Frustules are cylindrical and form colonies. Valves are 3-12 µm in diameter, with a mantle height of 5-15 µm. The ratio of the mantle height to valve diameter is greater than 1. The mantle has straight sides and the valve face is flat with slightly convex margins. The valve face of most valves do not have areolae, but a single ring of areolae might be found on the valve face of separation valves. The spiral rows of pervalvar areolae are curved to the right (dextrorse) and number 17-22 in 10 µm. The areolae are round to square in shape. Spines are located at the end of each pervalvar costa. Linking spines are short, triangular or bifurcated. Two lobes of the spines are rounded or acute. Separation spines are small and pointed. In some separation valves, rows of areolae coalesce when they approach the valve face, thus giving the appearance of spines originating from two pervalvar costae. The ringleiste is hollow, described in the literature as a "U-shaped sulcus". The valves have two rimoportulae, located at the ringleiste and opposite to one other.
Colonies are usually straight, but may be spiral with curved cells. Such populations have been described as separate forms of A. ambigua (Melosira ambigua f. spiralis Skuja 1948; M. ambigua f. curvata Skabichevskii 1960; M. ambigua f. spiroides Chalfina 1966), but there is no evidence that the trait has taxonomic significance.
This taxon is reported to be widespread in freshwater (Foged 1981, Cox 1996). Originally described from Belgium (Grunow 1882), in North America this taxon has been reported from lakes in the northeastern US (Camburn and Charles 2000, Siver et al. 2005), Virginia, Georgia, South Carolina (Bishop et al. 2017), the western US (Bahls 2021), Alaska (Foged 1981) and Ohio (Collins and Kalinsky 1977). Colonies are found in the plankton of oligotrophic (Bahls 2021), mesotrophic (Siver et al. 2005), and eutrophic waters (Cox 1996). This taxon appears to prefer large and deep waterbodies (Siver et al. 2005, Siver and Hamilton 2011), although it has also been reported from the plankton of rivers (Hansmann 1973, Bahls 2021). Reavie and Kireta (2015) report it to be a very weak indicator of moderate stress.
In the Great Lakes National Parks (Edlund et al. 2011, 2012, 2013), this taxon is very common (>10% relative abundance) in sediment core material from lakes in Isle Royale (Richie and Ahmik lakes), Voyageurs (Shoepack, Peary, Mukooda, Brown and Ek lakes), Sleeping Bear Dunes (Manitou Lake), and Pictured Rocks (Grand Sable and Beaver lakes).
This taxon prefers circumneutral to alkaline waters (Foged, 1981, Siver et al. 2005, Bahls 2021).
Foged (1981) describes it as an “oligohalobe (indifferent)” suggesting that this taxon prefers low conductivity systems but is not particularly sensitive to conductivity. Bahls (2021) also states that this taxon prefers water with low conductivity.
Many research groups have used this taxon as an indicator organism and published regional environmental optima and tolerances including:
Camburn and Charles (2000): Abundance Weighted Mean (AWM) pH – 6.47 +/- 0.77 AWM Acid Neutralizing Capacity – 76 +/- 122 µeq/L, AWM Total Al – 72 +/- 85 µg/L, AWM Dissolved Organic Carbon – 207 +/- 174 µmol/L, Total Phosphorus (TP) – 14.3 +/- 0.8 µg/L for populations from low alkalinity lakes of the American Northeast.
Reavie and Smol (2001): TP – 0.016 mg/L, pH – 8.14, Total Nitrogen – 0.469 mg/L, Max Depth – 19.4 m, Chla – 1.72 mg/L for populations from lakes in southeastern Ontario.
Siver et al. (2005): pH optima – 6.5 +/- 0.7, TP optima – 14.3 +/- 0.8 µg/L for populations from Cape Cod.
Reavie and Kireta (2015): Report TP optima well over 30 µg/L, and a Cl optima below 10 µg/L for populations from the Great Lakes.
Bahls (2021): Conductivity – 100 µS/cm, pH – 7.6, Temperature 14.0 °C, TN – 0.170 mg/L TP – 6 µg/L for populations from the Rocky Mountains, Cascades Range, Sierra Nevada Mountains, and the Great Plains.
From 2010 until 2024 the autecological information on this taxon page was limited. As of this update, information on ecology, biogeography, and environmental optima have been added. - Lane Allen & Mark Edlund
Potapova, M., English, J., Allen, L., Edlund, M. (2010). Aulacoseira ambigua. In Diatoms of North America. Retrieved December 09, 2024, from https://diatoms.org/species/45215/aulacoseira_ambigua
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Aulacoseira ambigua from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.