Highly Resolved Surface Phytoplankton Community Composition Along the British Columbia Coast, Derived From In Situ Hyperspectral Radiometry

Abstract

Quantitative measurements of phytoplankton community composition (PCC) are essential for understanding fisheries production, ocean nutrient cycling, and the export of particulate carbon to the ocean interior. However, these measurements are constrained in dynamic coastal waters due to the spatial-temporal constraints of in situ sampling, difficulty quantifying communities, and the challenges of deriving community compositions via satellites. Here, we work to address these issues by using highly resolved in situ hyperspectral radiometry, along a ship of opportunity track through Case-2 waters of the Strait of Georgia (SoG) British Columbia, to derive phytoplankton community composition. First, an empirical orthogonal function (EOF)-based algorithm was developed using HPLC CHEMTAX-derived phytoplankton group-level chlorophyll-a (Chla) and Total Chla (TChla) concentrations and corresponding principal components derived from hyperspectral remote sensing reflectance. Second, the outputs were evaluated using cross-validation, showing good retrievals for TChla and the regionally dominant phytoplankton groups: diatoms, cryptophytes, green algae, and raphidophytes, which followed expected spatial-temporal trends with diatom-dominated spring blooms and succession to high diversity flagellate-dominated summer conditions. Furthermore, the outputs captured fine spatial scale trends including strong harmful raphidophyte blooms over the narrow transition to low salinity Fraser River plume influenced waters. These findings highlight the potential of using highly resolved hyperspectral radiometry to derive fine-scale trends in phytoplankton group level community composition in optically dynamic coastal waters. Coupled with additional measures, this method could provide valuable information on phytoplankton dynamics in the SoG, which is a critical habitat for a high diversity of pelagic fish species, including Pacific salmon.