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

Abstract

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.

Akashiwo sanguinea (Dinophyceae) blooms in a sub-tropical estuary: An alga for all seasons

“…The observation of A. sanguinea blooms in the Caloosahatchee Estuary adds to the list of subtropical/ tropical ecosystems where these species play an important role in phytoplankton community structure and dynamics. The current study compliments other recent reports of A. sanguinea blooms in a number of other estuaries along the coast of Florida, including the northern Indian River Lagoon (Phlips et al 2011), the northern St. Lucie Estuary (Phlips et al 2012) and Apalachicola Bay (Viveros & Phlips, unpublished data). The eurythermal nature of A. sanguinea in Florida is illustrated by the wide range of temperatures over which blooms have been observed in the aforementioned ecosystems (Fig.…”

“…Corresponding salinity, temperature, total nitrogen, and total phosphorus values are reported and discussed within the context of possible factors related to A. sanguinea dynamics. The results of this study and recent observations of regular blooms of A. sanguinea in a number of other Florida estuaries, including the Indian River Lagoon (Phlips et al 2010(Phlips et al , 2011 and the St. Lucie Estuary (Phlips et al 2012), highlight the importance of this species in the subtropical environments of the Gulf of Mexico and the east coast of Florida, and provide further evidence of its tolerance to a wide range of environmental conditions.…”

“…From a hydrologic perspective another feature that appears to contribute to A. sanguinea blooms in the aforementioned Florida ecosystems, including the Caloosahatchee Estuary, is the existence of periods of relatively long water residence times that provide the temporal window needed for the accumulation of biomass (Phlips et al 2011(Phlips et al , 2012. By contrast, blooms of A. sanguinea have rarely been observed in well-flushed estuaries in Florida, such as the Suwannee River Estuary (Quinlan et al 2007), the central Indian River Lagoon (Phlips et al 2010), the southern St. Lucie Estuary (Phlips et al 2012) and the outer estuary of the St. Johns River (Cichra & Phlips, unpublished data).…”

“…The dinoflagellate Akashiwo sanguinea (Hirasaka) G. Hansen & Moestrup plays a major role in the ecology of many marine environments, including coastal ecosystems with variable salinities, where its euryhaline character makes it competitive (Steidinger & Tangen 1996, Phlips et al 2011, 2012. Gymnodinium sanguineum was first reported as a red tide-forming organism along the coast of Japan (Hirasaka 1922).…”

“…It was later renamed A. sanguinea (Hirasaka) G. Hansen & Moestrup, based on morphologic, ultrastructural, and phylogenetic relationships among a large assemblage of gymnoid-type dinoflagellates (Daughberg et al 2000). It is cosmopolitan in its distribution and has been observed to form blooms in coastal ecosystems around the world (Robinson & Brown 1983, Fukuyo et al 1990, Hallegraeff 1991, Voltolina 1993, Horner et al 1997, Lu & Hodgkiss 2004, Feyzioğlu & Öğüt 2006, including the Gulf of Mexico and the Atlantic coast of North America (Steidinger & Williams 1970, Robichaux et al 1998, Steidinger et al 1998, Badylak & Phlips 2004, Badylak et al 2007, Phlips et al 2011, 2012. Blooms of A. sanguinea have been associated with mass mortalities of invertebrates and fish in various regions of the world (Cardwell et al 1979, Jordán 1979, Harper & Guillen 1989, Shumway 1990, Kahru et al 2004).…”