File1: VERDI_samples_parameters.xlsx
- Physico-chemical variables obtained from CTD profile
- Inorganic nutrients concentrations
- Chlorophyll-a concentrations
- Organic carbon and nitrogen concentrations
- Phytoplankton abundances
- Detections of chytrids
File 2: VERDI_asv_table.tbl: ASV abundances from natural samples and incubations
File 3: VERDI_tax_table.tbl: Taxonomic assignments of ASVs
File 4: VERDI_asv_seqs.fa: Sequences of ASVs
File 5: VERDI_incubations_images.zip
- Compilation of images taken during incubations with diatoms, The presence of phytoplankton parasites along the water column was explored at the Long Term Ecological Station MareChiara (LTER-MC) in the Gulf of Naples (Mediterranean Sea) in October 2019. Microscopy analyses showed diatoms dominating the phytoplankton community in the upper layers (0-20 m). Metabarcoding data from the water column showed the presence of Chytridiomycota predominantly in the upper layers coinciding with the vertical distribution of diatoms. Laboratory incubations of natural samples enriched with different diatom cultures confirmed parasitic interactions of some of those chytrids – including members of Kappamyces – with diatom taxa. The temporal dynamics of diatoms and chytrids was also explored in a three-year metabarcoding time-series (2011-2013) from surface waters of the study area and in sediment samples. Chytrids were recurrently present at low relative abundances, and some taxa found to infect diatoms in the incubation experiments were also identified in the ASV time-series. However, co-occurrence analyses did not show any clear or recurrent pairing patterns for chytrid and diatom taxa along the three years. The chytrid community in the sediments showed a clearly different species composition compared to the recorded in the water column samples, with higher diversity and relative abundance. The combination of observations, incubations and metabarcoding confirmed that parasites are a common component of marine protist communities at LTER-MC. Host-parasite interactions must be determined and quantified to understand their role and the impact they have on phytoplankton dynamics, - European Union’s Horizon 2020 research and innovation programme under grant agreement No 730984, ASSEMBLE Plus project.
- Spanish MICINN Project SMART (PID2020-112978GB-I00)
- The research program LTER-MC is funded by the Stazione Zoologica Anton Dohrn, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), - Physico-chemical variables obtained from CTD profile - Inorganic nutrients concentrations - Chlorophyll-a concentrations - Organic carbon and nitrogen concentrations - Phytoplankton abundances - Detections of chytrids - Metabarcoding ASV abundances from natural samples and incubations - Metabarcoding Taxonomic assignments of ASVs - Metabarcoding Sequences of ASVs - Compilation of images taken during incubations with diatoms, Peer reviewed

This study describes the diversity and temporal dynamics of the microeukaryotic community in the biofilm of Mediterranean macroalgae during summer, focusing on parasitic groups, This study was funded by the Spanish Ministry of Science, Innovation, and Universities (MICINN) Project SMART PID2020-112978GB-I00, with institutional support from the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). It also contributes to the state-of-the-art objectives of the Horizon Europe GES4SEAS project HORIZON-CL6-2021-BIODIV-01-04. High-performance computing analyses were run at the Marine Bioinformatics Service (MARBITS) of the Institut de Ciències del Mar (ICM-CSIC) in Barcelona. E. Alacid was supported by the Beatriu de Pinós Postdoctoral Program (grant number BP2020-00174) of the Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya, Peer reviewed

A.R. acknowledges the institutional support of the grant ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) funded by AEI 10.13039/501100011033. S.V.W was supported by the Research Council of Finland (Decision Numbers 340659 and 346387). I.T. and M.S. were supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grant no. 451-03-66/2024-03/200178). A.T. has been supported by the project “LifeWatchPLUS” of the “Programma Operativo Nazionale (PON) Ricerca e Innovazione 2014-2020 - Azione II, potenziamento di Infrastrutture di Ricerca” of the Italian Ministry of University and Research. B.S. was supported by the Icelandic Research Fund in the frame of the project “Per- and poly-fluoroalkyl substances (PFASs) meet Arctic and sub-Arctic marine diatoms and their associated symbionts” (RANNIS ID: 239548-051). H.-P.G. received funding by the German Science Foundation (DFG) through the projects MostFun (GR1540/51-1), FUNACTION (GR1540/47-1), and Polar Parasites (GR1540/33-1 and GR1540/48-1). G.B.S was supported by the National Laboratory for Water Science and Water Security program (RRF-2.3.1-21-2022-00008) and NKFIH KKP 144068. S.N. received funding by the Austrian Science Fund (FWF) Y0801-B16. L.G. received fundings by the Ministry of Universities and Research (Italy) through the Biodiversa+ secretariat, co-funded by the European Commission, projects FUNACTION (GA no. 101052342) and MostFun, and with the funding organisations Ministry of Universities and Research (Italy), and the European Commission—NextGenerationEU, Project “Strengthening the MIRRI Italian Research Infrastructure for Sustainable Bioscience and Bioeconomy”, code n. IR0000005. D.S.S. received funding through the projects GloMEc (AXA Research Fund), FishME (ANR-21-BIRE-0002-01), and OneAquaHealth (EC-Project 101086521). N.T. was funded by the Spanish MICINN Project SMART PID2020-112978GB-I00, Peer reviewed

All data sets generated can be found in the Supplementary Material, including the list of primers used for sequencing and the phylogenetic sequence list data sets with corresponding accession numbers, This work was supported by fundings from Spanish MICINN Project DIVINE [PID2023-150672NB-I00]; and Project SMART [PID2020-112978GB-I00], with the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation [CEX2019– 000928- S]. The Japan Science and Technology Agency [JPMJCR24J2]; Japan Society for the Promotion of Science [JSPS KAKENHI 19H05667]; and Japan Society for the Promotion of Science [JSPS KAKENHI 24K18177], Peer reviewed