Direct Observations of the Life Cycle of Heterocapsa triquetra in the Elizabeth River

Heterocapsa triquetra is a marine thecate dinoflagellate harmful algal bloom (HAB) species known to bloom during the winter in the Chesapeake Bay. This study aimed to observe the onset and decline of a H. triquetra bloom in the Elizabeth River. Water samples were collected near-daily from 21 January 2020 to 13 March 2020 to observe a range of marine phytoplankton species including H. triquetra. Cells were identified and quantified using an imaging flow cytometer (IFCB) which produces images of the cells in the various stages of their life and reproductive cycles. To date, very few studies have made direct observations of the different life stages of dinoflagellate species in the field. As part of this study, we were able to observe the different life stages of H. triquetra cells in their vegetative states, undergoing binary fission, and ecdysis. The images from the IFCB were compiled, identified, and taxonomically classified using EcoTaxa, an open online platform. Environmental parameters including salinity, water temperature, and chlorophyll were also measured along with the time and location of each water sample. We used these additional data to examine how environmental conditions might impact the lifecycle of H. triquetra. We observed a significant change in the amount of vegetative cells in this population, and were able to follow the bloom cycle from initiation to decline. This study provides new insights into how H. triquetra populations change during the bloom cycle and can provide further understanding of other HAB species and their life cycles.