Microbial degradation of jellyfish detritus promotes phytoplankton growth in coastal marine ecosystems.

Abstract

Gelatinous zooplankton (hereinafter cnidarian Medusozoa and ctenophores or "jellyfish") are widespread in marine ecosystems and can form blooms, releasing large amounts of labile, protein-rich organic matter (jelly-OM) upon decay. This material fuels intense bacterial activity, yet its ecological consequences remain poorly understood. We conducted a two-stage microcosm experiment simulating a bloom decay of the invasive ctenophore Mnemiopsis leidyi to examine microbial processing of jelly-OM and its effect on primary production (PP). In the first stage, over the course of 3 days, we observed jelly-OM stimulating rapid growth of opportunistic bacterial community. The community was dominated by Pseudoalteromonadaceae-key degraders of diverse jellyfish, which exhibited enhanced metabolism of amino acids, lipids, and carbohydrates and elevated extracellular enzymatic activities, including leucine aminopeptidase, lipase, chitinase, and alkaline phosphatase. These processes led to marked ammonium accumulation. In the second stage, exposure of a fresh microbial assemblage to residues from jelly-OM degradation resulted in a significant increase of PP and phytoplankton biomass over a period of five days. This was dominated by diatoms and was fueled by accumulated ammonium. Concurrently, the bacterial community shifted toward taxa typically associated with phytoplankton blooms. Together, these results, further supported by in situ observations, reveal a likely coupling between jellyfish decay and phytoplankton growth, suggesting that jellyfish blooms act as transient but powerful nutrient sources capable of triggering ecosystem shifts. As jellyfish are projected to thrive under future ocean conditions, our findings underscore the need to re-evaluate their role in biogeochemical cycles-particularly as overlooked drivers of phytoplankton dynamics.