Stephanodiscus alpinus Hustedt

Diameter: 31

Areolae: 7

Collection 1189

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These two images of the specimen depict different focal planes.

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  • Stephanodiscus alpinus has been investigated by Hakansson and Stoermer (1984). Original material and Great Lakes material have been compared by Hakansson and Stoermer (1984) and Theriot and Stoermer (1982). The Great Lakes material shows greater variability than the type material, however material from the type locality show as much variability as the Great Lakes material (Hakansson and Stoermer 1984). The diameter range is 7-33 um. The striae are for the most part biseriate near the margin however triseriate fasicles are known (see Hakansson and Stoermer 1984, fig. 16). [Specimens from Lake Michigan have been found in which the striae are composed of a single series of areolae for most of the stria until just at the margin the areolae become a double series for one or two areolae.] This should be considered part of the morphological variability present in this taxon. The fascicles are separated by conspicuous interfascicles (sometimes called "ribs" in older literature). Generally spines are located at the margin of each interfascicle. There is some variation in this character. Sometimes spines are broken off while in other cases the spine never developed. It is impossible to differentiate between these conditions at the light microscope level. The valve face is concentrically undulate. Both concave and convex central areas are known.

    For SEM's of Stephanodiscus alpinus see Gaul et al. 1993.

  • Ecology
    According to Stoermer and Ladewski (1976) Stephanodiscus alpinus appears to prefer temperatures below 2 degrees Celcius however it is present in low numbers throughout the investigated temperature range (up to 24 degrees Celcius). It is a winter dominant in Lake Ontario (Stoermer et al. 1975) and a component of the spring pulse in Lake Erie continuing throughout the year (Hohn 1969). It is present in Lakes Huron and Superior where its abundance is low (Stoermer and Ladewski 1976). Huber-Pestalozzi (1942) states that it is bound to low temperatures and found in the hypolinmion of lakes in the eastern alps. It appears to tolerate slight nutrient enrichment (Stoermer and Yang 1970).

    Size ranges and morphology