Fragilaria synegrotesca

Fragilaria synegrotesca is well documented in shallow water, karstic, oligotrophic wetlands of the Florida Everglades and Caribbean. It is abundant in benthic and epiphytic calcareous periphyton communities and is typical of low phosphorus (P), long hydroperiod, and slightly high conductivity. In the freshwater interior of the Everglades the optimum total periphyton biovolume for F. synegrotesca presence is 900 mL/m with a tolerance from 0 (in benthic, flocculent detritus) – 2900 mL/m (Lee et al. 2013). In the Everglades, F. synegrotesca comprises 11.2 – 18% of diatom abundance in periphyton and is among the five most common diatom species encountered in transects across the Water Conservation Areas, Shark River Slough, and Taylor Slough (Gaiser et al. 2006, La Hée and Gaiser 2012, Lee et al. 2013), with a maximum abundance of 72.54% (Lee et al. 2013) and presence in 149 of 197 samples (Gaiser et al. 2006). In Caribbean wetlands, the relative abundances of F. synegrotesca in periphyton are 14% (New River Lagoon in Orange Walk, Belize), 6% (Sian Ka’an Biosphere Reserve in Quintana Roo, Mexico), and 6.6% (Black River Morass, St. Elizabeth, Jamaica).

In P-limited Caribbean wetlands, F. synegrotesca total phosphorus (TP) optimum is 266 µg P/g with a tolerance range of 145 – 488 µg P/g (La Hée and Gaiser 2012). In the Everglades, F. synegrotesca TP optima have been recorded as 270 ± 202 µg P/g (Gaiser et al. 2006) and 168 µg P/g with a tolerance range of 80 – 355 (La Hée and Gaiser 2012).

Fragilaria synegrotesca is characteristic of and abundant in periphyton communities of freshwater marshes with little drying, with a hydroperiod optimum of 258 ± 48 days inundated (Lee et al. 2013). Drying and subsequent rewetting of the periphyton mat decreases F. synegrotesca relative abundances from up to 18 ±11% to 6 ± 5% (Gottlieb et al. 2005), making this species a potentially “reliable indicator of the absence of periodic drying” in hydrologically controlled habitats like the Everglades (Gaiser et al. 2011).

Fragilaria synegrotesca is characteristic of low nutrient and low conductivity freshwater periphyton, but it has also been found in the oligohaline region of the Everglades. It has a salinity optimum and tolerance of 5 ±7.3 ppt – slightly higher than other freshwater Everglades taxa such as Encyonema evergladianum, Mastogloia calcarea and Brachysira neoexilis (Wachnicka 2010).

There are confirmed distribution records (by Gaiser and colleagues) of F. synegrotesca in freshwater and oligohaline regions of the Everglades and in three regions in the northern Caribbean Basin: the New River Lagoon in Orange Walk, Belize; the Sian Ka’an Biosphere Reserve in Quintana Roo, Mexico; and the Broad River in the Black River Morass, St. Elizabeth, Jamaica.