• Category
  • Diameter
    5.5-20.4 µm
  • Width Range
    8.9-18.3 µm
  • Striae in 10 µm
  • Synonyms
    Aulacoseira islandica ssp. helvetica (O.Müll.) Simonsen



Frustules are cylindrical, most often observed in girdle view as long filamentous colonies attached at the valve face to sister cells by linking spines. The valve face is flat and mantle is straight (8.9-18.3 µm high), becoming slightly curved near the valve face. The ratio of the mantle height to valve diameter greatly varies. Pervalvar rows of uniformly circular areolae form striae that run parallel to the mantle sides, occasionally curving slightly to the right (dextrorse). Interstriae terminate at the base of a spine. Separation spines are short and tapered, about as wide as a single areola. Linking spines are small and spathulate. Pervalvar rows of areolae occur 12-14 in 10 µm.

Valve polymorphism is common in A. islandica (Stoermer et al. (1981). Cell silicification and striae coarseness vary within populations, and attributed to silica availability (Stoermer et al. 1985). Early publications referred to filaments with only thickly silicified valves as alpha forms, filaments with only thinly silicified cells as beta forms, and filaments with valves with both types of silicification as gamma forms (Müller 1906). With more lightly silicified specimens occurring under low silica conditions, many authors regard this lightly silicified variety, often called A. islandica ssp. helvetica to be a morphotype (Stoermer et al. 1985, Genkal et al. 1986, Krammer and Lange-Bertalot 1991, Siver and Kling 1997). The images presented here document the moderately silicified form of A. islandica.

Alternatively, others have proposed that polymorphic variation is associated with seasonal life history strategies (Jewson et al. 2010). In the closely related species, Aulacoseira baicalensis (K. Meyer) Simonsen, longer and more heavily silicified forms were produced seasonally upon stratification. These cells functioned as resting cells capable of perennating in cooler waters of 50-150 m deep until autumn overturn.

Aulacoseira islandica also varies in striae and the spine structure. Two types of striae have been observed: 1) coarse striae comprised of complex areolae, which may be uniseriate or biseriate, and 2) fine striae that are uniseriate (Stoermer et al. 1981, Chou 1996). Furthermore, areolae may vary from round to slit-like (Siver and Kling 1997). In fact, the two types of areolae have been observed within the same filament (Siver and Kling 1997).

Both linking and separation spines differ within A. islandica. Separation spines are sharply tapered or lanceolate, while linking spines are spathulate (Chou 1996). The areolae and spine polymorphisms occur across the spectrum of silicification polymorphism (Stoermer et al. 1981).


Aulacoseira islandica is most often found in colonies occurring planktic or tychoplanktic in high latitude or high altitude oligotrophic to mesotrophic large waters (Stoermer et al. 1985, Genkal and Popovskaya 1991, Houk 2003), including large, shallow, and eutrophic post-glacial lakes such as Lake Winnipeg and Lake of the Woods (Siver and Kling 1997, Serieyssol et al. 2009). In the Laurentian Great Lakes A. islandica was observed most abundant in Lake Michigan and Lake Superior (Reavie & Kireta 2015). Recent, massive winter and spring blooms of A. islandica have also been occurring in Lake Erie (Lashaway and Carrick 2010, Twiss et al. 2012).

Original Description

  • Basionym
    Melosira islandica
  • Author
    O.Müll. 1906
  • Length Range
    7-27 µm

Original Images

Meislandica Original Image
Meislandica Original Text

Citations & Links



Cite This Page

Burge, D, and Edlund, M. (2015). Aulacoseira islandica. In Diatoms of North America. Retrieved July 22, 2018, from https://diatoms.org/species/aulacoseira_islandica


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Aulacoseira islandica 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.