Actinocyclus normanii f. subsalsus, Coscinodiscus radiatus Ehrenb, Coscinodiscus rothii  f. minor, Coscinodiscus rothii var. subsala, Coscinodiscus rothii var. subsalsum, Coscinodiscus subsalsus Juhlin-Dannfelt 1882, Coscinodiscus subtilis var. fluviatilis, Coscinodiscus subtilis var. rothii

Based on algal biovolumes and relative cell densities, Actinocyclus normanii f. subsalsa is considered more of a spring than summer diatom in the Great Lakes (Reavie et al. 2014), giving Actinocyclus normanii f. subsalsa a potentially lower thermal optimum than previously defined by Sicko-Goad et al. 1989. It may be limited by light in some environments but is generally considered well adapted to fluctuating light levels and turbulent vertical mixing. Although this species is heavily silicified, it is also well adapted to avoiding or tolerating silica limitations.

It can produce resting cells as auxospores that fall to the bottom of lakes and after rejuvenation migrate back towards the surface (Sicko-Goad et al. 1989). The journey up the water column may help in the collection of nutrients (Smetacek, 1985; Finkel, et al., 2005). Actinocyclus normanii f. subsalsa often blooms in summer and fall. It typically occurs in shallow bays and nearshore regions of the Great Lakes (Ferrario et al. 1989; Gomez 1991; Hasle 1977; Hughes et al. 2000; Liukkonen et al. 1997; Mercado 2003; Pappas and Ungelbach 2002; Rehbehn et al. 1993; Sala 1997; Stachura and Witkowski 1997; Sicko-Goad et al. 1989; Stoermer et al. 1985, 1993; Teubner 2000; Munawar et al. 2017; Sgro and Reavie 2018).

Hohn (1969) identified this taxon as Coscinodiscus radiatus in Lake Erie and reported it was most abundant in August and September while it was absent in the colder months of the year. A. normanii was dominant in the highly eutrophic western basin of Lake Erie from 1950 to 1985 with a peak in 1964 (Sgro and Reavie 2018). It appears to be common in eutrophic waters (Mills et al. 1993), Green Bay (Stoermer and Yang 1969), Saginaw Bay (Stoermer and Theriot 1985) but uncommon in the offshore waters of Lake Ontario (Stoermer et al. 1974).

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

Environmental	Socioeconomic	Beneficial

Actinocyclus normanii f. subsalsa has a moderate environmental impact in the Great Lakes.

Realized:
Actinocyclus normanii f. subsalsa was identified in both spring and summer seasons in the Great Lakes, giving it the potential for a distribution across a large temperature gradient (Reavie et al. 2014). Additionally, warmer waters may enhance their growth. A laboratory study observed sustained growth of Actinocyclus normanii f. subsalsa at temperatures greater than 20°C and benefits from the resuspension of resting cells under turbulent mixing conditions (Sicko-Goad et al 1989). As a result, its potential distribution within the Great Lakes basin may be more likely in shallow bays with sufficient light penetration.

Due to the high demand for silica for its heavily silicified walls, during blooms, A. normanii f. subsalsa may deplete the dissolved silica concentration of shallow bays. However, the diatom Aulacoseira islandica is generally associated with the silica depletion in Lake Erie (Reavie et al. 2016).  The resulting silica-limited environment is detrimental to species of native diatoms that are dependent on silica availability and promotes the growth of harmful blue-green algae (Edlund et al. 2000; Stoermer and Theriot 1985). Further, zooplankton preferentially consumes diatoms such as  A. normanii f. subsalsa over cyanobacteria, the latter of which lacks polyunsaturated fatty acids minimizing grazing pressure and competition for nutrients and potentially promoting harmful algae blooms (Dmitrieva & Semenova 2011). Sediment cores taken from Lake Ontario indicate the introduction of Stephanodiscus binderanus and A. normanii f. subsalsa is correlated with the extirpation of native species including S. transilvanicus, Cyclotella comta, C. michiganiana, C. ocellata, and C. stelligera (Stoermer et al. 1985).

Actinocyclus niagarae is the only other species of the same genus in the Great Lakes and no research indicates that the two species are influencing each other genetically (Stoermer and Kreis 1978).

Potential:
Actinocyclus normanii f. subsalsa was found to be a major source of particulate nitrogen in one New England estuary, where it reached 99% abundance—greater than that observed in the Great Lakes. Under these conditions, Actinocyclus normanii f. subsalsa supported many consumers, including planktonic copepods, benthic amphipods, grass shrimp, mud crabs, alewife, and white perch (Hughes et al. 2000). It is unclear if A. normanii f. subsalsa has a similar effect in the Great Lake populations.

There is little or no evidence to support that Actinocyclus normanii f. subsalsa has significant socio-economic impacts in the Great Lakes.

The potential for a high abundance of A. normanii f. subsalsa is associated with blue-green algae blooms, which can severely impact water quality (Edlund et al. 2000).

There is little or no evidence to support that Actinocyclus normanii f. subsalsa has significant beneficial effects in the Great Lakes.

Actinocyclus normanii f. subsalsa is a species that is used to identify the history of pollution in sediment cores from lakes (Stoermer et al. 1985). The size of the diatom can also be used to determine the salinity of the waterbody it resides in with size increasing with salinity (Vidal et al. 2018).

Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.
Note: Check federal, state/provincial, 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
Actinocyclus normanii f. subsalsa is one of the most pollution tolerant algal species and thrives in warm, shallow, and eutrophic waters (Edlund et al. 2000). The reduction of pollution and nutrient run-off would decrease the viable habitat for A. normanii f. subsalsa.

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

Debate continues whether or not the two forms of Actinocyclus normanii should be considered separate taxa due to its ability to shift its reproduction method and size based on salinity. At a salinity of  8 - 30 ppt, Actinocyclus normanii reproduces sexually, producing larger cells (> 40 μm) commonly referred to as var. normanii. In fresher waters (<8 ppt) it reproduces asexually, resulting in smaller cells (< 40 μm) typically identified as f. subsalsa (Vidal et al. 2018). The U.S. Environmental Protection Agency currently identifies the nominate Actinocyclus normanii as a single taxon including both forms (Sgro and Reavie 2018; USEPA 2020).