Midvalley fairy shrimp
Encyclopedia
The midvalley fairy shrimp, Branchinecta mesovallensis, is a small (7 millimetre) freshwater crustacean
in the Branchinectidae
family endemic to shallow ephemeral pools (pools that seasonally fill and dry up) near the middle of California
's Central Valley. These vernal pool
ecosystems are home to other unique organisms adapted to the ephemeral nature of the water cycle in the pools in California's mediterranean climate
.
It is one of eight known branchiopod species found only in Northern California. The species swims through the water on its back, using two stalked compound eyes to see where it is going. It propels itself along by beating its phyllopods. These are legs with leaflike or paddlelike structures. The moving phyllopods also serve as gills, extracting oxygen
from the water stream they create. This places the shrimp in the Class Branchiopoda ("branchio" meaning gill
, and "poda" meaning feet).
and VernalPools.Org to list the midvalley fairy shrimp as an endangered species pursuant to the Endangered Species Act, and to concurrently designate critical habitat for the species. On April 29, 2003, the U.S. Fish and Wildlife Service published a finding in Federal Register notice that the petition presented substantial information to indicate that listing might be warranted. After reviewing the available scientific and commercial information, the U.S. Fish and Wildlife Service have found that listing is not warranted at this time.
, a hard shell covering their heads and backs. The midvalley fairy shrimp uses its phyllopods to filter food out of the water, including phytoplankton
, detrital bacteria
l colonies, rotifer
s, protozoa
and small larva
e of various species, which it then passes up to its mouth via a food groove on its belly. In addition to providing for movement, oxygen and food, the phyllopods also contain cells responsible for salt exchange.
The midvalley fairy shrimp was only recently formally described as a species in 2000 by Belk and Fugate. Adult males of the species most closely resemble male Conservancy fairy shrimp
, in that their antennae
are relatively smooth and consist of two jointed segments of approximately equal length, the second of which bends inward about 90° at the tip. Viewed from the belly side of the animal, the tip has two humps, the larger of which is towards the front of the animal in the midvalley fairy shrimp and towards the rear in the Conservancy fairy shrimp. The antennal configuration has more significance than might at first appear. Males use these appendages to clasp females during mating. The females thrash about when clasped, and inappropriately shaped male antennae are less likely to successfully hold on. Females are easily distinguished from female Conservancy fairy shrimp because of their pear-shaped rather than spindle-shaped brood pouches, which do not extend as far down the body. Female midvalley fairy shrimp more closely resemble female vernal pool fairy shrimp, which also have pear-shaped brood pouches. However, female vernal pool fairy shrimp also possess a pair of conspicuous bumps on the sides of their third thoracic segments, which midvalley shrimp lack.
As might be expected from a species found in relatively small, potentially quick drying pools, midvalley fairy shrimp can mature very quickly in warm pools, which are typically small. However, they can mature more slowly in cooler (typically larger) pools. They can mature within about 8 days of hatching, although 26 seems to be the average. Multiple hatchings have been observed in a single rainy season.
The species has been found in shallow vernal pools, vernal swales and various artificial ephemeral wetland habitats in Sacramento County
, Solano County
, Contra Costa County
, San Joaquin County
, Madera County
, Merced County
and Fresno County
. Vernal pools are shallow depressions with impermeable soils that collect water during the wet season, dry completely during the dry season, and support a specific community of plants adapted to such conditions. Vernal swales are similar, but tend to convey surface runoff during wet seasons in somewhat defined vegetated channels that often connect vernal pools. Midvalley fairy shrimp have also been found in various roadside puddles, scrapes, and ditches, and in several railroad toe-drain pools. The species appears to do best in shallow, cool water pools that are low to moderate in dissolved salts. However, it can tolerate warm water. In one instance live adults were found swimming in 32 °C (89.6 °F) water. Members of the species have also been found in some relatively alkaline pools. A 1998 comparison of the characteristics of pools used by the eight branchiopod species endemic to Northern California found that midvalley fairy shrimp used the shallowest pools. The midvalley shrimp were found in pools averaging 10.1 centimetres (4 in) deep.
Midvalley fairy shrimp populations survive the seasonal drying of their ponds by laying eggs encased in nearly impervious shells. Embryos within these eggs enter a dormant state called diapause. Dormant eggs are referred to as cysts. Because not all cysts hatch with each refilling of a pool they can form a sort of "seed bank" in the soil that produces new populations of adult shrimp where none had been seen in years. In related species, cysts many decades old have been successfully hatched. Since the cysts can pass unharmed through the digestive systems of other animals, and since they are very small (0.27 millimetre or 0.0106299212598425 in), they can be transported to new locations by birds or mammals and thereby found new colonies.
The increase of known locations lends additional support to the idea that the range and distribution of midvalley fairy shrimp is greater than the distribution of known occurrences. The species has only been formally described since June 2000, and less formally described since 1999. The record of known occurrences therefore may poorly reflect the actual extent of the species distribution. The CNDDB does include occurrence sightings dating back to 1989, but these early sightings are all based on individual shrimp from the collection of Denton Belk, one of the authors of the formal description. Since male and female midvalley fairy shrimp closely resemble male Conservancy fairy shrimp and female vernal pool fairy shrimp, many occurrences could have been overlooked in many surveys conducted prior to about 1998.
High human population growth estimates in the counties occupied by the shrimp, and potential threats from specific proposed development projects such as the new University of California, Merced
campus are causes for concern.
The U.S. Fish and Wildlife Service believes that loss of habitat may constitute a threat to vernal pool species. It is less clear, however, to what extent previous listing actions and other regulatory mechanisms may reduce that threat in the case of the midvalley fairy shrimp.
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
in the Branchinectidae
Branchinectidae
Branchinectidae is a family in the order Anostraca , containing two genera – Branchinecta and Archaebranchinecta. The majority of the species are in the genus Branchinecta, with only Archaebranchinecta pollicifera and the fossil Archaebranchinecta barstowensis in the second genus....
family endemic to shallow ephemeral pools (pools that seasonally fill and dry up) near the middle of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
's Central Valley. These vernal pool
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
ecosystems are home to other unique organisms adapted to the ephemeral nature of the water cycle in the pools in California's mediterranean climate
Mediterranean climate
A Mediterranean climate is the climate typical of most of the lands in the Mediterranean Basin, and is a particular variety of subtropical climate...
.
It is one of eight known branchiopod species found only in Northern California. The species swims through the water on its back, using two stalked compound eyes to see where it is going. It propels itself along by beating its phyllopods. These are legs with leaflike or paddlelike structures. The moving phyllopods also serve as gills, extracting oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
from the water stream they create. This places the shrimp in the Class Branchiopoda ("branchio" meaning gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
, and "poda" meaning feet).
Federal protection denied
On August 31, 2001, the U.S. Fish and Wildlife Service was petitioned by the Center for Biological DiversityCenter for Biological Diversity
The Center for Biological Diversity based in Tucson, Arizona, is a nonprofit membership organization with approximately 220,000 members and online activists, known for its work protecting endangered species through legal action and scientific petitions...
and VernalPools.Org to list the midvalley fairy shrimp as an endangered species pursuant to the Endangered Species Act, and to concurrently designate critical habitat for the species. On April 29, 2003, the U.S. Fish and Wildlife Service published a finding in Federal Register notice that the petition presented substantial information to indicate that listing might be warranted. After reviewing the available scientific and commercial information, the U.S. Fish and Wildlife Service have found that listing is not warranted at this time.
Ecology and description
Fairy shrimp are in the order Anostraca ("an" meaning without, "ostraca" meaning hard plate or shell). They do not have a carapaceCarapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
, a hard shell covering their heads and backs. The midvalley fairy shrimp uses its phyllopods to filter food out of the water, including phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
, detrital bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l colonies, rotifer
Rotifer
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...
s, protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
and small larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of various species, which it then passes up to its mouth via a food groove on its belly. In addition to providing for movement, oxygen and food, the phyllopods also contain cells responsible for salt exchange.
The midvalley fairy shrimp was only recently formally described as a species in 2000 by Belk and Fugate. Adult males of the species most closely resemble male Conservancy fairy shrimp
Conservancy fairy shrimp
The conservancy fairy shrimp, Branchinecta conservatio, is a small crustacean in the family Branchinectidae. It ranges in size from about to long. Fairy shrimp are aquatic species in the order Anostraca. They have delicate elongate bodies, large stalked compound eyes, no carapaces, and eleven...
, in that their antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
are relatively smooth and consist of two jointed segments of approximately equal length, the second of which bends inward about 90° at the tip. Viewed from the belly side of the animal, the tip has two humps, the larger of which is towards the front of the animal in the midvalley fairy shrimp and towards the rear in the Conservancy fairy shrimp. The antennal configuration has more significance than might at first appear. Males use these appendages to clasp females during mating. The females thrash about when clasped, and inappropriately shaped male antennae are less likely to successfully hold on. Females are easily distinguished from female Conservancy fairy shrimp because of their pear-shaped rather than spindle-shaped brood pouches, which do not extend as far down the body. Female midvalley fairy shrimp more closely resemble female vernal pool fairy shrimp, which also have pear-shaped brood pouches. However, female vernal pool fairy shrimp also possess a pair of conspicuous bumps on the sides of their third thoracic segments, which midvalley shrimp lack.
As might be expected from a species found in relatively small, potentially quick drying pools, midvalley fairy shrimp can mature very quickly in warm pools, which are typically small. However, they can mature more slowly in cooler (typically larger) pools. They can mature within about 8 days of hatching, although 26 seems to be the average. Multiple hatchings have been observed in a single rainy season.
The species has been found in shallow vernal pools, vernal swales and various artificial ephemeral wetland habitats in Sacramento County
Sacramento County, California
Sacramento County is a county in the U.S. state of California. Its county seat is Sacramento, which is also the state capital. As of 2010 the county had a population of 1,418,788....
, Solano County
Solano County, California
Solano County is a county located in Bay-Delta region of the U.S. state of California, about halfway between San Francisco and Sacramento and is one of the nine San Francisco Bay Area counties. The county's population was reported by the U.S. Census to be 413,344 in 2010...
, Contra Costa County
Contra Costa County, California
Contra Costa County is a primarily suburban county in the San Francisco Bay Area of the U.S. state of California. As of the 2010 census, it had a population of 1,049,025...
, San Joaquin County
San Joaquin County, California
San Joaquin County is a county located in Central Valley of the U.S. state of California, just east of the San Francisco Bay Area. As of the 2010 census, the population was 685,306. The county seat is Stockton.-History:...
, Madera County
Madera County, California
Madera County is a county of the U.S. state of California, located in the Central Valley and the Sierra Nevada north of Fresno County. It comprises the Madera-Chowchilla, CA Metropolitan Statistical Area. As of the 2010 census the population was 150,865...
, Merced County
Merced County, California
Merced County , is a county located in the Central Valley of the U.S. state of California, north of Fresno and southeast of San Jose. As of the 2010 census, the population was 255,793, up from 210,554 at the 2000 census. The county seat is Merced...
and Fresno County
Fresno County, California
Fresno County is a county located in the Central Valley of the U.S. state of California, south of Stockton and north of Bakersfield. As of the 2010 census, it is the tenth most populous county in California with a population of 930,450, and the sixth largest in size with an area of . The county...
. Vernal pools are shallow depressions with impermeable soils that collect water during the wet season, dry completely during the dry season, and support a specific community of plants adapted to such conditions. Vernal swales are similar, but tend to convey surface runoff during wet seasons in somewhat defined vegetated channels that often connect vernal pools. Midvalley fairy shrimp have also been found in various roadside puddles, scrapes, and ditches, and in several railroad toe-drain pools. The species appears to do best in shallow, cool water pools that are low to moderate in dissolved salts. However, it can tolerate warm water. In one instance live adults were found swimming in 32 °C (89.6 °F) water. Members of the species have also been found in some relatively alkaline pools. A 1998 comparison of the characteristics of pools used by the eight branchiopod species endemic to Northern California found that midvalley fairy shrimp used the shallowest pools. The midvalley shrimp were found in pools averaging 10.1 centimetres (4 in) deep.
Midvalley fairy shrimp populations survive the seasonal drying of their ponds by laying eggs encased in nearly impervious shells. Embryos within these eggs enter a dormant state called diapause. Dormant eggs are referred to as cysts. Because not all cysts hatch with each refilling of a pool they can form a sort of "seed bank" in the soil that produces new populations of adult shrimp where none had been seen in years. In related species, cysts many decades old have been successfully hatched. Since the cysts can pass unharmed through the digestive systems of other animals, and since they are very small (0.27 millimetre or 0.0106299212598425 in), they can be transported to new locations by birds or mammals and thereby found new colonies.
Distribution
Midvalley fairy shrimp have been found in shallow vernal pools, vernal swales and various artificial ephemeral wetland habitats in the following California counties: Sacramento, Solano, Yolo, Contra Costa, San Joaquin, Madera, Merced and Fresno. Since the U.S. Fish and Wildlife Service published our 90-day finding on a petition to list the species in April, 2003, more new sites have been documented. The total number of occurrences documented in the California Natural Diversity Database is 63 as of February 2006.The increase of known locations lends additional support to the idea that the range and distribution of midvalley fairy shrimp is greater than the distribution of known occurrences. The species has only been formally described since June 2000, and less formally described since 1999. The record of known occurrences therefore may poorly reflect the actual extent of the species distribution. The CNDDB does include occurrence sightings dating back to 1989, but these early sightings are all based on individual shrimp from the collection of Denton Belk, one of the authors of the formal description. Since male and female midvalley fairy shrimp closely resemble male Conservancy fairy shrimp and female vernal pool fairy shrimp, many occurrences could have been overlooked in many surveys conducted prior to about 1998.
Threats
As stated in the U.S. Fish and Wildlife Service's 1994 listing of four other vernal pool shrimp species (59 FR 48136), California's remaining vernal pools have been under severe pressure from urban development, agricultural conversion and associated hydrological changes. Losses of vernal pool habitat were noted prior to 1997.High human population growth estimates in the counties occupied by the shrimp, and potential threats from specific proposed development projects such as the new University of California, Merced
University of California, Merced
The University of California, Merced, commonly referred to as UC Merced or UCM, is the tenth and newest of the University of California campuses. Located in the San Joaquin Valley in unincorporated Merced County, California, near Merced, UC Merced was the first American research university to...
campus are causes for concern.
The U.S. Fish and Wildlife Service believes that loss of habitat may constitute a threat to vernal pool species. It is less clear, however, to what extent previous listing actions and other regulatory mechanisms may reduce that threat in the case of the midvalley fairy shrimp.
Further reading
- Fugate, Michael. 1998. Branchinecta of North America: population structure and its implications for conservation practice. Pp 140-146 in C. W. Witham, E. Bauder, D. Belk, W. Ferren, and R. Ornduff, eds. Ecology, Conservation and Management of Vernal Pool Ecosystems. California Native Plant Society, Sacramento, California.
- United States Fish & Wildlife Service. 1994. Determination of endangered status for the Conservancy fairy shrimp, longhorn fairy shrimp, and the vernal pool tadpole shrimp; and threatened status for the vernal pool fairy shrimp. 59 Fed. Reg. 48136.
- U.S. Fish and Wildlife Service. 2005. Recovery Plan for Vernal Pool Ecosystems of California and Southern Oregon. Portland, Oregon.