''Branchinecta gaini'' is a species of

fairy shrimp Anostraca is one of the four orders of crustaceans in the class Branchiopoda; its members are referred to as fairy shrimp. They live in vernal pools and hypersaline lakes across the world, and they have even been found in deserts, ice-covered mou ...

from

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

and

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

. It is the largest freshwater invertebrate in Antarctica, at long. It lives on

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

and other organisms, surviving the winter as resting

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...

Distribution

''B. gaini'' is found from "half-way down the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

" northwards, including southernmost

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

and subantarctic islands such as South Georgia and the

South Orkney Islands The South Orkney Islands are a group of islands in the Southern Ocean, about north-east of the tip of the Antarctic Peninsula It is the only fairy shrimp on mainland Antarctica, where it is "rather widespread on the Antarctic Peninsula"; records of "''

Branchinecta granulosa ''Branchinecta'' is a genus of crustacean in family Branchinectidae. It includes around 50 species, found on all continents except Australia. ''Branchinecta gigas'', the giant fairy shrimp, is the largest species in the order, with a length of u ...

''" from Antarctica are all misidentifications of ''B. gaini''. In the

South Shetland Islands The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 195 ...

, ''B. gaini'' has been recorded from the lakes on the ice-free

Byers Peninsula Byers Peninsula is a mainly ice-free peninsula forming the west end of Livingston Island in the South Shetland Islands of Antarctica. It occupies , borders Ivanov Beach to the northeast and is separated from Rotch Dome on the east by the ridge of ...

Livingston Island Livingston Island (Russian name ''Smolensk'', ) is an Antarctic island in the Southern Ocean, part of the South Shetlands Archipelago, a group of Antarctic islands north of the Antarctic Peninsula. It was the first land discovered south of 60 ...

(alongside '' Boeckella poppei'' and the benthic

cladocera The Diplostraca or Cladocera, commonly known as water fleas, are a superorder of small crustaceans that feed on microscopic chunks of organic matter (excluding some predatory forms). Over 1000 species have been recognised so far, with many more ...

n '' Macrothrix ciliata''), in Lake Wujka, and in Sombre Lake on

Signy Island Signy Island is a small subantarctic island in the South Orkney Islands of Antarctica. It was named by the Norwegian whaler Petter Sørlle (1884–1933) after his wife, Signy Therese. The island is about long and wide and rises to above se ...

(alongside ''Boeckella poppei'' and the carnivorous '' Parabroteus sarsi''). The only known

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

records of the genus ''

Branchinecta ''Branchinecta'' is a genus of crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipod ...

'' are of ''B. gaini''; its

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

have been found in mid to late

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

(4,200 BP) lake deposits on

James Ross Island James Ross Island is a large island off the southeast side and near the northeastern extremity of the Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north–south ...

, on the east side of the Antarctic Peninsula. ''B. gaini'' no longer occurs on James Ross Island, presumably because the lakes are unfrozen for too short a period for ''B. gaini'' to complete its

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring * Life-cycle hypothesis ...

. The egg cases were found to be most abundant during the

Holocene climatic optimum The Holocene Climate Optimum (HCO) was a warm period that occurred in the interval roughly 9,000 to 5,000 years ago BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimu ...

, indicating that

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

l mats must have been present in the lake then. Eggs dating from 5,500 BP have also been found on

, where the species persists.

Description

''Branchinecta gaini'' can reach a total length of , making it the largest freshwater invertebrate in

. It uses its trunk limbs to scrape food from the substrate.

Ecology and life cycle

''Branchinecta gaini'' feeds on

epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...

s in bacterial mats, and on the mats themselves. The gut contents of ''B. gaini'' are dominated by

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

and remains of other ''B. gaini'' individuals. They live for over six months, and produce resting eggs which can survive the winter, when the lakes are frozen. Although ''B. gaini'' often coexists with the copepod '' Boeckella poppei'', they are rarely seen in close contact. They may be in

competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...

for food, or ''B. gaini'' may feed on the

nauplii Nauplius, Nauplia or Nauplios , may refer to : Greece-related * Nauplius (mythology), in Greek mythology, the son of Poseidon and Amymone, the father of Palamedes, and also the name of an Argonaut * Nauplia Nafplio ( ell, Ναύπλιο) is a ...

of the copepod. ''B. gaini'' can be quite abundant, dominating the crustacean

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

in freshwater bodies in the

South Orkney The South Orkney Islands are a group of islands in the Southern Ocean, about north-east of the tip of the Antarctic Peninsula South Shetland The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 195 ...

islands. The dispersal of ''B. gaini'' between

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s is probably passive, with the most likely

dispersal vector A dispersal vector is an agent of biological dispersal that moves a dispersal unit, or organism, away from its birth population to another location or population in which the individual will reproduce. These dispersal units can range from pollen t ...

s being birds; branchiopod eggs swallowed by

seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...

s, even if still being brooded by the mother, can survive passage through the bird's digestive system.

Taxonomic history

''Branchinecta gaini'' was first described by the Hungarian biologist Eugen von Daday de Deés (also called Jenö Daday or Jenö Daday de Dées) in 1910 based on material collected from

Petermann Island Petermann Island is a small, low and rounded island, lying off the northwest coast of Kyiv Peninsula in Graham Land, Antarctica, a short distance south of Booth Island and the Lemaire Channel. It is a popular tourist destination. Descriptio ...

by the ' aboard the ''Pourquoi Pas ?'', captained by

Jean-Baptiste Charcot Jean-Baptiste-Étienne-Auguste Charcot (15 July 1867 – 16 September 1936), born in Neuilly-sur-Seine, was a French scientist, medical doctor and polar scientist. His father was the neurologist Jean-Martin Charcot (1825–1893). Life Jean-Ba ...

; the

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

commemorates the French algologist Louis Gain, who was responsible for preserving the specimens from that expedition.

References

{{Taxonbar, from=Q4021747 Branchiopoda Freshwater crustaceans of South America Fauna of Antarctica Crustaceans described in 1910