Eubranchipus oregonus, commonly known as the Oregon fairy shrimp, belongs to the order Chirocephlidae.
E. oregonus thrives in a diverse range of habitats, including ephemeral pools within deciduous forests, particularly during colder seasons. While these habitats are often associated with tannin-rich environments and low dissolved solids, E. oregonus is not limited solely to these conditions.
In western Oregon and Washington, where the characteristic habitat prevails, pond water is typically neutral to mildly acidic under normal conditions. In contrast, ponds in eastern Oregon and likely eastern Washington exhibit mild to strongly alkaline conditions. Despite these regional variations, E. oregonus showcases adaptability across a spectrum of environments (Coopey, 1950).
The distribution of this species encompasses fewer than 40 locations in the Pacific Northwest, stretching from southern British Columbia, including the Lower Mainland, south Vancouver Island, and select Gulf Islands, to northern California. Additional occurrences include isolated populations in the wetter regions of the Sierra Nevada Mountain range and Oklahoma (“Eubranchipus oregonus,” Wikipedia). In the United States, the species is predominantly found in California, Washington, and Oregon.
Anatomy: The characteristics outlined below may exhibit variations influenced by environmental conditions, population dynamics, and the organism's age.
Head:
Second Antenna:
Male: The distinguishing feature lies in the triangular antennal appendage, and the distal segment of antenna II is sickle-shaped, with the tip directed medially. Particularly noteworthy is the fairly small second antenna on males compared to the rest of the body, serving as the primary key identifier (Belk, 1975).
Female: Females possess a reduced second antenna.
Thorax:
Dorsolateral Process:
Male: Absent.
Female: Absent.
Thoracopods:
This structure is similar between sexes, featuring fine setae on the edges of the limb.
Reproductive Segments:
Male: A pair of penes.
Female: In the current collections, mature females typically carried 150-250 fully developed eggs in their ovisac, characterized by a bulbous brood pouch that is elongated and slender, extending slightly to abdominal segments 3 and 4 (Coopey, 1950).
Cyst:
Spherical in shape with minor indentations and ridges.
Abdomen:
No unique features; consistent between sexes.
Tail:
Cercopods:
The elongated cercopods are affixed to the final abdominal segment. These cercopods may exhibit a coloration pattern with white tips shifting to red or deep red, or they may entirely display a red pigment, extending across both the telson and abdomen. Notably, these cercopods are characterized by the presence of plumose setae (Manson et al., 2022).
Morphology:
Size: In the current set of specimens, the typical measurements for those at their largest size were 15.6 mm males and 26 mm females, with variations contingent on the prevailing environmental conditions (Coopey, 1950).
Coloration: The Oregon Fairy Shrimp, often manifest variations in transparency, alongside tones of red, yellow, and green. Moreover, female specimens tend to showcase more distinct coloration, adorned with markings in purple or black (Manson et al., 2022).
Captivity and Growth:
Growth is influenced by multiple factors such as temperature, salinity, and care. These temperature ranges are based on our experience but do not represent the maximum or minimum.
Hatching Temperature Range: 32 to 50°F.
Temperature Range for Adults: 32 to 65°F.
Hatching:
As the vernal ponds are inundated during the wet seasons, E. oregonus emerge from cysts and proceed through the larval naupliar stage, experiencing swift growth in both length and appendage development. Following this, they transition into the metanauplii stage, exhibiting a blend of naupliar and adult features, ultimately progressing to the juvenile stage where tail formation takes place. Their activity is observed within a temperature range of about 4°C to 17°C, requiring a minimum temperature of 10°C to 15°C for sexual maturity (Manson et al., 2022).
In captivity, when exposed to temperatures ranging from approximately 7 to 15°C (45 to 60°F), nauplii of E. oregonus emerge from cysts enclosed in a membrane after 1 to 2 weeks. However, it's crucial to note that these timeframes can vary based on temperature and various environmental triggers. Throughout this period, they undergo metanauplii development within the membrane for an additional 1 to 2 weeks before ultimately emerging from the encased membrane
Growth Rate: The complete life cycle of E. oregonus lasts from late November to late May, spanning 23-25 weeks. Based on the current investigation, it seems that E. oregonus boasts one of the lengthiest life spans among North American fairy shrimp. This species exhibits a gradual growth rate, featuring early, middle, and late growth phases distinguished by rates of 0.19, 0.07, and 0.18 mm, ultimately reaching sexual maturity around 30 to 40 days (Coopey, 1950).
Behavior: E. oregonus engages in filter feeding, primarily consuming algae, bacteria, and protozoa suspended in the ponds. These fairy shrimp exhibit a relatively stationary swimming pattern as they predominantly filter feed on microbes present in the water column (Manson et al., 2022).
Reproduction: Males utilize their second antennae to latch onto females for copulation. The duration of this mating ritual may last from a few seconds to minutes, depending on whether the females can shake off the male.
References:
Coopey, R. W. (1950). The Life History of the Fairy Shrimp Eubranchipus oregonus. Transactions of the American Microscopical Society, 69(2), 125-132. https://doi.org/10.2307/322340
"Eubranchipus oregonus.” Wikipedia, https://en.wikipedia.org/wiki/Eubranchipus_oregonus.
Belk, Denton. "Key to the Anostraca (Fairy Shrimps) of North America." The Southwestern Naturalist, vol. 20, no. 1, May 15, 1975, pp. 91-103. JSTOR, https://doi.org/10.2307/3670015.
Manson, Clare, et al. "Short-term Monitoring from 2021-2022 of a Rare Invertebrate Species, Oregon Fairy Shrimp (Eubranchipus oregonus) Post-translocation at Pacific Spirit Regional Park: A Comparison of Translocation Success at Four Newly Constructed Vernal Ponds." Prepared for ENVR 400: Community Project in Environmental Science, Department of Earth, Ocean and Atmospheric Science, University of British Columbia (Vancouver), May 2022. In partnership with Metro Vancouver Regional Parks and the Pacific Spirit Park Society.