Marine Invertebrates of Bermuda Green Porcelain Crab (Petrolisthes armatus) By Dawn Simmons and James B. Wood (Ed) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Green Porcelain Crab, Petrolisthes armatus Image by Rebecca Karis
Abstract


Petrolisthes armatus is an invasive species of crab that has been found in many areas of the Atlantic and Pacific oceans including Georgia, South Carolina, the Mississippi, Bermuda, the Gulf of California, the West Indies, and West Africa. They are thought to be a native species of Brazil and are often engaged in a symbiotic relationship with sponges and other current-manipulating invertebrates. P. armatus filter feeds by using its large mouthparts to strain plankton and other particles from the water. They have had negative effects on commerical oyster fisheries because they reproduce rapidly and compete with the filter feeding mollusks for food and space. Recent research is being done to determine what adaptations P. armatus has that allows it to be such a successful invader as well as other adaptations that it uses to thrive in the intertidal environment.

Taxonomy


Phylum: Arthropoda
  Class: Malacostraca
    Order: Decapoda
      Family: Porcellanidae

Petrolisthes armatus is a member of the phylum Arthropoda because it has jointed and articulated appendages, a chitinous exoskeleton, and exhibits tagmatization. It belongs to the class Malacostraca because it has a head with 5 pairs of appendages (2 pairs being antennae), and a nauplius larvae. It belongs to the order Decapoda because it has 10 legs and is a member of the family Porcellanidae because it is very fragile and loses its appendages as a form of defense.

Habitat


Petrolisthes armatus is a filter feeding crab that is commonly found in shallow intertidal and subtidal areas throughout the Atlantic and Pacific oceans as well as mangrove habitats and coral reefs (Baeza, 2007). It has invaded the United States in Georgia, South Carolina, and the Mississippi as well as many other places in the world including West Africa, Bermuda, the Bahamas, the West Indies, the Caribbean, the Gulf of Mexico, and the Gulf of California. Because this crab filters plankton from the water column, it can be found utilizing the flow of sponges to assist it in obtaining its dietary requirements (Baeza, 2007). It can also be found in rubble areas as well as in oyster beds and other areas where there are an abundance of filter feeders (Lohrer, 2001).



Ecology


Petrolisthes armatus can reach a carapace length of up to 8mm as an adult but some have been known to grow to about 10mm (Boudreaux et al, 2006). They range in color from brown to green to speckled brown in juveniles and have blue mouthparts that are characteristic of porcelain crabs. Some specimens have also been found to be bright blue in color. P. armatus is not considered to be a "true crab" but rather a relative of the squat lobster that displays carcinisation, in which a non-crab-like animal evolves into a crab-like animal. It has 3 walking legs, long antennae that are positioned on the outside of the eyestalkes, and there is no carpal segment on the chelipeds.

P. armatus reproduces sexually. As with most crabs, the females hold the fertilized eggs between the flap of the abdomen. They can begin reproduction when they are as small as 3mm and reproduce rapidly in warmer temperatures (Hollebone and Hay, 2007). In Brazil, the sex ratios of males to females is about 1.05:1, and the population in Georgia maintained a 1:1 ratio despite variations in tidal heights and temporal location (Oliveira and Masunari, 1995; Hollebone and Hay, 2007)

P. armatus is a symbiotic filter feeder that depends on areas of high current for survival (Baeza, 2007). Most of the species within the genus Petrolisthes engage in either a free-living symbiosis or an obligatory symbiosis (Baeza, 2007). P. armatus tends to engage in a symbiotic relationship with other invertebrates, but the extent of the symbiosis varies among life stages (Baeza, 2007). The large mouthparts contain long hairs that strain the water for food particles. Smaller mouthparts then remove the particles from the hairs and move them to the mouth. This particular species has been known to utilize the water flow created by sponges in order to feed, possibly using the sponge as shelter to escape predation as well (Baeza, 2007).

P. armatus is believed to be a native crab of Brazil and is rapidly invading areas such as Georgia, South Carolina, and the Mississippi (Hartman and Stancyk, 2001). According to Hollebone and Hay (2007), the crabs have established themselves in high densities throughout the South Atlantic Bight in Georgia and are having a large impact on oyster reef communities. In some esturaries in Georgia, P. armatus densities were estimated to be in the thousands during warmer months of the year due to rapid reproduction rates (Hollebone and Hay, 2007). The crabs have been able to establish a year-round population, declining in colder months and growing in larger numbers in the warmer months (Hollebone and Hay, 2007).

According to Hollebone and Hay (2007), P. armatus is highly susceptible to dessication and thermal stressors due to their relativly small size. They tend to remain low in the intertidal zone and move lower during low tide (Hollebone and Hay, 2007). Because P. armatus are filter feeders, they don't tend to interfere with native crab populations and have been a food source for the native mud crabs under laboratory conditions (Hollebone and Hay, 2007). P. armatus is also considered euryhaline, and has the ability to adapt to a wide variety of salinity regimes; changes in salinity do not tend to determine P. armatus distribution because it can live in salinities ranging from 6.7 to 31.5% (Hollebone and Hay, 2007; Oliveira and Masunari, 1995).

Recent Research


Recent research of Petrolisthes armatus includes studies of growing population sizes, phylogeny, and adaptive features of the crabs themselves that allow them to live in the intertidal environment. Research also focuses on possible reasons as to why Porcelain crabs are invading so rapidly. Micheletti-Flores and Negreiros-Fransozo (1999), found that seasonal variations affected population densities of P. armatus . Densities are also increasing in certain areas suggesting that the crabs have a higher tolerance against changes in salinity (Micheletti-Flores and Negreiros-Fransozo, 1999). Population studies conducted by Hollebone and Hay (2007) suggest that populations of P. armatus are increasing at a rapid rate and have the potential to impact many communities such as fisheries and defense mechanisms of other organisms. In this particular study, mean densities were recorded as 11200 crabs per meter to the -2 which was the highest density recorded throughout the crabs recorded history (Hollebone and Hay, 2007).

Another study was performed by Stillman (1999) in which respiratory structures seen in the walking legs of P. armatus were studied to understand aerial respiration and how this adaptation may have evolved in Porcelain crabs. Stillman (1999) concluded that the ancestral relationship of this trait may have been large leg membranes which would serve as a means to accomodate an increased metabolism. In a study conducted by Stillman and Somero (2001), thermal stability of Porcelain crabs was examined by testing the efficiency of the enzyme LDH, or lactate dehydrogenase, to withstand high temperatures before it denatured. LDH is an enzyme that catalyzes the conversion of lactate to pyruvate and is needed in energy production of cells (Stillman, 1999). It was found that the temperature that was needed to denature the LDH (Lactate Dehydrogenase) within 10 minutes was 79 degrees Celsius, suggesting that Porcelain crabs have a high tolerance to thermal variations as well. Both of these adaptations, thermal and saline tolerance, contribute to the Porcelain crab's ability to invade.

Commercial Importance


Although Petrolisthes armatus has no direct commerical importance, it is a species that can have devastating effects on the commercial oyster beds that it lives abundantly in. In a study conducted by Hollebone and Hay (2003), oysters were able to settle easily in locations where there were no crabs and oyster recruitment was very low where P. armatus was present. Studies suggest that the effects of a growing populations of P. armatus on oyster beds can be detrimental to the oyster harvesting industry.

Bermuda Laws


No Bermuda laws were found that pertained to Petrolisthes armatus .

Personal Interest


Decapods have always been of interest to me partially due to the fact that I was raised in Rhode Island where intertidal areas are abundant and highly fascinating. I was very disappointed upon arriving in Bermuda and seeing a lack of crustaceans scurrying around amongst the rocks and crevices and it made me miss my home much more intensely. I knew I wasn't going to be doing my final research project on decapods since I fell in love with opisthobranchs during my stay here, but I still had the desire to see which crabs lived on Bermuda's shores.

During "worm week," when we spend an entire week learning about annelids and other vermiform organisms, we took a truck trip to the St. David's mudflats. This trip was initially designated to the collecting of various polychaetes and flatworms, but it was there that I saw an abundance of decapods, with one in particular catching my interest. I was quite excited to be turning over rocks and seeing large amounts of small crabs scurrying away. Most were brown and all were the same species: Petrolisthes armatus . This species of crab was not anything special to me, at first, since they looked like any other crab, if not slightly more ordinary. And then, soon after I found the brown specimens, I turned over a large rock and found a bright blue specimen. At first I was taken back, thinking that the blue I saw could not have possibly been a living organism, but rather a piece of trash from someone's candy wrapper, or aluminum can. As I looked closely at it, the bright blue moved frantically to hide and I saw the very distinct claws that are characteristic of P. armatus and realized that this beautiful and striking crab was not only a crab, but the same species as the ordinary brown ones.

Many crabs that inhabit the coastal intertidal zone are invasive species to that area and these crabs were no different. I soon realized that these crabs were a highly invasive species that originated in Brazil and had migrated throughout the world. As I began my research, I was interested to find out that this crab was also a filter feeder and did not use its large claws for catching prey. When a specimen was harrassed, it would release its claw or claws as a form of defense. I noticed while we were collecting worms that there seemed to be a great deal of claws being lost which I thought was because the crabs were small and delicate but in fact, this wasn't so. I was disappointed to see that the majority of the species are brown in color and not the beautiful blue that I had found. I was surprised to find so little information on recent research that is being done as well as a lack of commercial importance give their large abundance in certain areas.

References


Baeza, J. Antonio. 2007. The origins of symbiosis as a lifestyle in marine crabs (genus Petrolisthes armatus ) from the eatern Pacific: Does interspecific competition play a role? Revista de Biologia Marinia y Oceanografia . Vol. 42: 7-21.

Boudreaux, M.L., Stiner, J.L., and Walters, L.J. 2006. Biodiversity of sessile and motile macrofauna on intertidal oyster reefs in Mosquito Lagoon, Florida. Journal of Shellfisheries Research . Vol. 25: 1079-1089.

Hartman, M.J., Stancyk, S.E., and Lohrer, A.M. 2001. An invasive crab, Petrolisthes armatus , as alternative prey in an oyster reed ecosystem. 16th Biennial Conference of the Estuarine Research Federation, November 4-8, 2001. St. Petersburg Beach, FL.

Hollebone, A.L. and Hay, M.E. 2003. An invasive crab in the South Atlantic Bight; Friend or Foe? Third International Conference on Bioinvasions. March 16-19, 2003, La Jolla, CA .

Hollebone, A.L and Hay, M.E. 2007. Population dynamics of the non-native crab Petrolisthes armatus invading the South Atlantic Bight at densities of thousands m^-2. Marine Ecology Progress Series . Vol. 336: 211-223.

Lohrer, A.M. 2001. The threat of invasion in South Carolina estuaries: A focus of exotic decapod crabs. 16th Biennial Conference of the Estuarine Research Federation, November 4-8, 2001. St. Petersburg Beach, FL.

Micheletti-Flores, C.V. and Negreiros-Fransozo, M.L. 1999. Porcellanid crabs (Crustacea, Decapoda) inhabiting sand reefs built by Phragmatopoma lapidosa (Polychaeta sabellariidae) at Paranatua Beach, Sao Vicente, Sp, Brazil. Revista Brazilia de Biologia . Vol. 59 (1).

Oliveira, E. and Masunari, S. 1995. Estrutura populacional de Petrolisthes armatus (Gibbes) (Decapoda, Anomura, Porcellanidae) da Ilha do Farol, Matinhos, Parana, Brasil. Revista Brasilia Zoologica . Vol. 12: 355-371.

Stillman, J.H. 2000. Evolutionary history and adaptive significance of respiratory structures on the legs of intertidal Porcelain crabs, genus Petrolisthes . Physiological and Biochemical Zoology . Vol. 73: 86-96.

Stillman, J.H. and Somero, G.N. 2001. A comparative analysis of the evolutionary patterning and mechanistic bases of Lactate Dehydrogenase thermal stability in Porcelain crabs, genus Petrolisthes . The Journal of Experimental Biology . Vol. 204: 767-776.

Links

Petrolisthes armatus at the Smithsonian Marine Station at Fort Pierce
Porcelain Crabs at the Monterey Bay Aquarium: Online Field Guide
Porcelain Crabs