Diet and salinity effects on larval growth and development of the sand dollar Mellita isometra

Summary

Larval growth and development of Mellita isometra were investigated by assigning larvae to several single- and mixed-algal diets, three levels of salinity and salinity-diet combinations in the laboratory. Larvae-fed Isochrysis galbana were significantly smaller, developed significantly smaller rudiments and had significantly lower protein content than larvae in all other treatments. Larvae fed Chaetoceros muelleri or the mixed-algal diet of I. galbana and D. tertiolecta developed significantly faster, had significantly bigger rudiments and significantly higher protein content. Eight-arm larvae fed the mixed-algal diet consisting of two small algae, Isochrysis galbana and Chaetoceros muelleri, were significantly wider than those fed mixed-algal diets consisting of a small and a large algal cell (I. galbana and Dunaliella tertiolecta or C. muelleri and D. tertiolecta). No differences were observed in rudiment size and protein content of advanced 8-arm larvae fed these three mixed-algal diets. Larvae maintained at 27%_o produced significantly bigger rudiments. Larvae maintained at 32%_o and fed C. muelleri were significantly longer, wider and had longer posterodorsal arms than larvae in the other two treatments. In conclusion, a single-algal diet consisting of C. muelleri was just as effective as a mixed-algal diet for optimal larval growth and development of the sand dollar M. isometra. I. galbana was ineffective regardless of salinity. Therefore, the nutritional quality of an alga rather than its size may have a greater effect on larval development of echinoderms.

Key words:

• Sand dollars
• algal diets
• salinity
• larvae
• growth