 9.4%), but both means were greater than that of the SN regime (2.7 ± 2.1%). The postmetamorphic urchins from regime DN reached the largest size (413.9 ± 39.5 μm). The results suggest that daily larval feeding which includes a mixed diet of larger algal cells, including C. calcitrans but excluding T. suecica, may produce better results for large-scale production of competent larvae and juveniles of L. albus.