Distribution of the heterotrophic dinoflagellate Pfiesteria piscicida in Korean waters and its consumption of mixotrophic dinoflagellates, raphidophytes and fish blood cells

To explore the distribution of Pfiesteria piscicida in Korean coastal waters, we analyzed the morphology and DNA sequence of several isolates collected from 6 locations along the southern and western Korean coasts. We also investigated the prey species consumed by a Korean isolate and determined the growth and ingestion rates of P. piscicida when it fed on the dinoflagellate Amphidinium carterae, an unidentified cryptophyte species, and the raphidophyte Heterosigma akashiwo. Additionally, these parameters were measured when the isolate was fed perch blood cells and the cryptophyte Rhodomonas salina. Furthermore, we calculated grazing coefficients by combining field data on abundance of P. piscicida (and Pfiesteria-like dinoflagellates) with laboratory data on ingestion rates. The DNA sequence of a P. piscicida isolate from Masan Bay was identical to USA isolates, whereas DNA sequences of isolates from Busan, Incheon, Kunsan, Kwangyang, and Yeosu differed by 1 bp from USA isolates. Among the prey offered, P. piscicida was able to feed on all naked mixotrophic dinoflagellates, the smallest thecate mixotrophic dinoflagellates Heterocapsa rotundata, and all raphidophytes, but not on large thecate dinoflagellates. Perch blood cells were the optimal prey. Maximum growth rates of P. piscicida fed on perch blood cells, R. salina, A. carterae, the cryptophyte, and H. akashiwo were 1.74, 1.41, 1.22, 1.15, and 1.10 d–1, respectively. The maximum ingestion rate of P. piscicida when fed perch blood cells (4.3 ng C predator–1 d–1) was much higher than those when fed R. salina, H. akashiwo, A. carterae, or the cryptophyte (0.4 to 1.7 ng C predator–1 d–1). Calculated grazing coefficients on co-occurring Amphidinium spp., H. akashiwo, and cryptophytes were up to 1.07, 0.45, and 0.22 h–1, respectively. Our results suggest that grazing by P. piscicida potentially has a considerable effect on algal populations.