High-resolution Spatiotemporal Dynamics of Harmful Algae in the Indian River Lagoon (Florida)-A Case Study of , , and -.

The Indian River Lagoon (IRL), located on the east coast of Florida, is a complex estuarine ecosystem that is negatively affected by recurring harmful algal blooms (HABs) from distinct taxonomic/functional groups. Enhanced monitoring was established to facilitate rapid quantification of three recurrent bloom taxa, , , and spp., and included corroborating techniques to improve the identification of small-celled nanoplankton (<10 μm in diameter). Identification and enumeration of these target taxa were conducted during 2015-2020 using a combination of light microscopy and species-specific approaches, specifically immunofluorescence flow cytometry as well as a newly developed qPCR assay for presented here for the first time. An annual bloom index (ABI) was established for each taxon based on occurrence and abundance data. Blooms of (>2×10 cells L) were observed in all six years sampled and across multiple seasons. In contrast, abundance of , largely driven by the annual temperature cycle that moderates life cycle transitions and growth, displayed a strong seasonal pattern with blooms (10-10 cells L) generally developing in early summer and subsiding in autumn. However, bloom development was delayed and abundance was significantly lower in years and locations with sustained blooms. spp. were broadly distributed with sporadic bloom concentrations (reaching 10 cells L), but with minimal concentrations of the toxin domoic acid detected (<0.02 μg L). In summer 2020, multiple monitoring tools characterized a novel nano-cyanobacterium bloom (reaching 10 cells L) that coincided with a decline in and persisted into autumn. Statistical and time-series analyses of this spatiotemporally intensive dataset highlight prominent patterns in variability for some taxa, but also identifies challenges of characterizing mechanisms underlying more episodic yet persistent events. Nevertheless, the intersect of temperature and salinity as environmental proxies proved to be informative in delineating niche partitioning, not only in the case of taxa with long-standing data sets but also for seemingly unprecedented blooms of novel nanoplanktonic taxa.