Nitrogen　pollution　resulting　from　the　rapid　development　of　mariculture　poses　a　significant　threat　to　marine　ecosystems.　Heterotrophic　nitrification-　aerobic　denitrification　microorganisms　(HNADMs),　which　can　achieve　nitrification　and　denitrification　simultaneously　under　aerobic　conditions,　have　shown　great　potential　in　treating　nitrogen　pollution.　In　this　study,　a　laboratory-scale　heterotrophic　nitrification-　aerobic　denitrification　(HNAD)　biofilm　reactor　was　continuously　operated　for　72　days　to　evaluate　its　performance　in　treating　marine　recirculating　aquaculture　system　wastewater　(RAS　wastewater)　and　traditional　extensive　pond　aquaculture　tailwater　in　marine　farm　(Pond　tailwater).　The　results　indicated　that　with　ceramsite　as　the　filter　media　and　solid　polyhydroxyalkanoates　(PHA)　as　the　carbon　source,　yielded　the　most　effective　and　stable　nitrogen　removal.　Under　these　optimal　conditions,　the　system　achieved　simultaneous　nitrification　and　denitrification　by　the　7th　day,　with　total　inorganic　nitrogen　removal　efficiencies　of　87.37　f　4.23　%　for　RAS　wastewater　and　65.00　f　8.35　%　for　pond　tailwater.　Dominant　HNADMs　were　consistently　found　on　both　ceramsite　and　PHA　surfaces　across　different　water　sources.　A　more　complex　microbial　ecological　network　when　treating　pond　tailwater　compared　to　RAS　wastewater　was　found,　with　key　microorganisms　predominantly　from　HNADMs.　The　species　composition　and　abundance　of　nitrogen-transforming　microorganisms　vary　with　water　quality　and　carrier　type,　with　traditional　nitrifying　and　denitrifying　bacteria　being　relatively　less　prevalent　and　HNADMs　more　dominant.　Overall,　the　HNAD　biofilm　reactor　system　effectively　removed　nitrogen　from　both　RAS　wastewater　and　pond　tailwater,　providing　valuable　insights　for　simultaneous　nitrification　and　denitrification　processes　in　mariculture　wastewater　treatment.