Metadata CatalogueMetadata Cataloguehttps://metadatacatalogue.lifewatch.eu/https://metadatacatalogue.lifewatch.eu//srv/eng/portal.opensearch https://metadatacatalogue.lifewatch.eu//srv/eng/rdf.search?any= engContinents, countries, sea regions of the world.https://metadatacatalogue.lifewatch.eu//srv/eng/thesaurus.download?ref=external.place.regionsecoportal.fos_1.rdfhttps://metadatacatalogue.lifewatch.eu//srv/eng/thesaurus.download?ref=external.ecoportal.fos867f94ab-21a9-4c2b-8dbe-9de5dade0cb7Harmonised dataset of field observations on zoosporic parasites infecting aquatic primary producersZoosporic parasites play crucial ecological roles in aquatic environments, influencing algal population dynamics, nutrient cycling, and energy transfer within microbial food webs. Despite their importance, data on their diversity, distribution, and interactions with primary producers remain sparse and fragmented. Here, we present a harmonised dataset of field observations on zoosporic parasites infecting aquatic primary producers. The dataset integrates both published and previously unpublished records, encompassing more than 4,400 observations collected between 2007 and 2022 across 28 sites in Europe and North America. It includes data for 91 unique parasite taxa, along with confirmed and putative parasite–host associations derived from direct microscopic or molecular evidence. All records were standardised using the Darwin Core schema to ensure interoperability and long-term usability. This open-access resource provides a foundation for comparative and meta-analytical studies on parasite–host ecology, biodiversity assessments, and industrial applications related to algal production systems.algaefungidiatomsphytoplanktoncyanobacteriamacroalgaehost-parasite interactionOccurrenceParasitism <http://www.opengis.net/def/crs/OGC/1.3/CRS84> Polygon((-84.50989 39.3296944, -84.50989 59.9208333, 20.9097222 59.9208333, 20.9097222 39.3296944, -84.50989 39.3296944)) DOIhttps://doi.org/10.48372/d20t-xw44Info and download page on LifeWatch Italy Data Portalhttps://data.lifewatchitaly.eu/handle/123456789/326353National Research Council (CNR), Institute of Research on Terrestrial Ecosystems (IRET)Université Savoie Mont BlancInstitut de Ciències del MarUniversity of LeidenAlfred Wegener Institute Helmholtz Centre for Polar and Marine ResearchBaylor UniversityUniversity of TurkuEnglish