Effects of temperature, salinity, and prey organisms on the growth of three Pfiesteria-like heterotrophic dinoflagellates

Abstract

To clarify favorable environmental conditions for the population development of Pfiesteria-like dinoflagellates (PLDs), laboratory experiments were carried out using isolated strains of Cryptoperidiniopsis brodyi, Luciella masanensis, and Pfiesteria shumwayae. We examined the availability of 12 strains of phytoplankters which frequently cause red tides in coastal waters as food for these PLD species. In addition, the effect of temperature and salinity on the growth of these PLD species was also investigated. Three PLD species were able to feed on the cryptophyte Rhodomonas sp., the raphidophyte Heterosigma akashiwo and the dinoflagellate Akashiwo sanguinea, but not on thecate dinoflagellates. Among the three species tested, C. brodyi utilized the raphidophytes, Chattonella ovata, C. marina, and C. antiqua; however, two other species, L. masanensis and P. shumwayae, could not utilize these raphidophytes as food. The growth rates of PLD species generally increased with an increase in temperature in the range of 15 to 30°C. Below 10°C, their growth was negative. While the growth response of the three species as a function of the temperature was similar, that as a function of the salinity was different. The salinity ranges required for positive growth were 5–15, 5–25, and 5–30, respectively, for L. masanensis, P. shumwayae, and C. brodyi. The bloom of PLDs likely depends on high abundances of available phytoplankters in brackish waters when water temperature is >15°C.