Navicula rhynchocephala

Reported to be widespread in freshwater (Patrick and Reimer 1966, Hansmann 1973, Foged 1981, Cox 1996). In North America this taxon has been reported from Alaska (Foged 1981), Utah (Grimes and Rushforth 1982, Bateman and Rushforth 1984), Quebec (Reavie and Smol 1998) Cape Cod (Siver et al. 2005), Virginia, South Carolina (Bishop et al. 2017), and all states and ecoregions in the northwest (Bahls 2021). This taxon is reported to occur in rivers, streams (Bahls 2021), ponds (Siver et al. 2005), and lakes (Grimes and Rushforth 1982, Bateman and Rushforth 1984). Bahls (2021) reported that this taxon mostly occurs in the mountains.

In the Great Lakes National Parks (Edlund et al. 2011, 2012, 2013), this taxon is common (1-10% relative abundance) in sediment core material from lakes in Sleeping Bear Dune (Shell and Bass lakes) and Isle Royale (Ahmik Lake).

Reported to prefer alkaline waters (Sovereign 1958, Foged 1981, Siver et al. 2005, Novais et al. 2014, Bahls 2021). Most sources also report a preference for low to moderate conductivity (Foged 1981, Cox 1996, Bahls 2021); however, Patrick and Reimer (1966) reported it to be, “halophilous to indifferent to small amounts of chloride”, and Çelekli et el. (2018) report this taxon to be associated with elevated conductivity and nutrient content. Bahls (2021) reported this taxon to prefer waters with low to moderate nutrients. Cox (1996) reported this taxon to occur in β-α-saprobic conditions. Novais et al. (2014) reported that this taxon is indicative of permanent waterbodies, but also report it to occur in periodic water or wet subaerial habitats. Novais et al. (2014) also report this taxon to be indifferent to current and trophic state. Reavie and Andresen (2020) report this taxon to be a very weak indicator of moderate environmental stress in the Great Lakes.

Several research groups consider this taxon as an indicator organism and published regional environmental optima and tolerances including:

Sovereign (1958): pH 6.0-9.5 for populations from the pacific northwest.

Novais et al. (2014): Current Velocity – 0.57 m/s, range – 0.17-0.97 m/s, Temperature – 24.4°C, range 11.8-29.2°C, Conductivity – 210 µS/cm, range 65-616 µS/cm, pH – 6.7, range – 5.7-7.7, Dissolved Oxygen – 82.3%, range – 31.5-106.5%, Alkalinity – 43 mg/L, range – 25-157 mg/L, Calcium – 14.3 mg/L, range – 5.6-58.0 mg/L, Chloride – 34.1 mg/L, range – 9.9-163.8 mg/L, Hardness – 40 mg/L, range – 10-165 mg/L, Magnesium – 4.6 mg/L, range – 0.7-11.9 mg/L, Sodium – 4.3 mg/L, range - 0.7-13.1 for populations from Portugal.

Reavie and Andresen (2020): Total Phosphorus (TP) optima in excess of 30 µg/L, and Chloride optima between 10 and 50 µg/L for populations from the Great Lakes.

Bahls (2021): pH – 7.4, Conductivity – 685 µS/cm, Total Nitrogen – 1.140 mg/L, TP – 101 µg/L, Temperature – 13.9 °C for populations in the Northwest.