Palaemon elegans

Invasion History

First Non-native North American Tidal Record: 2010
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2010

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General Invasion History:

Palaemon elegans (Rockpool Shrimp, Rockpool Prawn) has a wide native range in the northeast Atlantic, from the west coast of Norway to Namibia, and offshore islands, including the Azores, Cape Verde and Canary Islands (Holthuis 1989; Gonzalez-Ortegon and Cuesta 2006; Reuschel et al. 2010). It has been introduced to the Caspian and Aral Seas (Aladin 2002, Aladin, undated), and to the Persian Gulf (Holthuis and Hassan 1975). After the year 2000, this shrimp became abundant in the central and eastern Baltic (Grabowski 2006). Genetic analysis confirmed that this was an invasion, with animals belonging to a Mediterranean-Black Sea lineage (Reuschel et al. 2010). In 2010, the first population of P. elegans was discovered in the Western Atlantic, in Hawthorne Cove, Salem, Massachusetts (Commonwealth of Massachusetts Executive Office of Energy and Environmental Affairs 2010; MIT Sea Grant 2010). 

North American Invasion History:

Invasion History on the East Coast:

On July 31, 2010, during a Rapid Assessment Survey, organized by MIT Sea Grant and state agencies, an unfamiliar shrimp was collected in Hawthorne Cove, Salem, Massachusetts, on Massachusetts Bay. In subsequent collecting, more than 70 specimens were found. The animals were identified by James T. Carlton and confirmed by Dr. Sammy De Grave of Oxford University (Commonwealth of Massachusetts Executive Office of Energy and Environmental Affairs 2010; MIT Sea Grant 2010). In 2011, this shrimp was discovered at Kennebunk Beach, Maine (MIT Sea Grant 2012). The extent of this species' range on the East coast of North America is currently unknown.

Invasion History Elsewhere in the World:

In the 1930s, Palaemon elegans from the Black Sea were accidentally introduced to the Caspian Sea with stocked fish (Aladin 2002). This shrimp is now established and abundant there (Yazdani et al. 2009). In 1960, it was introduced to the Aral Sea, also with stocked marine fish. It became abundant as the drying sea reached marine salinities, but as salinity increased, it became confined to the impounded Small Aral Sea (11-17 g/l, Aladin et al. 2008).

In 1968, about 200 shrimp from al Fao, Iraq, on the Persian Gulf, were transplanted into Lake Abu-Dibic, a brackish lake (about 7 PSU), in the Euphrates Delta. In 1972, these shrimp were identified as P. elegans (Holthuis and Hassan 1975). The current status of this species in the Persian Gulf is not known, but it is presumed to still be established.

Before the year 2000, P. elegans was limited to the southern Baltic Sea, and usually to salinities above 7 PSU, while the predominant species in the Baltic was Palaemon adspersus. Experiments with animals from the west coast of Sweden found that hatching of eggs and short-term survival of larvae were reduced at salinities below 10 PSU, and that P. adspersus had better reproductive success in brackish water than P. elegans (Berglund 1985). However, in 2000, P. elegans was collected in the Dead Vistula estuary and subsequently spread east and west, largely replacing P. adspersus in the southeast Baltic. In a 2004 survey, it was found at 11 locations on the Pomeranian Coast (Szczecin to Puck), while P. adspersus was found only at one (Grabowski 2006). There have been some collections of this shrimp in Finnish waters, the mouth of the Gulf of Finland and in the Archipelago Sea (Kekkonen 2003, cited by Grabowski 2006; Vesakoski 2011). This shrimp is now established and reproducing in this region (Katajisto et al. 2013). Genetic studies indicate that Baltic specimens belong to the Mediterranean-Black Sea lineage (Reuschel et al. 2010), which could differ from the Atlantic form in its reproductive salinity tolerance. Ballast water seems the most likely vector for the introduction of P. elegans to the eastern Baltic (Reuschel et al. 2010).

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Description

Palaemon elegans, the Rockpool Shrimp or Rockpool Prawn, is a caridean shrimp with a distinct, well-developed rostrum, with 7-9 dorsal teeth (three, occasionally two, dorsal teeth lie posteriorly to the orbit), and usually three (sometimes two or four) ventral teeth. The rostrum has a strong ventral expansion and has a single row of setae on the ventral margin. Supraorbital, suborbital and hepatic spines are absent, but an antennal and a branchiostegal spine is present, on the front margin of the carapace near the base of the antenna. The antennules are triramous. The shorter ramus of the outer antennule is about equal to the length of its peduncle- it is fused for about 2/5 of its length to the longer flagellum. Both legs of the first pair are chelate (with claws). The palp of the mandible has two segments. This shrimp is translucent with reddish-brown lines on the carapace (Hayward and Ryland 1990; Ashelby et al. 2004; d'Udekem d'Acoz,et al. 2005; Gonzalez-Ortegon and Cuesta 2006; MarLin 2011; Gonzalez-Ortegon et al. 2015). Larval development of several northeast Atlantic Palaemon, including P. elegans, is described, with a key, in Fincham and Figueras (1986).

Palaemon elegans is a species complex containing several lineages, one from the Atlantic (Type I) and two from the Mediterranean (Type II and Type III), which occur sympatrically, and may represent distinct species. Recently established populations in the Baltic Sea are Type III, of Mediterranean-Black Sea origin (Reuschel et al. 2010).

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Taxonomy

Ecology

General:

Life History- During reproduction in caridean shrimps, the copulating pair is usually oriented at right angles to one another, with the genital regions opposing each other. The modified first and second pairs of pleopods are used to transfer a spermatophore to a receptacle between the thoracic legs of the female (Barnes 1983). After mating, female palaemonid shrimps carry broods of fertilized eggs on their abdomen. Females of P. elegans can carry 222-2628 eggs, varying with body size and among populations (Janas and Mancucka 2010). These hatch into planktonic larvae with feathery appendages, called zoeae. Shrimp zoeae lack the prominent spines seen in brachyuran crabs, and look shrimplike (Johnson and Allen 2005; Fincham and Figueras 1986). They go through several molts and metamorphose into postlarvae, which have well-developed walking legs and pleopods (swimmerets). After a subsequent molt, the body takes on the adult shape. Adults mature in about a year, and longevity was estimated at 2.5 years for a Black Sea population (Bilgin et al. 2009). Males generally mature at a smaller size (13-21 mm length) than females (28-40 mm), and reach smaller maximum sizes (41-60 mm) compared to females (50-65 mm) (Janas and Mancucka 2010).

Ecology- Palaemon elegans inhabits coastal rockpools, shallow rocky areas, vegetated areas, and man-made structures (Grabowski 2006; MarLin- Marine Life Information Network 2011). Palaemon elegans from the Baltic tolerate salinities as low 1 PSU at 12 and 22°C, but had much greater mortality at 2ºC. Adult shrimp in colder regions may migrate into deeper water in winter, because of a reduced ability to regulate body fluids at low temperatures (Janas and Spicer 2008; Janas et al. 2013). A stable isotope study in the Baltic Sea showed that Palaemon elegans fed on both animal prey (60%) and green algae (40%). Most of the animal prey appeared to belong to the pelagic foodweb. Mysids were readily eaten in experiments (Lesutiene et al. 2014).

Food:

algae, detritus, invertebrates

Consumers:

Fishes

Trophic Status:

Omnivore

Omni

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Habitats

General Habitat	Rocky	None
General Habitat	Unstructured Bottom	None
General Habitat	Marinas & Docks	None
General Habitat	Grass Bed	None
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None
Vertical Habitat	Nektonic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	2	Lowest tested (Janas and Spicer 2010)
Maximum Temperature (ºC)	25	Highest tested (Dalla Via 1985)
Minimum Salinity (‰)	0.9	Field (Grabowski 2006) and lab (Janas and Spicer 2010)
Maximum Salinity (‰)	40	Field (Dalla Via 1985)
Minimum Reproductive Temperature	15	Larval development, experimental (Rochanaburanona and Williamson 1976)
Maximum Reproductive Temperature	20	Larval development, experimental, highest tested (Rochanaburanona and Williamson 1976)
Minimum Reproductive Salinity	17	Larval development, experimental (Rochanaburanona and Williamson 1976)
Maximum Reproductive Salinity	34	Larval development, experimental, highest tested (Rochanaburanona and Williamson 1976)
Minimum Duration	25	BALESTRA V; CARLI A; VIGNOLA S 1981. LABORATORY CULTURE OF PALAEMON-ELEGANS CRUSTACEA DECAPODA Bollettino Societa Italiana Biologia Sperimentale Volume: 57 Issue: 22 Pages: 2252-2256 Published: 1981
Maximum Duration	30	BALESTRA V; CARLI A; VIGNOLA S 1981. LABORATORY CULTURE OF PALAEMON-ELEGANS CRUSTACEA DECAPODA Bollettino Societa Italiana Biologia Sperimentale Volume: 57 Issue: 22 Pages: 2252-2256 Published: 1981
Minimum Length (mm)	13	For Caspian Sea males. Minimum lengths of males vary from 16 (Mediterranean)-21 mm (Black Sea) at other sites For Black Sea females. 50% of the females were mature at 34 mm length (Bilgin et al. 2009; Janas and Mancucka 2010).
Maximum Length (mm)	60	Holthuis 1980. Maximum lengths of males from different populations varied from 41 (Caspian and Baltic Seas) to 60 mm (Black Sea) (Bilgin et al. 2009; Janas and Mancucka 2010). For females ,the range was 50 mm (Caspian Sea) to 65 mm (Kattegat, Denmark) Janas and Mancucka 2010).
Broad Temperature Range	None	Cold temperate-Tropical
Broad Salinity Range	None	Oligohaline-Euhaline

General Impacts

Economic Impacts- Because of its small size, Palaemon elegans is rarely utilized as a fisheries species (Holthuis 1989). However, it has some importance to fisheries as a food for commercial fishes in the Caspian Sea, and is being considered as a food for fish in aquaculture (Yazdani et al. 2009).

Ecological Impacts- Palaemon elegans has largely replaced the native P. adspersus and Palaemonetes varians at many locations in the southeastern Baltic. However, the mechanism of competition is unclear (Grabowski 2006).

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Regional Impacts

B-V	None		Ecological Impact	Competition
Palaemon elegans has largely replaced the native Palaemon adspersus and Palaemonetes varians at many locations in the southeastern Baltic (Grabowski 2006).
B-VII	None		Ecological Impact	Competition
Palaemon elegans has largely replaced the native Palaemon adspersus and Palaemonetes varians at many locations in the southeastern Baltic (Grabowski 2006).
CASP	Caspian Sea		Ecological Impact	Food/Prey
Palaemon elegans is now a major food item for commercially caught fish in the Caspian Sea (Yazdani et al. 2009).
B-VIII	None		Ecological Impact	Predation
Predation rates of Palaemon elegans in the Baltic do not differ from that of native P. adspersus, but the invasion has increased the overall density of prawns in the Baltic, and increaed the predation rate (
B-IX	None		Ecological Impact	Competition
Palaemon elegans and P. adspersus has a stronger preference for vegetated substrate than the native P. adspersus but the species habitat preferences overlap, and some competiton is likely (Kuprinanov et al. 2017).
B-VIII	None		Ecological Impact	Competition
Palaemon elegans and P. adspersus has a stronger preference for vegetated substrate than the native P. adspersus but the species habitat preferences overlap, and some competiton is likely (Kuprinanov et al. 2017).
B-X	None		Ecological Impact	Competition
In experiemnts, native Threespine Sticklebacks (Gasterosteus aculeatus) displayed agression against introduced shrimps (Palaemon elegans), but that reduced numbers of sticklebacks may have permitted the invasions (Jakubaviciute & Candolin 2021).

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