Removal of Volatile Organic Compounds by Marine Sponges: Implications for Coastal Bioremediation

Sponges (Porifera) are among the oldest known animal-microbe symbioses and are key players in marine biogeochemical cycles. Ubiquitous across benthic marine habitats, they process dissolved organic matter and participate in chemosynthetic pathways. We quantified, for the first time, volatile organic compounds (VOCs, namely, halomethanes, sulfur-containing compounds, and isoprene) in the inhaled and exhaled water of three Mediterranean sponge species: two high-microbial abundance (HMA), Aplysina aerophoba and Agelas oroides, and one low-microbial abundance (LMA), Dysidea avara. Using the Vacusip-INEX method in aquaria and in situ in a NW Mediterranean marine-protected area, we found that HMA sponges efficiently removed bromomethanes and dimethyl disulfide (DMS) and less clearly iodomethanes, carbon disulfide (CS₂), and isoprene, while the LMA species removed methyl iodide (CH₃I), DMS, and isoprene depending on the ambient seawater concentration. In preliminary experiments with A. aerophoba specimens, chemical inhibition of nitrification (with nitrapyrin) arrested bromomethane, DMS removal, and nitrate production, consistent with co-metabolic consumption by endosymbiotic nitrifying bacteria. Sponge VOC removal rates exceeded those of bacterioplankton by orders of magnitude. These findings underscore sponges as major sinks for VOCs in sponge-rich littoral ecosystems, with potential for bioremediation and mitigation of coastal VOC emissions, and call for further research into the ecological implications, impact on coastal air quality, and contributions to elemental cycling.