Navicula aurora

This taxon has been recorded in the benthos of streams and lakes, primarily in the Pacific Northwest. It prefers cool and somewhat alkaline waters with low conductivity and low to moderate concentrations of nutrients. Common associates in the Northwest include Diploneis ovalis, Nitzschia innominata, Planothidium peragalli, Planothidium daui, Cavinula cocconeiformis, Geissleria schoenfeldii, Achnanthes oblongella, Planothidium rostratum, Planothidium lanceolatoides, and Achnanthidium rivulare (Bahls 2011).

Originally described based on populations from Crater Lake, Emerald Pool, and Diamond Lake with a total of 30 collections reported from Washington state (Sovereign 1958). Reported to be widespread in the Pacific Northwest (Sovereign 1958, Patrick and Reimer 1966). In North America, this taxon has been reported from Washingthon, Oregon (Sovereign 1958), mountain streams and lakes in the Rockies, the Coast and Cascade ranges and the Sierras (Bahls 2021) and Alaska (Foged 1981).

In the Great Lakes National Parks (Edlund et al. 2011, 2012, 2013), it is rare except (>1% relative abundance) in sediment core material from Shell Lake in Sleeping Bear Dunes National Lakeshore.

Originally reported from slightly alkaline waters (Sovereign 1958) Foged (1981) stated “Oligohalobe (indifferent). pH: indifferent” regarding populations from Alaska. Bahls (2021) reported this taxon to prefer cold alkaline waters with moderate nutrients and conductivity. This is also supported by the report by Clark and Rushforth (1977) regarding the abundance of this diatom in their study of the headwaters of Henry’s Fork in Idaho.

Both Clark and Rushforth (1977) and Bahls (2021) report this taxon to be highly variable in morphology, with Bahls specifying that lacustrine populations are typically larger than those found in lotic systems.

Several research groups have used it as an indicator organism and published regional environmental optima and tolerances including:

Sovereign (1958): pH tolerance range 6.5-9.0 for populations from the Pacific Northwest.

Bahls (2021): pH – 8.0, Conductivity – 213 µS/cm, Temperature – 12.4 °C , Total Nitrogen – 0.590 mg/L, Total Phosphorus – 57 µg/L for populations from the western US.