Prevalence of Dissolved Homarine in Puget Sound and North Pacific

Abstract

Due to the analytical challenges faced during metabolomic analyses of seawater, there has been very little research on the distribution and cycling of dissolved homarine in natural waters. Therefore, the role of homarine as a dissolved metabolite is unknown. This study uses water samples collected from the North Pacific Transition Zone, North Pacific Subtropical Gyre, and Puget Sound to evaluate, for the first time, the concentrations of homarine in different sea water samples. Metabolites were extracted using cation-exchange solid phase extraction (SPE) followed by high-performance liquid chromatography mass spectrometry (HPLC-MS). Homarine concentrations were compared to three other metabolites – dimethylsulfoniopropionate (DMSP), trimethylamine-n-oxide (TMAO), and proline – as also compared to physical, biological, and chemical factors. Homarine was most prevalent in Puget Sound with a concentration of 63.3 nM and least prevalent in the North Pacific Subtropical Gyre with a concentration of 0.8 nM. Homarine was negatively correlated with salinity and temperature but positively correlated with chlorophyll a and nitrate concentrations. This is similar to distributions with TMAO but opposite distribution with DMSP and proline. Between two different latitudes, North Pacific Subtropical Gyre versus the North Pacific Transition Zone, homarine made up 0.3% of the dissolved organic N pool in the lower latitude but 1.6% in the higher latitude. Homarine’s dissolved to particulate ratio also increased from 0.49 to 0.91. This data leads to a broad prediction that there may be a greater source to sink ratio or lower affinity for homarine in the NPTZ.