Dynamics of the Toxic Dinoflagellate Alexandrium pacificum in the Taiwan Strait and Its Linkages to Surrounding Populations

Abstract

The dinoflagellate Alexandrium pacificum can produce paralytic shellfish toxins and is mainly distributed in the Pacific. Blooms of A. pacificum have been frequently reported in offshore areas of the East China Sea, but not along the coast. To investigate the bloom dynamics of A. pacificum and their potential origins in the Taiwan Strait, we performed intensive sampling of both water and sediments from 2017 to 2020. Ellipsoidal cysts were identified as A. pacificum and enumerated based on microscopic observation. Their abundances were quite low but there was a maximum of 9.6 cysts cm−3 in the sediment near the Minjiang River estuary in May 2020, consistent with the high cell abundance in the water column in this area. Cells of A. pacificum were examined using a quantitative polymerase chain reaction, and they appeared to be persistent in the water column across the seasons. High densities of A. pacificum (103 cells L−1) were observed near the Jiulongjiang and Minjiang River estuary in early May 2020, where high nutrients (dissolved inorganic nitrogen and phosphate), and relatively low temperatures (20–21 °C) were also recorded. Strains isolated from the East and South China Sea exhibited the highest division rate (0.63 and 0.93 divisions d−1) at 20 and 23 °C, respectively, but the strain from the Yellow Sea showed the highest division (0.40 divisions d−1) at 17–23 °C. Strains from the East and South China Sea shared similar toxin profiles dominated by the N-sulfocarbamoyl toxins C1/2, but the strain from the Yellow Sea predominantly produced the carbamoyl toxins GTX1/4 and no C1/2. Our results suggest that both cyst germination and persistent cells in the water column might contribute to the bloom formation in the Taiwan Strait. Our results also indicate that the East and South China Sea populations are connected genetically through similar toxin formation but separated from the Yellow Sea population geographically.

Deciphering organic matter distribution by source-specific biomarkers in the shallow Taiwan Strait from a source-to-sink perspective

“…As one of typical marine phytoplanktonic biomarkers in marginal sea systems, the distribution of dinoflagellate-sourced dinosterol in the TS seafloor shows analogous traits as the three terrestrial biomarkers, which show higher contents where fine particles are deposited along the southern distal of the Min-Zhe mud belt (Figure 5C). This implies that dinoflagellate-produced OM buried in the TS shows the same behavior as the terrestrial materials during the predeposition histories, which is also consistent with a massive dinoflagellate algal bloom breakout in the Yangtze River estuary and its adjacent shelf (Zhang et al, 2015) and a high density of dinoflagellate cysts commonly buried in muddy sediments (Dale, 1976;Yamaguchi et al, 2002;Liu et al, 2021b). Therefore, better preservation in muddy sediments should be attributed to high abundances of dinoflagellate cysts and associated OM.…”

Co-occurrence of Alexandrium minutum (Dinophyceae) ribotypes from the Chinese and Malaysian coastal waters and their toxin production

“…NEO and STX were only detected in strains from the Yellow Sea and New Zealand (MacKenzie and Berkett, 1997; present study). Toxin profiles of strains from Daya Bay, China and Penninsular Malaysia were distinct, as the former was dominated by GTX2/3 and the latter by GTX1/4 (Lim et al, 2006;Liu et al, 2021a;present study). Several strains of unknown ribotypes seem to follow this rule as well.…”

“…Currently, Western Pacific A. minutum strains with the molecular sequences available are still limited, thus future efforts are needed to reveal the biogeography of these novel ribotypes. All examined A. minutum strains are toxic and produce carbamoyl toxins dominated by GTX1/4 except one strain of ribotype D. This contrasts with the common toxic PSTs producing A. pacificum and Gymnodinium catenatum in the region, which produce predominantly less potent C1/2 toxin (Liu et al, 2020a(Liu et al, , 2021a, highlighting the potential risk of shellfish poisoning by A. minutum and the importance of routine monitoring.…”

“…Ribotype C prefers warmer waters thus the presence in the water might be the source of GTX1/4 detected in the phytoplankton samples from a station adjacent to the Changjiang River in the summer (Liu et al, 2020b). Although Alexandrium pacificum and Gymnodinium catenatum Graham have been reported in this area and were suspected to be the species contributing to the toxicity, they produced predominantly C1/2 with little or no GTX1/4 (Liu et al, 2020a(Liu et al, , 2021a. Strain BK280604 (ribotype D) did not produce any detectable toxin (<0.048 pg cell − 1 ), comparable to the detection limit (0.035 pg cell − 1 ) of a nontoxic strain from Scotland (Brown et al, 2010).…”

“…Cell pellets were resuspended in 500 µL 0.03 M acetic acid and homogenized with 0.9 g of lysing matrix D by reciprocal shaking at 6.5 m s The supernatants were transferred to spin-filters of 0.45 µm pore-size (Millipore Ultrafree, Eschborn, Germany) and centrifuged for 30 s at 800 g, and then transferred to autosampler vials until measurement by LC-MS/MS. Measurements were performed in the selected reaction monitoring (SRM) mode on a Xevo TQ-XS triple quadrupole mass spectrometer equipped with a Z-Spray source (Waters, Eschborn, Germany) as described previously in detail (Liu et al, 2021a). PSTs were quantified by external calibration with standard mix solutions of four concentration levels consisting of the following PSTs: STX, NEO, GTX2/3, GTX1/4, dcSTX, dcNEO, dcGTX2/3, dcGTX1/4, B1 (GTX5), B2 (GTX6), C1/2, and C3/4 purchased from the Certified Reference Materials Program (CRMP) of the Institute for Marine Biosciences, National Research Council (Halifax, NS, Canada).…”