Spatiotemporal distribution, composition, and influencing factors of lipophilic marine algal toxins in the Beibu Gulf, China: Implications for necessity of offshore seawater monitoring

Abstract

Lipophilic marine algal toxins (LMATs) are persistent, bioaccumulative metabolites that pose significant threats to marine biodiversity and seafood safety. To comprehensively understand LMATs pollution in offshore natural fishing grounds, we investigated the spatiotemporal distribution and composition of 13 LMATs in surface seawater in Beibu Gulf's offshore area, along with their key influencing factors and latitudinal variations across coastal regions in China. We detected 20-methyl spirolide G (SPX20G) for the first time in coastal waters in China, alongside other frequently detected LMATs, including okadaic acid (OA), dinophysistoxin-1 (DTX1), pectenotoxin-2 (PTX2), azaspiracid-1 (AZA1), azaspiracid-2 (AZA2), gymnodimine (GYM), and 13-desmethyl spirolide C (SPX1). Significant seasonal variations were observed, with summer exhibiting eight LMAT types and higher total LMAT concentrations (ΣLMATs) (16.92 ± 20.45 ng/L) compared to winter's five LMAT types and ΣLMATs concentrations at 5.63 ± 3.30 ng/L. Predominant PTX2 and OA concentrations showed a decreasing trend from northern to southern Beibu Gulf, while other LMATs were distributed in patches, particularly in summer. Notably, cyclic imines (GYM and SPX1) were detected with high frequencies and concentrations, underscoring the need for their monitoring. Spearman correlation and redundancy analyses identified water depth, chlorophyll a (Chla), temperature, salinity, nutrients (DIN:DIP and SiO₃²⁻), and dissolved oxygen (DO) as key factors influencing LMATs distribution in the Beibu Gulf. Latitudinal analysis of LMAT contents across Chinese waters revealed DTX1 as more prevalent at higher latitudes, and GYM, SPX1, and AZA1 more common at lower latitudes, while ΣLMATs concentrations from this study ranked at moderate to high levels compared to other regions. Therefore, special attention is required for LMATs pollution in offshore fishing areas.