Identifying the Source Organisms Producing Paralytic Shellfish Toxins in a Subtropical Bay in the South China Sea

Abstract

Identifying the exact phytoplanktonic sources of paralytic shellfish toxins (PSTs) is crucial for monitoring and preventing the buildup of toxin pollution, especially for causative species occurring at low levels. Phytoplankton and shellfish samples were simultaneously collected from representative mariculture zones in Daya Bay, China. Low concentration/low toxicity PSTs predominated with N-sulfocarbamoyl toxins 1, 2 (C1/2) being detected in phytoplankton (≤6.25 pmol L–1) and shellfish (≤0.21 μg STXeq g–1), which pose a potential risk of seafood poisoning. High-throughput sequencing of the phytoplankton samples based on 18S rDNA V4 regions identified 93 genera in 445 operational taxonomic units (OTUs). Five OTUs were assigned to Alexandrium hiranoi, Ambicodamus leei, Alexandrium pacificum, Alexandrium minutum, and an uncertain Alexandrium sp. A. pacificum and A. minutum are candidate PST producers and observed under the light microscope with densities of 66–972 cells L–1. Three strains of toxigenic species were successfully isolated and identified as A. pacificum and A. minutum based on their 18S rDNA V4 regions. The predominant toxins in A. pacificum were C1/2 (43.9–53.6 fmol cell–1) and resembled the toxins found in field samples predominated with C1/2. A. minutum produced only gonyautoxins 2/3 (8.03 fmol cell–1). Therefore, A. pacificum was identified as the predominant PST contributor in this area. This research makes a valuable contribution to the understanding of the traceability of phycotoxins in marine waters.

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

“…In contrast, populations from the East and South China Sea are probably the same as there is no strong physical barrier between them. Our new strain TIO866 from the Beibu Gulf shared similar toxin profile with strains from the South China Sea, which also predominantly produce C1/2 toxins [21,24,26], thus supporting the idea of a single population. Strain TIO1210 from New Zealand produced a similar toxin profile to those from the Taiwan Strait, but differed from those in the Bay of Plenty by the lack of C3/4 [65], indicating that there are also variable strains and populations in New Zealand.…”

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

“…However, molecular sequences of strains from this region are limited and all available strains fell within the Pacific clade (Lilly et al, 2005). In contrast, strains from Taiwan showed the highest variability in toxin profiles (Lewis et al, 2018), although strains from mainland China, Vietnam and Malaysia always produced predominately GTX1-4 (Yoshida et al, 2000;Lim and Ogata, 2005;Lim et al, 2006;Liu et al, 2021b).…”

“…In addition to these bloom events, A. minutum displays a wider biogeography in the Asian Pacific, recorded in Japan, Korea, Daya Bay, China, Vietnam, northeast coast of Peninsular Malaysia, Gulf of Thailand, and Philippines (Yuki, 1994;Yoshida et al, 2000;Piumsomboon et al, 2001;Usup et al, 2002;Park and Kang, 2009;Baula et al, 2011;Liu et al, 2021b). However, molecular sequences of strains from this region are limited and all available strains fell within the Pacific clade (Lilly et al, 2005).…”

Community changes of gut microbes highlight their importance in the adaptation of copepods to toxic dinoflagellates

“…and Paracalanus sp., in our study and fed them two dinoflagellates species from the same genus, the toxic Alexandrium tamarense (as toxic microalgae) and the nontoxic Alexandrium andersonii (as control). The two copepods and dinoflagellates are typically abundant and frequently coexist in subtropical coastal waters (Liu et al, 2021;Xiang et al, 2021). In particular, the two copepod species are from different taxonomic families and have different feeding modes (Acartia sp.…”