Hellige, Inga; Buck-Wiese, Hagen; Bligh, Margot; Thomson, Timothy; White, Lydia; Arnosti, Carol; Baiko, Dariya; Fernández-Méndez, Mar; Ghobrial, Sherif; Gustafsson, Camilla; Kajee, Mohammed; Lloyd, C Chad; Philippi, Miriam; Potin, Dan; Potin, Philippe; Rothman, Mark; Salgado Murillo, Beatriz; Seidel, Michael; Uth, Catharina; Wieters, Evie; Magnusson, Marie; Hehemann, Jan-Hendrik: Microbial cell abundance quantified via DAPI-cell counting during mesocosm experiments with brown algae [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.980716 (dataset in review),

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In: Hellige, I et al.: Mesocosms of brown algae of Laminariales and Fucales to quantify fucoidan secretion, persistence and aggregation [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.980715 (dataset in review)

Six mesocosm experiments with specimens of Fucales or Laminariales were conducted across six georegions (3 mesocosms with brown algae, 3 mesocosms without brown algae). Incubations lasted 24 days, followed by a year-long monitoring of incubation water. During the first 12 days, brown algae were maintained in mesocosms adjacent to control mesocosms, with 1 L of water sampled every second day. Half of the mesocosm water was replaced with fresh seawater after each sampling. Environmental conditions and primary productivity of specimens was recorded during the incubation. After 12 days, specimens were removed and incubation continued for another 12 days, maintaing the same sampling routine. At the end of the 24 day- incubation period, long-term monitoring was set-up with 6-10L of incubation water in two different conditions: one exposed to a controlled light cycle at 20°C, the second set in darkness at 4°C with added nutrients (40 µM NO3- and 3µM PO43-). Additional water samples were collected along transects extending from near-shore brown algae poplulations. Water samples were filtered over pre-combusted GFF filters (450°C, 4.5h), and both the filtrate and filters were analysed for dissolved organic carbon (DOC), particulate organic carbon (POC). Fucoidan was quantified in dissolved (>1kDa) fraction and surface active fraction (SAF) (> 1kDa and negative charged fraction purified with anion exchange chromatography) fractions through monosaccharide quantification after acid-hydrolysis (100°C, 24h) using HPAEC-PAD, according to Engel and Händel, 2011. Intact polysaccharides were detected using structure-sensitive monoclonal antibodies (Torode et al., 2015; Vidal-Melgosa et al., 2021). Microbial cells were quantified using DAPI-cell staining and counting. Semi-quantitative measurements of particulate fucoidan were performed via acid hydrolysis of GFF filter pieces, followed by monosaccharide analysis via HPAEC-PAD. Sedimented particles to bottom of mesocosms were scooped out on day 24 for monosaccharide analysis and BAM1 antibody binding specific to fucoidan.

Additional funding: Simons Collaboration on Principles of Microbial Ecosystems, the Entrepreneurial Universities Macroalgal Biotechnologies Programme supported by the Tertiary Education Commission (TEC) and the University of Waikato, New Zealand, the Centre for Coastal Ecosystem and Climate Change Research (CoastClim) supported by the Jane and Aatos Erkko Foundation and the Ella and Georg Ehrnrooth Foundation, Finland