Water from this intake flows through a 10 mm coarse sieve before being pumped through a three-layer sand filtration system (6 -8 mm; 3 -4 mm; 1 -2 mm) into a water reservoir. This reservoir feeds an extensive aquarium seawater system which includes a series of seawater taps (www.gu.se/en/tjarno/study-and-work/sea-water-systems). Water was drawn from this system on a daily basis between 16th and 20th May, 2022, during which time salinity (mean ± standard deviation = 33.3 ± 0.2 PSU; range = 32.9 -33.7 PSU) and water temperature (mean ± standard deviation = 9.6 ± 0.5 ℃; range = 9.0 -10.4 ℃) at the intake were relatively stable (Figure ). A PuriFlash C18-AQ F1600 flash column (Interchim) was pre-conditioned with ~ 5 column volumes (12.5 L) of LCMS grade methanol (MeOH), starting at a rate of 20 mL min -1 and gradually increasing to 250 mL min -1 (4.5 bar pressure), followed by ~ 10 column volumes (25 L) MilliQ water acidified to pH 2.0 using ACS grade hydrochloric acid (HCl), at a rate of 400 mL min -1 (4 bar pressure). An operating pH of 2 was initially used based on standard protocols (e.g. Dittmar et al. 2008) but this appeared to strip a small amount of material from the column, and so the operating pH was raised to 3. A further 2.5 L acidified MilliQ and 2.5 L 100 % MeOH were passed through the column at a reduced flow rate to 250 mL min -1 (4.5 bar pressure), and then it was stored in 50 % MeOH for 4 days. Immediately prior to use, the column was flushed with 5 L of 50 % MeOH, 5 L of 20 % MeOH, and 5 L acidified MQ (pH 3) with the flow rate gradually increased from 20 mL min -1 to 180 mL min -1 (3 -4 bar pressure).