Overview

Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Widespread throughout the Arctic, North Pacific and North Atlantic regions; in the Pacific occurs as far south as the southern Japan Sea and the south coast of British Columbia, in the Atlantic south to the coast of Maine and north coast of Spain. The southern boundary of distribution is about 40 to 41° N (Bieri 1959, Van der Spoel and Heyman 1983). Bieri (1959) suggested distribution in the Pacific is limited to the subarctic water mass.

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circum-arctic
  • UNESCO-IOC Register of Marine Organisms
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Physical Description

Size

Length: 36 cm

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Type Information

Type for Sagitta elegans Verrill
Catalog Number: USNM 15630
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Alcohol (Ethanol)
Collector(s): Verrill, Smith & Todd
Year Collected: 1871
Locality: Gay Head, Off Gay Head, Massachusetts, United States, North Atlantic Ocean
  • Type:
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Ecology

Habitat

Comments: A marine species; most abundant near shore (Bieri 1959). Typical of the upper 100 to 150 m of the water column in arctic and subarctic regions, but also occurs in the mesopelagic layer to around 1,000 m (Terazaki 1998). In recent studies it was also found in the benthic zone near the ocean floor (Brodeur and Terazaki 1999, Choe and Deibel 2000). Eurythermal; reported at water temperatures ranging from -1.5 to 21.0°C (Alvarino 1965), although growth and mortality rates may be greatest between 1.0 and 12.0°C (Sameoto 1966). Distribution thought to be limited to water with oxygen concentrations of at least 6 ml/l (Alvarino 1964 in Marumo 1966); however, in Sagami Bay, North Pacific Ocean, S. elegans were found in deep water with oxygen concentrations less than 4 ml/l (Marumo 1966). Generally occur at salinities around 32 to 33 pph (Sund 1959, Welch et al. 1996).

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upper and glacial epipelagic regions and the upper Mesopelagic
  • North-West Atlantic Ocean species (NWARMS)
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Depth range based on 5132 specimens in 1 taxon.
Water temperature and chemistry ranges based on 2725 samples.

Environmental ranges
  Depth range (m): 0 - 2167.35
  Temperature range (°C): -1.883 - 16.148
  Nitrate (umol/L): 0.007 - 37.013
  Salinity (PPS): 19.323 - 35.027
  Oxygen (ml/l): 2.991 - 9.319
  Phosphate (umol/l): 0.048 - 2.965
  Silicate (umol/l): 0.965 - 90.291

Graphical representation

Depth range (m): 0 - 2167.35

Temperature range (°C): -1.883 - 16.148

Nitrate (umol/L): 0.007 - 37.013

Salinity (PPS): 19.323 - 35.027

Oxygen (ml/l): 2.991 - 9.319

Phosphate (umol/l): 0.048 - 2.965

Silicate (umol/l): 0.965 - 90.291
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

There is no consensus on the diel vertical migration of S. elegans. Some investigators have observed typical diel migration by adults (i.e. found near surface at night and in deeper waters during the day) (Nishiuchi et al. 1997, Terazaki 1998) but not by immature individuals (Choe and Deibel 2000). Brodeur and Terazaki (1999) described an inverse diel migration pattern for juveniles, with higher abundance near the surface during the day. These patterns likely follow changes in light levels or vertically migrating prey. Average speed of upward and downward migration has been recorded as 30 meters/hr in adult individuals in the Japan Sea (Terazaki 1998).

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Trophic Strategy

Comments: Primary food is small copepod zooplankton including Pseudocalanus spp., Metridia pacifica, Neocalanus spp. and Oithona spp. (Alvarez-Cadena 1993b, Terazaki 1998, Brodeur and Terazaki 1999). Will secondarily consume other small zooplankton including barnacle nauplii and larval stages of euphausiids, occasionally cannibalistic upon smaller individuals, and will also eat herring larvae (Alvarez-Cadena 1993b). Arrow worms are raptorial ambush predators; will remain still using mechanoreceptors that sense water movements to detect prey, then dart forward to grab and ingest organisms using grasping spines on either side of the head. Some chaetognaths may also inject a potent neurotoxin called tetrodotoxin into prey (Brusca and Brusca 1990).

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Comments: Beaufort, Chukchi, and Bering Seas, throughout the Aleutian Islands and Gulf of Alaska including the Alaska Peninsula, Lower Cook Inlet, Prince William Sound, and in waters surrounding and south of Kodiak Island; also in Southeast Alaska in Glacier Bay (Sund 1959, Redburn 1974, Cooney 1975, Wing and Hoffman 1976, Brodeur and Terazaki 1999, Robards et al. 2003).

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General Ecology

Arrow worms are an important and abundant part of the marine food chain of oceans of the Northern Hemisphere; in general, chaetognaths often rank second in abundance to copepods among all marine zooplankton groups. May compete with fish larvae for their primary food, copepod zooplankton (Baier and Purcell 1997). Larval and juvenile forms preyed upon by many higher trophic level planktivores (Robards et al. 2003) and fishes including walleye pollock (Theragra chalcogramma) and herring (Clupea spp.; Brodeur and Terazaki 1999).

Chaetognaths alternately swim and float, with fins acting as flotation devices; when the body begins to sink, trunk muscles contract rapidly and the animal darts swiftly forward. The same movement is used to capture prey (Barnes 1987).

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Life History and Behavior

Behavior

Diet

Predator
  • North-West Atlantic Ocean species (NWARMS)
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Diet

copepods and other zooplankton
  • North-West Atlantic Ocean species (NWARMS)
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Reproduction

Chaetognaths are hermaphroditic, with paired ovaries in the trunk and paired testes in the tail; each individual produces both eggs and sperm (Brusca and Brusca 1990). Self-fertilization probably does not occur; instead, mating is believed to occur when two individuals exchange sperm packets and ova are fertilized internally (Brusca and Brusca 1990, Todd et al. 1996). Eggs released as fertilized zygotes (coated in a jelly-like substance); development is direct and lacks any larval stage or metamorphosis; from egg release to hatching is rapid, probably within 48 hours (Brusca and Brusca 1990). Number of eggs per ovary ranges from 30-1,000 (McLaren 1966). Adults may spawn once or several times over a period of months, then die shortly thereafter. Spawning periods are variable: in coastal waters off southern Hokkaido, Japan, spawning was observed in April-June, while in the southern Japan Sea two spawning periods have been observed, in March-May and also later in August (Terazaki 1998). Dunbar (1941) observed a single spawning period for this species in the western Atlantic, from June-July through October. Number of broods produced per year increases with distance from the North Pole; one brood annually in arctic-subarctic waters (Kramp 1939 in Terazaki 1998); 2 to 5 broods near southern boundary of distribution in temperate regions (Dunbar 1941, Terazaki 1998). Life span estimated at one (Alvarez-Cadena 1993a, Terazaki 1998) or two years (Dunbar 1962, Welch et al. 1996), depending on latitude of occurrence within range. Welch et al. (1996) reported S. elegans grew during winter and presumably fed continually year-round despite water temperatures as low as -1.8°C in the Canadian arctic.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Parasagitta elegans

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 4
Species With Barcodes: 1
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Genomic DNA is available from 1 specimen with morphological vouchers housed at Western Australian Museum
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N5 - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

Reasons: Widespread and abundant in nearshore coastal waters of the arctic and subarctic. An important component of marine planktonic communities. Threatened by pollution to the marine environment as a result of oil spills, sewage dumping, industrial runoff, or contamination from mariculture practices.

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Global Short Term Trend: Unknown

Comments: Unknown.

Global Long Term Trend: Unknown

Comments: Unknown.

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Threats

Degree of Threat: Low

Comments: Possible threats include pollution of marine habitats from oil spills, sewage dumping, forestry and mining runoff, and introduction of pesticides from mariculture and agricultural activities. Climate change may pose an indirect threat by altering primary productivity and the production of zooplankton prey species; temperature is also linked directly to this species' growth rate and generation time (Oresland 1985, Oresland 1986 in Clark et al. 2003). General lack of knowledge about factors that may limit population growth (e.g., habitat conditions, prey availability, predation pressure) may pose a threat to management of zooplankton populations.

In Alaska, possible threats include pollution of marine habitats from oil spills, sewage dumping, forestry and mining runoff, and introduction of pesticides from mariculture and agricultural activities. Marine oil spills are a potential threat in Alaska, but because this species occurs in the water column as opposed to surface waters it may be less impacted by oil slicks than other marine animals. Pesticides applied to mariculture crops may harm invertebrates other than those targeted, and their impacts on S. elegans are unknown.

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Management

Biological Research Needs: Research needed on the trophic significance of arrow worms in diets of forage fishes, commercially harvested fishes, and sea birds. Determine if pesticides used in mariculture practices are harmful to S. elegans and associated prey species. Study factors that may be limiting to population growth including habitat characteristics, prey availability, and predator pressure; examine potential effects of increased water temperatures as a result of climatic warming.

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Needs: No official protection for this species in Alaska. Protect marine habitats from pollution and the introduction of pesticides from mariculture and agriculture while researching the potential effects of these and other threats. Develop and establish a long-term monitoring plan for zooplankton populations in Alaskan waters using protocols established by CalCOFI as a model (see State inventory needs).

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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: Protect marine habitats from pollution and the introduction of pesticides from mariculture and agriculture while researching the potential effects of these and other threats. Develop and establish a long-term monitoring plan for zooplankton populations in Alaskan waters using protocols established by CalCOFI as a model (see State inventory needs).

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Wikipedia

Parasagitta elegans

Parasagitta elegans is a small chaetognatha, preveously named Sagitta elegans

Morphology[edit]

Parasagitta elegans (prev. Sagitta elegans). Body of adult animal is narrow, firm and opaque (this image: animal very see-through. Visible opaque animal needs better picture).

Fins are separated, rounded, and completely rayed. Anterior fins beginning below the ventral ganglion. Alimentary diverticula present. Eyes with small, round pigment spot. Ovaries long and narrow. Seminal vesicles conical in shape, either exactly next to or very close to the tail fin, separated from posterior fins.

For anatomy, reproduction, classification, and fossil record; see Chaetognatha

Taxonomy[edit]

Three subspecies are discovered - Sagitta elegans arctica, Sagitta elegans baltica and Sagitta elegans elegans.[1] The subspecies is considered to vary in size depending on the temperature of the waters in which they develop, which could be an indication of them being synonymous species. The numbers of hooks and teeth vary slightly in the three subspecies [2]

Ecology[edit]

General[edit]

With exception for the benthic species Spadella, arrow worms are all adapted for planktonic existence. They swim to the surface at night, and descend during daytime. Most of the time they drift passively, but they can dart forward in swift spurts, using their caudial fin and longitudinal muscles. Horizontal fins bordering the trunk serve largely as stabilizers, and are used in flotation rather than in active svimming.

Distribution[edit]

Parasagitta elegans and three subspecies occur in arctic and subarctic waters. S. elegans elegans is a coastal subspecies with oceanic influence. S. elegans arctica is a boreal-arctic form, and S. elegans baltica is the smallest form, found only in or near the Baltic Sea [3]

References[edit]

  1. ^ Thuesen, Erik V. (2014). "Parasagitta elegans (Verrill, 1873). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=105440 on 2014-08-21". WoRMS. 
  2. ^ A. C. Pierrot-Bults and K. C. Chidgey, edited by Doris M. Kermack and R. S. K. Barnes, 1988. Chaetognatha. 
  3. ^ Fraser, J. H. 1952. The Chaetognatha and other zooplankton of the Scottish area and their value as biological indicators of hydrographical conditions. 
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Names and Taxonomy

Taxonomy

Comments: Taxonomy unclear; some authors have divided genus Sagitta into different genera and included this species in Parasagitta instead of Sagitta (Tokioka 1965, Bieri 1991, see Terazaki 1998). Three subspecies recognized: S. e. elegans, S. e. arctica and S. e. baltica; they differ in maximum body length, number of hooks and teeth, and length of ovaries. The entire phylum Chaetognatha, known as arrow worms or chaetognaths, is marine and consists of about 100 species (Brusca and Brusca 1990).

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