Inter-oceanic　scale　studies　allow　us　to　understand　the　global　spread　of　micro-organisms　in　marine　ecosystems.　In　this　study,　micro-eukaryotic　communities　in　marine　surface　sediment　were　collected　from　tropical　to　Arctic　sites.　We　found　that　micro-eukaryotic　generalists　had　much　higher　intraspecific　variation　than　specialists　which　allow　them　to　distribute　more　widely　through　higher　spatiotemporal　asynchrony　and　complementary　niche　preferences　among　conspecific　taxa.　Moreover,　comparing　to　the　host-associated　protozoa　and　small　metazoa,　the　algae　and　free-living　protozoa　with　higher　intraspecific　variation　allow　them　to　have　wider　distribution　ranges.　Species　abundance　also　played　an　important　role　in　driving　the　distribution　ranges　of　generalists　and　specialists.　The　generalists　had　important　effects　on　regional　α-diversity　even　at　an　inter-oceanic　scale　which　led　to　the　micro-eukaryotic　species　richness　in　polar　sites　to　be　mainly　influenced　by　the　regional　generalists　but　not　the　local　specialists.　In　particular,　more　than　97%　of　algal　species　in　polar　sites　were　shared　with　the　tropical　and　subtropical　sites　(including　toxic　dinoflagellate).　Overall,　our　study　suggests　that　the　effects　of　global　change　and　human　activities　on　the　vulnerable　high　latitude　habitats　may　lead　to　biotic　homogenization　for　the　whole　microbial　community　(not　only　the　dispersal　of　some　harmful　algae)　through　the　potential　long-distance　spread　of　generalists.　©　2023　Elsevier　Ltd