Feeding and growth of the new mixotrophic dinoflagellate Gymnodinium sp. GSTY2405 and the prey spectrum extension of its sister species Gymnodinium smaydae

Mixotrophic dinoflagellates play critical roles in marine food webs and biogeochemical cycles. To investigate the feeding of the newly described mixotrophic dinoflagellate Gymnodinium sp. GSTY2405, its feeding mechanism and edible prey species were explored. Its growth and ingestion rates on the optimal prey Heterocapsa rotundata as a function of prey concentration were also measured. To compare the feeding behaviors of Gymnodinium sp. GSTY2405 and its sister species Gymnodinium smaydae, 11 algal species not previously tested for feeding by G. smaydae were examined. Gymnodinium sp. GSTY2405 fed on prey using a peduncle, like G. smaydae. Among 28 algal prey species offered, Gymnodinium sp. GSTY2405 ingested dinoflagellates but did not feed on the prymnesiophyte, cryptophyte, chlorophyte, raphidophyte, or diatom. Gymnodinium sp. GSTY2405 was able to feed on 15 of 21 dinoflagellate species, including Alexandrium fraterculus, Alexandrium minutum, Alexandrium tamarense, Amphidinium carterae, Lingulaulax polyedra, and four Prorocentrum species that G. smaydae does not feed on. The number of edible prey species for Gymnodinium sp. GSTY2405 is greater than that for G. smaydae. While the autotrophic growth rate of Gymnodinium sp. GSTY2405 was − 0.08 d− 1, the maximum growth and ingestion rates on H. rotundata were 0.46 d− 1 and 0.74 ng C predator− 1 d− 1, respectively, which are considerably lower than those of G. smaydae on the same prey. Therefore, Gymnodinium sp. GSTY2405 may trade off the kinds of its edible prey species with growth and ingestion rates. These results provide a basis for better understanding the ecological roles of mixotrophic dinoflagellates in marine ecosystems.