Algae as Bioindicators - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 122

Ta b l e 3 . 8 Freshwater and Saltwater Wetland Diatoms (Florida, USA): Salinity
Optima and Tolerance.

Salinity
Optimum a

Salinity
Tolerance a Species

Diatoms with lowest salinity optima
Achnanthidium minutissimum

1.80 0.20

Nitzschia nana 1.83 0.72

Navicula subrostella 1.84 0.21

A. Open freshwater marshland
Nitzschia palea var. debilis 2.06 1.24

Encyonema evergladianum 2.25 1.51

Brachysira neoexilis 2.69 1.77

B. Forested freshwater marshland
Nitzschia semirobusta 2.19 0.86

Fragilaria synegrotesca 3.41 2.68

Mastogloia smithii 4.20 2.75

C. Mangrove Saltwater swamp
Amphora sp.

11.79 1.57

Achnanthes nitidiformis 17.28 0.51

Tryblionella granulata 18.38 0.92

Diatoms with highest salinity optima
Caloneis sp. 20.52 1.06

Tryblionella debilis 20.86 1.33

Mastogloia elegans 20.99 1.03

Source : Gaiser et al ., 2005. Reproduced with permission of Taylor and Francis.
Diatoms are listed in relation to
∙ Dominant species in three major wetland ecosystems (A, B, C)
∙ Three species with lowest salinity optima (Ecosystem A), shaded area - top of table
∙ Three species with highest salinity optima (Ecosystem C), shaded area - bottom of table
a Salinityvaluesgivenasppt.Optimumandtolerancelevelsforindividualspeciesarederived
from environmental analyses (see text).

Predictive model The salinity optima and tolerance data shown in Table 3.8 were derived from environ-
mental samples. Analysis of diatom species composition and salinity (along with other water parameters) was
carried out over a wide range of sites. Salinity optima for individual species were determined from those sites
where the species had greatest abundance, and salinity tolerance was recorded as the range of salinities over
which the species occurred.
The species-related data were incorporated into a computer model that could predict ambient salinity (in
an unknown environment) from diatom community analysis. Environmental salinity at a particular site was
determined as the mean of the salinity optima of all species present, weighted for their abundances. Predicted
values for salinity based on such diatom calibration models are highly accurate (error < 10%). Measurement
of salinity using a portable meter has a high degree of accuracy, but values often show considerable variation
along a time sequence of readings. One advantage of the use of bioindicator species in this context is that such
variability is reduced because the effects of salinity on diatom communities are integrated over a period of time.