Petrolisthes armatus

Invasion History

First Non-native North American Tidal Record: 1991
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1991

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General Invasion History:

See East Coast invasion history, below.

North American Invasion History:

Invasion History on the East Coast:

Petrolisthes armatus was absent from early collections on the Atlantic Coast (e.g. Kingsley 1879). It was first collected on the Atlantic coast of Florida in the 1930s at Miami, in Biscayne Bay (Knott et al. 2000), and became abundant in the Indian River Lagoon in the 1970s (Knott et al. 2000). It was collected from worm reefs near Fort Pierce, and at Hutchinson Island in 1974–1975 (USNM 169902, 169905, US National Museum of Natural History). In the 1980s, this crab was not mentioned in guidebooks covering the East Coast of the southern states (Kaplan 1988; Williams 1984). However, in the 1990s, the range expanded to include St. Catherines Island, Georgia, in 1994, and various sites in South Carolina in 1995. In recent years, it was extremely abundant on the coast of Georgia and South Carolina (Knott et al. 2000; Prezant et al. 2002; Power 2006; Hollebone and Hay 2007 a, b; Tilburg et al. 2010). However, a severe winter cold in 2009-2010 caused a sharp population decline in South Carolina (Canning-Clode et al. 2011). Interannual temperature fluctuations may slow or limit the range expansion of P. armatus. Cold winters are associated with later and reduced larval recruitment (Popp and Wilber 2020). The northernmost record, to our knowledge, is from Beaufort, North Carolina (Blakeslee et al. 2024). The rapid range extension of P. armatus' range is a response to climate change, and may involve a mixture of natural larval dispersal and anthropogenic transport. Possible human vectors include ballast water, hull fouling, and local oyster transplants. Hiller and Lessios (2017) found that recently established populations in Georgia and the Carolinas show high genetic diversity, suggesting that they were founded by many individuals, with human mediated transport of P. armatus with oysters as a likely vector. Georgia and South Carolina populations were founded by movement of individuals from Florida (Hiller and Lessios, 2017).

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Description

Petrolisthes armatus is an anomuran, known as a porcelain crab, with proportionately large claws. The 4th pair of walking legs is vestigial, and the abdomen is more developed than in brachyuran crabs ('true crabs'). The carapace is roughly circular, and is covered with narrow, low ridges and granules. The front is bluntly triangular, with a depression at the midpoint. The first joint of the antenna has a lobe, usually tipped with a spine. The chelipeds (claws) are long and narrow, about 3–4 times as long as wide, while the carpus (segment next to the claws) is 2 ½ times as long as wide, and bears three spines on its anterior side. The color is variable, often orange-brown to dark brown, or olive green to dark green. The mouthparts (mandible and maxillipeds) are bright blue, a distinctive mark for this species (Mantelatto et al. 2011; Smithsonian Marine Station at Fort Pierce 2011).

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Taxonomy

Ecology

General:

Life History- Male and female anomuran crabs press their ventral surfaces together and release eggs and spermatophores simultaneously. The female carries a 'sponge' of eggs brooded between the abdomen and the body (Barnes 1983). Fecundity varied with body size and sampling site, ranging from ~25 to 900 eggs over a range of carapace width of 3-10 mm (Wassick et al. 2018). Fecundity was greater at a northern site (North Inlet SC) in the introduced range than southern introduced sites, or sites in the native range (Wassick et al. 2018). Each egg hatches into a zoea, a larva about 1.6 mm long, armed with a long rostral spine, and two shorter posterior spines, which drifts in the plankton. The zoea goes through a molt into a second zoea stage (2.0 mm long), and then molts into a postlarval megalopa larva, about 1.5 mm long, with prominent eyes and fully developed appendages (Gore 1972). 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 (Gore 1972; Brossi-Garcia and Moreira 1992). Females have broods fter each molt, on average, every 6 dyas (Popp et al. 2020).Field sampling and modeling suggest that the larvae tend to move toward deeper water during development, leading to upstream transport in the bottom 'salt wedge' of an estuary, and retention of most of the recruits within an estuary (Tilburg et al. 2010).

Ecology- Petrolisthes armatus inhabits intertidal and shallow-water rocky, oyster-reef and mangrove communities. It is a suspension feeder, filtering phytoplankton and detritus form the water column (Hollebone and Hay 2008). This crab was positively associated with rugosity (vertical height and complexity) of oyster reefs (Margiotta et al. 2016). Crabs overwintered in subtidal waters, and low inter temperatures onset of breeding and population growth (Popp et al. 2021). Ziegler et al. (2024) documented a positive association of this species with native mud crabs, an association that “may be a result of hydrodynamic aggregating (the) species… or attraction by both crabs for the same fine-scale habitat structural attributes."

Food:

Phytoplankton, detritus

Trophic Status:

Suspension Feeder

SusFed

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Habitats

General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Rocky	None
General Habitat	Mangroves	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Vertical Habitat	Epibenthic	None

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Life History

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	6	Experimental, temperature regime corresponding to 2010 temperature regime near Savannah Georgia, dropping from 14 to 6 C in about 15 days, ~40% survival (Canning-Clode et al. 2011)
Maximum Temperature (ºC)	40.5	Stillman and Somero 2000, cited by Hollebone and Hay 2007, Pacific crabs.
Minimum Salinity (‰)	20	Experimental, Crabs from Brazil, nearly half of animals dead or lethargic after 5 days at 13.6 PSU. Some mortality and lethargy was seen at 20 PSU (Shumway 1983).
Minimum Duration	12	Zoea-Megalopa, 28 C, 34 ppt, animals from Florida (Gore 1972).
Maximum Duration	24	Zoea-Megalopa, 28 C, 34 ppt, animals from Florida (Gore 1972).
Minimum Width (mm)	3	For reproductive females, SC (Knott and King undated)
Maximum Width (mm)	14	Knott and King undated
Broad Temperature Range	None	Warm temperate-Tropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

Petrolisthes armatus has reached extraordinary abundances (up to 20,000-30,000 crabs per m²) in Georgia and South Carolina since its invasion of the southern US Atlantic coast (Knott et al. 2000; Hollebone and Hay 2007a). Experimental and field studies in Georgia have shown a wide range of ecological impacts, including decreasing recruitment of native crabs through competition, suppression of phytoplankton blooms, and promotion of macroalgae abundance, through filter-feeding and altering feeding patterns of predators. High abundances of P. armatus on oyster reefs in Georgia increased recruitment of Oyster Drills (Urosalpinx cinerea), due to switching of predation by mud crabs Panopeus herbstii to P. armatus, decreasing predation on the oyster drills (Hollebone and Hay 2008).

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Regional Impacts

CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Competition
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus suppressed recruitment of oysters and mud crabs (Panopeus herbstii) (Hollebone and Hay 2008).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Food/Prey
In Georgia estuaries, where Petrolisthes armatus is very abundant, P. armatus was readily consumed by native fishes and the native crabs Callinectes sapidus and Panopeus herbstii in tethering experiments (Hollebone and Hay 2008).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Habitat Change
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus promoted macroalgal growth (Ulva spp.) (Hollebone and Hay 2008).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Herbivory
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus suppressed a phytoplankton bloom, through filter-feeding (Hollebone and Hay 2008).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Trophic Cascade
In oyster reefs in Georgia, high abundances of Petrolisthes armatus increased recruitment of Oyster Drills (Urosalpinx cinerea), due to switching of predation by mud crabs Panopeus herbstii to P. armatus, decreasing predation on the oyster drills (Hollebone and Hay 2008).
S130	Ossabaw Sound		Ecological Impact	Competition
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus suppressed recruitment of oysters and mud crabs (Panopeus herbstii) (Hollebone and Hay 2008).
S130	Ossabaw Sound		Ecological Impact	Food/Prey
In Georgia estuaries, where Petrolisthes armatus is very abundant, P. armatus was readily consumed by native fishes and the native crabs Callinectes sapidus and Panopeus herbstii in tethering experiments (Hollebone and Hay 2008).
S130	Ossabaw Sound		Ecological Impact	Habitat Change
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus promoted macroalgal growth (Ulva spp.) (Hollebone and Hay 2008).
S130	Ossabaw Sound		Ecological Impact	Herbivory
In mesocosm experiments conducted in Georgia, high abundances of Petrolisthes armatus suppressed a phytoplankton bloom, through filter-feeding (Hollebone and Hay 2008).
S130	Ossabaw Sound		Ecological Impact	Trophic Cascade
In oyster reefs in Georgia, high abundances of Petrolisthes armatus increased recruitment of Oyster Drills (Urosalpinx cinerea), due to switching of predation by mud crabs Panopeus herbstii to P. armatus, decreasing predation on the oyster drills (Hollebone and Hay 2008). High abundances of P. armatus also influenced the effects of mud crabs on Hard Clam (Mercenaria mercenaria behavior. In experiments, the absence of P. armatus, clams reduced their filtering in the presence of mud crabs. When P. armatus, was abundant, clam filtering rates were not reduced. Howver, P. armatus did not significantly affect overall filtering rates, either by their own filtering, or by effects on mud crabs or oysters (Byers et al. 2014).

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