Susan Badylak

Climatic Influences on Autochthonous and Allochthonous Phytoplankton Blooms in a Subtropical Estuary, St. Lucie Estuary, Florida, USA

The St. Lucie Estuary, located on the southeast coast of Florida, provides an example of a subtropical ecosystem where seasonal changes in temperature are modest, but summer storms alter rainfall regimes and external inputs to the estuary from the watershed and Atlantic Ocean. The focus of this study was the response of the phytoplankton community to spatial and temporal shifts in salinity, nutrient concentration, watershed discharges, and water residence times, within the context of temporal patterns in rainfall. From a temporal perspective, both drought and flood conditions negatively impacted phytoplankton biomass potential. Prolonged drought periods were associated with reduced nutrient loads and phytoplankton inputs from the watershed and increased influence of water exchange with the Atlantic Ocean, all of which restrict biomass potential. Conversely, under flood conditions, nutrient loads were elevated, but high freshwater flushing rates in the estuary diminished water residence times and increase salinity variation, thereby restricting the buildup of phytoplankton biomass. An exception to the latter pattern was a large incursion of a cyanobacteria bloom from Lake Okeechobee via the St. Lucie Canal observed in the summer of 2005. From a spatial perspective, regional differences in water residence times, sources of watershed inputs, and the proximity to the Atlantic Ocean influenced the composition and biomass of the phytoplankton community. Long water residence times in the North Fork region of the St. Lucie Estuary provided an environment conducive to the development of blooms of autochthonous origin. Conversely, shorter residence times in the mid-estuary limit autochthonous increases in biomass, but allochthonous sources of biomass can result in bloom concentrations of phytoplankton.

A Comparison of Water Quality and Hydrodynamic Characteristics of the Guana Tolomato Matanzas National Estuarine Research Reserve and the Indian River Lagoon of Florida

Abstract The lagoons that border the east coast of the Florida peninsula provide an opportunity to study water chemistry and phytoplankton characteristics over a wide range of water residence and nutrient load conditions. This article includes the results of a 2-year study of eight study sites. The northern half of the sampling range included four sampling sites within the newly established Guana Tolomato Matanzas National Estuarine Research Reserve. The southern half of the sampling range consisted of four study sites distributed in ecologically distinct sub-basins of the Indian River Lagoon. The Guana Tolomato Matanzas National Estuarine Research Reserve and Indian River Lagoon include estuaries with water residence times ranging from days to months and watersheds with widely differing nutrient load characteristics. The results of this study revealed wide temporal and spatial variability of physical and chemical characteristics. Mean salinities for the study period ranged from 9.7 to 31.5‰ over the eight sites. Mean orthophosphate and total phosphorus concentrations ranged from 0.26 to 1.55 μM and 1.45 to 3.00 μM, respectively. Mean dissolved inorganic nitrogen and total nitrogen concentrations ranged from 3.14 to 9.77 μM and 26.43 to 71.14 μM, respectively. Individual phytoplankton standing crops, in terms of chlorophyll a concentrations, ranged from less than 1 μg L−1 to more than 60 μg L−1. Comparisons of the relationships between nutrient and phytoplankton standing crops at the eight study sites indicated that water residence times and nutrient loads provided important insights into the basis for observed temporal and spatial patterns of variability. Indices for water residence time and nutrient load were determined for each site. A combination of the character of watershed inputs and residence time was most useful in interpreting patterns of nutrient concentrations, whereas water residence time appeared to be the pre-eminent factor dictating phytoplankton standing crop potential among the eight study sites.

Phytoplankton biomass and composition in a well-flushed, sub-tropical estuary: The contrasting effects of hydrology, nutrient loads and allochthonous influences

The primary objective of this study was to examine trends in phytoplankton biomass and species composition under varying nutrient load and hydrologic regimes in the Guana Tolomato Matanzas estuary (GTM), a well-flushed sub-tropical estuary located on the northeast coast of Florida. The GTM contains both regions of significant human influence and pristine areas with only modest development, providing a test case for comparing and contrasting phytoplankton community dynamics under varying degrees of nutrient load. Water temperature, salinity, Secchi disk depth, nutrient concentrations and chlorophyll concentrations were determined on a monthly basis from 2002 to 2012 at three representative sampling sites in the GTM. In addition, microscopic analyses of phytoplankton assemblages were carried out monthly for a five year period from 2005 through 2009 at all three sites. Results of this study indicate that phytoplankton biomass and composition in the GTM are strongly influenced by hydrologic factors, such as water residence times and tidal exchanges of coastal waters, which in turn are affected by shifts in climatic conditions, most prominently rainfall levels. These influences are exemplified by the observation that the region of the GTM with the longest water residence times but lowest nutrient loads exhibited the highest phytoplankton peaks of autochthonous origin. The incursion of a coastal bloom of the toxic dinoflagellate Karenia brevis into the GTM in 2007 demonstrates the potential importance of allochthonous influences on the ecosystem.

PSEUDO-NITZSCHIA CALLIANTHA (BACILLARIOPHYCEAE) FROM THE INDIAN RIVER LAGOON, FLORIDA

Recent reclassification of Pseudo-nitzschia pseudodelicatissima and Pseudo-nitzschia cuspidata prompted a reexamination of the P. pseudodelicatissima designation assigned to recently observed blooms in the Indian River Lagoon (IRL) in Florida. Light microscopy, SEM and TEM were used to study morphological features of Pseudo-nitzschia from the IRL and compare these features to the new classification scheme. The valve shape, density of fibulae and striae, structure of poroid hymen and band striae provided the basis for a re-assignment of the species designation for the IRL specimens. Results of the analyses indicate that the species of Pseudo-nitzschia from the IRL are more closely aligned to the recently described species Pseudo-nitzschia calliantha.

In situ observations of Akashiwo sanguinea (Dinophyceae) displaying life cycle stages during blooms in a subtropical estuary

Abstract This study reports on the harmful algal bloom (HAB) dinoflagellate Akashiwo sanguinea in the upper, mid and lower Caloosahatchee estuary, Florida during monthly sample events at four sites from February 2009 through February 2010. Akashiwo sanguinea cells were microscopically quantified throughout the course of the study and scanning electron microscopy was used to confirm certain life stage observations. Water temperature and salinity were recorded for each collection. A rare observation of a major sexual reproduction event was made from water samples collected in situ during February 2009. This sample event included 600 cells ml−1 of small cells, 25 cells ml−1 of perpendicularly connected cells in the fusing position, 17 cells ml−1 of planozygotes, cells surrounded by mucoid halos and asexual pairs. Structures consistent with a fertilization tube in the apical or sulcal regions of the small cells were also observed. A bloom of A. sanguinea vegetative cells was observed in the upper estuary in May with cell densities near 700 cells ml−1 and again in June with densities greater than 300 cells ml−1. Results provide insights into environmental conditions during the occurrence of reproduction stages and vegetative cell blooms of A. sanguinea.

Phytoplankton dynamics in a subtropical tidal creek: influences of rainfall and water residence time on composition and biomass

Concerns about global climate change have heightened awareness of the role changing rainfall regimes play in altering plankton communities of coastal ecosystems. In this study spatial and temporal patterns of phytoplankton composition and biomass in a sub-tropical tidal creek in Florida were observed over three wet and dry seasons, which included the major storm year of 2005 and the drought year of 2006. Shifts in rainfall levels were associated with changes in phytoplankton composition and biomass, but the effects varied between the upper and lower reaches of the creek. The upper reach of the creek was fresh throughout the study period. The oligohaline to mesohaline lower creek alternated between fresh and marine species in response to shifts in salinity regimes. Blooms of the freshwater dinoflagellate Peridinium sp., small centric diatoms and nitrogen-fixing cyanobacteria were common in the upper Ten Mile Creek during low rainfall years. The euryhaline marine dinoflagellate Akashiwo sanguinea and centric diatoms (e.g. Leptocylindrus minimus) were observed at bloom levels in the lower creek during low to average rainfall periods. The results are discussed within the context of how variability in rainfall influence water residence times, nutrient concentrations and salinity regimes, which in turn influence phytoplankton composition and biomass.