Spatial-temporal distribution of phytoplankton HAB species and contamination status of oyster toxins under intensive oyster farming in Jiangmen coasts, the South China Sea

The diversity and spatial-temporal distribution of phytoplankton HAB species, contamination status of oyster toxin, and their sources were investigated in Jiangmen oyster farming area based on morphological observation and liquid chromatography-tandem mass spectrometry analysis. The results revealed there were 28 HAB species, including 19 harmless HAB species, two toxic species (Akashiwo sanguinea and Karenia brevis), and seven toxin-producing microalgae (Alexandrium pacificum, Dinophysis caudata, D. miles, D. fortii, Gonyaulax spinifera, Gymnodinium catenatum, and K. mikimotoi). The mean abundance of total HAB species generally showed a trend of increasing from winter to autumn. The total average abundances of toxic HAB species were 269, 265, 321 and 2.6 × 10³ cells L^-1 in winter, spring, summer and autumn, respectively. Redundancy analysis showed temperature, dissolved oxygen, silicate and phosphate were the key factors related with variations of HAB species. Only spring oyster samples were detected paralytic shellfish toxins (PSTs) (1/15), and the composition included gonyautoxins (GTX1&2) and decarbamoyl gonyautoxin 2 (dcGTX2), with a total toxicity level of 9.96 µg STXeq kg^-1. N-sulfocarbamyl (C1) and decarbamoyl gonyautoxin 3 (dcGTX3) were observed in the net-concentrated phytoplankton samples. It is inferred that these five types of PSTs derived from A. pacificum. The cultured oysters were observed five types of low-concentration lipophilic marine toxins (LMTs) including okadaic acid (OA), dinophysis-1 (DTX1), pectenotoxin-2 (PTX2), gymnodimine (GYM), and homo-yessotoxin (homo-YTX). Though the levels of PSTs and LMTs in the cultured oysters were low, the presence highlights a potential threat to the safety of oyster products from HAB species.