Fairy Shrimp Dispersal and Colonization

Dispersal of Fairy Shrimp
Examples of Colonization or Extirpation of Fairy Shrimp
Fairy Shrimp Colonization Experiments

Dispersal of Fairy Shrimp

The page on Distribution of Fairy Shrimp showed that fairy shrimp are all over Earth. How did they spread so widely? Fairy shrimp can’t swim from pond to pond. Many ponds with fairy shrimp don’t have outlets. For ponds that do have outlets, fairy shrimp can’t swim upstream to reach the ponds unless the current is very weak. Consequently, fairy shrimp rely on various dispersal vectors to carry resting eggs from pond to pond.

Wind is a means of dispersal that can work at relatively low velocities. Large branchiopod eggs in a wind tunnel were lifted by wind velocities as low as 5.9 meters per second (12.3 miles per hour) (Graham and Wirth, 2007, abstract only). On the playas of Nevada, wind velocities occasionally exceed 15 meters per second (34 miles per hour), as predicted by the National Weather Service on “blowing dust” days. Wind transport of fairy shrimp eggs has been demonstrated experimentally. Dust collected passively adjacent to “Yellow Lake” playa in Texas yielded some ostracod and fairy shrimp eggs which hatched upon immersion in water. (Rivas and others, 2018).

Overflow into an ephemeral channel connecting ponds could carry fairy shrimp eggs from one pond to another. Overflow traps between South African rock pools contained large numbers of fairy shrimp eggs (Vanschoenwinkel and others, 2008a, abstract only). This could be important in areas with the appropriate topography and hydrology.

Birds are the preeminent long distance dispersal agents for fairy shrimp simply because no other animals can match their ranges. Birds commonly move up to a few kilometers between feeding and roosting sites (Brochet and others, 2010) and shorter distances between feeding sites but short distance dispersal by birds is not considered further here. Although fairy shrimp eggs have been found in plumage (Brochet and others, 2010) and likely get stuck to feet and legs in mud, the most reliable and efficient dispersal method is by consumption and defecation. Gulls, ducks, flamingos, eared grebes, phalaropes, avocets, black-tailed godwits, and other bird species consume fairy shrimp (see Predators of Fairy Shrimp). In consuming female fairy shrimp, they also consume eggs. Northern shovelers, at least, have bills which allow them to strain fairy shrimp eggs directly from the water and those at “Great Salt Lake” eat a lot of eggs (Vest and Conover, 2010).

For the consumption-defecation method to work, fairy shrimp eggs must survive bird digestion. Some experiments hatching fairy shrimp from the feces of various bird species had success rates over 50% (Figuerola and Green, 2002; Sanchez and others, 2007).

The next question, then, is how far can birds fly before they have to defecate, whether in flight or on the ground? The modal and maximum food retention times by killdeer are 90 minutes and 26 hours, respectively (Sanchez and others, 2007, citing Proctor and others, 1967). In the absence of species-specific data, these times were used to bracket a range of possible dispersal distances. In the case of redshank and godwits, which frequent the salt marshes of southwestern Spain, their flying speed of 58 km/h (35 miles/hour) would allow them to carry fairy shrimp eggs up to 1,500 km (900 miles) (Sanchez and others, 2007, citing Welham, 1994). Most eggs would be dumped within 70 km (42 miles). Ducks have somewhat faster flight speeds of 60-78 km/h (36-47 miles/hour) and other waders somewhat slower flight speeds of 48-60 km/h (29-36 miles/hour) (Figuerola and Green, 2002, citing Welham, 1994). Eared grebes fly about 1,000 km (600 miles) from “Great Salt Lake” to the Salton Sea or Gulf of California at an average speed of 59 km/h (35 miles/hour) without stopping (Conover and Caudell, 2009). There may be a few eggs left in their digestive systems when they land after 17 hours. Some green-winged teal have flown 1,200 km (720 miles) in 24 hours (Figuerola and Green, 2002, citing P. Clausen, personal communication). Whatever the details of food retention times and of flight speeds and durations for different species, dispersal of fairy shrimp eggs over distances of 10s to 100s of kilometers by birds is plausible.

Salamanders can completely exclude fairy shrimp from some ponds while also acting as dispersal agents. At the Mexican Cut Nature Preserve in Colorado, salamanders and fairy shrimp inhabit several ponds (Bohonak and Whiteman, 1999). 8 of 9 permanent ponds contained salamanders and only one of those had fairy shrimp over the 2 years of observation. 7 of 8 temporary ponds with fairy shrimp also had salamanders at some time during the summer. The salamanders over-winter in the permanent ponds and don’t routinely wander into the temporary ponds before the fairy shrimp have already hatched and produced eggs. That allows the fairy shrimp populations to persist from year to year in spite of heavy summer predation. In the permanent ponds, salamanders can eat fairy shrimp soon after they hatch and prevent the establishment of a permanent population.

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For the salamanders to disperse fairy shrimp eggs, the eggs have to survive salamander digestion. 12 salamanders were fed 6 egg-bearing females each, which which were swallowed whole. Their feces were transferred separately in mesh-topped vials to ponds in the field. Some fairy shrimp were found in the vials the next year (Bohonak and Whiteman, 1999). The mean hatching rate of ingested eggs was estimated to be 0.9%. The highest estimated hatching rate for a single pond was 6.2%. The hatching rate for control eggs which were collected from females directly was about 50%. In spite of the low hatching rate of the ingested eggs, the abundance of eggs ingested by salamanders and the common movements of salamanders between ponds likely result in more than 1 dispersed egg hatching in each pond of the Preserve annually, on average (Bohonak and Whiteman, 1999).

Part of the reason for the lower hatching rate of the ingested eggs is likely due to incomplete development of the eggs. The experimental salamanders ate the females before the eggs had been released from their ovisacs. Later stages of development of the embryo in the resting egg could have been missed. This explanation was confirmed when eggs that had been removed from females before being released from their ovisacs were found to have an estimated mean hatching rate of only 7% (Bohonak and Whiteman, 1999).

Flying and diving insects may eat fairy shrimp in the water and then carry eggs to other ponds when they fly off. To prove the eggs remain viable after consumption, Beladjal and Mertens (2009) fed egg-bearing fairy shrimp to 3 species of dytiscids (Dytiscus marginalis, Ilybius fenstratus, and Colymbetes fuscus) and collected their fecal pellets. From 0 to 61 eggs per day were collected from the fecal pellets over 4 days of observation. Of those eggs, 3-20% hatched, depending on dytiscid species. 20% is higher than the 12% hatching rate of the control experiment. Dytiscids are common inhabitants of temporary ponds and may fly several kilometers in search of additional food sources (Beladjal and Mertens, 2009).

Mammals sometimes drink from ponds, feed on the shores of ponds, or just wander through ponds. They have fur which may collect fairy shrimp eggs or mud with fairy shrimp eggs. Wild boar rooting around in the Camargue wetlands of southern France pick up mud containing the eggs or other resting stages of rotifers (phylum Rotifera), copepods (Crustacea: class Maxillopoda, subclass Copepoda), cladocerans (Crustacea: class Branchiopoda, orders Anomopoda, Ctenopoda, Onychopoda, Haplopoda), and ostracods (Crustacea: class Ostracoda) (Vanschoenwinkel and others, 2008b, abstract only). If the boars had been in ponds with fairy shrimp they probably would have picked up fairy shrimp eggs, too.

Fairy shrimp eggs were found in the fur of a fossilized woolly mammoth in Siberia (Rogers and others, 2021).

I haven’t read of bears carrying fairy shrimp eggs but I’ve seen bears in fairy shrimp ponds. On my first visit to Bald Mountain Big Dry Lake in 2017, I was too late to find water but I did see a bear sniffing around in the remaining patch of mud. I observed bear tracks in the mud around Bald Mountain Dry VABM Saddle Pond (Pine Grove Hills) in 2019 when the pond had fairy shrimp. When I returned to the pond in 2023, I saw a bear run from the far shore as I emerged from the woods. All 5 ponds near Bald Mountain in the Pine Grove Hills have fairy shrimp. I’ve never seen water birds in my few visits to the ponds. The area is now within the Wovoka Wilderness and does not seem to be grazed. Wind is probably ineffective for dispersal as the ponds have grassy bottoms and the surrounding sagebrush and pinyon woodlands would disrupt ground-level winds. That leaves bears. Of course, water birds or other animals could visit the ponds on occasion.

The Sweetwater Mountains also have bears and are only about 20 km (12 miles) west of the Pine Grove Hills. 4 of the 6 ponds I have visited there have fairy shrimp. There was a bear at South Sister Dead Cow Pond on my first visit and I saw bear tracks distant from ponds on other visits. The bears could have helped to spread fairy shrimp eggs. In addition to bears, cows, sheep, sheep dogs, killdeer, and maybe blackbirds are possible dispersal agents that I have observed in the Sweetwater Mountains. Cow feces are abundant near South Sister Dead Cow Pond.

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A lot of potential fairy shrimp habitat has been created by the digging of stock-watering ponds in the western United States. Cows (both domesticated and feral) and horses (both domesticated and feral) using the ponds are consequently well placed to act as dispersal vectors. I’ve never seen sheep using a stock pond but maybe they do. I’ve found fairy shrimp in several stock ponds in Nevada but none in Wyoming stock ponds for reasons I have never figured out. The most likely way for fairy shrimp eggs to hitch a ride on cows or horses is to get stuck to their legs in mud. Cows, at least, routinely wade into stock ponds to drink and trample the mud even when there is no water left (see photograph Win Wan Flat West Pond 2022 #12). With longer necks, horses may more commonly drink from the shore. Both cows and horses could conceivably wallow in dry ponds and pick up fairy shrimp eggs that way. It is also possible that they ingest floating fairy shrimp eggs when they drink and then defecate the eggs in another pond.

Scenic view of dry Win Wan Flat West Pond 2022-08-16 with extensive cow pocks, #12, lacks fairy shrimp; Stillwater BLM Office.
Win Wan Flat West Pond 2022-08-16, #12, Gabbs Valley Range.

Dry mud of Win Wan Flat West Pond churned up with intensive trampling by cows. Both Win Wan Flat West Pond and Win Wan Corral Pond have fairy shrimp and they are about 800 m (2,620′) apart. Cows and horses drink from both and could have carried eggs between the ponds. However, they are not the only possibility. To my surprise, I have seen ducks, phalaropes, killdeer, and semi-palmated sandpipers(?) at the puny, opaque Win Wan Corral Pond. Wind could easily do the job, too.

Raven Roost Reservoir Fairy Shrimp Video 2023-04-15r (Fairy Shrimp Videos, Rambling ‘Round Some Hoof Prints in Railroad Valley) also shows a stock pond that has been intensely trampled. Remarkably, fairy shrimp were still living in pockets of water in the hoof prints when I visited.

Dispersal is a numbers game. Enough eggs must be deposited in a new pond so that enough hatch so that enough adults survive to maturity so that enough adults mate so that enough eggs are produced so that enough fairy shrimp hatch in the next generation to sustain the population. A few eggs is probably not enough. Examples of hatching rates are given on the Resting Eggs of Fairy Shrimp and Their Hatching page. The anecdotal range is 0% (Hildrew, 1985, 6th wet period for samples collected at 7 of 8 distances from the center of a pond) to 99% (Saengphan and others, 2005, for non-dried eggs of the 11th clutch monitored for hatching after a delay of 28 days). The environmental conditions of the new pond will affect the hatching rate. After hatching, survival is key. There are reports that less than 10% of hatched nauplii survive to adulthood (e.g., Conover and Caudell, 2009; Horvath and Vad, 2015) but nauplii survival rates in natural environments have not been well studied. Then, the race to maturity is on. The table Life Spans of Adult Fairy Shrimp in Natural and Laboratory Settings gives examples of days needed to reach maturity. The anecdotal range is 5-50 days. If the pond dries up before fairy shrimp mature, colonization fails. The density of mature fairy shrimp (individuals per cubic meter of pond water) needed for individuals to find and mate with the opposite sex is not known. Mating success for the same number of mature fairy shrimp is more likely in smaller ponds. The number of eggs produced for the next generation depends on the number of females, clutch size, and the number of times females produce eggs and mate. The table of Numbers of Eggs per Clutch and per Lifetime in Fairy Shrimp gives anecdotal range for clutch sizes of 1-368. The range for lifetime eggs per female is 0-5,000. 1 clutch of 1 female could conceivably result in a sustainable population but the more females there are and the more clutches they produce, the better the chances for colonization.

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To get a rough idea of the number of eggs that must arrive in a pond for successful colonization, assume a mature fairy shrimp density of 1 individual per 1,000 cubic meters (i.e., 10 m cube) (35,315 cubic feet, 32.8 feet cube) is needed for 1 successful mating and the pond has an area of 1 ha (100 m square) (2.47 acres, 328 feet square) and a depth of 0.5 m (1.6′), or a volume of 5,000 cubic meters (172,130 cubic feet). Then 5 mature fairy shrimp must be present in the pond for a successful mating, assuming there is at least 1 female and at least 1 male. If the hatching rate is 50%, the nauplii survival rate is 10%, and 80% of the surviving nauplii reach maturity, then 125 fairy shrimp eggs would be needed to result in 1 successful mating (125 eggs x 0.5 x 0.1 x 0.8 = 5 mature adults). This estimate may or may not be close to reality. It does not consider pond duration and implicitly assumes 1 clutch of 1 female is enough to start a new population and that the pond has physical and chemical conditions suitable for the new population. Nonetheless, this simple calculation does suggest that dispersal of 100s of eggs rather than 10s of eggs is needed for successful colonization. That means the egg-rich feces of predatory birds likely offer better chances for colonization than wind-borne eggs or eggs stuck to the exteriors of animals.

Predation may be an important obstacle to colonization. If predators such as dytiscids, backswimmers, amphipods, or frogs, which co-exist with fairy shrimp in some ponds, are already established when the fairy shrimp eggs arrive, then they may eat enough of the small number of hatched individuals to prevent successful mating. The success of cold-tolerant fairy shrimp in the Arctic, such as Branchinecta paludosa (Lindholm and others, 2016) and Artemiopsis stefanssoni (Johansen, 1921), may be due to their ability to colonize the ponds following deglaciation before the insect and amphibian predators got there, even if they are there now. Fairy shrimp may have been similarly successful in recently deglaciated alpine terrains but we don’t really know because fish-stocking has wiped out an unknown number of populations. Fairy shrimp may be less successful in temperate environments where predator populations are present near any newly established ponds and may get there first. The biological history of reservoirs could be insightful except that reservoirs are usually stocked with fish or have been constructed on streams with fish. Stock ponds in southwestern North America could also be revealing but construction dates are rarely known and the aquatic species present have not been routinely monitored.

Artemia parthenogenetica is cheating in the colonization game. This species reproduces without fertilization of eggs so, in theory, just one egg could be enough for a new population. Genetic analysis of diploid (normal 2 sets of chromosomes, other populations have more sets) samples of Artemia parthenogenetica and sexually reproducing species in Asia showed that the species probably evolved from an as yet undescribed sexual species found in Kazakhstan and possibly also from one in Iran within the last 1 million years or so (Munoz and others, 2010). The recent origin is suggested by the lack of genetic diversity within the species. The fact that A. parthenogenetica is now widely distributed from the Canary Islands to China whereas many sexual species have smaller regional distributions (Munoz and others, 2010) does suggest some evolutionary advantage. If this is such a great idea, why now? Maybe the glacial cycles in Europe, northern Asia, and Tibet provided favorable conditions for the spread of a parthenogenetic species by freezing out existing populations and leaving unpopulated habitats for when things warmed up again.

Continuing the digression on parthenogenetic fairy shrimp, such populations consistently have males but at a rate of less than 0.1% of the total population (Maccari and others, 2013). These males have the surprisingly jargon-free label of “rare males”. Rare males are morphologically normal and fertile but cannot fertilize eggs from females of their own population because parthenogenetic females produce diploid (2 sets of chromosomes) rather than haploid (1 set of chromosomes, as in normal gametes) eggs. However, the rare males produce viable eggs when mated with females of the Asian species Artemia urmiana, A. sinica, A. tibetiana, and an undescribed Artemia species from Kazakhstan (Maccari and others, 2013). The percentages of fertilized eggs were very close to those of intraspecies controls and in one case was actually greater. The hybrid offspring were normal (Maccari and others, 2013). This “suggests an evolutionary role” for rare males (Maccari and others, 2013) in a parthenogenetic species but I will leave it to you to ponder how this came about and what the ramifications could be.

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Examples of Colonization or Extirpation of Fairy Shrimp

To understand colonization, it is helpful to understand extirpation, a term commonly used to refer to extinction or extermination of a population(s) within a relatively small area. Causes of extirpation could prevent successful colonization. For example, the introduction of fish into a lake with fairy shrimp eliminates the fairy shrimp populations. Hence, introducing fairy shrimp eggs into a lake with fish will not result in colonization. Extirpations of fairy shrimp in alpine lakes by fish-stocking are discussed further on the Wind River Mountains and East-Central Sierra Nevada pages.

There are at least 2 examples of extirpations that resulted in global extinctions. Tanymastix stellae was known to occur in only 2 rock pools in Sardinia. The pools were “eliminated by urbanization” (Mura, 1999). Dexteria floridana had only been found in a “temporary pool approximately 6 km south of Gainesville”, Florida (Rogers, 2002). The type locality has probably been destroyed by development (Rogers, 2002). In reviewing a petition to list Dexteria floridana, the U.S. Fish and Wildlife Service (2011) found that the information presented in the petition “suggests the species is already extinct” and consequently declined to list it as threatened or endangered.

As mentioned on the Distribution of Fairy Shrimp page, a population of Branchinecta paludosa was extirpated from a pond in the Tatra Mountains of Poland and thereby eliminated from Poland (Kownacki and others, 2000). The fairy shrimp had been found in “Dwoisty Staw lakes” as recently as the 1960s. The disappearance of B. paludosa was probably not due to changes in water chemistry but “might have been caused by other factors like uncontrolled introduction of fish or outbreak of parasites” (Kownacki and others, 2000). The lake was fishless during the 1996-1998 surveys but fish could have been introduced and died out due to natural draining of the lake during the winter.

Extirpation of Branchinecta paludosa from a few alpine ponds in southern Norway may have been caused by the combined effects of warming and predation. Surveys in 2011 failed to find the fairy shrimp in ponds below an elevation of 1,100 m (3,610′) where it had been present in 1970 (Lindholm and others, 2012, abstract only). Fairy shrimp were still present in higher ponds. Doubling of the number of warm summer days (not defined in the abstract) from 1965-1970 to 2005-2010 at the elevations of the ponds without fairy shrimp likely contributed to the extirpations (Lindholm and others, 2012, abstract only). At the same time predation by Chaoborus nyblaei increased (Lindholm and others, 2016b, abstract only). The abstract did not say C. nyblaei was present in the ponds where fairy shrimp had been extirpated but did state that fairy shrimp “suffered major population declines in ponds where the predator was present”. An increase in vegetative cover in parallel with the temperature increase resulted in pond browning due to higher dissolved organic carbon concentrations (Lindholm and others, 2016b, abstract only). This in turn allowed the expansion of C. nyblaei populations by protecting the larvae from ultraviolet radiation which proved to be lethal in clear water (Lindholm and others, 2016b, abstract only).

A 14-year study of a pond near Calgary, Alberta, found changing abundances of 5 species of fairy shrimp; some of the changes could have been due to extirpation (Donald, 1983). The pond is situated in an area with many small temporary and a few permanent ponds in a glacial knob and kettle topography. Water birds are common. The pond has a maximum area of 0.3 ha (0.74 acres) and a maximum depth of 58 cm (23″). Although most precipitation is received during June through August, on average, the pond typically fills with snowmelt by the end of April. The pond commonly dries up by the end of June but fills again during the summer in some years. In 2 of the 14 years, the pond remained dry during the spring and summer. In years with fairy shrimp, 42-443 individuals were collected and identified and each species’ percentage of the total population was presented in Table 1 of Donald (1983).

3 possible extirpation events are indicated in Table 1 of Donald (1983):

  1. Branchinecta paludosa was absent for 6 years (including 2 dry years and 1 year when no fairy shrimp hatched) and reappeared in spring 1980, when it accounted for 1% of the total population.
  2. Branchinecta lindahli was absent for 6 years (including 2 dry years and 1 year when no fairy shrimp hatched) and reappeared in spring 1980, when it accounted for 61% of the total population.
  3. Eubranchipus intricatus was absent for 3 years (including 1 year when no fairy shrimp hatched and 1 year when the pond was dry during the spring but filled in the summer) and reappeared in 1982, when it accounted for 28% of the total population.

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In the year prior to the year without fairy shrimp, which preceded the 3-year absence of Eubranchipus intricatus, E. intricatus accounted for 51% of the total population. The collection of more than 400 individuals that year suggests fairy shrimp were abundant. It can be assumed that abundant fairy shrimp leave abundant eggs for the next generation although the actual egg production capacity of E. intricatus near Calgary is not known. It seems unlikely that all the eggs died within the 3-year absence of E. intricatus. Like E. intricatus, Eubranchipus bundyi and Eubranchipus ornatus were also absent in summer, but not spring, 1980, and in 1981 but appeared again in 1982 with at least a 15% share of the total population. It seems that inhibition of hatching by environmental factors is the more likely cause of E. intricatus’s 3-year absence than extirpation.

Fairy shrimp eggs can remain viable for 6 years so the disappearance of Branchinecta lindahli in 1974-1979 is not necessarily due to extirpation. Some B. lindahli eggs remain viable for at least 2 years. B. lindahli hatched from a soil sample collected in 1972 even though the species did not appear in the pond in 1971 or in 1972 (Donald, 1983). B. lindahli was the most common fairy shrimp when it reappeared in spring 1980. If its absence was due to extirpation, this implies a massive influx of eggs by birds or other dispersal agents compared to the eggs produced in the pond by the other 2 species that hatched in 1978 and again in spring 1980 after an absence of all fairy shrimp in 1979. Unfavorable environmental conditions seems the more likely cause for the 6-year absence of B. lindahli than extirpation.

The case of Branchinecta paludosa is closer to what would be expected for extirpation and recolonization (Donald, 1983). Small numbers of fairy shrimp would be expected during the first few years after colonization (Donald, 1983) as it takes time to build up a population, particularly when other fairy shrimp species are present in greater numbers and compete for the available food. B. paludosa accounted for only 1% of the total population in spring 1980 and only 3% in the second pond of summer 1980 before expanding to 38% of the total in summer 1981 (after a dry spring).

However, a small hatch from a few or many viable old eggs could be indistinguishable from a small hatch from a few newly arrived eggs. The experiments of Hildrew (1985) demonstrated that some fairy shrimp eggs hatch during their 8th immersion in water even though they did not hatch under the same experimental conditions during the previous 7 immersions (cycles of 28 days dry and 28 days wet). In fact, for 4 of 7 soil samples, more eggs hatched during the 8th immersion than during any previous immersion (Hildrew, 1985). To prove colonization, one would have to show that the pond had no viable fairy shrimp eggs prior to the arrival of new eggs. While hatching experiments could disprove colonization if eggs collected from the pond soil before the (re)appearance of fairy shrimp hatched, lack of hatching could be due to unfavorable experimental conditions or to opportunity skipping, as in Hildrew (1985), rather than to lack of viable eggs. A method for determining egg viability independently of hatching success is needed. One possibility is the method of De Roeck and others (2005), who checked for viability by pinching eggs with tweezers. Only if there were no viable eggs left could the 6-year absence of B. paludosa be considered extirpation.

In a curious role reversal, what humanity giveth, natural processes can taketh away. Constructing stock watering ponds creates potential fairy shrimp habitat. Many stock ponds in the western United States are created by damming streams or ephemeral drainage channels. Floods can breach the dams and destroy the habitats.

Bass Flat Southwest Pond is a stock pond behind a dam on the clay floor of Bass Flat, which is adjacent to “Carson Lake”. In early February 2022, the pond had dimensions of about 75 m x 60 m (250′ x 200′). Fairy shrimp were present. During the unusually wet year of 2023, a rain storm generated a flash flood that breached the dam. In this case though, there is a ray of hope for the fairy shrimp. When I visited again in February 2024, I found a few small puddles on the mud flat behind the dam. One 1 m x 2 m (3.3′ x 6.6′) puddle less than 8 cm (3.2″) deep had fairy shrimp. The prospects for this population do not look promising but maybe . . .

Scenic view of Bass Flat Southwest Pond 2024-02-15, #01, dam breach; dry; Stillwater BLM Office
Bass Flat Southwest Pond 2024-02-15, #01, “Carson Lake” Playa.

Breached dam at Bass Flat Southwest Pond, from downstream side. The channel is more than 20 cm lower than the ground surface north of the dam.

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I also found a breached stock pond dam at Raven Roost Reservoir in Railroad Valley in April 2023. The breach did not look recent. I had not visited the pond before so I don’t know what it was like before the breach. I saw some wet mud behind the dam and decided I might as well have a look, expecting nothing. Remarkably, I found mature fairy shrimp with eggs swimming in the meager bits of water in many cow hoof prints. For a better appreciation of this population, go to the Fairy Shrimp Videos page. If any rancher is still running cows out there, maybe the dam will get fixed some day.

The above examples of extirpation provide a few lessons for successful colonization and sustainable populations.

  • Avoid areas of human disturbance or your pond may soon get filled in or built over.
  • Avoid large bodies of water or ponds on streams or you may get gobbled up by fish.
  • Avoid ponds with temperatures near your upper limits. The water may get too hot for you in the not too distant future or warmer temperatures may invite new predators into your home.
  • Avoid ponds that may be impacted by flash flooding.

I could offer other lessons gleaned from other examples of extirpation but I would have to find them first. Of course, none of this matters to fairy shrimp eggs as they have no choice.

Published examples of fairy shrimp colonization offer slim pickings.

Returning to the case of the pond near Calgary observed by Donald (1983), the reappearance of B. paludosa in spring 1980 would be colonization if the species had been extirpated.

A population of Tanymastix stagnalis inhabits pond O2 in the “Malladas de El Salar” complex of interdune ponds on the Mediterranean coast of eastern Spain (Olmo and others, 2015). The pond is now within Albufera Natural Park. There is good evidence that pond O2 has been colonized since its destruction by human activities in 1929 and in the 1960s. The pond was purportedly drained by drilling through an underlying impermeable layer of limestone or caliche (“lime layer”) for mosquito control in 1929 (Olmo and others, 2015). Whether or not that effort was completely successful, pond O2 was “silted for urbanisation” in the 1960s (Olmo and others, 2015). If T. stagnalis was present in pond O2 before 1929, then it had been extirpated by 1970. The pond was restored in 1998 by excavating the sediment fill down to the lime layer. The previous silting may have plugged the drainage hole. Fairy shrimp were first reported in pond O2 in a 2010 publication. Therefore, T. stagnalis colonized pond O2 within 12 years of pond restoration. One does not have to look far for a likely dispersal agent. “Several nesting reserves for birds” are nearby (Olmo and others, 2015). Bird species were not identified but the regional ecology suggests they include water birds capable of consuming fairy shrimp. One reserve is less than 300 m (980′) from the pond (Fig. 1 in Olmo and others, 2015).

Colonization success in pond O2 was not duplicated in pond O1, which has the same history as O2 and is about the same size and less than 300 m (980′) away (Olmo and others, 2015). Conductivity (as a measure of TDS) and pH in ponds O2 and O1 are nearly the same but soluble reactive phosphorus is significantly lower in pond O1. In microcosm experiments, distilled water was added to soil from ponds O1 and O2 to mimic pond conditions. Eggs collected from pond O2 in 2009 hatched in both the O2 and O1 waters but those collected in 2010 hatched only in O2 water (Olmo and others, 2015). The proximity of both ponds to bird nesting sites does not suggest differences in the probabilities of bird dispersal but sometimes probable events don’t happen for a long time. So, colonization within 12 years in pond O2 and no colonization within 12 years in pond O1 for T. stagnalis in the “Malladas de El Salar”.

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A survey of 146 fish-free alpine and subalpine ponds in the mountains of British Columbia over a 5 year period doesn’t offer an example of fairy shrimp colonization but does provide information on the frequency, or likelihood, of colonization. Anderson (1971) mostly documented copepods (Crustacea: class Maxillopoda, subclass Copepoda) and cladocerans (Crustacea: class Branchiopoda, orders Anomopoda, Ctenopoda, Onychopoda, Haplopoda) but 14 ponds had fairy shrimp. All of the fairy shrimp observed were in “ponds”, not “lakes”. This make sense if many of the “lakes” were previously stocked with fish but Anderson (1971) made no mention of that possibility. Anderson (1971) identified the northern phalarope as “possibly the most important dispersal vector in the lakes of this study” and concluded that “it is unlikely that many waters in this area escape potential colonization by the most commonly occurring” zooplankton. If that is true, the scarcity of fairy shrimp implies that colonization by fairy shrimp is infrequent even in the presence of abundant apparently suitable water bodies and effective dispersal agents.

From one perspective the drying of the Aral Sea is an ecological catastrophe, from another it is an opportunity. The Aral Sea began drying up in the 1960s due diversions of water for irrigation, industry, and public water supply (Marden and others, 2012). Fresh- and brackish-water fish and invertebrate species had been eliminated by 2007 when mean annual TDS reached 100,000 mg/L in the remaining western basin (Marden and others, 2012). That created an opportunity for Artemia parthenogenetica. A. parthenogenetica colonized the lake sometime between 1989 (Andreev and others, 1992) and 2000 (Mirabdullayev and others, 2004, abstract only) even though some flounder and atherina fish survived in the western basin after 2002 (Mirabdullayev and others, 2004, abstract only). Surveys in the western and eastern basins of the Aral Sea (the southern Large Aral) in 2005-2007 indicated that commercial collection of Artemia eggs in the western basin might become economically justified (Marden and others, 2012). That probably hasn’t happened. Satellite images collected on the Wikipedia page (en.wikipedia.org/wiki/Aral_Sea) show that the eastern basin disappeared again in 2021 and remained dry in 2024 while the western basin is smaller than it was in 2009-2014. Although Kazakhstan has partially restored the northern Small Aral Sea (it has fish again), Uzbekistan has evidently not taken steps to restore the Large Aral Sea. A. parthenogenetica may be living in the western basin for some time to come. If TDS exceeds
175,000 mg/L or so, even A. parthenogenetica will die out.

The processes that result in fairy shrimp colonization can also result in invasion. The difference is that an invaded pond already has a species of fairy shrimp. Artemia franciscana is native to North, Central, and South America. With humans as dispersal agents, the species has been introduced into high TDS waters throughout the world to raise eggs which can be easily hatched into live food for young fish and shellfish. Almost all of the introduced eggs came from “Great Salt Lake” as those eggs dominated the “Artemia cyst” market from the mid-1980s through the 1990s (Lavens and Sorgeloos, 2000). The details of timing and locations are elusive but have been at least partially documented in western Europe. The native Artemia species in western Europe are A. salina and A. parthenogenetica. A. franciscana appeared in salterns of the Algarve Province of Portugal in the early 1980s and then spread into the Sado and Tejo estuaries by the early 1990s (Amat and others, 2005). In the Sado estuary, A. franciscana was the only fairy shrimp collected in the 1990s. 2002 Algarve samples contained only A. franciscana. In the Esmolas salterns of the Aveiro District, A. parthenogenetica was collected in 1985 but only A. franciscana in 1991 and 1993 (Amat and others, 2005). The salterns of Spain and southern France were also invaded in the 1990s. Except in the “N.S. del Rocio” saltern, 2002 and 2003 samples from Cadiz Province of Spain contained only A. franciscana eggs. In Huelva Province, the Esteros Odiel saltern still had A. parthenogenetica in 2002. A. franciscana had reached the Mediterranean coast of France by 1992 (Amat and others, 2005). A 2002 sample from the Aigues Morte saltern in France, captured a snapshot of the invasion. 2% of the eggs were A. parthenogenetica but 98% were A. franciscana. 2002 samples from 5 other salterns in France contained only A. franciscana eggs. The invasion has also reached Morocco. A 2000 sample from Laguna Mar Chica saltern was 80% A. parthenogenetica and 20% A. franciscana (Amat and others, 2005). A. franciscana may not have reached Italy before 2002. 1985-2002 samples of salterns in Sicily, Sardinia, and the provinces of Apulia, Lacio, and Veneto had only native species (Amat and others, 2005). However, A. franciscana was found in Margherita di Savoia by 2006 (Mura and others, 2006, abstract only). Although humans are responsible for the initial introduction of A. franciscana into Europe, they are not the only dispersal agents. Both A. franciscana and A. parthenogenetica eggs have been found in the feces of waterbirds visiting salterns in Portugal and Spain (Green and others, 2005). Although the successful invasion of Europe by A. franciscana was launched by the ultimate ecosystem meddlers, it has drawn attention to the importance of water birds and European flyways to natural fairy shrimp colonization processes and gene flow.

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A. franciscana has also invaded Australia, also as a result of intentional introduction by humans (Ruebhart and others, 2008). Native fairy shrimp adapted to high TDS waters include many species of the genus Parartemia, family Parartemiidae, which is present only in Australia (Timms, 2012). A. parthenogenetica is present in Australia and may also have been introduced by humans but a recent introduction by birds cannot be ruled out (Ruebhart and others, 2008). “It appears” that A. franciscana was first introduced into a “saltfield” on the Fitzroy River delta in Queensland, Australia, in the early 1960s (Ruebhart and others, 2008). A 1987 publication reported A. franciscana in South Australia. The dispersal agent in this case was probably employees of the company that owned the contaminated saltfield in Queensland and the Dry Creek saltfield in South Australia, where A. franciscana was found (Ruebhart and others, 2008). Fisheries Western Australia “apparently” contaminated salt works in Western Australia using A. franciscana eggs from the Queensland saltfield (Ruebhart and others, 2008), possibly as early as the 1980s. Ruebhart and others (2008) did not report any co-occurrences of A. franciscana and Parartemia species or of the extirpation of Parartemia species by A. franciscana. The consequences of the A. franciscana invasion were unpredictable as of the mid-2000s. The lessons of the A. franciscana invasion of Australia for colonization are meager. As in Europe, waterbirds have been suspected of dispersing A. franciscana within Australia. However, Ruebhart and others (2008) did not give specific examples.

It is unfortunate that the significance of A. franciscana invasions of Europe and Australia for natural fairy shrimp colonization has been largely overlooked. That is because authors have chosen to frame their studies in terms of something scary, such as “invasion”, presumably to improve their chances of publication. The threat of extirpation of native species is certainly worth noting and taking action to prevent but there is so much more to fairy shrimp biology. How many eggs does it take to start a new population? Is one introduction enough? How important are founder effects? When is the best time to deposit the eggs in the new pond? If the dispersal agent is water birds, the pond would have to be wet but there might be differences between the success rates of the early and late arrivals. Is wind dispersal during dry periods disadvantaged? What effects do established predators and competitors in the new pond have on colonization success? Artemia species don’t have many predators or competitors due to the high TDS of the water they live in. Does this make them more successful colonizers than species living in low or moderate TDS water? Artemia eggs can be live or resting. Which are more successful at colonization? Do both have similar survival rates in bird feces? To gauge the effectiveness of birds or other animals as dispersal agents, it would certainly be helpful to know what proportion of ponds with invasive A. franciscana were contaminated by humans directly. If the human introduction was limited to a single pond in 1 area, how long did it take for fairy shrimp to colonize similar habitat nearby, if any? The Branchinecta gigas in the room, so to speak, is what other fairy shrimp species are invading (or colonizing) other ponds? Is there some temperate species charging poleward, or upward, and on the verge of wrecking havoc in the tundra?

Stock watering ponds of the western United States are a testament to the colonizing abilities of fairy shrimp. When were they built? Native Americans of the southwestern United States didn’t have livestock until they were introduced by Europeans. Coronado brought hundreds of horses, cows, and sheep into Arizona and New Mexico in 1540 and he didn’t leave with all of them. Native Americans definitely made use of stray horses. Horses can travel long distances without water so stream watering rather than ponds may have been sufficient. Spanish settlers and missionaries brought more livestock into the area over the 1600s. Most resided near the Rio Grande in the vicinity of Santa Fe and Albuquerque while troubles with the native Americans may have kept their numbers down.

The Navajo eventually became avid sheep herders. The Hopi and Pueblo tribes also acquired livestock at some time. I haven’t tried to track down when that happened or when the tribes may have started digging water holes.

Comanche raids in the 1700s likely discouraged much expansion of the Spanish settlements. A table on a Wikipedia web page (en.wikipedia.org/wiki/History_of_New_Mexico) indicates a Spanish population of only 19,276 in 1800. Probably not many stock ponds among the Spanish by then. Mexico declared independence from Spain in 1821 and trade with the United States increased after that. More livestock likely entered New Mexico by way of the Santa Fe Trail and the Spanish population rose to 46,998 by 1842. That number may include some foreigners from the United States. Mexico ceded most of New Mexico, Arizona, and California to the United States in 1848. Immigration from the United States subsequently increased. For convenience, I assume stocks ponds in New Mexico and Arizona could be as old as 1800.

The minimum age of a stock pond can be determined by looking at a 7.5-minute topographic quadrangle. It must be at least as old as the age of the aerial photographs used to create the map on which it appears. In the context of colonization, this isn’t very useful. A maximum age of colonization may seem similarly unhelpful but it provides an alternative perspective to genetic analyses which yield expected times to the most recent common ancestor (TRMCA) of different populations of the same species of tens of thousands of years, such as 22,000-222,000 years for populations of Chirocephalus kerkyrensis on the island of Corfu (Kerkyra), off the west coast of Greece (Ketmaier and others, 2012). Corfu is 64 km (38 miles) long and has a width up to 32 km (19 miles) (en.wikipedia.org/wiki/Corfu). Unfortunately for Ketmaier and others (2012), they don’t know how old the ponds are.

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The work of Belk (1977) showed that stock ponds in Arizona are important habitats for fairy shrimp. Stock ponds accounted for 16 of 27 occurrences of Streptocephalus dorothae, 23 of 46 occurrences of Streptocephalus mackini, 13 of 34 occurrences of Thamnocephalus platyurus, and 2 of 2 occurrences of Thamnocephalus mexicanus. All those ponds were probably colonized in less than 177 years. Belk’s (1977) maps don’t have scale bars but, scaled to the north-south dimension of Arizona, the 2 T. mexicanus ponds are about 95 km (57 miles) apart. The pond(s) from which the colonizing eggs came could have been much closer to each, or not so close. The S. dorothae ponds are scattered widely across the state. The greatest distance between any 2 ponds is 577 km (346 miles) and the smallest is 12 km (7 miles). The most isolated S. dorothae pond is 170 km from the nearest other S. dorothae pond. If the nearest pond sampled by Belk (1977) is in fact the nearest pond with S. dorothae, then S. dorothae colonized a pond 170 km away within 177 years.

Many fairy shrimp populations have also been found in anthropogenic ponds in New Mexico that I also assume are no older than 1800. Most of the 80 ponds with fairy shrimp in New Mexico surveyed by Lang and Rogers (2002) were anthropogenic. 26 were “stock tanks”, 25 were “tanks” without the name “stock”, 7 were road side pools, 2 were in canals, and 1 was a retention basin. Only 24% of the ponds were natural. The stock tanks were colonized within 202 years and the roadside pools, canal pools, and retention basin probably in much less than 202 years. The success rate is unknown because the total number of ponds surveyed is unavailable. Dispersal agents are unknown. The Bug Guide gave the geographic coordinates of the ponds and the species names so if you want to calculate potential colonization distances, go to bugguide.net/node/view/1329020.

Stock watering ponds in Wyoming have a different timeline. I’ve read of native Americans driving buffaloes over cliffs but I haven’t read of them constructing ponds. Fur trappers killed a lot of beaver in the early 1800s but I’m pretty sure they didn’t construct stock watering ponds for their horses. The first settler wagon trains headed west on the Oregon Trail in the early 1840s. The Homestead Act of 1862 gave 160 acres (65 ha) of federal lands to anyone who purported to build a dwelling on the land and live there for 5 years. It’s possible a few people did that, had livestock, and dug a watering hole for them among the hundreds of thousands (?) of homestead claims. Simultaneously in the years after the Civil War, cattle barons flooded the non-fenced public lands with large cow herds. They probably made no effort to construct stock ponds. In Wyoming, the cattle boom lasted from 1868 to 1886. It ended with the 1886-1887 winter of death when 15-25% of the cows on the range in Wyoming froze to death (www.wyohistory.org/encyclopedia/wyoming-cattle-boom-1868-1886). That coincided with a collapse of beef prices and the cattle industry of the public lands never fully recovered. I suspect most stock ponds in Wyoming, and maybe elsewhere, were constructed after that as ranchers with smaller herds settled the lands and fences began going up. Fences prevented easy access to water in some places. For convenience, I assume stock ponds could be as old as 1890.

My observations of ponds in Wyoming began in 1985. I found fairy shrimp in 4 of 23 stock ponds or reservoirs. That’s a 17% colonization success rate for ponds that could be as old as 95-103 years but are likely much younger. Excluding 12 other anthropogenic ponds of even less certain maximum age (e.g., road side ponds), the colonization success rate for the natural ponds in Wyoming that I observed was 38%. These numbers are biased by my failure to record all the ponds that I visited that lacked fairy shrimp.

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Early settlement in Nevada was concentrated near streams due to the arid climate or near mines. Most cattle operations in Nevada today make use of stock ponds or stock tanks and hauling water for cows is common. I have seen evidence of that even in the Owyhee Desert of northern Nevada. Large, early cattle operations that used lands away from the streams may well have relied on stock ponds. As I don’t know when such operations first developed, I can only guess that stock ponds are no older than 1890, as in Wyoming. Nonetheless, I have found a greater percentage of stock ponds with fairy shrimp in Nevada than in Wyoming. Stock ponds I have visited in Nevada, whether they have fairy shrimp, and their maximum ages are summarized below.

Only stock ponds are listed above because it would be misleading to list road side ponds that have much shorter, but unknown, maximum ages.

Candelaria Playa Ponds (Candelaria Hills) are anthropogenic even if the playa collected water before excavation. Large-scale open-pit, heap-leach mining occurred at the Candelaria Silver Mine in the 1980s. The playa may have been excavated to provide clay for a liner under the heap leach pad. If so, fairy shrimp colonized the Candelaria Playa Ponds within 37 years.

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Fairy shrimp have colonized road side ditches where there may be some age control. I have found a couple of examples. The first is the ponds along the West Northumberland Road (Big Smoky Valley), in Nevada. The West Northumberland Road leads across Big Smoky Valley and up to the Northumberland Mine at the crest of the Toquima Range. Silver was discovered nearby in 1866 and a town existed at the site from 1879 to 1881 (Kral, 1951). For access to the Northumberland Mine area, Kral (1951) described the route from Tonopah to Belmont, in Monitor Valley, and up the east side of the Toquima Range, not a route across Big Smoky Valley. Gold was discovered in 1936 and the Northumberland Mine, proper, operated during the years 1936-1942. This was a significant operation with a mill, a “complete camp”, general office, shops, and other buildings (Kral, 1951). There is no mention of a new access route across Big Smoky Valley for the gold mine. A large, open-pit, gold mine was operated at the Northumberland Mine over the years 1981-1991 (Fronteer Development Group Inc., 2008). The current road had almost certainly been constructed by this time. The raised, graveled bed of the road across part of the playa would have been needed for heavy trucks and other equipment. Moreover, the East of Millett Ranch 7.5-minute topographic quadrangle shows the current road alignment and was based on 1983 aerial photographs. The Plate 1 map of Big Smoky Valley in Rush and Schroer (1971) shows a difference in the alignment of the first 2.8 km (1.7 miles) at the western end of the road. Instead of a nearly west-east alignment with a sharp bend to the southeast at 2.8 km from Nevada 376, the 1971 map shows the segment following the access road to the Triple T Ranch off Nevada 376 and then continuing to the south to join the south-southeasterly segment across the playa. This is similar to the less detailed Map 3 of Kral (1951). Both maps  support a post-1971 reconstruction of the road across Big Smoky Valley.

The West Northumberland Road Ponds are clearly on the constructed part of the road and not on the adjacent playa (see photos). Pond 8 is within a drainage channel dug away from the road. The ponds cannot be older than the road and may be younger than reconstruction of the road. I first found fairy shrimp in a pond along West Northumberland Road in 2013. Fairy shrimp colonized the ponds within 78 years if the road was constructed in 1935 or 32 years if the road was constructed in 1981. The ponds are a few kilometers northeast of The Granites Playa Lake. I couldn’t get to the water because of soft mud on my one visit to The Granites Playa Lake but I presume fairy shrimp are there. If so, there may well have been wind-deposited fairy shrimp eggs on the playa at the current locations of the ponds even before the road was constructed. That still counts as colonization.

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The other example is Sweetwater Mill Road Pond in the Great Divide Basin. It is a road side pond that has been colonized by Branchinecta coloradensis (identified by D. Belk). The road adjacent to the pond has been paved from US 287 north of Rawlins to the Sweetwater Uranium Mill. As the mill is in the middle of nowhere, the road was almost certainly not paved prior to construction of the mill. A document for the “Kennecott-Sweetwater Uranium Recovery Facility” on a Nuclear Regulatory Commission web page indicates the mill was constructed in 1980. I infer that the road was paved at that time. Although there was probably a non-paved road there before, the width and shape of the current road suggest that any older road was obliterated. Consequently, the ditches also probably date from about 1980. I found the fairy shrimp in the ditch in 1993. They managed to colonize the pond within 13 years.

I can make a guess of the dispersal agent that dropped eggs of B. coloradensis into Sweetwater Mill Road Pond. Although Wyoming is windy and the Great Divide Basin doesn’t have a lot of vegetation to keep the dust and eggs down, wind is not a likely dispersal agent in this case. I found only Branchinecta lindahli, Branchinecta readingi, Branchinecta gigas, Branchinecta campestris, and Artemia elsewhere in the Great Divide Basin. The nearest known occurrences of B. coloradensis are Bull Canyon Pond (77 km, 46 miles, to the northwest in the Antelope Hills), Bivouac Lake (143 km, 86 miles, to the northwest in the Wind River Mountains), and in the Snowy Range 120 km to the southeast (Horne, 1967). Considering the distances involved, birds are the most likely dispersal agents. Water birds are rare in the Wind River Mountains and Snowy Range and birds that don’t eat fairy shrimp are much less likely to be carrying fairy shrimp eggs. In contrast, avocets nest in the Antelope Hills and Great Divide Basin. I haven’t seen avocets at Bull Canyon Pond but I’ve seen them at “Coyote Lake”, which is only 9 km (5.4 miles) away. I haven’t seen them at Sweetwater Mill Road Pond but they visit Separation Rim “Soda Lake”, 11.5 km (6 miles) away. Avocets are not likely to nest near a pond in a road side ditch, like they do at “Coyote Lake”, but maybe one stopped at Sweetwater Mill Road Pond hoping for a quick snack. Finding nothing, one could have defecated when it took off, as they often do.

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In contrast, Beaver Rim Snow Fence Pond offers a cautionary tale. The pond had been there for at least 17 years before my visit and there is a pond with fairy shrimp nearby. Nonetheless, I found ostracods and ducks at Beaver Rim Snow Fence Pond (Granite Mountains) but no fairy shrimp. There are fairy shrimp in Beaver Rim Quack Pond, which is only 1.5 km (0.9 mile) away. Beaver Rim Quack Pond has also been visited by ducks as well as avocets and phalaropes and has a thriving aquatic fauna, including dytiscids, backswimmers, dragonflies, and cladocerans. The age of Beaver Rim Snow Fence Pond is constrained by a revision of the Red Canyon 7.5-minute topographic quadrangle that used 1975 aerial photographs. The revised map shows the realignment of US 287 and Beaver Rim Snow Fence Pond in purple as new features. The pond is not on the 1957 version. The pond was at least 17 years old when I got there and no older than 35 years.

What can we learn from these meager examples?

Colonization Scorecard

  • “Malladas de El Salar” Pond 02 – colonization within 12 years, or less.
  • “Malladas de El Salar” Pond 01 – no colonization within 12 years.
  • Esmolas salterns – A. franciscana invasion and extirpation of A. parthenogenetica within 6 years but could be intentional human introduction.
  • Arizona stock ponds – colonization within 177 years, or less.
  • New Mexico stock ponds – colonization within 202 years, or less.
  • Wyoming stock ponds – 4 colonized within 103 years, or less, and 23 not colonized.
  • Nevada stock ponds – 15 colonized within 133 years, or less, and 6 not colonized.
  • Candelaria Playa Ponds – colonization within 37 years.
  • West Northumberland Road Ponds – colonization within 78 or 32 years.
  • Sweetwater Mill Road Pond, Wyoming – colonization within 13 years, or less.
  • Beaver Rim Snow Fence Pond, Wyoming – no colonization within 17 years.

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Fairy Shrimp Colonization Experiments

An experiment using plastic wading pools as potential fairy shrimp habitat was not about colonization but provides important context for designing such experiments. The pools were 140 cm (55″) in diameter and 30 cm (12″) deep (Helm, 1996). The pools were fertilized with soil known to contain fairy shrimp eggs and left exposed to the weather free of human interference. 5 species of fairy shrimp hatched in the pools as well as 1 species of tadpole shrimp, 1 species of clam shrimp, abundant tadpoles, larvae of the predatory insect order Odonata, larvae of the predatory insect families Notonectidae and Dytiscidae, larvae of the insect family Corixidae, and mosquitoes. Which species hatched in which pools and how many pools were used in the experiments over a period of 6 years was not reported (Helm, 1996). Many of the aquatic animals could have hatched from eggs in the soil and other eggs could have been introduced by wind or animal dispersal agents. Similarly, the sources and abundances of food species such as algae, cyanobacteria, and rotifers are not known. For a real colonization experiment, it would be important to use a sterile substrate or to search any soil used for the presence of fairy shrimp eggs. Infrared and visible-wavelength cameras could be used to record visits by possible animal dispersal agents. While Helm’s (1996) experiments provided considerable fairy shrimp life cycle information (see “Example Classification of Fairy Shrimp Habitats” on the Habitats of Fairy Shrimp page), their only relevance to colonization experiments is that soils from ponds with fairy shrimp are likely to hatch fairy shrimp and a variety of fairy shrimp predators.

A California vernal pool field experiment had successful but poorly described results. 37 ponds were dug in a 245 hectare (605 acres) area with 273 natural “vernal pools” on flat uplands (site 1 area), on a 100-year flood plain (site 2 area), and between a subdivision and a creek (site 3 area) near Sacramento, California (Rogers, 1996). Soil from the natural ponds was used as starter for the constructed ponds. Zooplankton larger than 2 mm were collected 3 times annually from the constructed ponds and from 27 natural ponds used as controls. Summary results were given for the first 2 years of a planned 9-year project. Site area averages of macroinvertebrate densities for constructed ponds for each sampling event in 1995 and 1996 were at least 50% of natural pond densities except for 2 sampling events in 1995. They were at least 80% of natural pond densities for all events in 1996 (Rogers, 1996, my visual estimates of bar graphs). The numbers of species did not differ by more than 20% between new and natural ponds in either year (Rogers, 1996). Other measures also indicated that the macrozooplankton communities which developed in the constructed ponds of sites 1 and 2 were pretty close to those of the natural ponds. The samples of natural pond soil and close proximity were all it took for reasonably successful colonization.

Although “fairy shrimp” were not mentioned by Rogers (1996), the experiment took place in an area known to have fairy shrimp and fairy shrimp are an important component of “vernal pool” communities. The constructed ponds were intended as “mitigation for impacted vernal pools” and the “suitability of created pools as special-status shrimp habitat” was “an additional consideration” (Rogers, 1996). If “shrimp” means “fairy shrimp”, then this was a fairy shrimp experiment. The colonization aspect is somewhat trivial as humans were the dispersal agents and they transported soil samples which may have had large numbers of resting eggs. Those who funded the project certainly know how many of the new ponds fairy shrimp hatched in and whether they established stable populations. Maybe more detailed results were published elsewhere.

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Next – Fairy Shrimp in the Long Term

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