A salp (: salps, also known colloquially as “sea grape”) or salpa (: salpae or salpas) is a barrel-shaped,
planktonic
Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...
tunicate in the family Salpidae. The salp moves by contracting its gelatinous body in order to pump water through it; it is one of the most efficient examples of
jet propulsion in the animal kingdom. The salp feeds on
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 ...
, which it collects by straining water through its internal feeding filters.
Distribution
Salps are common in
equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
ial, temperate, and cold seas, where they can be seen at the surface, singly or in long, stringy
colonies
A colony is a territory subject to a form of foreign rule, which rules the territory and its indigenous peoples separated from the foreign rulers, the colonizer, and their '' metropole'' (or "mother country"). This separated rule was often or ...
. The most abundant concentrations of salps are in the
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean, generally taken to be south of 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...
(near
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
), where they sometimes form enormous swarms, often in deep water, and are sometimes even more abundant than
krill
Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...
. Since 1910, while krill populations in the Southern Ocean have declined, salp populations appear to be increasing. Salps have been seen in increasing numbers along the coast of
Washington, United States.
Life cycle
Salps have a complex life cycle, with an obligatory
alternation of generations
Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of life cycle in plants and algae. In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploi ...
. Both portions of the life cycle exist together in the seas—they look quite different, but both are mostly transparent, tubular, gelatinous animals that are typically between long. The
solitary life history phase, also known as an
oozooid, is a single, barrel-shaped animal that
reproduces asexually by producing a chain of tens to hundreds of individuals, which are released from the parent at a small size.
The chain of salps is the 'aggregate' portion of the life cycle. The aggregate individuals are also known as
blastozooids; they remain attached together while swimming and feeding, and each individual grows in size. Each blastozooid in the chain reproduces sexually (the blastozooids are sequential
hermaphrodites, first maturing as females, and are fertilized by male gametes produced by older chains), with a growing embryo oozooid attached to the body wall of the parent. The growing oozooids are eventually released from the parent blastozooids, and then continue to feed and grow as the solitary asexual phase, closing the life cycle of salps. The alternation of generations allows for a fast generation time, with both solitary individuals and aggregate chains living and feeding together in the sea. When phytoplankton is abundant, this rapid reproduction leads to fairly short-lived blooms of salps, which eventually filter out most of the phytoplankton. The bloom ends when enough food is no longer available to sustain the enormous population of salps. Occasionally,
mushroom corals and those of the genus ''
Heteropsammia'' are known to feed on salps during blooms.
History
The incursion of a large number of salps (''
Salpa fusiformis'') into the
North Sea
The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...
in 1920 led to a failure of the Scottish herring fishery.
Oceanographic importance
A reason for the success of salps is how they respond to
phytoplankton blooms. When food is plentiful, salps can quickly bud off
clones, which graze on the phytoplankton and can grow at a rate which is probably faster than that of any other
multicellular
A multicellular organism is an organism that consists of more than one cell (biology), cell, unlike unicellular organisms. All species of animals, Embryophyte, land plants and most fungi are multicellular, as are many algae, whereas a few organism ...
animal, quickly stripping the phytoplankton from the sea. But if the phytoplankton is too dense, the salps can clog and sink to the bottom. During these blooms, beaches can become slimy with mats of salp bodies, and other
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 species can experience fluctuations in their numbers due to competition with the salps.
Sinking
fecal pellets and bodies of salps carry
carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
to the seafloor, and salps are abundant enough to have an effect on the ocean's
biological pump
The biological pump (or ocean carbon biological pump or marine biological carbon pump) is the ocean's biologically driven Carbon sequestration, sequestration of carbon from the atmosphere and land runoff to the ocean interior and seafloor sedim ...
. Consequently, large changes in their abundance or distribution may alter the ocean's
carbon cycle
The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
, and potentially play a role in
climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.
Nervous systems and relationships to other animals
Salps are closely related to the pelagic tunicate groups
Doliolida and
Pyrosoma, as well as to other bottom-living (benthic)
tunicates.
Although salps appear similar to
jellyfish
Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...
because of their simple body form and planktonic behavior, they are
chordates: animals with
dorsal nerve cord
The dorsal nerve cord is an anatomical feature found in chordate animals, mainly in the subphyla Vertebrata and Cephalochordata, as well as in some hemichordates. It is one of the five embryonic features unique to all chordates, the other fo ...
s, related to
vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
s (animals with
backbones).
Small fish swim inside salps as protection from predators.
Classification
The
World Register of Marine Species
The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms.
Content
The content of the registry is edited and maintained by scien ...
lists the following
genera
Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
and
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
in the order Salpida:
*Order Salpida
**Family Salpidae
***Subfamily Cyclosalpinae
**** Genus ''
Cyclosalpa''
de Blainville, 1827
***** ''
Cyclosalpa affinis''
(Chamisso, 1819)
***** ''
Cyclosalpa bakeri''
Ritter, 1905
***** ''
Cyclosalpa foxtoni''
Van Soest, 1974
***** ''
Cyclosalpa ihlei''
van Soest, 1974
***** ''
Cyclosalpa pinnata''
(Forskål, 1775)
***** ''
Cyclosalpa polae''
Sigl, 1912
***** ''
Cyclosalpa quadriluminis''
Berner, 1955
***** ''
Cyclosalpa sewelli''
Metcalf, 1927
***** ''
Cyclosalpa strongylenteron''
Berner, 1955
**** Genus ''
Helicosalpa''
Todaro, 1902
***** ''
Helicosalpa komaii''
(Ihle & Ihle-Landenberg, 1936)
***** ''
Helicosalpa virgula''
(Vogt, 1854)
***** ''
Helicosalpa younti''
Kashkina, 1973
***Subfamily Salpinae
**** Genus ''
Brooksia''
Metcalf, 1918
***** ''
Brooksia berneri''
van Soest, 1975
***** ''
Brooksia rostrata''
(Traustedt, 1893)
**** Genus ''
Ihlea''
Metcalf, 1919
***** ''
Ihlea magalhanica''
(Apstein, 1894)
***** ''
Ihlea punctata''
(Forskål, 1775)
***** ''
Ihlea racovitzai''
(van Beneden & Selys Longchamp, 1913)
**** Genus ''
Metcalfina''
***** ''
Metcalfina hexagona''
(Quoy & Gaimard, 1824)
**** Genus ''
Pegea''
Savigny, 1816
***** ''
Pegea bicaudata''
(Quoy & Gaimard, 1826)
***** ''
Pegea confederata''
(Forsskål, 1775)
**** Genus ''
Ritteriella''
Metcalf, 1919
***** ''
Ritteriella amboinensis''
(Apstein, 1904)
***** ''
Ritteriella picteti''
(Apstein, 1904)
***** ''
Ritteriella retracta''
(Ritter, 1906)
**** Genus ''
Salpa''
Forskål, 1775
***** ''
Salpa aspera''
Chamisso, 1819
***** ''
Salpa fusiformis''
Cuvier, 1804
***** ''
Salpa gerlachei''
Foxton, 1961
***** ''
Salpa maxima''
Forskål, 1775
***** ''
Salpa thompsoni''
(Foxton, 1961)
***** ''
Salpa tuberculata''
Metcalf, 1918
***** ''
Salpa younti''
van Soest, 1973
**** Genus ''
Soestia'' (also accepted as ''Iasis'')
***** ''
Soestia cylindrica''
(Cuvier, 1804)
***** ''
Soestia zonaria''
(Pallas, 1774)
**** Genus ''
Thalia''
***** ''
Thalia cicar''
van Soest, 1973
***** ''
Thalia democratica''
Forskål, 1775
***** ''
Thalia longicauda''
Quoy & Gaimard, 1824
***** ''
Thalia orientalis''
Tokioka, 1937
***** ''
Thalia rhinoceros''
Van Soest, 1975
***** ''
Thalia rhomboides''
Quoy & Gaimard, 1824
***** ''
Thalia sibogae''
Van Soest, 1973
**** Genus ''
Thetys''
Tilesius, 1802
***** ''
Thetys vagina''
Tilesius, 1802
**** Genus ''
Traustedtia''
***** ''
Traustedtia multitentaculata''
Quoy & Gaimard, 1834
**** Genus ''
Weelia''
Yount, 1954''Weelia'' Yount, 1954
World Register of Marine Species. Retrieved 2011-11-16.
***** '' Weelia cylindrica'' (Cuvier, 1804)
References
External links
Plankton Chronicles
Short documentary films & photos
Pelagic tunicates (including salps) overview
*[http://www.boston.com/news/local/massachusetts/articles/2006/10/09/sludge_of_slimy_organisms_coats_beaches_of_new_england/ Sludge of slimy organisms coats beaches of New England Boston Globe October 9, 2006]
The salps on earthlife.net
* ttps://www.sciencedaily.com/releases/2006/07/060702085004.htm Jellyfish-like Creatures May Play Major Role In Fate Of Carbon Dioxide In The Ocean ScienceDaily.com, July 2, 2006
"Ocean 'Gummy Bears' Fight Global Warming"
LiveScience.com, July 20, 2006
How salps might help counteract global warming
BBC News, September 26, 2007
ABC Radio, The World Today - Monday, 17 November 2008
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