We observed whether bacterial settlement would vary in presence vs. absence of seaweed extract. Fluorescence was measured using a plate reader machine. Samples are seaweed extracts from different salinity treatments. Experiment performed: Following an initial extraction of surface-associated metabolites (immediately after field collection), we conducted a long-term mesocosm experiment for 5 months to test the effect of two different salinities (low = 8.5 and medium = 16.5) on the microbial “gardening” capacity of the alga over time. We tested “gardening” capacity of A. vermiculophyllum originating from two different salinity levels (after 5 months treatments) in settlement assays against three disease causing pathogenic bacteria and seven protective bacteria. We also compared the capacity of the alga with field-collected samples. The data was collected at GEOMAR, Kiel, Germany. The data collection was done between Jan-March 2016. Data was collected using a plate reader. Bacteria cells were stained with SYTO 9 (Invitrogen, GmbH), a fluorescent dye that binds DNA. Fluorescence measured (excitation, 477–491 nm; emission, 540 nm) by a plate reader was used as an estimate of the cell density of settled bacteria. The data was collected to test if bacterial settlement would vary in presence vs. absence of seaweed extract originating from different salinity and time treatments.