Loxothylacus panopaei

Invasion History

First Non-native North American Tidal Record: 1964
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1964

---

General Invasion History:

Loxothylacus panopaei was described in 1884 from specimens on the panopeid crab Panopeus lacustris (then known as P. herbsti), from Tampa, Florida (Gissler 1884; Hines et al. 1997). Its native range extends through the Gulf of Mexico, into the Caribbean and Venezuela (Boschma 1955), and northward on the Atlantic coast to Cape Canaveral, Florida (Hines et al. 1997). In 2006, L. panopaei was found on a grapsid crab (Aratus pisonii) in Recife, Brazil, extending its native range southward, although the possibility that this is an introduced population cannot be ruled out (Farrapeira et al. 2008). Loxothylacus panopaei is introduced along the Eastern U.S. and was first found in Chesapeake Bay in 1964. Since then it has expanded southward to just north of Cape Canaveral, almost reaching the northern limit of native populations (Kruse et al. 2012).

North American Invasion History:

Invasion History on the East Coast:

The first occurrence of Loxothylacus panopaei outside its native range was in 1964, when L. panopaei was collected on Eurypanopeus depressus in the York River at Gloucester Point, Virginia in the lower Chesapeake Bay (Van Engel et al. 1966). At this time, it was not found in other rivers, or in older preserved samples of panopeid crabs (Van Engel et al. 1966). By 1967-68, the parasite ranged from Lynnhaven Bay to the mouth of the Potomac (Point Lookout, Maryland), and from Old Plantation Creek (Cape Charles City, Virginia) to Deal Island, Maryland. Loxothylacus panopaei was seen on E. depressus (37% of crabs examined) and Rhithropanopeus harrisii (5%), but not on Panopeus herbsti or Dyspanopeus sayi (Daugherty 1969). Crabs carrying the parasite are believed to have been transported northward with transplants of oysters from the Gulf of Mexico, following mortalities of native Atlantic Coast oysters due to the Haplosporidium nelsoni (MSX) parasite (Van Engel et al. 1966; Hines et al. 1997; Kruse et al. 2012). Subsequently, the parasite colonized estuaries between Chesapeake Bay and Edgewater, Florida and it now ranges fairly continuously up the southeast coast of the US (Hines et al. 1997; Kruse and Hare 2007; Kruse et al. 2012).

A 1983 survey including five lower Chesapeake Bay stations, from Hampton, Virginia to Great Rock (Tangier Sound, Maryland), found that prevalence averaged 9.7% for E. depressus, but only 1.6% of D. sayi were also parasitized (Hines et al. 1997). Considerable year-to year variability and spatial patchiness has been noted in the occurrence of L. panopaei in lower Chesapeake Bay and elsewhere (Daugherty 1969; Hines et al. 1997). Crabs were examined for L. panopaei in the Rhode River, Maryland, from 1979 to the present. They were absent until 1986, when they were found at low prevalence, but then disappeared again until 1990. In 1991 they reached 70% prevalence on R. harrisii, but then declined to lower levels (30-40%) in 1992-93 (Hines et al. 1997). Loxothylacus panopaei was not seen in the Rhode River for several years around 2000 (Hines, Ruiz et al. unpublished data), but it is currently abundant there (Amy Fowler 2011, personal communication). This parasite has also been found in the adjacent Atlantic coastal bays (Hog Island Bay and Chincoteague Bay), beginning in 1986 (Hines et al. 1997).

In 1974-1976, L. panopaei was collected from brackish water in the Neuse River, and in Bogue Sound, in the vicinity of Beaufort, North Carolina. Six parasitized crabs (R. harrisii) were found in 1974; 'dozens' in 1976, but only one parasitized E. depressus (Turquier and Payen 1978). Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled E. depressus were found to be parasitized (Hines et al. 1997). No parasitized crabs were found in April 1986, but L. panopaei was abundant in 1993 among R. harrisii, 22% of sampled crabs were parasitized.

In 2004 and 2005, Kruse et al. (2007) surveyed mud crabs along the coast at 13 sites from Fort Pierce (Indian River Lagoon) to the Savannah River, Georgia. The parasite was seen only in E. depressus. Rates of infection were low in the Indian River Lagoon (0-6%), but higher from Cape Canaveral to the Savannah River (0-93%) and also varied greatly between the two years, being absent at some sites in one year and abundant in the other year.

In August 2012, 12 mud crabs (E. depressus), infected with L. panopaei were collected in Hempstead Harbor, Long Island Sound, New York, a substantial range extension for this parasite. Loxothylacus panopaei was not found in three other sites on Long Island (Freeman et al. 2013).

---

Description

The adult form of the rhizocephalan parasitic barnacle Loxothylacus panopaei bears no resemblance to the conventional acorn barnacles (suborder Balanomorpha) which attach to hard substrates. The adults consist of a kidney-shaped mass of yellow-orange tissue (the externa) attached to the third abdominal segment of a mud crab (Panopeidae), by a stalk, which branches into a mass of tubes surrounding the intestinal tract of the crab (Gissler 1884). The externa superficially resembles an egg mass, but is surrounded by a mantle and is found both on female and male crabs. The male genital organs are in the posterior half of the visceral mass, and are completely separated (Boschma 1972). However, since this form (probably a species group) is the only rhizocephalan parasite of panopeid crabs in the Northwest Atlantic, identifying the host crab is probably sufficient. The only evidence of its barnacle ancestry is in its larval development, which consists of four non-feeding nauplius stages and a cypris stage (Walker et al. 1992). The cypris settles in the branchial chamber of the crab, and injects embryonic cells which develop into the parasitic mass (Gissler 1884; Barnes 1983; Gould 1996; Walker et al. 1992).

The host range of L. panopaei is considered to include at least nine species of panopeid crabs: Eurypanopeus depressus (Flatback Mud Crab), Dyspanopeus sayi (Say's Mud Crab), Panopeus lacustris (Knotfinger Mud Crab), P. obessus, P. occidentalis (Furrowed Mud Crab), P. simpsoni (Oystershell Mud Crab), Rhithropanopeus harrisii (Harris Mud Crab), Tetraplax quadridentata, and Tetraxanthus rathbunae (Inflated Mud Crab) (Hines et al. 1997). Recent genetic studies have indicated that 'L. panopaei' represents a complex of cryptic species. One species infects E. depressus and R. harrisii, while one or possibly two species infect only crabs of the genus Panopeus (Kruse and Hare 2007; Kruse et al. 2012). We will use the name L. panopaei for the parasite infecting E. depressus and R. harrisii, but this name could change with future taxonomic studies.

---

Taxonomy

Ecology

General:

The life cycle of Loxothylacus panopaei is fairly typical for the rhizocephalan barnacles. Nauplius and cypris larvae are morphologically distinct for the two sexes (Walker et al. 1992). There are four non-feeding nauplius stages, followed by the cypris stage. The female cypris settles in the branchial chamber of a recently molted crab, of the megalopa stage or older. Inside the cypris shell, a new stage, called the kentrogon, develops. This stage is marked by a dart-shaped injection stylet which penetrates the crab's cuticle. Through this stylet, a motile vermiform body, composed of embryonic cells, covered in a fibrous acellular sheath, is injected into the crab's hemolymph. The injection process takes about two minutes, and the vermiform body remains intact and motile for 8-16 hours, before it breaks up into ~25 separate, motile, embryonic cells. Each cell has the potential to form a complete parasite, but normally only one succeeds (Glenner and Hoeg 1995; Gould 1996). This cell begins a phase of rapid proliferation which results in the growth of the interna, a mass of rootlike tissue which pervades the visceral mass of the crab. As the interna matures, growth of the externa, a sac protruding from the abdomen of the crab begins. This sac resembles an egg mass, but is found on both male and female crabs (Barnes 1983; Gissler 1884; Gould 1996; Walker et al. 1992).

Male cyprids are attracted to virgin (unmated) externae and settle around the aperture of the externa (Walker et al. 1992). These cyprids inject a distinct life stage composed of undifferentiated cells, the trichogon, into the mantle cavity of the externa (Barnes 1974; Gould 1996; Walker et al. 1992). These cells move into receptacles in the mantle cavity, where they develop into two testicular masses, connected to the brood chamber by a short vas deferens (Dillon and Zwerner 1966). Settlement of the male triggers rapid growth and final maturation of the externa, which culminates in the production and release of nauplii. Broods are released every 5-6 days (Walker et al. 1992). While one externa per crab is typical, Daugherty (1969) found that 10% of crabs had multiple externae, usually 2-3, but sometimes as many as six.

Food:

nine xanthid crab species

Trophic Status:

Parasite

Paras

---

Habitats

General Habitat	Coarse Woody Debris	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Salt-brackish marsh	None
General Habitat	Unstructured Bottom	None
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None

---

---

Tolerances and Life History Parameters

Minimum Salinity (‰)	1	Daugherty 1969; Hines et al. 1997; Reisser and Forward 1991; Walker and Clare 1994
Maximum Salinity (‰)	31.6	Experimental and field- Daugherty 1969; Hines et al. 1997; Reisser and Forward 1991; Walker and Clare 1994
Maximum Reproductive Temperature	29	Temperature- Loxothylacus panopaei was found on crabs over the full temperature range of lower Chesapeake Bay, 3-28 C, in 1967-68 (Daugherty 1969). Reproductive temperatures are those at which collected L. panopaei subsequently released nauplii when brought into the laboratory (Daugherty 1969).
Minimum Reproductive Salinity	10	Reisser and Forward 1991
Maximum Reproductive Salinity	31.6	Reisser and Forward 1991
Minimum Duration	5.5	Walker et al. 1992
Maximum Duration	11.5	Walker et al. 1992
Minimum Width (mm)	4.8	None
Maximum Width (mm)	11.2	None
Broad Temperature Range	None	Warm temperate-Tropical
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

Economic Impacts

Since Panopeidae ('mud crabs') are not fished directly, parasitism by Loxothylacus panopaei has no direct effects on fisheries or other human economic activities in Chesapeake Bay. However, indirect effects on fisheries are possible since panopeid crabs are known to feed on juvenile oysters (Crassostrea virginica) and clams (Mercenaria mercenaria) (Ryan 1956). Panopeid crabs are also a likely prey item for many commercial fishes, but since quantitative effects of the parasite on mud crab densities are unknown, any effects on shellfish and finfish populations would be difficult to prove.

Ecological Impacts

Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs in Chesapeake Bay, Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997).

Parasitism – The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1974; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior.

Substances excreted by L. panopei suppress ovarian development in female crabs (Barnes 1974), spermatogenesis of male crabs (Rubiliani 1983; Rubiliani 1985), and molting in both sexes (Daugherty 1969; O'Brien and Skinner 1990). Another sacculinid (Lernaeodiscus porcellanae) suppresses cleaning behavior in its host (Petrolisthes cabrilloi; Anomura, Porcellanidae) (Ritchie and Hoeg 1981). This effect would prevent removal of the parasite and is likely in L. panopei also. The host crabs (R. harrisii, in these experiments) treat the externa of the parasite as though it were an egg mass, and before the release of parasite nauplii, show the same behavior as before the release of their own larvae. Loxothylacus panopaei releases peptides similar to those released by hatching eggs, and parasitism apparently induces sensitivity to these hormones in males and increases it in females (DeVries et al. 1989). Parasitism decreases survival of parasitized R. harrisii in the laboratory, although no significant effects on growth rate were seen (Alvarez et al. 1995).

Quantitative effects of the L. panopaei invasion on densities of panopeid crabs in Chesapeake Bay have not been demonstrated. The qualitative nature of earlier studies (e.g. Ryan 1956) and the highly aggregated nature of panopeid populations (Grosholz and Ruiz 1995) make it difficult to assess the effects of this parasite. Daugherty (1969) cited personal observations of J. D. Andrews and W. A. Van Engel suggesting that since the invasion, the relative abundance of Eurypanopeus depressus had decreased compared to the then unparasitized Dyspanopeus sayi. In the Matanzas River estuary, Florida, after the first appearance of the parasite in 2004, the abundance of Eurypanopeus depressus was greatly reduced, at least through 2012 (Eash-Loucks et al. 2014). Infected and uninfected populations of R. harrisi in the Rhode River, Maryland did not differ in host susceptibility to L. panopaei, indicating that selection for parasite resistance had not yet occurred (Grosholz and Ruiz 1995). Studies on a larger geographic and temporal scale, comparing populations of crabs in the parasite's native region, and populations invaded at different times, to naive, uninvaded populations, indicates that resistance to the parasite evolves over time (Tepolt et al. 2020).

Since panopeid crabs are abundant predators and a frequent food item of fishes, effects on other trophic levels are possible, but have not been demonstrated. Mud crabs have been observed feeding on juvenile oysters (Crassostrea virginica) and clams (Mercenaria mercenaria) (Ryan 1956), so that fluctuations in crab populations could affect bivalve recruitment.The feeding rates of the mud crab, Eurypanopeus depressus, on the Scorched Mussel (Brachidontes exustus) in North Inlet, South Carolina were greatly reduced by infection with L. panopaei. The crabs' handling time was not affected, but their overall activity level, including the frequency of feeding was reduced (Toscano et al. 2014). High prevalence of the parasite could result in increased survival and density of the mussels.

---

Regional Impacts

M130	Chesapeake Bay		Ecological Impact	Parasitism
Parasitism- Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs in Chesapeake Bay, Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1974; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. Quantitative effects of the L. panopaei invasion on densities of panopeid crabs in Chesapeake Bay have not been demonstrated. The qualitative nature of earlier studies (e.g. Ryan 1956) and the highly aggregated nature of panopeid populations (Grosholz and Ruiz 1995) make it difficult to assess the effects of this parasite. Daugherty (1969) cited personal observations of J. D. Andrews and W. A. Van Engel suggesting that since the invasion, the relative abundance of Eurypanopeus depressus had decreased compared to the then unparasitized Dyspanopeus sayi.
NA-ET3	Cape Cod to Cape Hatteras		Ecological Impact	Parasitism
Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs in Chesapeake Bay, Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884;  Barnes 1983;  Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. Quantitative effects of the L. panopaei invasion on densities of panopeid crabs in Chesapeake Bay have not been demonstrated. The qualitative nature of earlier studies (e.g. Ryan 1956) and the highly aggregated nature of panopeid populations (Grosholz and Ruiz 1995) make it difficult to assess the effects of this parasite. Daugherty (1969) cited personal observations of J. D. Andrews and W. A. Van Engel suggesting that since the invasion, the relative abundance of Eurypanopeus depressus had decreased compared to the then unparasitized Dyspanopeus sayi.
S030	Bogue Sound		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In Bogue Sound, North Carolina, Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled Eurypanopeus depressus were found to be parasitized (Hines et al. 1997).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In the Neuse River, North Carolina, six parasitized crabs (Rhithropanopaeus harrisii) were found in 1974 and 'dozens' were found in 1976, but only one parasitized E. depressus (Turquier and Payen 1978). No parasitized crabs were found in April 1986 (Hines et al. 1997), but L. panopaei was abundant in 1993 among R. harrisii, 22% of sampled crabs were parasitized. In Bogue Sound, North Carolina, Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled Eurypanopeus depressus were found to be parasitized (Hines et al. 1997). The feeding rates of Eurypanopeus depressus on Brachidontes exustus), in North Inlet SC, were grealty reduced by infection with L. panopei. The crabs' handling time was not affected, but their overall activity level, including the frequency of feeding was reduced (Toscano et al. 2014; O’Shaughnessy et al. 2014). In the Matanzas River estuary (FL), after the 1st appearance of the parasite in 2004, the abundance of Eurypanopeus depressus was greatly reduced, at least through 2012 (Eash-Loucks et al. 2014).
S120	Savannah River		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In 2004, four of six Eurypanopeus depressus collected in the Savannah river were parasitized (Kruse and Hare 2007).
S140	St. Catherines/Sapelo Sounds		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2004, eight of 16 Eurypanopeus depressus collected in the Sapelo Sound were parasitized (Kruse and Hare 2007).
S160	St. Andrew/St. Simons Sounds		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2005, 63% of 19 Eurypanopeus depressus collected in the Sapelo Sound were parasitized (Kruse and Hare 2007).
S175	_CDA_S175 (Nassau)		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2004, 54% of 24 Eurypanopeus depressus collected in St. Marys River were parasitized (Kruse and Hare 2007).
S180	St. Johns River		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In 2004, 46% of 26 Eurypanopeus depressus collected at Jacksonville were parasitized. In 2005, 31% of 48 crabs had the parasite (Kruse and Hare 2007).
S183	_CDA_S183 (Daytona-St. Augustine)		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2004, 46% of 26 Eurypanopeus depressus collected at Jacksonville were parasitized. In 2005, 30% of 33 crabs had the parasite (Kruse and Hare 2007). In the Matanzas River estuary (FL), after the 1st appearance of the parasite in 2004, the abundance of Eurypanopeus depressus was greatly reduced, at least through 2012 (Eash-Loucks et al. 2014).
S020	Pamlico Sound		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In Bogue Sound, North Carolina, Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled Eurypanopeus depressus were found to be parasitized (Hines et al. 1997).
S050	Cape Fear River		Ecological Impact	Parasitism
The feeding rates of Eurypanopeus depressus on Brachidontes exustus), in North Inlet SC, were grealty reduced by infection with L. panopei. The crabs' handling time was not affected, but their overall activity level, including the frequency of feeding was reduced (Toscano et al. 2014; O’Shaughnessy et al. 2014)
FL	Florida		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2004, 54% of 24 Eurypanopeus depressus collected in St. Marys River were parasitized (Kruse and Hare 2007)., In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In 2004, 46% of 26 Eurypanopeus depressus collected at Jacksonville were parasitized. In 2005, 31% of 48 crabs had the parasite (Kruse and Hare 2007)., In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism - The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In 2004, 46% of 26 Eurypanopeus depressus collected at Jacksonville were parasitized. In 2005, 30% of 33 crabs had the parasite (Kruse and Hare 2007). In the Matanzas River estuary (FL), after the 1st appearance of the parasite in 2004, the abundance of Eurypanopeus depressus was greatly reduced, at least through 2012 (Eash-Loucks et al. 2014).
NC	North Carolina		Ecological Impact	Parasitism
In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species. In Bogue Sound, North Carolina, Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled Eurypanopeus depressus were found to be parasitized (Hines et al. 1997)., In southeast US estuaries, Loxothylacus panopaei is an abundant parasite of three species of panopeid crabs: Dyspanopeus sayi (Say's Mud Crab), Eurypanopeus depressus (Flatback Mud Crab), and Rhithropanopeus harrisii (Harris mud crab). As of 1983-86, its prevalence was greater on the last two species (Hines et al. 1997). Parasitism- The effects of L. panopaei on individual crabs are complex and diverse. The major impact is that both male and female infected crabs are castrated and unable to reproduce (Gissler 1884; Barnes 1983; Gould 1996), so that all of the host's feeding activity serves to support reproduction of the parasite. In order to maintain itself on a crab, L. panopaei extensively modifies the host's physiology and behavior. Details of the mechanisms are given in the "General Impacts" summary for this species.  In Bogue Sound, North Carolina, Loxothylacus panopaei was discovered and found to be abundant in 1983; 47.4% of sampled Eurypanopeus depressus were found to be parasitized (Hines et al. 1997).  , The feeding rates of Eurypanopeus depressus on Brachidontes exustus), in North Inlet SC, were grealty reduced by infection with L. panopei. The crabs' handling time was not affected, but their overall activity level, including the frequency of feeding was reduced (Toscano et al. 2014; O’Shaughnessy et al. 2014)

References

Órfão, Inês; Ramalhosa, Patrício; Kerckhof, Francis; Canning-Clode, João (2024) The expansion and establishment of the New Zealand mud snail Potamopyrgus antipodarum (Gray, 1843) in the freshwater ecosystems, Bioinvasions Records 13(1): 171-182
https://doi.org/10.3391/bir.2024.13.1.15

Alvarez, Fernando; Hines, Anson H.; Reaka-Kudla, Marjorie L. (1995) Effects of parasitism by the barnacle Loxothylacus panopaei (Gissler) (Cirripedia: Rhizocephala) on growth and survival of the host crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae), Journal of Experimental Marine Biology and Ecology 192: 221-232

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Boschma, H. (1955) The described species of the family Sacculinidae., Zoologische Verhandelingen 27: 48-76

Boschma, H. (1972) On the occurrence of Carcinus maenas (Linnaeus) and its parasite Sacculina carcini Thompson in Burma, with notes on the transport of crabs to new localities, Zoologische Mededelingen 47: 146-155

Carlton, James T.; Mann, Roger (1996) Transfers and world-wide introductions., In: Kennedy, V. S., Newell, R. I. E., Eble, A. F.(Eds.) The Eastern Oyster. , College Park. Pp. 691-706

Carlton, James T.; Newman, William A.; Pitombo, Fábio Bettini (2011) In the wrong place- Alien marine crustaceans: Distribution, biology, impacts, Springer, Dordrecht. Pp. 159-213

Darling, John A.; Bagley, Mark J.; Roman, Joe; Tepolt, Carolyn K; Geller, Jonathan B.. (2008) Genetic patterns across multiple introductions of the globally invasive crab genus Carcinus., Molecular Ecology 17: 4992-5007

Daugherty, Seth J. (1969) <missing title>, College of William and Mary (M.S. Thesis), <missing place>. Pp. <missing location>

DeVries, M. C.; Rittschof, D.; Forward, Richard B., Jr. (1989) Response by rhizocephalan-parasitized crabs to analogues of crab larval-release pheromones, Journal of Crustacean Biology 9: 517-524

Dillon, William, A.; Zwerner, David E. (1966) Contributions to the biology of the sacculinid parasite Loxothylacus panopaei (Gissler, 1884), Transactions of the American Microscopical Society 85: 407-414

Eash-Loucks, Wendy E.; Kimball, Mathew E.; Petrinec, Kathryn M. (2014) Long-term changes in an estuarine mud crab community: Evaluating the impact of non-native species, Journal of Crustacean Biology 36(6): 731-738

Endriss, Stacy B.; Nuzzo, Victoria; Blossey, Bernd (2019) Success takes time: History and current status of biological control of Purple Loosestrife in the United States, In: Van Driesche, Roy G.; Winston, Rachel L.; Perring, Thomas M.; Lopez, Vanessa M.(Eds.) Contributions of classical biological control to the U.S. food security, forestry, and biodiversity. , Morgantopwn, WV. Pp. 312–328

Farrapeira, Cristiane Maria Rocha; de Melo, Arthur Vinícius de O. Marrocos; Barbosa, Débora Ferreira (2008) Introduction of Loxothylacus panopaei (Cirripedia: Rhizocephala), a marine non-indigenous parasitic castrator in estuarine area of Recife, Pernambuco, Brazil, Biociencias 16(2): 157-159

Freeman, Aaren S.; Blakeslee, April M. H.; Fowler, Amy E. (2013) Northward expansion of the rhizocephalan Loxothylacus panopaei (Gissler, 1884) in the northwest Atlantic, Aquatic Invasions 8: in press

Gissler, Carl F. (1884) The crab parasite, Sacculina, The American Naturalist 18: 225-229

Glenner, Henrik; Hoeg, Jens T. (1995) A new motile, multicellular stage involved in host invasion by parasitic barnacles (Rhizocephala), Nature 377: 147-150

Gould, Stephen Jay (1996) Triumph of the root-heads, Natural History 106: 10-17

Grosholz, Edwin D.; Ruiz, Gregory M. (1995) Does spatial heterogeneity and genetic variation in populations of the xanthid crab Rhithropanopeus harrisii (Gould) influence the prevalence of an introduced parasitic castrator?, Journal of Experimental Marine Biology and Ecology 187: 129-145

Hines, Anson H.; Alvarez, Fernando; Reed, Sherry A. (1997) Introduced and native populations of a marine parasitic castrator: Variation in prevalence of the rhizocephalan Loxothylacus panopaei in xanthid crabs, Bulletin of Marine Science 61(2): 197-214

Kroft, Kelley L.; Blakeslee, April M.H. (2016) Comparison of parasite diversity in native panopeid mud crabs and the invasive Asian shore crab in estuaries of northeast North America, Aquatic Invasions 11s: In pres

Kruse, Inken; Hare, Matthew P. (2007) Genetic diversity and expanding nonindigenous range of the rhizocephalan Loxothylacus panopaei parasitizing mud crabs in the western North Atlantic., Journal of Parasitology 93(3): 575-582

Kruse, Inken; Hare, Matthew P.; Hines, Anson H. (2012) Genetic relationships of the marine invasive crab parasite Loxothylacus panopaei: an analysis of DNA sequence variation, host specificity, and distributional range, Biological Invasions 14(3): 701-715

O'Brien, Jack J.; Skinner, Dorothy M. (1990) Overriding of the molt-inducing stimulus of multiple limb autotomy in the mud crab Rhithropanopeus harrisii by parasitization with a rhizocephalan., Journal of Crustacean Biology 10: 440-445

O’Shaughnessy, Kathryn A.; Harding, Juliana M.; Burge, Erin J. (2014) Ecological effects of the invasive parasite Loxothylacus panopaei on the flatback mud crab Eurypanopeus depressus with implications for estuarine communities, Bulletin of Marine Science 90(2): 611-621

Reisser, Christelle; Forward, Richard B., Jr. (1991) Effect of salinity on osmoregulation and survival of a rhizocephalan parasite, Loxothylacus panopaei, and its crab host, Rhithropanopeu harrisii, Estuaries 14(1): 102-106

Ritchie, Larry Edward; Hoeg, Jens Thorvald (1981) Life history of Lernaeodiscus porcellanae (Cirripedia: Rhizocephala) and co-evolution with its porcellanid host, Journal of Crustacean Biology 1: 334-347

Rubiliani, Claudio (1983) Action of a rhizocephalan on the genital activity of host male crabs: Characterization of a parasitic secretion inhibiting spermatogenesis, International Journal of Invertebrate Reproduction 6: 137-147

Rubiliani, Claudio (1985) Response by two species of crabs to a rhizocephalan extract, Journal of Invertebrate Pathology 45: 302-310

Ryan, Edward Parsons (1956) Observations on the life histories and the distribution of the Xanthidae (Mud Crabs) of Chesapeake Bay., American Midland Naturalist <missing volume>: 138-162

Tobias, Zachary; J. C.;and 7 authors (2021) Invasion history shapes host transcriptomic response to a body-snatching parasite, Molecular Ecology <missing volume>: Published online

Toscano, Benjamin J.; Newsome, Burns; Griffen, Blaine D. (2014) Parasite modification of predator functional response, Oecologia published online: <missing location>

Turquier, Yves; Payen, Geneviève (1978) Contribution a la connaissance de Loxothylacus panopei (Gissler), rhizocephale parasite de Rhithropanopeus harrisii (Gould), decapode Xanthidae, Cahiers de Biologie Marine 19: 99-114

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. http://collections.nmnh.si.edu/search/iz/



Van Engel, W. A.; Dillon, William A.; Zwerner, David; Eldridge, Dana (1966) Loxothylacus panopaei (Cirripedia, Sacculinidae) an introduced parasite on a xanthid crab in Chesapeake Bay, U.S.A., Crustaceana 10: 110-112

Varela-Álvarez, Elena; Balau, Ana C.; Marbà, Núria; Afonso Carrillo, Julio ; Duarte, Carlos M. Serrão, Ester A. (2015) Genetic diversity and biogeographical patterns of Caulerpa prolifera across the Mediterranean and Mediterranean/Atlantic transition zone, Marine Biology 162: 557-569

Walker, Graham; Clare, A. S.; Rittschof, D.; Mensching, D. (1992) Aspects of the life-cycle of Loxothylacus panopaei (Gissler), a sacculinid parasite of the mud crab Rhithropanopeus harrisii(Gould): A laboratory study, Journal of Experimental Marine Biology and Ecology 157: 181-193

Walker, Graham; Clare, Anthony S. (1994) Effect of salinity on the development of Loxothylacus panopaei larvae (Crustacea: Cirripedia: Rhizocephala), Estuaries 14: 276-282

Zullo, Victor A. (1979) Marine flora and fauna of the Northeastern United States. Arthropoda: Cirripedia, NOAA Technical Report NMFS Circular 425: 1-29

---