Biofouling　significantly　affects　membrane　system　performance,　however,　microbial　ecological　processes　and　behaviors　within　the　bio-cake　layer　during　operation　remain　poorly　understood.　In　this　study,　four　lab-scale　gravity-driven　membrane　(GDM)　ultrafiltration　systems　were　operated　in　parallel　to　monitor　flux　variations　and　membrane　fouling　characteristics　throughout　GDM　operation.　Results　showed　that　a　gradual　decrease　and　stabilization　in　flux　(44.69,　7.19,　3.78,　3.1　L/(m2　h),　respectively),　accompanied　by　bio-cake　layer　homogenization,　compaction,　and　an　increase　in　extracellular　polymeric　substances　(EPS)　content　over　time　(8.7,　46.99,　79.93,　69.64　mg/m2,　respectively).　Microbial　community　succession　was　primarily　driven　by　ecological　drift　and　other　stochastic　processes.　Distinct　bacterial　community　structures　emerged　at　different　stages,　with　interspecies　relationships　tending　toward　competition.　Predation　shifted　from　nematodes　and　flagellates　in　early　stages　to　flagellates　dominating　in　later　stages.　N-doctanoyl-L-homoserine　lactone　(C8-HSL)　and　N-dodecanoyl-L-Homoserine　lactone　(C12-HSL)　were　identified　as　the　dominant　quorum　sensing　signal　molecules,　with　alanine,　aspartate,　and　glutamate　metabolism　identified　as　key　metabolic　pathways.　EPS　production　evolved　from　microbial　metabolites　in　early　stages　to　quorum　sensing-induced　in　later　stages.　Aestuariicella　hydrocarbonica　and　Methylotenera　sp.　were　identified　as　principal　quorum　sensing　bacteria.　C8-HSL　significantly　determined　the　flux　of　GDM.　Regulating　microbial　community　behavior　was　more　effective　in　mitigating　fouling　than　shaping　community　structure.　This　study　is　the　first　to　investigate　microbial　ecological　processes　and　behavior　changes　within　the　bio-cake　layer　throughout　GDM　operation,　providing　valuable　insights　into　balancing　biofouling　mitigation　and　performance　enhancement.