In the paper "Salinity as a tool for strain selection in recirculating land-based production of Ulva spp. from germlings to adults" (Cardoso et al. 2023) the relative growth rates of germlings of different Ulva species and strains were measured to evaluate the impact of different salinity treatments. We hypothesised that, since their early stages, salinity impacts the relative growth rate of the seaweeds and that different strains are adapted to different salinities. With this data it was possible to use salinity as a tool for selecting the strain with the highest and determine the optimal salinity to grow its germlings under a nursery setting to supplement a large-scale production. Four strains were tested (U. lacinulata and U. linza from the NE-Atlantic and U. lacinulata and U. flexuosa from the Mediterranean). The NE- Atlantic strains were collected in the Óbidos Lagoon, Portugal in January 2021 and were cultivated in laboratory conditions in the Alfred Wegener Institute (AWI), Bremerhaven, Germany. The Mediterranean strains belong to an AWI collection and were isolated in 1986 and 1987 (U. flexuosa and U. lacinulata, respectively). The cultivation of the Mediterranean species with the purpose of using them for experiments started in June 2021. To recreate the conditions of a nursery system, the strains were grown previously and during the experiment in a medium of artificial seawater (Seequasal-Salz, Seequasal Salz Production and Trade GmbH, Münster, Germany) enriched with half-stregth Provasoli (PES; Provasoli 1968; modifications: HEPES-buffer instead of TRIS, double concentration of Na₂glycerophosphate; iodine enrichment following Tatewaki, 1966). Three germlings with similar size from each species and population were placed into multi-well plates and subjected to different salinity treatments (10, 15, 20 and 30 PSU) (n = 3). The germlings were cultivated for 3 weeks. Because of the small size of the germlings, measuring the fresh weight was not possible and, in this experiment, pictures of the germling development were taken every week and the area of the germlings was measured with the software Image J (Rasband 2012). The difference in size was later used to determine their relative growth rate.

We have written confirmation by the Instituto da Conservação da Natureza e das Florestas (ICNF) in its function as ABS National Focal Point as well as Competent National Authority that although Portugal is party to the Nagoya Protocol no national legislation nor any regulatory requirements drawing from the Nagoya Protocol for access to genetic resources in mainland Portugal exist presently. As the samples for this project were collected in mainland Portugal, there are no applicable prior informed consent requirements. The Mediterranean Ulva material was isolated in 1986 (AWI culture number 1262) and in 1967 (AWI culture number 1290). Hence, the samples were taken before the Nagoya Protocol came into force in 2014. Although Regulation EU-No. 511/2014 does not apply accordingly, we complied with our due diligence by asking the Greek National Focal Point about national ABS permit requirements and were granted access with a research permit for flora (RECALL/Δ PΔ/12548/797) issued by the Ministry of The Environment & Energy- Gdd & Dp - Forest Protection Directorate).