Spatiotemporal distribution and a survival strategy of harmful dinoflagellates Alexanderium spp. in Korean coastal waters and application to controlling scuticociliates

Abstract

Dinoflagellates play various roles in the marine ecosystem. They act as primary producers, prey, and predators. Moreover, they compete other microalgal groups using physical and/or chemical means to survive in coastal waters. As a result of the competition, they often dominate in coastal waters and form red tides or harmful algal blooms (HABs). Species of the genus Alexandrium is one of the most major phototrophic dinoflagellates to form HABs over the world. Some of them are lethal to human bodies as producing paralytic shellfish poisoning (PSP) toxins. However, in spite of their ecological and pathological importance, the distribution and ecophysiological characteristics of Alexandrium species have not been fully understood yet. Here, I explored both eco-physiological characteristics of Alexandrium species and an application utilizing Alexandrium species. First, the species-specific distributions of Alexanderium species in Korean coastal waters were analyzed using quantitative real-time PCR. Also, a survival strategy of Alexandrium species to resist their potential predators was studied. Finally, the possibility to control parasitic scuticociliates using the characteristics of Alexandrium species was explored. Each of the West, South, and East Sea of Korea has unique properties depending on oceanographic features, such as topography, currents, or influence of seasonal winds, etc. Also, seasonal characteristics of Korea are very clear, so the gap of its sea surface temperature between winter and summer is around 10-20 ℃. Therefore, depending on season and region, distribution patterns of Alexandrium species may be various in Korean coastal waters. This study shows the distribution patterns of 12 Alexandrium species in Korean coastal waters are different from each other. The difference may result from their physiological features responding to environment. Biologically, dynamics of the microalgae depend on their growth and mortality. The mortality of Alexandrium species have not well understood yet, while growths of them depending on environmental factors, such as light, nutrients, or temperature, have been relatively well known. This study shows that toxic effects of Alexandrium species to heterotrophic protists may be one of reasons Alexandrium species are distributed all over the world and frequently form HABs. In this study, some heterotrophic protists were lysed when incubated with Alexandrium species, and any of them did not feed on Alexandrium pohangense. Scuticociliatosis, caused by parasitic protistan pathogens known as scuticociliates, is one of the most serious fish diseases in worldwide marine aquaculture. In this study, to develop a safe method of controlling scuticociliate populations in aqua-tanks or small-scale natural environments, cultures of 16 phototrophic dinoflagellates including 11 species of the genus Alexandrium were tested to determine whether they were able to control populations of the common scuticociliates Miamiensis avidus and Miamiensis sp. isolated from Korean waters. Among the tested dinoflagellates, both cells and culture filtrates of Alexandrium andersonii effectively killed M. avidus and Miamiensis sp. Through above field data analysis and co-incubation experiments with heterotrophic protists and scuticociliates, this study is expected to deepen comprehension of Alexandrium species and marine ecology. Also, it provides a hint to solve a problem of fisheries about scuticociliatosis.