Neurotoxin β-N-methylamino-L-alanine (BMAA) produced by cyanobacteria and microalgae has been concerned by scientists due to its toxicity to human motoneurons. The source and environmental behaviors of BMAA in marine ecosystem are important to understand its risk to human health. Here a diatoms-dominated marine ecosystem in Jiaozhou Bay, China, was investigated for BMAA contamination in phytoplankton, zooplankton, and marine animals, during four seasons in 2019. Results showed that BMAA was migrated and biomagnified along the food chains from phytoplankton to higher trophic organisms, in which the trophic magnification factors (TMF) for zooplankton, bivalve mollusks, carnivorous crustacea and saprophytic gastropod mollusks were approximately 4.58, 30.1, 42.5, and 74.4, respectively. An isomer of BMAA, β-aminomethyl-L-alanine (BAMA), was ubiquitous in phytoplankton samples and its content ratios to BMAA looks gradually decreased with increasing trophic levels. A total of 56 diatom strains (Pseudo-nitzschia spp., Thalassiosira spp., Chaetoceros spp., Planktoniella spp., Minidiscus spp.) were isolated from the Chinese coast and cultured in the laboratory, among which 21 strains produced BMAA mainly presented in the precipitated bound fraction ranging from 0.11 to 3.95 µg g-1 dry weight. BMAA was firstly detected in both Pseudo-nitzschia and Planktoniella genera in this study. Only 2,4-diaminobutyric acid (DAB) but not BMAA or BAMA was detected in seven symbiotic bacteria isolated from the gut of Neverita didyma, which further proves that the benthic vector of BMAA, N. didyma, accumulated BMAA through food chains. These findings demonstrated that the coastal residents have a risk to accumulate BMAA by consumption of seafood products.