During the collection of the moon snail egg collars, field observations suggested that these egg masses were less prone to biofouling than other substrates (shells and seagrass). This led to our hypothesis that the microbiota of these egg collars chemically defends the eggs from micro-biofouling. To test this, we screened the microbial fraction library for biofilm inhibition and disruption against two pathogens, S. aureus and P. aeruginosa. First, we screened for biofilm inhibition, where each fraction was incubated overnight with the pathogen. Plates were rinsed to remove planktonic cells and residual biofilms were stained with crystal violet for quantification (see experimental methods). In total, twenty-six and thirty-eight fractions inhibited > 50% of P. aeruginosa (3.2% hit rate) and S. aureus (4.7% hit rate) biofilm formation (Fig. and). The phylogenetic diversity of the active fractions was highly similar among the active fractions for each pathogen, with a 1:1 ratio of the active fractions being produced by gram-positive versus gram-negative strains. In addition, ~36% of the active fractions were produced by Bacilli, ~31% by Gammaproteobacteria, ~13% by Actinomycetia, ~10% by Alphaproteobacteria, and ~10% by Flavobacteriia (Table ). However, despite this high phylogenetic similarity of the producing organisms, there was minimal overlap in the actual active fractions, with only two fractions (produced by Aquimarina sp. and Staphylococcus sp., respectively) exhibiting biofilm inhibition activity against both S. aureus and P. aeruginosa.