The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Prymnesium parvum
(golden algae)

Copyright Info
Prymnesium parvum N.Carter

Common name: golden algae

Taxonomy: available through www.itis.govITIS logo

Identification: Prymnesium parvum is a microscopic, single-celled algae with four morphologically distinct forms (Larsen 1998). Three of the forms are scaled, bi-flagellated, and have a flexible, non-coiling, needle-like filament called a haptonema. The fourth form is a scaled, non-motile, siliceous cyst (Manton 1966; Genitsaris et al. 2009). The scales are found in two layers: inner scales have narrow, inflexed rims, and outer scales have wide, inflexed rims (Green et al. 1982). Two of the flagellated forms are haploid, and are described as two separate forms: P. parvum f. patelliform and P. parvum f. parvum. Both have two layers of scales but ornamentation differs between forms when viewed with a transmission electron microscope (Larsen 1999, Johnsen et al. 2010). The cyst and third flagellated forms are both diploid. All forms contain two, yellow-green, saddle-shaped chloroplasts in the front of the cell near the flagella (Holdway et al. 1978). Flagella are 10 to 14.5 μm long and the haptonema is 3 to 5 μm long. Body scales are 0.3 μm long. Cysts are ovoid, 9.3 to 10.8 μm long and 6 to 6.4 μm wide and have a sub-anterior pore 2.75 to 3 μm in diameter (Green et. al 1982).

Size: Cells are 6 to 12 µm long and 3.5 to 8 µm wide

Native Range: Unknown, but P. parvum is ubiquitous worldwide in temperate zones and was first documented in the eastern hemisphere in the early 1900s (Liebert and Deerns 1920). The first confirmed P. parvum bloom in North America was in 1985 in Texas on the Pecos River (James and De La Cruz 1989). 

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, 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 Prymnesium parvum are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
TX199720198Brady; Chambers; Colorado Headwaters; Concho; Lower Prairie Dog Town Fork Red; North Fork Double Mountain Fork Brazos; Toyah; Wichita

Table last updated 12/6/2021

† Populations may not be currently present.

Ecology: Prymnesium parvum inhabits a variety of waterbodies including rivers, lakes, estuaries, fjords, coastal oceans, and ponds, including eutrophic, alkaline, and brackish waters (Granéli et al. 2012). Under optimal conditions, P. parvum can reproduce rapidly and form a nearly monocultural bloom by releasing toxins into the water that immobilize or kill zooplankton and other phytoplankton to increase available food sources. It can survive in a range of water temperatures, from 5°C to 35°C, with blooms increasing between 10°C to 27°C (Larsen et al. 1998; Baker et al. 2007; Grover et al. 2007). P. parvum can live in near-freshwater to marine conditions, from 0.5 practical salinity units (psu) to 45 psu, (Larsen et al. 1993; Larsen et al. 1998; Baker et al. 2007) with optimum growth between 7 to 22 psu (Baker et al. 2007; Weissbach and Legrand 2012; Rashel and Patino 2017). Roelke et al. (2016) hypothesized that P. parvum bloom formation is most common when cells are in intermediate salinity and under moderate environmental stress because allelopathic and toxic chemical production is too low in low salinity/high stress and vice versa. The opposite trend is seen for nutrient concentrations, where P. parvum growth and toxicity is minimal when nitrogen and phosphorus ratios are balanced, and increase as the environment becomes more deficient in one of the nutrients (Granéli and Johansson 2003a,b; Granéli et al. 2012), particularly phosphorus (Granéli and Johansson 2003b; Uronen et al. 2005; Hambright et al. 2014). Toxicity was also consistently higher in pH of 8.5 compared to 6.5 and 7.5 (Valenti et al. 2010).
Prymnesium parvum has a sexual haploid-diploid life cycle with four forms, 3 motile and one resting cyst form that may serve to reseed populations following unfavorable conditions (Garcés et al. 2001; Granéli et al. 2012). It’s growth rate ranges from 0.3 to 1.15 cell divisions per day via mitosis, increasing as environmental conditions become more favorable (Larsen et al. 1998).

It is mixotrophic, supporting its growth with autotrophy (photosynthesis) or heterotrophy if nutrients are scarce (typically during a bloom event) (Fistarol et al. 2003; Tillmann 2003; Granéli and Johansson, 2003a). During a P. parvum bloom when toxin concentrations are high enough to lyse the cells of zooplankton and other phytoplankton, P. parvum can consume them by phagotrophy and absorb the recently released dissolved organic material by saprophy, effectively resisting potential inorganic nutrient limitation from their rapid growth (Granéli et al. 2012; Roelke et al. 2016). As competition is reduced, P. parvum blooms can grow and begin to produce toxin concentrations capable of killing larger organisms, including fish and invertebrates (Ultizer and Shilo 1966; Ulitzer 1973; Granéli et al. 2012; Svendsen et al. 2018). A few grazers, including some ciliates, rotifers, and dinoflagellates, do consume P. parvum but only when it is not in bloom or producing toxins (Tillman 2003; Rosetta and McManus 2003; Schwierzke et al. 2010).

Means of Introduction: Vectors are thought to be ballast water and global trade of aquaculture (Hallegraeff and Gollasch 2006), and local dispersal is attributed to transportation by birds, wind, and anthropogenic movement (drilling equipment, water tankers, and recreational boats) (Kristiansen 1996; Renner 2009).

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


Prymnesium parvum produces toxins that can destroy fish gills (Ulitzur and Shilo 1966), and can kill both fish and other aquatic organisms such as tadpoles (Shilo and Aschner 1953). Dense agregations of P. parvum lead to eutrophic conditions that produce large fish and animal kills in both freshwater in marine systems around the world (Karlson et al 2021; Renner 2009; Southard et al 2010), including aquacultural areas and fish farms (Gordon and Colorni 2008).

Remarks: A genetic analysis of U.S. P. parvum strains from northern and southern states revealed that their DNA sequences were more similar to various European strains than to each other, indicating that invasions may have been independent and relatively recent (Lutz-Carrillo et al. 2010).

References: (click for full references)

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Baker, J.W. et al. 2007. Growth and toxicity of Prymnesium parvum (Haptophyta) as a function of salinity, light, and temperature. Journal of Phycology 43(2):219-227.

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Author: Bartos, A., and C.R. Morningstar

Revision Date: 10/21/2021

Citation Information:
Bartos, A., and C.R. Morningstar, 2021, Prymnesium parvum N.Carter: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=3234, Revision Date: 10/21/2021, Access Date: 12/7/2021

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.


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Citation information: U.S. Geological Survey. [2021]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [12/7/2021].

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