''Halocaridina rubra'', the Hawaiian red shrimp or volcano shrimp is a small red

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Atyidae Atyidae is a family of shrimp, present in all tropical and most temperate waters of the world. Adults of this family are almost always confined to fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water conta ...

, with the common Hawaiian name (meaning "red shrimp").

Description and distribution

''Halocaridina rubra'' are small red shrimp, which can also appear yellow or orange, and are rarely longer than . They have a short and pointed rostrum, up to the end of the basal segment of the antennular peduncle. It is dorsoventrally depressed, being broadly triangular in dorsal view and narrow in lateral view. It does not have teeth or spines. They are typically found in

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuary ...

pools near the sea shore, sometimes in large numbers. Such pools are referred to as

anchialine pool An anchialine system (, from Greek ''ankhialos'' 'near the sea') is a landlocked body of water with a subterranean connection to the ocean. Depending on its formation, these systems can exist in one of two primary forms: pools or caves. The primary ...

s (from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

' = near the sea). They have also been found in caverns in the coral plains near the seashore and wells close to the ocean. ''Halocaridina rubra'' is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the

Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...

, and most commonly found in anchialine pools in fresh

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

substrates on

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

and

Maui Maui (; Hawaiian language, Hawaiian: ) is the second largest island in the Hawaiian archipelago, at 727.2 square miles (1,883 km2). It is the List of islands of the United States by area, 17th-largest in the United States. Maui is one of ...

Island; it has also been found in

limestone karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. There is some eviden ...

pools and

hypogeal Hypogeal, hypogean, hypogeic and hypogeous (; ) are biological terms describing an organism's activity below the soil surface. In botany, a seed is described as showing hypogeal germination when the cotyledons of the germinating seed remain no ...

habitats in limestone on older islands, such as

Oahu Oahu (, , sometimes written Oahu) is the third-largest and most populated island of the Hawaiian Islands and of the U.S. state of Hawaii. The state capital, Honolulu, is on Oahu's southeast coast. The island of Oahu and the uninhabited Northwe ...

. Its habitat is unique and sparsely represented on five of the eight high Hawaiian Islands (Maui, Kahoolawe, Oahu, Molokai and Hawaii).

Ecology

are

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

and detritivorous shrimp occupying both hypogeal (subterranean) and epigeal (surface) anchialine waters. Typical food of is

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

l and

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

l mats on the surface of rocks and other substrates in anchialine pools.

Cheliped A chela ()also called a claw, nipper, or pinceris a pincer-shaped organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through Neo-Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds ...

s are adapted for scraping and filtering of algal-bacterial layers. Serrated setae scrape the substrate surface, and filamentous setae collect the loosened food materials. The latter can also act as filters for

filter feeding Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a spe ...

during

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

blooms. The grazing activity of this shrimp is essential in maintaining the integrity of the crust, an actively growing matrix of plants, bacteria, diatoms, protozoans, and underlying siliceous and carbonate materials. ''Halocaridina'' is well adapted to the epigeal-hypogeal habitat in the pools. It reproduces in the subterranean portion of the habitat.

Aquaria

Recent popularity of as a low-maintenance pet in Hawaii and elsewhere has brought this otherwise obscure decapod crustacean into popular consciousness. A long-lived species, have been known to live for as long as 20 years in captivity. Sexes are difficult to distinguish, except when

gravid In biology and medicine, gravidity and parity are the number of times a female has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These two terms are usually coupled, sometimes with additional terms, t ...

females carry clusters of red/maroon eggs under their pleopods. Early larvae are

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic filter-feeders. They occasionally molt their shells, which can be seen as silvery exoskeletons at the bottom of the tank. There may be some evidence that mate after molting, or that molting and mating may be related. Stressed ʻōpaeʻula tend to hide, though if given plenty of places to hide they are more likely to venture into open spaces. are social creatures and are rarely seen fighting, in fact when unstressed they often cluster together while eating or sunbathing. Shrimp in tanks can also be seen cleaning themselves or swimming slow laps. The shrimp is the animal featured in the Ecosphere closed-system aquarium.

Description and distribution

Ecology

Aquaria

References

Further reading