Species Profile - Chaetoceros muelleri var. subsalsus

Chaetoceros muelleri var. subsalsus (Lemmermann) J.R. Johansen and Rushforth

Common Name: A centric diatom

Synonyms and Other Names:

C. muelleri var. subsalsa; C. hohnii

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Dr. Mary Ann Tiffany Copyright Info

Identification: This small, somewhat silicified diatom species exhibits around 8 costae per µm on the valve, valve mantle, and girdle bands, arranged in a radiating pattern. At the valve and mantle joints there are centric tubular setae. There is no central labiate process on the valves. Valves are round to oval in shape and cells are cylindrical in side view. Cells occur singly or occasionally in groups of 2–3 forming short filaments. Spores are silicified. Living cells contain one chromatophore (Wujek and Graebner 1980; Johansen and Rushforth 1985). C. muelleri var. subsalsum valves range in length from 3–20 µm. Resting spores are around 4–12 µm in length. The range for specimens recorded from the Great Lakes is 3–10.5 µm and there have been no recorded spores (Wujek and Graebner 1980; Johansen and Rushforth 1985).

Size: Up to 20 microns

Native Range: Widespread. Originally reported from Europe and subsequently from Russia and North America. According to Rushforth and Johansen (1986) the taxonomy of this group is somewhat unresolved. Chaetoceros muelleri var. subsalsum probably originated in a marine or brackish water environment.

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This map only depicts Great Lakes introductions. Click here for Great Lakes region collection information

Great Lakes Nonindigenous Occurrences: C. muelleri var. subsalsum was recorded for the first time in Saginaw Bay, Lake Huron, and tributaries flowing into this bay in 1978 (Wujek and Graebner 1980; Mills et al. 1993).

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Chaetoceros muelleri var. subsalsus are found here.

State/Province	First Observed	Last Observed	Total HUCs with observations†	HUCs with observations†
MI	1978	1978	1	Lake Huron

Table last updated 4/26/2025

† Populations may not be currently present.

Ecology: The genus Chaetoceros is generally a marine taxon. It is likely that C. muelleri var. subsalsum is an introduced species and not native to the Great Lakes, even though it was first described there. Other nonindigenous species in the genus Chaetoceros have been recorded in ballast water samples from vessels entering the Great Lakes (Mills et al. 1993).

The only Chaetoceros spp. known from North America are C. elmorei and C. muelleri. C. muelleri var. subsalsum is a mesohalobe variant of C. muelleri, originally described from the Great Lakes as a new species, C. hohnii. Extensive studies on material from North America and South Africa indicate that C. muelleri var. subsalsum is distinct from C. muelleri (Wujek and Graebner 1980; Johansen and Rushforth 1985).

Saginaw Bay, the area of the Great Lakes where C. muelleri var. subsalsum was collected historically, has high nutrient levels. Water salinity is the primary factor controlling population growth rates of C. muelleri var. subsalsum. In the Tittabawassee River, which is part of the Lake Huron drainage, water chemistry at the time C. muelleri var. subsalsum was recorded fell within a preference range expected for a species of brackish or marine origin. Conductivity ranged from 570-2690 µmhos/cm and ion concentrations (such as chloride, potassium, sodium, magnesium, and calcium) were higher than those normally expected in freshwater. The pH at the time was 7.8–8.0 and the water temperature was 17–18°C. Abundance of C. muelleri var. subsalsum ranged up to 188 cells per ml, which is less than 1% of the phytoplankton present at the time (Wujek and Graebner 1980). In the Pecos River, New Mexico, C. muelleri var. subsalsum has been recorded to reach a maximum abundance at conductivities of 1100-5200 µmhos/cm and temperatures around 25°C (Johansen and Rushforth 1985).

Chaetoceros muelleri var. subsalsum is capable of producing spores. It is unknown what triggers spore production in freshwater populations, as some populations produce none while others produce many. Salinity may be a factor. No spores have been recorded in populations from the Great Lakes (Wujek and Graebner 1980; Johansen and Rushforth 1985).

Means of Introduction: C. muelleri var. subsalsum was very likely introduced to the Great Lakes via ballast water (Mills et al. 1993).

Status: Reported. There have been no records since the first publication by Wujek and Graebner (1980).

Great Lakes Impacts:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental

There is little or no evidence to support that Chaetoceros muelleri var. subsalsum has significant environmental impacts in the Great Lakes.

Potential:
Given the right water chemistry, Chaetoceros muelleri var. subsalsum is capable of sustaining abundant populations (Fuji et al. 1995). Saginaw Bay, the area of the Great Lakes where C. muelleri var. subsalsum was collected historically, has high nutrient levels. Water salinity is the primary factor controlling population growth rates of C. muelleri var. subsalsum. Nutrient conditions in Saginaw Bay, particularly regarding salinity levels, are not available and therefore limit predictions of the potential impacts of C. muelleri var. subsalsum (Chapra et al. 2009). Large populations of C. muelleri could alter predator-prey relationships, but the water conditions for a large population are not currently being met in Saginaw Bay. Depending on other restoration initiatives this could change.

Chaetoceros muelleri var. sublasum is the only species in the Great Lakes of this genus and there is only one other species of its order found in the Great Lakes, making hybridization unlikely.

There is little or no evidence to support that Chaetoceros muelleri var. subsalsum has significant socio-economic impacts in the Great Lakes.

There is little or no evidence to support that Chaetoceros muelleri var. subsalsum has significant beneficial effects in the Great Lakes.

Management:

Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.

Note: Check federal, state, and local regulations for the most up-to-date information.

Control
Biological
There are no known biological control methods for this species.

Physical
There are no known physical control methods for this species.

Chemical
The reduction of nutrient pollution, specifically of NaCl, would eliminate viable water conditions for C. muelleri var. subsalsum in the Great Lakes.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: C. muelleri var. subsalsum is synonymous with C. hohnii (Johansen and Rushforth 1985). Stoermer and Kreis (1978) recorded Chaetoceros spp. in the Great Lakes but gave no further details as to species, location, or description.

References (click for full reference list)

Other Resources:

Great Lakes Waterlife

Author: Kipp, R.M., M. McCarthy, and A. Fusaro

Contributing Agencies:

Revision Date: 9/12/2019

Citation for this information:
Kipp, R.M., M. McCarthy, and A. Fusaro, 2025, Chaetoceros muelleri var. subsalsus (Lemmermann) J.R. Johansen and Rushforth: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=1674, Revision Date: 9/12/2019, Access Date: 4/26/2025

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.