Abstract: In this study, we investigated whether Zoanthus sp. feed on two common microalgae, Platymonas subcordiformis and Isochrysis galbana, using the methods of carbon clearance rate, DNA marker, and histological analyses. The results showed that carbon clearance rate of I. galbana by Zoanthus sp. was significantly higher than that of P. subcordiformis, which were 0.44 and 0.11 pg·mL^-1·polyp^-1·h^-1, respectively. 162 bp of 18S rRNA gene from P. subcordiformis and 442 bp of enoyl-ACP reductase gene from I. galbana were used as molecular nutrition markers, both of them were successfully amplified from the Zoanthus sp. fed by both algae species. Results of the histological analyses demonstrated that pholyp from feeding group showed a widen mesentery. Lots of food vacuoles presented in tissues of mesentery and gastrodermis. Undigested cell body of P. subcordiformis and I. galbana could also be found in some food vacuoles around siphonoglyphe as well as the gastrodermis in body wall. Therefore, results from carbon clearance rate, histological and DNA marker results all indicated that Zoanthus sp. could feed on P. subcordiformis and I. galbana.

Key words: Zoanthus sp., heterotrophic nutrition, Platymonas subcordiformis, Isochrysis galbana, molecular nutrition indicator