Hemigrapsus sanguineus

Invasion History

First Non-native North American Tidal Record: 1988
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1988

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General Invasion History:

Hemigrapsus sanguineus, the Asian Shore Crab, is native to rocky shores of the western Pacific, from Sakhalin and Peter the Great Bay (Russia), Korea, and North China to Hong Kong, and the entire coast of Japan from Hokkaido to Okinawa (Levin 1976; Sakai 1976; Williams and McDermott 1990). It has been introduced to the East Coast of the US, from North Carolina to Maine (McDermott 1998), the coast of Northern Europe from France to Germany (Dauvin 2009), the Mediterranean Sea (Schubart 2003; Ruiz, personal communication), and the Black Sea (single specimen, Micu et al. 2010). It is abundant in the polyhaline regions of estuaries such as Chesapeake Bay, Delaware Bay, and Long Island Sound, but requires salinities above 20 PSU for successful breeding (Epifanio et al. 1998). It is associated primarily with natural and artificial intertidal rocky habitats (McDermott 1998), but has been collected in salt marshes (Brousseau et al. 2003) and from subtidal habitats (Gilman and Grace 2009). Ballast water is the most likely vector for its initial introduction, though ship/boat fouling and natural dispersal of larvae may contribute to its local spread.

North American Invasion History:

Invasion History on the East Coast:

Hemigrapsus sanguineus was first found in North America in 1988 in Cape May County, New Jersey by a biology student on a class field trip (Williams and McDermott 1990). The first collection was a single ovigerous female. Subsequently in June-October 1990 at Townsend Inlet, New Jersey, and Jan-Feb 1990 at Cape May Harbor (23 km south) 36 specimens of both sexes were found. The crabs varied in ages and included ovigerous females, indicating a breeding population (McDermott 1991). By 1995, it ranged from Oregon Inlet, North Carolina, to Sagamore, Massachusetts, at the north end of the Cape Cod Canal (McDermott 1998). As of 2008, H. sanguineus range extends north to Schoodic Point, Maine and south to Beaufort North Carolina (McDermott 2000; Friedlander 2002; USGS Nonindigenous Aquatic Species Program 2008; Delaney et al. 2008). It is the most abundant crab in rocky intertidal regions from the mouth of Chesapeake Bay to the Maine-New Hampshire border (McDermott 2000; Delaney et al. 2008). North of Great Bay, New Hampshire, its absolute and relative abundance (compared to Carcinus maenas, Green Crab, and native crabs) declines sharply (Delaney et al. 2008). Stephenson et al. (2009) suggest that the northward spread of this crab has stalled, because temperatures in coastal waters north of Casco Bay do not maintain sufficient temperatures (above 15°C) long enough for successful reproduction. The authors suggest that populations might develop in the warmer waters of upper estuaries, and that the occurrence of H. sanguineus near its northern range limits depends on advection of larvae from southern regions (Stephenson et al. 2009). A recent survey suggests that the northern population boundary of H. sanguineus is moving north of Casco Bay (Lord and Williams 2016). A recent, very extensive, genetic analysis indicates that Japan is likely source of H. sanguineus populations in the Northwest Atlantic, and that multiple invasions have occurred. The highest genetic diversity was seen in Long Island Sound and the New York Bight, also an area of high ballast water discharge (Blakeslee et al. 2017).

Invasion History Elsewhere in the World:

Hemigrapsus sanguineus was first reported in Northern European waters at Le Havre, France, on the English Channel in 1999 (Breton et al. 2002). It has spread to the southwest and northeast, reaching Goury, Normandy, by 2008, and Norderney, Lower Saxony, Germany, on the Wadden Sea by 2007 (Obert et al. 2008, reference not seen). In the Mediterranean Sea, the range and population status of H. sanguineus is less clear. A single specimen was found in Croatia (Schubart 2003), and according to personal communications from Italian scientists to Greg Ruiz, this crab is established near the Po River Delta. It has also been reported from the Lake of Tunis, Tunsia (Ben-Souissi et al. 2004, abstract only). One specimen was collected from a yacht harbor in Constanta, Romania, on the Black Sea, but reproduction here is unlikely, because of the low salinity (~ 18 PSU) (Micu et al. 2010).

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Description

As an adult, Hemigrapsus sanguineus, has a roughly square-shaped carapace, with a smooth texture and three anterior-lateral teeth. The third tooth is small. The frontal edge, between the eyes, is about half the width of the carapace. The claws of the male have a membranous welling at the base of the movable finger. The carpus (wrist) has a robust spine on the inner anterior margin. The propodus (lower leg segment) of each walking leg is longer than the dactyl (tip segment), while the merus of each leg has a spine on the anterior margin near the distal end. The claws are symmetrical, but males have proportionally large claws than females (Payne and Kraemer 2013). The carapace is mottled greenish brown, with small reddish spots on the upper surface of the claws (Sakai 1976; Galil et al 2002). Adult crabs in Japan mature at 18-19 mm carapace width, and reach 39-42 mm carapace width (Fukui 1988).

The 1st zoea and megalopa larvae are described and compared with larvae of other East Coast crabs by Johnson and Allen (2005). A more detailed comparison of the 1st zoea with those of other Pacific Hemigrapsus species is given by Lee and Ko (2008). Kornienko et al. (2008) describe all the larval stages, and compare them with other northwest Pacific grapsoid crabs, including H. penicillatus and Eriocheir japonica.

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Taxonomy

Ecology

General:

Ecology- Hemigrapsus sanguineus is most abundant in rocky intertidal habitats (McDermott 1998), but it has been collected in fouling communities in marinas and docks (Ruiz et al., unpublished data), in salt marshes (Brousseau et al. 2003), and in subtidal habitats down to 4 m depth (Gilman and Grace 2009). It is tolerant of rapid salinity changes, to 5 or 10 PSU, such as those that occur in tidepools and estuaries due to rainfall. Males show a stronger preference for high salinity (35 PSU) pools than females, but both are capable of moving out of water to find more favorable water conditions (Hudson et al. 2018). In salt marshes, it tends to occur in stony and debris-filled areas, but will also occupy the burrows of the fiddler crab Uca pugnax (Brousseau et al. 2003). Hemigrapsus sanguineus is omnivorous, and feeds on algae and a variety of invertebrates, including barnacles, snails, mussels, amphipods, and smaller crabs (Gerard et al. 1999; Bourdeau and O'Connor 2003; Brousseau and Baglivo 2005; Tyrell et al. 2006). Diet varies greatly with seasons, and regional and local prey availability, and also by individual specilaization (Griffen et al. 2012);  Adults tend to feed at night, unless starved (Spilmont et al. 2015)..  Introduced populations in France, fed heavily on an introduced amphipod, Ptilohyale littoralis, native to the northwest Atlanitic, but males had a stronger preference for mussels (Mytilus edulis), compared to females.(Spilmont et al. 2023).

It is eaten by larger crabs (Griffen and Byers 2006), fishes (Brousseau et al. 2008; Heinonen and Auster 2012), and shorebirds (Fofonoff, personal observations). Hemigrapsus sanguineus has few parasites. Only 3 species were found in a recent survey (an acanthocephalan, a trematode, a nematode, all probably of North Ameircan origina) compared with 9 in its native range (Kroft and Blakeslee 2016).

Food:

Macroalgae; invertebrates

Consumers:

Crabs, fishes, shorebirds

Competitors:

Trophic Status:

Omnivore

Omni

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Habitats

General Habitat	Rocky	None
General Habitat	Marinas & Docks	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Low Intertidal	None
Tidal Range	Mid Intertidal	None
Tidal Range	High Intertidal	None
Vertical Habitat	Epibenthic	None

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Life History

Life History- Male brachyuran crabs copulate with females, inserting the first pair of pleopods, carrying sperm, into the female's seminal receptacles. The eggs are fertilized internally, and then the eggs are extruded as a 'sponge' or a mass of eggs and brooded between the abdomen and the body (Barnes 1983). Female Hemigrapsus sanguineus had 4,000 to 45,000 eggs, increasing with size from 13-33 mm carapace width (McDermott 1998). The eggs hatch into a zoea, a planktonic larva about 1 mm long, armed with long spines. The zoea goes through six molts, and eventually molts into a postlarval megalopa, about 2 mm long, with prominent eyes and partially developed appendages (Kornienko et al. 2008). The megalopa molts into a miniature 'first crab' which has all the features of an adult crab, and is capable of crawling on the bottom. (Barnes 1983; Kornienko et al. 2008). Settlement occurs at 25-38 days after hatching (Epifanio et al. 1998). Adult crabs produce a chemical cue that triggers metamorphosis in megalopae (Anderson et al. 2010), and may contribute to the ability of Hemigrapsus sanguineus to rapidly build up populations.

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	-2	Field observations (Ruiz et al., unpublished)
Maximum Temperature (ºC)	30	Field observations (Ruiz et al., unpublished)
Minimum Salinity (‰)	5	Hudson et al. 2018. Other experiments found a salinity tolerance of 10 PSU (Epifanio et al. 1998; McDermott 2000; Ruiz et al., unpublished). Acclimation could explain differences in results.
Maximum Salinity (‰)	61	Experimental (Wantanabe 1982)
Minimum Reproductive Temperature	15	Field (ovigerous females, Fukui 1988, Japan), Experimental (larval development, 20C, Epifanio et al. 1998, Delaware)
Maximum Reproductive Temperature	25	Field (ovigerous females, Fukui 1988, Japan), Experimental (larval development, Epifanio et al. 1998, Delaware)
Minimum Reproductive Salinity	20	Experimental (larval development, Epifanio et al. 1998, Delaware)
Maximum Reproductive Salinity	35	Experimental (larval development, Epifanio et al. 1998, Delaware)
Minimum Duration	10	From hatching to first crab stage-, 25 C, 40 ppt ( Epifanio et al. 1998, Delaware)
Maximum Duration	25	From hatching to first crab stage, 20 C, 30 ppt (Fukui 1988; Hwang et al. 1993; Epifanio et al. 1998)
Minimum Width (mm)	18.4	Adult male, 29.4, adult female 18.4.0, Japan (Fukui 1988)
Maximum Width (mm)	48	Adullt male, subtidal habitat Long Island Sound (Gilman and Grace 2009); Adult male, 42.4, adult female 39.0, Japan (Fukui 1988)
Broad Temperature Range	None	Warm-temperate Tropical
Broad Salinity Range	None	Polyhaline-Hyperhaline

General Impacts

The invasion of Hemigrapsus sanguineus has had major ecological impacts on the fauna of natural and artificial rocky intertidal communities of the East Coast of North America. This is especially the case from Long Island north to Casco Bay, Maine, where natural rocky shore habitat is plentiful, and summer water temperatures are suitable for reproduction (McDermott 1998; Gerard et al. 1999; Jensen et al. 2002; Lohrer and Whitlach 2002; Kraemer et al. 2007; Delaney et al. 2008). Hemigrapsus sanguineus is a potential invader on the West Coast of North America. In experiments, it had a higher feeding rate than the native Pachygrapsus crassipes, H. nudus, and Hemigrapsus oregonensis, but did not show dominant agonsitic behavior (Lord 2017).

Economic Impacts

Although ecological impacts of H. sanguineus on rocky shore communities are quite significant, the economic impacts are unclear, because most of the major fisheries resources in this region are subtidal. This crab preys on young Blue Mussels (Mytilus edulis), but since most commercially reared or wild harvested mussels are subtidal, the effect on this resource is likely to be small. Young American Lobsters (Homarus americanus), frequently occur in the intertidal zone, especially north of Cape Cod. In laboratory trials, adult H. sanguineus preyed on small juvenile American Lobsters (Homarus americanus) (Demeo and Riley 2006). However, the effect of this predation on lobster fisheries is unknown.

Ecological Impacts

Competition: The invasion of Hemigrapsus sanguineus has led to a dramatic decline in the abundance of Carcinus maenas (Green Crab) in rocky intertidal regions, from Long Island to Cape Ann, Massachusetts, where Green Crabs, especially juveniles, were formerly abundant (Gerard et al. 1999; Lohrer and Whitlatch 2002; Kraemer et al. 2007). On a local scale, within coves at Odiorne Point, New Hampshire, a negative correlation was seen in abundance of H. sanguineus and C. maenas (Griffen et al. 2008). In comparison with Panopeus herbstii (the native Black-Fingered Mud Crab), in Long Island Sound, H. sanguineus had higher fecundity, multiple broods, a longer reproductive season, and more rapid dispersal (Brousseau and McSweeney 2016). The native Dyspanopeus sayi (Say's Mud Crab) and Eurypanopeus depressus (Flatback Mud Crab) have also declined sharply in intertidal habitats in Long Island Sound, though they remain abundant in subtidal waters (Gerard et al. 1999; Griffen and Delaney 2007; Kraemer et al. 2007). North of Cape Ann, Massachusetts, C. maenas greatly outnumbered H. sanguineus in 2006, indicating that impacts on Carcinus were likely to be small (Griffen and Delaney 2007). By 2009, at Odiorne Point NH, H. sanguineus outnumbered C. maenas, and the two species were inversely correlated. Stable isotope analyses indicated that the diet of C. maenas was increasingly dominated by algae, and the hepatopancreas energy content of females, during the breeding season was declining, leading to an expected decrease in fecundity (Griffen et al. 2011). As H. sanguineus extends its range northward, C. maenas can be expected to gradually decline in abundance in rocky shore areas.

Competition among crabs for habitat, especially for shelter and food, often involves aggression and interference. In experimental trials, H. sanguineus interfered with the feeding of C. maenas at baits, frequently displacing the green crabs (Jensen et al. 2002). In another set of laboratory experiments, interference between the two species lowered the predation rates of both species on mussels (Griffen 2006) and amphipods (Griffen and Byers 2006). A similar reduction in predation rates of the two crabs was seen in field enclosure experiments (Griffen and Byers 2009). In the presence of H. sanguineus, C. maenas decreased its consumption of mussels, and did not switch to other foods (Griffen and Byers 2009).

Predation: Field and experimental studies, from Long Island Sound to New Hampshire, indicate that Hemigrapsus sanguineus prey on small shore fauna (mussels, snails, etc.), but also on juvenile crabs, particularly Carcinus maenas. In experimental trials, adult Hemigrapsus sanguineus fed on mussels (Mytilus edulis), hard clams (Mercenaria mercenaria), and common Periwinkles (Littorina littorea). Small mollusks were preferred. In one study, very few L. littorea were consumed (Bourdeau and O'Connor 2003), while in another, many where eaten (Gerard et al. 1999). In laboratory trials, 71% of H. sanguineus preferred animal food (mussels, M. edulis, and barnacles, Semibalanus balanoides) over algae (Ulva sp. and Chondrus crispus) (Brousseau and Baglivo 2005).

The replacement of C. maenas by H. sanguineus in rocky intertidal regions of southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen in Narragansett Bay, RI (Griffen and Delaney 2007; Griffen 2011). In addition, there is some evidence that H. sanguineus feeds at higher weight-specific rates than C. maenas, both due to smaller body size and higher metabolism of H. sanguineus (de Graff and Tyrrel 2004). In laboratory experiments, C. maenas showed a reduction in feeding rates at high population densities due to intraspecific interference, while H. sanguineus maintained its feeding rates at high densities (Griffen and Delaney 2007). In field enclosures, (single species trials) at Odiorne Pt., New Hampshire, H. sanguineus fed at lower rates per capita on mussels and snails (Littorina spp.) than C. maenas, due to their smaller average body size (Griffen and Byers 2009). In laboratory and field mesocosms, H. sanguineus and C. maenas had similar patterns of predation on mussels (M. edulis) and ephemeral algae, but H. sanguineus caused greater declines on barnacles (S. balanoides) (Tyrell et al. 2006). Predation by H. sanguineus on Molgula manhattensis altered the composition of fouling communities, favoring the introduced tunicates Botryllus violaceus and Diplosoma listerianum (Freeman et al. 2016).

In an 8-year field survey in Rye, New York, by 2005, L. littorea had declined to 25% of its 1998 density, and was negatively correlated with the abundance of H. sanguineus (Kraemer et al. 2007). Enclosure studies in Long Island Sound found a measurable effect on recruitment of barnacles during larval settlement, but this effect was short-lived (Brouseau and Goldberg 2007). Blue Mussels (Mytilus edulis) from southern New England, which have coexisted with H. sanguineus for about 15 years, show a shell thickening response when exposed to chemical cues from the crabs, an apparent evolutionary response (Freeman and Byers 2006).

Predation among crabs often co-occurs with competition, especially when juveniles of one species encounter adults of another. Concomitant with a steady increase in abundance of H. sanguineus, a decline in abundance of C. maenas, to 10-20% of its initial abundance, and a scarcity or absence of small juveniles, was seen at Point Judith in 1996-1999 (Lohrer and Whitlatch 2002) . In laboratory experiments, predation on small C. maenas by large H. sanguineus (and vice versa) was common, reducing overall predation rates on other prey, such as amphipods and snails (Griffen and Byers 2006). At small sizes, 5-15 mm, estimated claw strength of both female and male H. sanguineus is greater or equal than that of C. maenas, which would facilitate predation on juvenile C. maenas (Payne and Kraemer 2013). In laboratory trials, in which Hemigrapsus sanguineus were given alternate food (mussels) and shelter, adult H. sanguineus preyed on juvenile American Lobsters (Homarus americanus with a 11-14 mm carapace length) (Demeo and Riley 2006). The extent to which Hemigrapsus preys on lobsters in the wild is unclear.

Food/Prey: The high densities of H. sanguineus in intertidal zones have probably provided a food source for shorebirds and littoral fishes. However, the extent and importance of this new prey species for bird and fish predators is poorly known. Brousseau et al. (2009) found low rates of predation by Fundulus heteroclitus (Mummichog) and F. majalis (Striped Killifish). However, Heinonen and Auster (2012) found that larger predatory fishes (Tautogolabrus adspersus- Cunner; Tautoga onitis-Tautog; Centropristis striata-Black Sea Bass) had a preference for H. sanguineus over native crabs. They suggest that overfishing of these predatory fishes has favored the invasion of H. sanguineus, and the crabs expansion into subtidal waters.

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Regional Impacts

NA-ET3	Cape Cod to Cape Hatteras		Ecological Impact	Predation
Field and experimental studies in the Cape Cod-Cape Hatteras region support the occurence of strong impacts of Hemigrapsus sanguineus predation on small shore fauna (mussels, snails, etc.), but also on juvenile crabs, paticularly Carcinus maenas. In experimental trials, adult Hemigrapsus sanguineus fed on Blue Mussels (Mytilus edulis), Hard Clams (Mercenaria mercenaria), and Periwinkles (Littorina littorea). Small mollusks were preferred. Enclosure experiments at Black Rock Harbor, Connecticut, indicated that H. sanguineus predation accounted for up to 25% of mortality of Blue Mussels (Mytilus edulis (Brousseau et al. 2014). In one study, very few L. littorea were consumed (Boudreau and O'Connor 2003), while in another, many where eaten (Gerard et al. 1999). In laboratory trials, 71% of H. sanguineus preferred animal food (mussels, M. edulis., and barnacles, Semibalanus balanoides) over algae (Ulva sp. and Chondrus crispus) (Brousseau and Baglivo 2005). In experimental feeding trials using M. edulis, H. sanguineus was found to feed at higher rates than Carcinus maenas (Green Crabs) of equal weight (de Graff and Tyrrel 2004), but feeding rates per crab were lower due to their smaller average body size (Griffen and Byers 2009). In laboratory experiments, C. maenas showed a reduction in feeding rates at high population densities due to intraspecific interference, but H. sanguineus maintains its feeding rates at high densities (Griffen and Delaney 2007). The replacement of C. maenas by H. sanguineus in rocky intertidal regions of southern New England waters (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (Lohrer and Whitlach 2002a; Griffen and Delaney 2007). Blue Mussels (Mytilus edulis) from southern New England, which have coexisted with H. sanguineus for about 15 years, show a shell thickening response when exposed to chemical cues from the crabs, an apparent evolutionary response (Freeman and Byers 2006). In an 8-year field survey in Rye, New York, by 2005, L. littorea had declined to 25% of its 1998 density, and was negatively correlated with the abundance of H. sanguineus (Kraemer et al. 2007). Enclosure studies in Long Island Sound found a measurable effect of H. sanguineus on recruitment of barnacles during larval settlement, but this effect was short-lived (Brousseau and Goldberg 2007). Predation by H. sanguineus on Molgula manhattensis altered the composition of fouling communities, favoring the introduced tunicates Botryllus violaceus and Diplosoma listerianum (Freeman et al. 2016). In a study of Littorina saxatilis (Rough Periwinkle, native) from 3 populations near Stony Brook NY, one population showed morphogical responses in shellll proportions to H. sanguineus, while two populations did not.repond. None of the populations showed shell growth reponses to the native Dyspanopeus sayi (Hooks and Padilla 2020).
M040	Long Island Sound		Ecological Impact	Predation
Field and experimental studies support the occurrence of strong impacts of Hemigrapsus sanguineus predation on small shore fauna (mussels, snails, etc.), and juvenile crabs, paticularly Carcinus maenas. Enclosure studies in Long Island Sound found a measurable effect of H. sanguineus on recruitment of barnacles during larval settlement, but this effect was short-lived (Brousseau and Goldberg 2007). The replacement of C. maenas by H. sanguineus in rocky intertidal regions of southern New England waters (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to higher population densities of H. sanguineus (Lohrer and Whitlach 2002a; Griffen and Delaney 2007). In an 8-year field survey in Rye, New York, by 2005 L. littorea had declined to 25% of its 1998 density, and was negatively correlated with the abundance of H. sanguineus (Kraemer et al. 2005). Enclosure experiments at Black Rock Harbor, Connecticut, indicated that H. sanguineus predation accounted for up to 25% of mortality of Blue Mussels (Mytilus edulis (Brousseau et al. 2014). Field sampling at Crane Pt., New York, in 1997-1998 indicated that H. sanguineus outnumbered C. maenas by ~100 to 1 at sites where juvenile C. maenas had been formerly abundant in intertidal rocky habitats (Gerard et al. 1999). Similar declines, to 10-20% of initial abundance, and a scarcity or absence of small juvenile C. maenas were seen at New Haven and Millstone Point, Connecticut (Lohrer and Whitlatch 2002b). A survey of crab abundance at Rye, New York, from 1998 to 2005, found that C. maenas was only 1% of the crab population in 1998, and was not seen at all after 2000. Eurypanopeus depressus went from 45% of the population to 0%, and in 2005, H. sanguineus comprised 100% of the intertidal crabs (Kraemer et al. 2007). Field enclosure experiments indicated that predation by adult H. sanguineus on juvenile C. maenas was a major cause for the decline in the Green Crab population (Lohrer and Whitlatch 2002b). In a study of Littorina saxatilis (Rough Periwinkle, native) from 3 populations near Stony Brook NY, one population showed morphogical responses in shellll proportions to H. sanguineus, while two populations did not.repond. None of the populations showed shell growth reponses to the native Dyspanopeus sayi (Hooks and Padilla 2020).
NA-ET2	Bay of Fundy to Cape Cod		Ecological Impact	Predation
Concomitant with a steady increase in abundance of H. sanguineus, a decline in abundance of C. maenas and a scarcity or absence of small juveniles was seen at Point Judith in 1996-1999 (Lohrer and Whitlatch 2002). The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen in Narragansett Bay, RI) (Griffen and Delaney 2007). In experimental feeding trials using M. edulis, H. sanguineus was found to feed at higher rates than individuals of Carcinus maenas (Green Crabs) of equal weight (de Graff and Tyrrel 2004). However, in field enclosure experiments (single species trials) at Odiorne Pt., New Hampshire, H. sanguineus fed at lower rates per capita on mussels and snails (Littorina spp.) than C. maenas, due to their smaller average body size (Griffen and Byers 2009). In laboratory and field mesocosms, H. sanguineus and C. maenas had similar patterns of predation on mussels (M. edulis) and ephemeral algae, but H. sanguineus caused greater declines in barnacles (S. balanoides) (Tyrell et al. 2006). In laboratory experiments, predation of small C. maenas by large H. sanguineus (and vice versa) was common, reducing overall predation rates on other prey, such as amphipods and snails (Griffen and Byers 2006). In laboratory trials, in which Hemigrapsus sanguineus were given alternate food (mussels) and shelter, adult H. sanguineus preyed on juvenile American Lobsters (Homarus americanus with a 11-14 mm carapace length) (Demeo and Riley 2006). ;Experiments and modeling indicate that predation by Carcinus maenas and Hemigrapsus sanguineus is likely to reduce the use of intertidal habitats by the native Cancer irroratus (Rock Crab) in the Gulf of Maine (Griffen and Riley 2015). Caging experiments indicate that intraguild predation by adult Hemigrapsus sanguineus has decreased recruitment of Carcinus maenas in Massachusetts Bay, but variation iun recruitment with depth and season has enabled C. amenas to persist (Baillie and Grabowski 2018).
NA-ET2	Bay of Fundy to Cape Cod		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass at sites in Cape Cod and Massachusetts Bays (near Marshfield, Boston and Cape Ann) (Griffen and Delaney 2007; O'Connor 2013). Interference competition and aggression occur between Carcinus maenas and Hemigrapsus sanguineus. In laboratory experiments, interference between the two species lowered the predation rates of both species on mussels (Griffen 2006) and amphipods (Griffen and Byers 2006). A similar reduction in predation rates of the two crabs was seen in field enclosure experiments (Griffen and Byers 2009). In enclosures with H. sanguineus, C. maenas decreased its consumption of mussels, and did not switch to other foods. On a local scale, within coves at Odiorne Point, NH, a negative correlation was seen in the abundance of H. sanguineus and C. maenas (Griffen et al. 2008). At Odiorne Point, a shift in diet, towards algae, was seen in Carcinus maenas, resulting in a decrease in hepatopancreas energy content, and probably a decrease in fecundity (Griffen et al. 2011).
N130	Great Bay		Ecological Impact	Predation
In field enclosure experiments (single species trials) at Odiorne Pt., New Hampshire, H. sanguineus fed at lower rates on mussels and snails (Littorina spp.) than C. maenas (Griffen and Byers 2009). Increasing densities of H. sanguineus and the displacement of C. maenas at Odiorne Point are expected to result in increased predation rates in the intertidal community, because predation by H. sanguineus is less affected by intraspecific interference at high density (Griffen and Delaney 2007; Griffen et al. 2008). In laboratory and field mesocosms, H. sanguineus and C. maenas had similar patterns of predation on mussels (M. edulis) and ephemeral algae, but H. sanguineus caused greater declines in barnacles (S. balanoides) (Tyrell et al. 2006). In laboratory experiments, predation of small C. maenas by large H. sanguineus (and vice versa) was common, reducing overall predation rates on other prey, such as amphipods and snails (Griffen and Byers 2006).
N130	Great Bay		Ecological Impact	Competition
In laboratory experiments, interference between H. sanguineus and C. maenas lowered the predation rates of both species on mussels (Griffen 2006) and amphipods (Griffen and Byers 2006). A similar reduction in predation rates of the two crabs was seen in field enclosure experiments (Griffen and Byers 2009). In enclosure experiments, in the presence of H. sanguineus, C. maenas decreased its consumption of mussels, and did not switch to other foods. On a local spatial scale, within coves at Odiorne Point, a negative correlation was seen in abundance of H. sanguineus and C. maenas (Griffen et al. 2008). At Odiorne Point, a shift in diet, towards algae, was seen in Carcinus maenas, resulting in a decrease in hepatopancreas energy content, and probably a decrease in fecundity (Griffen et al. 2011).
M050	Great South Bay		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen at one site near Montauk, NY (Griffen and Delaney 2007). Predation by H. sanguineus on Molgula manhattensis altered the composition of fouling communities, favoring the introduced tunicates Botryllus violaceus and Diplosoma listerianum (Freeman et al. 2016).
M023	_CDA_M023 (Narragansett)		Ecological Impact	Predation
Concomitant with a steady increase in the abundance of H. sanguineus, a decline in abundance of C. maenas (up to 10-20% of initial abundance) and a scarcity or absence of small juveniles was seen at Point Judith in 1996-1999 (Lohrer and Whitlatch 2002). The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey results from one site near Point Judith, RI) (Griffen and Delaney 2007).
M010	Buzzards Bay		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (recorded in two field surveys near New Bedford and Woods Hole MA) (Griffen and Delaney 2007).
NA-ET3	Cape Cod to Cape Hatteras		Ecological Impact	Competition
Field observations indicate that Hemigrapsus sanguineus has largely displaced Carcinus maenas from rocky intertidal habitats from Cape Cod to New Jersey (Gerard et al. 1999; Jensen et al. 2002; Lohrer and Whitlatch 2002b; Kraemer et al. 2007). The native Dyspanopeus sayi (Say's Mud Crab) and Eurypanopeus depressus have also declined sharply from intertidal habitats in Long Island Sound, although they remain abundant in subtidal waters (Gerard et al. 1999; Kraemer et al. 2007). In experimental trials, H. sanguineus interfered with the feeding of C. maenas at bait stations, and frequently displaced green crabs from the bait (Jensen et al. 2002). Hemigrapsus sanguineus, in experiments, accepted conspecific individuals in shelters, but excluded similarly sized Green Crabs (Carcinus maenas and native Rock Crabs (Cancer irrorarus (Hobbs et al. 2017). In comparison with Panopeus herbstii, the native Black-Fingered Mud Crab), in Long Island Sound, H. sanguineus had higher fecundity, multiple broods, a longer reproductive season, and more rapid dispersal (Brousseau and McSweeney 2016).
N195	_CDA_N195 (Cape Cod)		Ecological Impact	Competition
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (results from field survey at one site on Marthas Vineyard, MA) (Griffen and Delaney 2007).
N180	Cape Cod Bay		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at a site near Marshfield (Griffen and Delaney 2007; O'Connor 2013).
N170	Massachusetts Bay		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of the Southern Gulf of Maine (Cape Cod to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey results from sites near Boston and Cape Ann, MA) (Griffen and Delaney 2007).
M040	Long Island Sound		Ecological Impact	Competition
Field observations indicate that Hemigrapsus sanguineus has largely displaced Carcinus maenas from rocky intertidal habitats in Long Island Sound (Gerard et al. 1999; Jensen et al. 2002; Lohrer and Whitlatch 2002b; Kraemer et al. 2007). The native Dyspanopeus sayi (Say's Mud Crab) and Eurypanopeus depressus have also declined sharply from intertidal habitats in Long Island Sound, although they remain abundant in subtidal waters (Gerard et al. 1999; Kraemer et al. 2007). In comparison with Panopeus herbstii, the native Black-Fingered Mud Crab), in Long Island Sound, H. sanguineus had higher fecundity, multiple broods, a longer reproductive season, and more rapid dispersal (Brousseau and McSweeney 2016).
M020	Narragansett Bay		Ecological Impact	Predation
Concomitant with a steady increase in abundance of H. sanguineus, a decline in abundance of C. maenas (to 10-20% of initial abundance) and a scarcity or absence of small juveniles was seen at Point Judith in 1996-1999 (Lohrer and Whitlatch 2002).The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey results from Narragansett Bay, RI) (Griffen and Delaney 2007).
M020	Narragansett Bay		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, in Narragansett Bay (Griffen and Delaney 2007). Hemigrapsus sanguineus, in experiments, accepted conspecific individuals in shelters, but excluded similarly sized Green Crabs (Carcinus maenas and native Rock Crabs (Cancer irroratus (Hobbs et al. 2017). Cobble beaches, in Narragansett Bay, stabilized by Saltmarsh Cordgrass Spartina alterniflora and Ribbed Mussels (Geukensia demissa) are dominated by H. sanguineus, while native mud crabs (mostly Eurypanopeus depressus). Hemigrapsus sanguineus has heavy successful recruitment in the cordgrass-mussel habitat, apperntly excluding mud crabs, and diffusing into the adjacent mud crab-dominated upper and lower cobble zones. Predation by mid crabs limits H. sanguineus in the 'pure' cobble zones (Altieri and Irving 2017).
M023	_CDA_M023 (Narragansett)		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at a site near Point Judith (Griffen and Delaney 2007).
M010	Buzzards Bay		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at sites near New Bedford and Woods Hole (Griffen and Delaney 2007).
N195	_CDA_N195 (Cape Cod)		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen at two sites near New Bedford and Woods Hole MA) (Griffen and Delaney 2007).
N180	Cape Cod Bay		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (results of a field survey near Marshfield) (Griffen and Delaney 2007).
N170	Massachusetts Bay		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at sites near Boston and Cape Ann (Griffen and Delaney 2007).
NA-ET3	Cape Cod to Cape Hatteras		Ecological Impact	Food/Prey
Prey selection experiments generally support the hypothesis that H. sanguineus is preferred by crab-eating fishes (Tautoga onitis, Tautogolabrus adspersus, and Centropristis striata), but this preference varies with fish size and substrate. Over-fishing of these predators may be favoring the invasion of H. sanguineus and its spread into deeper waters (Heinonen and Auster 2012).
NEA-II	None		Ecological Impact	Competition
In field experiments in rock jetties on the Ise of Sylt, in the Wadden Sea, Germany, H. sanguineus displaced juvenile Carcinus maenas (Green Crabs) from patches of boulders. However, this displacement would have no effect on the large populaiton of C. maenas in other habitats (Landschoff et al. 2013). On the island of Helgoland, the abundance of H. sanguineus is increasing. It outnumbered C. maenas at some locations, but this may be the result of increased larval settle ment in sheltered locations (Jungblut et al. 2017).
N165	_CDA_N165 (Charles)		Ecological Impact	Predation
Caging experiments indicate that intraguild predation by adult Hemigrapsus sanguineus has decreased recruitment of Carcinus maenas in Massachusetts Bay, but variation iun recruitment with depth and season has enabled C. amenas to persist (Baillie and Grabowski 2018).
MA	Massachusetts		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at sites near New Bedford and Woods Hole (Griffen and Delaney 2007)., Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at sites near Boston and Cape Ann (Griffen and Delaney 2007)., Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at a site near Marshfield (Griffen and Delaney 2007; O'Connor 2013)., The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (results from field survey at one site on Marthas Vineyard, MA) (Griffen and Delaney 2007).
MA	Massachusetts		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (recorded in two field surveys near New Bedford and Woods Hole MA) (Griffen and Delaney 2007)., Caging experiments indicate that intraguild predation by adult Hemigrapsus sanguineus has decreased recruitment of Carcinus maenas in Massachusetts Bay, but variation iun recruitment with depth and season has enabled C. amenas to persist (Baillie and Grabowski 2018)., The replacement of C. maenas by H. sanguineus in rocky intertidal regions of the Southern Gulf of Maine (Cape Cod to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey results from sites near Boston and Cape Ann, MA) (Griffen and Delaney 2007)., The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (results of a field survey near Marshfield) (Griffen and Delaney 2007)., The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen at two sites near New Bedford and Woods Hole MA) (Griffen and Delaney 2007).
RI	Rhode Island		Ecological Impact	Competition
Field sampling shows an overwhelming dominance of Hemigrapsus sanguineus over Carcinus maenas, both in numbers and biomass, at a site near Point Judith (Griffen and Delaney 2007).
RI	Rhode Island		Ecological Impact	Predation
Concomitant with a steady increase in the abundance of H. sanguineus, a decline in abundance of C. maenas (up to 10-20% of initial abundance) and a scarcity or absence of small juveniles was seen at Point Judith in 1996-1999 (Lohrer and Whitlatch 2002). The replacement of C. maenas by H. sanguineus in rocky intertidal regions of Southern New England (Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey results from one site near Point Judith, RI) (Griffen and Delaney 2007).
NY	New York		Ecological Impact	Predation
The replacement of C. maenas by H. sanguineus in rocky intertidal regions of southern New England (from Long Island to Cape Ann) has resulted in a likely increase in predation rates, due to much higher population densities of H. sanguineus (field survey, seen at one site near Montauk, NY (Griffen and Delaney 2007). Predation by H. sanguineus on Molgula manhattensis altered the composition of fouling communities, favoring the introduced tunicates Botryllus violaceus and Diplosoma listerianum (Freeman et al. 2016).

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