After 16 weeks in the mesocosm, straw samples were recovered using ethanol-sterilized tweezers and placed in 2 mL molecular biology-grade microcentrifuge tubes (ThermoScientific, Catalog #3453). Seawater samples were collected in autoclaved glass bottles, as well. All samples were subjected to DNA extraction using the DNeasy PowerBiofilm kit (Qiagen) according to the manufacturer's protocol. Amplicon libraries for variable region V4 were prepared following previously established procedures. The pooled amplicon libraries were sequenced using a 2250 bp MiSeq platform (Illumina) at the Institute for Genome Sciences at the University of Maryland. Amplicon reads were processed in R (4.0.2) using the DADA2 (1.16) pipeline for quality control, merging sequences, and assigning amplicon sequence variants (ASVs). Taxonomy was assigned to the family level using the naïve Bayesian classifier method against the SILVA v138.1 database. Statistical analyses for bioinformatics Statistical analyses and plotting were performed using R (4.0.2). Beta-diversity was calculated using Bray-Curtis dissimilarity and visualized using the principal coordinate analysis (PCoA) plot in R with packages ggplot2 and phyloseq. Statistical differences in microbial communities among different materials were determined using permutational multivariate analysis of variance (PERMANOVA) in R using the adonis function in vegan with 999 permutations. 14