Salp

Sea Salp
A chain of salps near the surface in the Red Sea.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Tunicata
Class: Thaliacea
Order: Salpida
Family: Salpidae
Genera and species

See text.

Another salp chain

A salp (plural salps) or salpa (plural salpae or salpas[1]) is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body. Salp jet propulsion is one of the most efficient in the animal kingdom.[2] The salp strains the pumped water through its internal feeding filters, feeding on phytoplankton.

Distribution

Salps are common in equatorial, temperate, and cold seas, where they can be seen at the surface, singly or in long, stringy colonies. The most abundant concentrations of salps are in the Southern Ocean[3] (near Antarctica), where they sometimes form enormous swarms, often in deep water, and are sometimes even more abundant than krill.[4] 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.[5]

Life history

Salps have a complex lifecycle, with an obligatory alternation of generations. Both portions of the lifecycle exist together in the seas—they look quite different, but both are mostly transparent, tubular, gelatinous animals that are typically between 1 and 10 cm (0.39 and 3.94 in) tall. The solitary life history phase, also known as an oozoid, 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 lifecycle. 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 oozoid attached to the body wall of the parent. The growing oozoids are eventually released from the parent blastozooids, and then continue to feed and grow as the solitary asexual phase, thus closing the lifecycle 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 genera Heteropsammia are known to feed on salps during blooms[6]

History

The incursion of a large number of salps (Salpa fusiformis) into the North Sea in 1920 led to a failure of the herring fishing.[7]

Oceanographic importance

Pegea confederata on a 1995 stamp from Azerbaijan

One 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 the phytoplankton and can grow at a rate which is probably faster than that of any other multicellular 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 planktonic species can experience fluctuations in their numbers due to competition with the salps.

Sinking fecal pellets and bodies of salps carry carbon to the sea floor, and salps are abundant enough to have an effect on the ocean's biological pump. Consequently, large changes in their abundance or distribution may alter the ocean's carbon cycle, and potentially play a role in climate change.

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 because of their simple body form and planktonic behavior, they are chordates: animals with dorsal nerve cords, related to vertebrates, animals with backbones.

Salps appear to have a form preliminary to vertebrates, and are used as a starting point in models of how vertebrates evolved. Scientists speculate that the tiny groups of nerves in salps are one of the first instances of a primitive nervous system, which eventually evolved into the more complex central nervous systems of vertebrates.[8]

Classification

The World Register of Marine Species lists the following genera and species in the order Salpida:[9]

Bibliography

Bone, Q. editor (1998) The Biology of Pelagic Tunicates. Oxford University Press, Oxford. 340 pp.

References

  1. ↑ "salp - Definitions from Dictionary.com". Retrieved 2008-09-28.; Peter Forsskål, in introducing the genus Salpa from waters off Yemen (1763, publication 1775), gave no derivation for his word; the English salp first appeared in 1835 (OED, "salp)
  2. ↑ Jet propulsion in salps (Tunicata: Thaliacea)
  3. ↑ "Now that's a jelly fish!". Daily Mail. 22 January 2014. Retrieved 22 January 2014.
  4. ↑ "Dive and Discover: Scientific Expedition 10: Antarctica". Retrieved 2008-09-03.
  5. ↑ "Odd creatures wash ashore on Washington beach". NBC. 16 February 2013. Retrieved 17 February 2013.
  6. ↑ Mehrotra, R; Scott, C.M.; Hoeksema, B.W. (2015). "A large gape facilitates predation on salps by Heteropsammia corals". Marine Biodiversity. doi:10.1007/s12526-015-0379-8.
  7. ↑ Scottish Fisheries During the War in David T. Jones; Joseph F. Duncan; H.M. Conacher; W.R. Scott (1926). Rural Scotland During the War. Oxford University Press.
  8. ↑ Lacalli, T.C.; Holland, L.Z. (1998). "The developing dorsal ganglion of the salp Thalia democratica, and the nature of the ancestral chordate brain". Philosophical Transactions of the Royal Society B. 353 (1378): 1943–1967. doi:10.1098/rstb.1998.0347.
  9. ↑ Salpida World Register of Marine Species. Retrieved 2011-11-16.
  10. ↑ Brooksia Metcalf, 1918 World Register of Marine Species. Retrieved 2011-11-16.
  11. ↑ Cyclosalpa de Blainville, 1827 World Register of Marine Species. Retrieved 2011-11-16.
  12. ↑ Helicosalpa Todaro, 1902 World Register of Marine Species. Retrieved 2011-11-16.
  13. ↑ Ihlea World Register of Marine Species. Retrieved 2011-11-16.
  14. ↑ Metcalfina World Register of Marine Species. Retrieved 2011-11-16.
  15. ↑ Pegea World Register of Marine Species. Retrieved 2011-11-16.
  16. ↑ Ritteriella World Register of Marine Species. Retrieved 2012-9-17.
  17. ↑ Salpa World Register of Marine Species. Retrieved 2011-11-16.
  18. ↑ Soestia World Register of Marine Species. Retrieved 2011-11-16.
  19. ↑ Thalia World Register of Marine Species. Retrieved 2011-11-16.
  20. ↑ Thetys de Blainville, 1827 World Register of Marine Species. Retrieved 2011-11-16.
  21. ↑ Traustedtia World Register of Marine Species. Retrieved 2011-11-16.
  22. ↑ Weelia Yount, 1954 World Register of Marine Species. Retrieved 2011-11-16.
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