Fluoro-Electrochemistry Based Phytoplankton Bloom Detection and Enumeration; Field Validation of a New Sensor for Ocean Monitoring

Phytoplankton are essential for the health of our oceans,
yet existing in situ methods for monitoring phytoplankton
abundance and
community structure are limited, with relatively poor spatiotemporal
coverage and taxonomic resolution, particularly among the nanoplankton
size range. Here, we build on previous work and present field testing
of a novel reagent-free fluoro-electrochemical technique for monitoring
changes in nanoplankton abundance and community structure in natural
seawater samples. This was achieved through the construction of a
prototype sensor, which was then tested over a 3-month Spring–Summer
period in 2023 with samples collected from the L4 station (Western
English Channel). The measurements made by our sensor were successfully
validated alongside microscope-based taxonomic enumerations and analytical
flow cytometry. Of the phytoplankton functional groups of interest,
our results demonstrate particularly strong correlations between the
sensor and both microscope-based taxonomy and flow cytometry for enumerating
small coccolithophorids (i.e., calcifying Isochrysidales, of the Gephyrocapsa genus) and between the prototype and microscope-based
taxonomy for enumerating diatoms. We demonstrate that the inclusion
of traditionally hard to identify nanoflagellates in our classifications
has minimal effect on our ability to monitor overall shifts in community
structure and bloom detection. Taking things forward, the potential
for in situ deployment is discussed.