Mass spectrometry (MS)-based metabolomics and bioassay-guided isolation led to identifying pseudochelin A (6), a known siderophore, 29 as the active metabolite in twenty-four fractions possessing biofilm inhibition activity against S. aureus. In addition, a key biosynthetic gene responsible for producing 6 was amplified from DNA samples of single moon snail egg collars, suggesting that the microbiome associated with egg collars can produce this compound under certain conditions. Consequently 6 may have an ecological role in shaping the microbiome and/or protecting the egg collars from biofouling.