Achnanthidium minutissimum

This taxon is reported to be widespread in freshwater (Patrick and Reimer 1966, Hansmann 1973, Lawson and Rushforth 1975, Clark and Rushforth 1977, Foged 1981, Cox 1996, Camburn and Charles 2000, Antoniades et al. 2008, Bahls 2021), and in some habitats quite abundant (Hansmann 1973, Lawson and Rushforth 1975, Clark and Rushforth 1977, Antoniades et al. 2008). This taxon has been reported from North America in Idaho, Montana (this page), Ohio (Collins and Kalinsky 1977), the northeastern US (Camburn and Charles 2000), Cape Cod (Siver et al. 2005), and the western US (Bahls 2021).

In the Great Lakes National Parks (Edlund et al. 2011, 2012, 2013), this taxon is common (>5% relative abundance) in predominantly shallow lake sediment cores of lakes in Voyageurs (Locator, Little Trout, Mukooda, Brown, Ryan, and Ek lakes), Sleeping Bear Dunes (Florence and Bass lakes), and Apostle Islands (Outer Lake).

This species is considered a generalist, known to tolerate a wide variety of environmental conditions (Patrick and Reimer 1966, Foged 1981, Cox 1996, Siver et al. 2005), although many sources report that it prefers alkaline systems (Patrick and Reimer 1966, Foged 1981, Antoniades et al. 2008) and is most commonly found in streams (Bahls 2021). As noted in the original description (Kützing 1833), it can often be found growing epiphytically on chlorophytes but is also commonly observed in epilithic communities (Hansmann 1973). Cells typically attach to substrate by mucilage secreted from the cell.

It is commonly regarded as an oligohalibe (Patrick and Reimer 1966, Foged 1981), although these sources also indicate that it is relatively indifferent to salinity. Bahls (2021) states that this taxon prefers low to moderate conductivity. Cox (1996) reports it to be sensitive to wastewater and β-α-mesosabrobic conditions.

Many research groups have considered it an indicator organism and published regional environmental optima and tolerances including:

Wilson et al. (1994): Salinity optimum - 0.62 g/L with a lower limit of 0.03 g/L and an upper limit of 12.97 g/L for populations from lakes on the interior plateau of British Colombia.

Camburn and Charles (2000): pH – 7.04 +/- 0.68,  Acid Neutralizing Capacity – 168 +/- 119 µeq/L, Total Aluminum – 53 +/- 75 µg/L, Dissolved Organic Carbon – 194 +/- 151 µmol/L, Total Phosphorus (TP) – 8.24 +/- 5.45 µg/L for populations from the northeastern US.

Reavie and Smol (2001): TP – 0.016 mg/L, pH – 8.01, Total Nitrogen (TN) – 0.459 mg/L, Max Depth – 20.6 m, Chla – 1.71 mg/L for populations from lakes in southeastern Ontario.

Lim et al. (2001): TN – 0.808 +/- 0.221 mg/L for populations from Bathurst Island, Nunavut, Canada.

Siver et al. (2005): pH optima – 6.7 +/- 0.5, TP optima – 13.2 +/- 7.0 µg/L for populations from Cape Cod.

Lim et al. (2007): TN – 0.500 mg/L for populations from Banks Island in the N.W.T. of Canada.

Antoniades et al. (2008): pH – 8.4, pH Tol - 7.6-8.6, Conductivity – 132 µS/cm, Conductivity Tol – 60-290 µS/cm, DOC – 4.5 mg/L, DOC Tol – 2.09-9.67 mg/L for populations from the Canadian Arctic This taxon was treated as sensu lato in this publication.

Siver and Hamilton (2011): pH – 6.5 +/- 0.7, TP – 16.4 +/- 13.1 µg/L for populations from the eastern US, though this taxon was treated as sensu lato in this publication.

Bahls (2021): Conductivity – 338 µS/cm, pH – 7.5, Temperature – 12.6 °C, TN – 0.620 mg/L, TP – 50 µg/L for populations from the American northwest.