RESUMEN
In 2016, an unprecedented Pseudo-nitzschia australis bloom in the Gulf of Maine led to the first shellfishery closures due to domoic acid in the region's history. In this paper, potential introduction routes of P. australis are explored through observations, a hydrodynamic model, and a Lagrangian particle tracking model. Based on particle tracking experiments, the most likely source of P. australis to the Gulf of Maine was the Scotian Shelf. However, in 2016, connectivity between the Scotian Shelf and the bloom region was not significantly different from the other years between 2012 and 2019, nor were temperature conditions more favorable for P. australis growth. Observations indicated changes on the Scotian Shelf in 2016 preceded the introduction of P. australis: increased bottom salinity and decreased surface salinity. The increased bottom salinity on the shelf may be linked to anomalously saline water observed near the coast of Maine in 2016 via transport through Northeast Channel. The changes in upstream water mass properties may be related to the introduction of P. australis, and could be the result of either increased influence of the Labrador Current or increased outflow from the Gulf of St. Lawrence. The ultimate source of P. australis remains unknown, although the species has previously been observed in the eastern North Atlantic, and connectivity across the ocean is possible via a subpolar route. Continued and increased monitoring is warranted to track interannual Pseudo-nitzschia persistence in the Gulf of Maine, and sampling on the Scotian Shelf should be conducted to map upstream P. australis populations.
RESUMEN
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, Aureoumbra lagunensis, Pyrodinium bahamense, and Pseudo-nitzschia 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 A. lagunensis presented here for the first time. An annual bloom index (ABI) was established for each taxon based on occurrence and abundance data. Blooms of A. lagunensis (>2×108 cells L-1) were observed in all six years sampled and across multiple seasons. In contrast, abundance of P. bahamense, largely driven by the annual temperature cycle that moderates life cycle transitions and growth, displayed a strong seasonal pattern with blooms (105-107 cells L-1) generally developing in early summer and subsiding in autumn. However, P. bahamense bloom development was delayed and abundance was significantly lower in years and locations with sustained A. lagunensis blooms. Pseudo-nitzschia spp. were broadly distributed with sporadic bloom concentrations (reaching 107 cells L-1), but with minimal concentrations of the toxin domoic acid detected (<0.02 µg L-1). In summer 2020, multiple monitoring tools characterized a novel nano-cyanobacterium bloom (reaching 109 cells L-1) that coincided with a decline in A. lagunensis 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.
RESUMEN
Despite nearly annual blooms of the neurotoxic dinoflagellate Karenia brevis (Davis) G. Hansen and Moestrup in the Gulf of Mexico, defining the suite of biological traits that explain its proliferation has remained challenging. Studies have described K. brevis as a low-light-adapted species, incapable of sustaining growth under high light, which is at odds with observed surface aggregations sometimes within centimeters of the sea surface and also with short-term experiments showing photosynthetic machinery accommodating high irradiances. Here, growth and photophysiology of three K. brevis isolates were evaluated under a range of environmentally relevant irradiances (10-1500 µmol photons m-2 s-1) in the laboratory. No differences in growth-irradiance curves were observed among isolates; all sustained maximum growth rates at the highest irradiances examined, even in exposures as long as three weeks. The growth efficiency α of K. brevis under light-limiting conditions appeared mediocre among dinoflagellates, and poorer than that of other phytoplankton (e.g., diatoms, cyanobacteria), implying that K. brevis is not a low-light specialist. This finding substantially alters earlier parameterizations of K. brevis growth-irradiance curves. Therefore, a model was developed to contextualize how these new growth-irradiance curves might affect bottom growth rates. This model was subsequently applied to a case study comparing seasonal light forcing offshore of Pinellas County, FL, USA, with a single empirical value for light attenuation, and seasonal bottom water temperatures. Predictions suggested that light may limit bottom growth as close as 1 km from shore in winter, but would only begin limiting growth 20 km from shore in summer. Population maintenance (no net growth) was possible as far offshore as 90 km in summer and 68 km in winter. These ranges intercept areas thought to be important for bloom initiation.
