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The First Record of Palaemon macrodactylus (Oriental Shrimp) from the Eastern Coast of North America
Barbara E. Warkentine and Joseph W. Rachlin

Northeastern Naturalist, Volume 17, Issue 1 (2010): 91–102

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2010 NORTHEASTERN NATURALIST 17(1):91–102 The First Record of Palaemon macrodactylus (Oriental Shrimp) from the Eastern Coast of North America Barbara E. Warkentine1 and Joseph W. Rachlin2,* Abstract - Palaemon macrodactylus (Oriental Shrimp), native to estuarine waters of Southeast Asia, has been reported outside of its native range. The spreading of this species to new regions has been well documented, and its disjunct distribution strongly speaks for its transport being attributed to ballast water. In this paper, we report the first record of P. macrodactylus from the eastern coast of the United States and in the estuarine system of New York City (NYC). While this animal has been reported to have crossed the Pacific, and has been found in the eastern Atlantic along the coasts of Spain, France, Germany, and the British Isles, and in the southwestern Atlantic off the coast of Argentina, it has not been previously sighted in the northwest Atlantic. Our preliminary life-history data indicate that the size range for the 98 adult individuals in the 2001 collection was from 2.05 to 5.05 cm, and exhibited a one-to-one sex ratio. The finding of gravid females among these shrimp collected from 2001–2002 and again in 2008 indicates that the oriental shrimp populations in the coastal waters of NYC have become established, and show reproductive activity from May through October. Further studies are required to evaluate whether P. macrodactylus poses a threat to native aquatic organisms in this region. Introduction Non-native aquatic species continue to be found in our local waters. Their occurrence outside their native habitats has been attributed to such things as ballast water, aquaculture practices, and aquarium releases (Mc- Dermott 1991, Nalepa and Schloesser 1993, Newman 1963, Worsfold and Ashelby 2006). One such species which is currently being tracked by many investigators (Gonzalez-Ortegon and Cuesta 2006, Worsfold and Ashelby 2006.) is Palaemon macrodactylus M.J. Rathbun (Oriental Shrimp). This species is native to estuarine waters of Southeast Asia, particularly Japan, China, and Korea (Beguer et al. 2007). Prior to 1957, P. macrodactylus was discovered in the San Francisco Bay area of California (Newman 1963), which represents the first reported finding of the shrimp outside its native habitat. It has since extended its range along the northwest coast of the United States from Oregon to San Diego California (Gonzalez-Ortegon et al. 2007, Spivak et al. 2006). Palaemon macrodactylus has also been found in a number of estuaries in Europe. Its occurrence and establishment in England (Ashelby et al. 2004), Spain (Cuesta et al. 2004), Germany (Gonzalez-Ortegon et al. 2007), and 1SUNY Maritime College, Science Department, 6 Pennyfield Avenue, Bronx, NY 10465-4198. 2Laboratory for Marine and Estuarine Research (La MER), Department of Biological Sciences, Lehman College of CUNY, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589. *Corresponding author - rachlin@lehman.cuny.edu. 92 Northeastern Naturalist Vol. 17, No. 1 France (Beguer et al. 2007) are well documented. Populations have also been reported from Australia (Pollard and Hutchings 1990) and from Argentina (Spivak et al. 2006). The occurrence of P. macrodactylus in Argentina represents the first record from southwestern Atlantic waters. In this paper, we present the first occurrence of P. macrodactylus from the eastern coast of North America in the waters off New York City. We also present aspects of its life history from this region. Methods In 2001 and 2002, as part of a larger faunal survey (Rachlin et al. 2007), our gear collected over 3000 shrimp specimens from the estuarine reaches of the Bronx River, the East River, and the western end of Long Island Sound (Fig. 1). These three water bodies are contiguous and constitute an estuarine system. Salinity and water temperature were recorded during the collecting periods. Killitraps, pushnets, and shrimp trawls were used to collect organisms for the faunal survey (Rachlin et al. 2007). All shrimp collected in the gear were preserved in 10% formaldehyde and transported back to the laboratory. After two weeks of preservation, the organisms were transferred to 75% ethanol. All shrimp were identified to the species level. Typically, in coastal waters around New York City, the shrimp population consists of three species of Palaemonetes—P. pugio Holthuis (Daggerblade Grass Shrimp), P. vulgaris (Say) (Common Grass Shrimp), and P. intermedius Holthuis (Brackish Grass Shrimp)—and Crangon septemspinosa Say (Sand Shrimp) (Pollock 1998, Weiss 1995). However, 125 shrimp specimens were separated out from among the Palaemonetes group as being suspect. The characteristic that called attention to these specimens was the presence of elongated second pereiopods beyond what is typically seen among the Palaemonetes species from our study sites. Based on our extensive experience with the variations presented by the three species of Palaemonetes typical of the area, these shrimp were recognized as being different. These 125 individuals were subjected to further microscopic examination of their anatomical features, which were carefully compared with the published literature describing this species (Rathbun 1902). These shrimp were also weighed to the nearest 0.001 gm using a Mettler analytical balance. Lengths, as measured from the tip of the rostrum to the extreme posterior end (Spivak et al. 2006), were recorded to the nearest 0.05 cm. The sex of the shrimp was determined by looking for the presence or absence of the appendix masculine on the endopodite of the second pleopod (Siegfried 1980). This structure, present only in the male, is a finger-like projection, or stylet, on the inner portion of the second abdominal appendage and is used to transfer spermatozoa to the female. The number of females containing eggs was also noted. Voucher specimens have been deposited at the New York State Museum, Albany NY, with accession catalog number NYSM-C3762. A length-frequency histogram and length-weight relationships were generated for the 2001 collection only, since this group included the bulk 2010 B.E. Warkentine and J.W. Rachlin 93 of the specimens (n = 98). The 2002 collection, which consisted of only 27 individuals, was not analyzed in this way. On 2 August 2008, killitraps were set at the western end of our Long Island Sound study site to collect fresh shrimp specimens. Although this manuscript presents data and analysis from the 2001–2002 collections, the Figure 1. Map showing the three locations where P. macrodactylus were collected. A = Bronx River (40°49'04.42"N, 073°52'52.17"W); B = East River (40°48'26.94"N, 073°51'34.05"W); C = Long Island Sound (40°49'04.42"N, 073°52'52.17"W). 94 Northeastern Naturalist Vol. 17, No. 1 finding of P. macrodactylus in samples taken in 2008 indicate that this species has become established in our coastal waters. Results Within our study area, during the collecting seasons, salinities ranged from 11 parts per thousand (ppt) to 29 ppt, with lower values being found in surface waters of the Bronx River Estuary during high river flows. Water temperatures ranged from 19 °C to 25 °C over this same period. All three species of Palaemonetes normally found in the area were present in these waters. A subset of the collected shrimp (n = 125) were set aside for careful anatomical examination because they possessed characteristics not typical of Palaemonetes species, including two features that were strikingly obvious upon capture: 1) what appeared to be a longer than normal second walking leg (pereiopod) which extended well beyond the rostrum, and 2) a pale dorsal stripe extending from the cephalothorax to the end of the abdomen. We also examined the 125 suspect specimens more carefully using an Olympus SZX12 stereomicroscope adapted for photography. An image showing the morphological regions used for determining the key characteristics involved in the identification is shown in Figure 2. Using the stereomicroscope, we observed the presence of a mandibular palp (Fig. 3A), another characteristic not typical of Palaemonetes. The presence of the mandibular palp places these individuals within the genus Palaemon (Gonzalez-Ortegon and Cuesta 2006). By using various keys to the Palaemon (Ashelby et al. 2004, d’Udekem d’Acoz et al. 2005, Gonzalez-Ortegon and Cuesta 2006) and reviewing the original description as given by Rathbun (1902), we Figure 2. The morphological regions used for determining the key characteristics involved in the identification of P. macrodactylus from the New York Estuary, with positions shown on whole shrimp (scale bar = 10 mm). 2010 B.E. Warkentine and J.W. Rachlin 95 found these Palaemon specimens to agree with the diagnostic characteristics associated with Palaemon macrodactylus. According to the literature cited above, P. macrodactylus exhibits the following key characteristics: 1) mandibular palp is three-jointed, 2) there are three teeth on the dorsal surface of the rostrum positioned behind the posterior margin of the orbit, Figure 3. Diagnostic characteristics observed in the identification of P. macrodactylus from the New York Estuary. (A) Mandible showing the presence of a palp. Palp also shows the presence of three segments; scale bar = 3 mm. (B) Rostrum showing three dorsal spines behind orbit of the eye socket, and the rostrum lacks a strong upward curve; scale bar = 5 mm. (C) Posterolateral margin of the sixth abdominal segment has a smooth curve; scale bar = 3 mm. (D) Second pereiopod showing that the propodus is not significantly shorter than the carpus; scale bar = 10 mm. (E) The free section of the shorter ramus of the upper antennular flagellum is longer than the fused part; scale bar = 3 mm. (F) Presence of a double row of setae along the ventral margin of the rostrum; scale bar = 1 mm. 96 Northeastern Naturalist Vol. 17, No. 1 3) the rostrum does not show a strong upward curve, 4) the area above the spine of the posterolateral margin of the sixth abdominal segment is smooth, 5) the propodus of the second pereiopod is not significantly shorter than the carpus, and 6) the free part of the shorter ramus of the upper antennular flagellum is longer than the fused part. All of these characteristics were found in our 125 specimens (Fig. 3A–E). Closer examination of the rostrum confirmed the presence of a double row of setae along the ventral margin of the rostrum (Fig. 3F), another characteristic unique to P. macrodactylus (Gonzalez-Ortegon and Cuesta 2006). According to d’Udekem d’Acoz et al. (2005), P. macrodactylus can be readily identified in the field by the presence of a “whitish longitudinal dorsal stripe running all along their back.” Since the individuals examined in this present study had been preserved for some time, the presence of this stripe was no longer observable. Six fresh specimens collected in August 2008 clearly exhibited this striped pattern (Fig. 4). Further examination of these individuals confirmed the presence of the key characteristics 1–6 outlined above, as well. Among these P. macrodactylus specimens, a gravid female was present. Figure 4. Pale longitudinal dorsal stripe of P. macrodactylus; scale bar = 10 mm. 2010 B.E. Warkentine and J.W. Rachlin 97 The original 125 individuals ranged in size from 2.05 to 5.05 cm, and the greatest number of these Palaemon specimens was collected in July 2001 from the Bronx River Estuary, associated with old wooden wharf pilings (Table 1). A length-frequency histogram for the 2001 collection, which consisted of 98 individuals, shows that the greatest number of shrimp in the collection were between 3 and 4 cm in length, and the total size range of the collection was from 2.05 to 5.05 cm (Fig. 5). In this collection, 50 were males ranging in size from 2.05 to 4.10 cm, and the remaining 48 female shrimp ranged in size from 2.55 to 5.05 cm. All but eight of these females had eggs, and we determined that these shrimp maintained reproductive activity from May through October (Table 1). The number of shrimp of this species in the 2002 collection consisted of only 27 individuals—18 females and 9 males—and was too few to perform a meaningful regression analysis. Table 1. Dates, locations and number of P. macrodactylus collected from various sites within the New York estuary. Numbers in parentheses indicate gravid females. Dashes indicate times when shrimp samples were not taken. Please note that sampling did not necessarily occur in consecutive months. East River Bronx River Long Island Sound Total Total Year Month Male Female Male Female Male Female male female 2001 July 6 21(20) 37 18(16) - - 43 39(36) Sept. - - 7 5(3) - - 7 5(3) Oct. - - - - 0 4(1) 0 4(1) 2001 total 6 21(20) 44 23(19) 0 4(1) 50 48(40) 2002 May 0 0 3 5(1) - - 3 5(1) June 1 1(1) 2 1(0) - - 3 2(1) July 1 4(4) 2 6(6) - - 3 10(10) Aug. - - 0 1(1) - - 0 1(1) 2002 total 2 5(5) 7 13(8) - - 9 18(13) Grand total 8 26(25) 51 36(27) 0 4(1) 59 66(53) Figure 5. Lengthfrequency histogram for P macrodactylus collected in 2001. 98 Northeastern Naturalist Vol. 17, No. 1 Length-weight relationships for the 2001 collection were performed, and these relationships are defined by the following regression equations where W = weight in g, L = length in cm: 1) for the total group: Log W = -2.51 + 3.63 Log L; n = 98; r2 = 0.94 (Fig. 6A); 2) for males: Log W = -2.00 + 2.57 Log L; n = 50; r2 = 0.94 (Fig. 6B); and 3) for females: Log W = -2.31 + 3.36 Log L; n = 48; r2 = 0.94 (Fig. 6C). Discussion The 125 unidentified shrimp, originally collected as part of our faunal survey of urban waterways of New York City, presented us with an interesting challenge. Regional shrimp keys (Abele and Kim 1986, Pollock 1998, Weiss 1995) proved useless in identifying these individuals, as they exhibited characteristics not in compliance with diagnostic features of the Palaemonetes or any other rostrum-bearing shrimp found in this region. Therefore, a more extensive review of the literature on shrimp outside our region was conducted. Using various keys to the Palaemonidea (Ashelby et al. 2004, d’Udekem d’Acoz et al. 2005, Gonzalez-Ortegon and Cuesta 2006) and reviewing the original description given by Rathbun (1902) on the Japanese stalk-eyed crustaceans, we came to the conclusion that our originally unidentified shrimp are Palaemon macrodactylus. The presence of the dorsal pale whitish stripe in conjunction with the observation of the diagnostic characteristics presented in the literature for P. macrodactylus (Ashelby et al. 2004, d’Udekem d’Acoz et al. 2005, Gonzalez-Ortegon and Cuesta 2006, Rathbun 1902) confirms our identification of this species. This report represents the first documented finding of P. macrodactylus, a non-native Palaemonidae, from waters off the east coast of North America. Palaemon macrodactylus is a euryhaline and eurythermal species (Newman 1963), characteristics which clearly enhance its ability to be a successful colonizing species. While the exact mode of distribution is not known, the disjunct distribution documented in the literature supports the idea of ballast water (d’Udekem d’Acoz et al. 2005, Newman 1963) as the most likely mode of dispersal. New York City, an active port city with ships continuously moving through its estuarine system, including the collecting sites in this study, has been subjected to ballast water introduction (McDermott 1991). Ballast water was the mode of introduction of Dreissena polymorpha (Pallas) (Zebra Mussel; Nalepa and Schloesser 1993) and Hemigrapsus sanguineus (De Haan) (Asian Shore Crab; McDermott 1991). Therefore, it is probable that Palaemon macrodactylus was transported to and introduced to these waters as well. The data presented on aspects of its life history show that there are established populations occupying the Bronx River Estuary, East River, and western end of Long Island Sound. The presence of gravid females over many years is support for this species’ establishment within this local aquatic community. The extent of their reproductive cycle reported in this study is congruent with that documented for populations occupying the San Francisco Bay-Delta 2010 B.E. Warkentine and J.W. Rachlin 99 F i g u r e 6 . (A) Lengthweight relationship for the 2001 sample. (B) Lengthweight rel a t i o n s h i p for males. (C) Lengthweight relationship for females. 100 Northeastern Naturalist Vol. 17, No. 1 area (Siegfried 1980). All males in our collections were greater than 2.0 cm and exhibited the secondary sexual characteristic, the appendix masculine on the endopodite of the second pleopod, documented by Siegfried (1980). This secondary sexual characteristic first manifests itself when males reach 2.0 cm. Siegfried (1980) concluded that the absence of this secondary sexual characteristic on P. macrodactylus indicates the juvenile state. An exhaustive search of the literature on P. macrodactylus, other than the paper by Siegfried (1980), presents no life-history data. Siegfried (1980) presented regression analyses of males, juveniles, and non-gravid females. As a result, we could only compare the regression analysis of our male New York specimens with the regression analysis of his mature males. This comparison of length-weight relationships of our New York specimens with those presented by Siegfried (1980) appears to show a real difference; however, a statistical comparison could not be made since Siegfried’s 1980 paper does not contain the standard errors for his slope values—a necessary parameter for a statistical test (Zar 1974). The California mature males had a slope of 3.27, while the New York population (Fig. 6B) had a shallower slope of 2.57. This difference might be attributed to the relatively small number of shrimp used in both these analyses. Other variables, such as water quality and habitat availability, which could contribute to growth relationship differences, were not looked at and therefore cannot be elaborated on at this time. In our study, a comparison of the slopes of the length-weight relationships of our male (slope = 2.57) and female (slope = 3.36) populations (Fig. 6B, C) did show a significant difference (P < 0.05) based on a Student’s t-test (Zar 1974). We attribute this to the fact that 40 out of 48 females were gravid, increasing the female body mass. Since only 8 of the females were non-gravid, we determined this would be an insufficient number of animals to treat separately, and so all 48 females were treated together to generate the regression analysis. Palaemon macrodactylus is tolerant of polluted environments (Siegfried 1980), which indicates that these animals can do well in urban estuarine systems. The areas of our study, particularly the Bronx River, are systems that for many years have been considered to be highly polluted areas (Rachlin et al. 2007, 2008). These estuarine systems receive waters from urban runoff and from industrial facilities, as well as from the city’s combined sewage outflow system (Litten 2003). However, the higher numbers of P. macrodactylus found in the Bronx River cannot, at this time, be taken as an indicator of habitat conditions, since the collection of these shrimp was not the main objective of our original project. The establishment of this non-native species in waters along the eastern coast of the United States warrants further study. Individuals collecting aquatic organisms in estuarine systems along the east coast of the United States should examine any rostrum-bearing shrimp more closely. The presence of the pale whitish stripe running longitudinally along the dorsal surface of these shrimp serves as the quickest field identifier (d’Udekem d’Acoz et al. 2005). If observed, specimens should be preserved for further 2010 B.E. Warkentine and J.W. Rachlin 101 analysis and the dates and location(s) documented. Identification should be confirmed by a taxonomist, and the specimens should be deposited in a museum collection. While there is currently no indication in the literature of this species posing a threat to native species, some authors (Ashelby et al. 2004, Newman 1963) indicate that P. macrodactylus could, in addition to foraging on native caridean shrimp and other native fauna, potentially engage in resource competition, both for food and habitat, with native species. The movement of P. macrodactylus throughout the northwest Atlantic should be monitored, as well as the impact that it might have on native species. At present, the indications are that this species exists in low numbers relative to the native shrimp species in the area as evidenced by our 2001– 2002 sampling results, which consisted of over 3000 individuals. This low density would indicate that at that time they had not yet become invasive, i.e., causing ecological damage to native habitats or species (McDermott 1991). Our smaller sampling effort in 2008 still indicates low numbers relative to native species (J.W. Rachlin, unpubl. data), but this would need to be confirmed by a more intense sampling effort. A study of the extent of the presence of this species throughout our coastal waters and an indication of the population numbers relative to native species is appropriate. In addition, a more extensive study of its life history and population dynamics in this area is also warranted. Acknowledgments The authors wish to thank Cindy Walsh for her help in sorting out these shrimp from among the thousands collected. We also acknowledge several undergraduate and graduate students from SUNY Maritime College and Lehman College’s Laboratory for Marine and Estuarine Research, respectively, for their field assistance. We also acknowledge several anonymous reviewers, whose comments on an earlier draft greatly improved this manuscript. This research was supported in part by PSC-CUNY Research Awards # 66276-0035, 67291-0036, 68464-0037, 69142-0038, and from Congressman Jose E. Serrano’s WCS/NOAA Lower Bronx River Partnership Grants Program. Literature Cited Abele, L.G., and W. Kim. 1986. An Illustrated Guide to the Marine Decapod Crustaceans of Florida. State of Florida Department of Environmental Regulation Technical Series 8(1):1– 244. Ashelby, C.W., T.M. Worsfold, and C.H.J.M. Fransen. 2004. First records of the oriental prawn Palaemon macrodactylus (Decapoda: Caridea), an alien species in European waters, with a revised key to British Palaemonidae. 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