Paralytic shellfish toxins (PSTs) toxification of zooplankton in association with appearance of toxic dinoflatellate genus Alexandrium, and PSTs production according to temperature and salinity condition of the A. catenella and A. pacificum

Abstract

Alexandrium catenella and A. pacificum produce Paralytic Shellfish Toxins (PSTs) such as saxitoxin and analogues which can cause paralysis and eventula death. Over the last several decades, PSTs have become more frequent throughout the world due to an increase in water temperatures caused by global warming. In Korea, PST occurs every spring centered on Jinhae Bay. As a result, exceeding the standard value of prohibited shipments of toxins (80 µg/100 g) in bivalves aquareculture around April caused economic damage and raised social concerns. Ingestion of toxic dinoflagellates containing PST toxins by zooplankton leads to the transmission of these toxins by zooplankton to high trophic levels. In this study, growth characteristics and changes in PST by caused A. catenella and A. pacificum were observed at different water temperatures and salinities in laboratory. The purpose is to provide the necessary basic information for the A. catenella and A. pacificum emergence forecast system. Moreover PST changes in suspended matter and zooplankton were measured around Jinhae Bay. To basic data for predicting PSTs of bivalve, this study was conducted to estimate the effects temperature and salinity on the growth and PSTs production of A. catenella and A. pacificum in the laboratory, and to temporal and spatial variations characteristics of PST of the suspended matter and zooplankton collected from 5 stations of Jinhae Bay. Based on laboratory culture experiments, the changes in growth rate and PST of toxic dinoflagellates A. catenella (JM-1) and A. pacificum (LIMS-PS-2611) were investigated under different water temperature and salinity conditions. The maximum growth rate (0.34/day) of A. catenella was observed under 15℃ and 30 psu. Optimal growth (≥ 70% of maximum growth rate) was obtained between 10-20℃ and 25-35 psu. Maximum toxin content was observed under 25℃ and 35 psu, and the toxin content increased with the increase of salinity. Among the PSTs of A. catenella, the principal toxins were C1+2 in N-sulfocarbamoyl toxin group and neoSTXs and GTX1+4 in the carbamate toxin group. High toxin contents were measured under the temperature and salinity conditions of the maximum growth rate. Also the maximum growth rate (0.38/day) of A. pacificum was observed under 25℃ and 30 psu. Optimal growth (≥ 70% of maximum growth rate) was obtained between 20-30℃ and 25-35 psu. Maximum toxin content was observed under 20℃ and 30 psu, and the toxin content increased with the increase of salinity. Among the PSTs of A. pacificum, the principal toxins were C1+2 and GTX5 in N-sulfocarbamoyl toxin group, and minor components were characterized as neoSTX in the carbamate toxin group. Low toxin contents were measured under the temperature and salinity conditions of the maximum growth rate. In addition, zooplankton and suspended matter were collected in Jinhae Bay, a sea area where PST occurs frequently in spring, for PST detection. The water temperature at the time of sample collection was known to be between 8-15℃ and the salinity was between 31-33 psu. Based on the results of the samples collected in the field, as water temperature increased, the toxin content and toxicity of suspended matter increased, but decreased over time. Among the PSTs of suspended matter, the principal toxins were C1+2 in the N-sulfocarbamoyl toxin group. Pearson correlation analysis showed a significant positive correlation between the amount of PST toxin content detected in suspended matter and the cell density of toxic dinoflagellates in Jinhae Bay (r = 0.75; p < 0.05; n = 33). In Korea, this was the first reported of PSP intoxication in zooplankton. There was an increasing trend in toxin content and toxicity among zooplankton as the water temperature increased. Among the PSTs of zooplankton, the principal toxins were GTX1+4 in the carbamate toxin group. Pearson correlation analysis showed a significant positive correlation between the amount of PST toxin content detected in zooplankton and the cell density of toxic dinoflagellates in Jinhae Bay (r = 0.70; p < 0.05; n = 35). There was also a significant positive correlation between the amount of PST toxin content detected in zooplankton and the PST toxin content detected in suspended matter (r = 0.75; p < 0.05; n = 35). Based on the above experimental results, A. catenella and A. pacificum are the causative species that lead to the emergence of PST every spring. Zooplankton PST toxification was associated with the appearance of the toxic toxic dinoflagellates Alexandrium in spring. Therefore the results of this experiment can provide basic data for the PST prediction system.