Fluoro-Electrochemistry\nBased Phytoplankton Bloom\nDetection and Enumeration; Field Validation of a New Sensor for Ocean\nMonitoring

Phytoplankton are essential for the health of our oceans,\nyet existing <i>in situ</i> methods for monitoring phytoplankton\nabundance and\ncommunity structure are limited, with relatively poor spatiotemporal\ncoverage and taxonomic resolution, particularly among the nanoplankton\nsize range. Here, we build on previous work and present field testing\nof a novel reagent-free fluoro-electrochemical technique for monitoring\nchanges in nanoplankton abundance and community structure in natural\nseawater samples. This was achieved through the construction of a\nprototype sensor, which was then tested over a 3-month Spring–Summer\nperiod in 2023 with samples collected from the L4 station (Western\nEnglish Channel). The measurements made by our sensor were successfully\nvalidated alongside microscope-based taxonomic enumerations and analytical\nflow cytometry. Of the phytoplankton functional groups of interest,\nour results demonstrate particularly strong correlations between the\nsensor and both microscope-based taxonomy and flow cytometry for enumerating\nsmall coccolithophorids (i.e., calcifying Isochrysidales, of the <i>Gephyrocapsa</i> genus) and between the prototype and microscope-based\ntaxonomy for enumerating diatoms. We demonstrate that the inclusion\nof traditionally hard to identify nanoflagellates in our classifications\nhas minimal effect on our ability to monitor overall shifts in community\nstructure and bloom detection. Taking things forward, the potential\nfor <i>in situ</i> deployment is discussed.