• Category
  • Diameter
    18-27 µm
  • Synonyms
    Coscinodiscus balticus (Grunow) Grunow



Valves are disc-shaped, with a flat valve face and broadly curved valve/mantle interface. The areolae are loculate and are organized into radiate, sectored rows. Areolae number 15-18 in 10 µm, at mid-radius. Marginal fultoportulae are organized in two rows, one interior to the other. Close to the margin, the lower row of fultoportulae often appears spine-like. Up to seven central fultoportulae are organized concentrically around the valve center. Three rimoportulae are present on the valve face, closer to the valve margin than to the center of the valve.


Thalassiosira baltica is regarded as a non-native species in North America because it was recently introduced to the Laurentian Great Lakes (Edlund et al. 2000). This taxon was originally described from the Baltic Sea and is similar to many other euryhaline species. The observed range in diameter for North American freshwater populations of T. baltica is much smaller than the observations by Hasle (1978) in the Baltic Sea (20-120 µm).

Original Description

  • Basionym
    Coscinodiscus polyacanthus var. baltica
  • Author
    Grunow 1880
  • Length Range
    30-80 µm

Original Images

Coscinodiscus polyacanthus var. baltica orig descr

EMAP Assessment

EMAP Distribution

Thalassiosira Baltica   Grunow   Ostenfeld 40
Map 40

Response Plots

Thalassiosira Baltica   Grunow   Ostenfeld

Cite This Page

Burge, D, and Edlund, M. (2015). Thalassiosira baltica. In Diatoms of North America. Retrieved July 23, 2018, from https://diatoms.org/species/thalassiosira_baltica


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