Detection of a late autumn Karenia papilionacea bloom in Virginia, USA, coastal waters

Abstract

A late autumn Karenia papilionacea bloom was detected within Virginia, USA shellfish harvesting areas in mid-November 2023. Using Imaging FlowCytobot (IFCB) data collected during the Northeast Fisheries Science Center Ecosystem Monitoring October – November 2023 cruise, we were able to document a larger Karenia bloom composed of K. papilionacea, K. brevis-like, K. mikimotoi, and Karenia sp. #3 cells offshore of Virginia three weeks prior to detection inshore. Both K. papilionacea and K. mikimotoi were detected in Virginia state waters (including shellfish harvesting areas) and offshore waters of the Delmarva Peninsula, whereas K. brevis-like and Karenia sp. #3 were only detected offshore. The IFCB data showed that along the cruise track the greatest cell concentrations were east of the Chesapeake Bay mouth on November 1, 2023. However, when conducting a match-up assessment of IFCB in situ data with Sentinel-3 Ocean and Land Colour Instrument (OLCI) satellite imagery using the Red Band Difference (RBD) algorithm, the majority of the bloom was undetected. By comparing in situ match-ups and RBD imagery with NOAA-20 satellite's Visible Infrared Imaging Radiometer Suite (VIIRS) chlorophyll anomaly product we hypothesize that the in situ sampling occurred along the bloom's edge, where cell concentrations were at or below the limit of satellite detection, and/or this particular Karenia bloom was either not fluorescing, expressing relatively low solar-induced chlorophyll fluorescence, or occurring at depths below satellite detection. For this bloom event, the IFCB dataset was also used as a training tool for students learning microscopy-based phytoplankton identification in a virtual environment.