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Profile: Crabs

Assessment full text: 

Estuaries, bays, and other Massachusetts coastal habitats are home to a variety of both native and non-native crab species.
Native crab species include:

  • Blue crabs
  • Cancer crabs (Jonah and Rock crab)
  • Purple marsh crabs
  • Fiddler crabs*

Non-native invasive species include:

  • Green crabs (introduced from Europe and Africa)
  • Asian shore crabs (introduced from Asia)

Although these species are different, they all require beach and marsh habitats for survival. Their distribution, therefore, is highly dependent on the availability of suitable habitat. Crabs live in close proximity to coastlines and are key organisms for connecting aquatic and terrestrial ecosystems.
Crabs are an important part of coastal ecosystems and economies. In 2013, crabs were the second most valuable fishery in the U.S., with commercial landings of approximately $700,000 (second only to salmon) 14. Blue crabs make up a majority of commercial catches and are recognized as the most important crab fishery in the U.S. 10.
Crabs are also important prey resources for many coastal species, including migratory birds, fish, and terrestrial and marine mammals.

* Note that fiddler crabs have not been historically found in Massachusetts, but have expanded their range northward due to climate change.

Native Crabs

  • Blue Crab: Blue crabs occupy coastal waters from Massachusetts Bay south to the eastern coast of South America, including the Gulf of Mexico 10. Occasionally, blue crabs have been found as far north as Maine and Nova Scotia 10. They primarily occur in bays and estuaries and feed on plankton, small invertebrates, fish, and other crabs. Blue crabs mate in upper estuaries (the area farthest from the sea) and areas of low salinity during early spring to winter 10. After mating, females bury and overwinter in the mud at the mouths of bays. When waters warm in spring, females produce egg masses that they carry on their abdomen (underside of shell). Adult blue crabs typically migrate inshore to bays and upper estuaries in the summer months, and out to more saline coastal waters in the winter. Blue crabs can live up to about 3 years in age 10.
  • Cancer Crab: Cancer crabs range from Nova Scotia in Canada down to Florida along the eastern U.S. coast 18. Rock and Jonah crabs, subspecies of Cancer crabs, are harvested in coastal habitats along the eastern US 8. These and other cancer crabs are found in habitats spanning tidal waters to the continental shelf slope, with conditions that vary across a wide range of temperatures and bottom types (rocky to sandy environments). Females spawn between April and October and early life stages are moved towards the shore by wind and tides.
  • Purple Marsh Crab: In Massachusetts, purple crab populations have risen to high levels likely because of a reduction in their predators such as striped bass due to overfishing 1. Purple crabs eat marsh plants, and the crabs’ high abundance has thus led to a decrease in coastal vegetation in some areas, leaving the areas more vulnerable to erosion 15,21.
  • Fiddler Crabs: Fiddler crabs are native to the U.S. Atlantic coast, but have not been observed in Massachusetts waters until recently; they are now found in coastal New Hampshire and Massachusetts. Fiddler crabs represent a species that is benefiting from warming ocean temperatures and expanding their range northward 11. A diversity of other marine (as well as terrestrial and aquatic) species are expected to move into Massachusetts as they respond to climate change and follow optimal conditions.

Non-native Invasive Crabs

  • Green Crabs: Green crabs are native to coastal waters of Europe and Africa 16. Invasive European green crabs were first documented along the Atlantic coast of the U.S. in 1817, but not until 1989 on the Pacific coast 7,16. Currently, green crabs reside in coastal habitats along the eastern U.S. from the Chesapeake Bay to Nova Scotia and feed on a wide range of mollusks, clams, mussels, and other bivalves (species with two shells hinged together) 20. They live in a variety of ecosystems, ranging from rocky to sandy bottom habitats, and have been associated with other invasive species, such as the plant- smooth cordgrass. Green crabs are a nuisance in many areas to shellfish fisheries due to predation on clams, mussels, and other bivalves 7,20. Green crabs can tolerate a wide range of salinities, which, like other invasive species, allows them to infiltrate a diversity of habitats and areas, often outcompeting native species 3,5,7.
  • Asian Shore Crabs: Asian shore crabs were first discovered in eastern U.S. in New Jersey in 1988, and have since spread as far south as North Carolina and as far north as Maine 23. In many areas, Asian shore crabs are more abundant than all the native crabs combined 3. Non-native Asian shore crabs are generalists, feeding on mussels, snails, and algae 3. The abundance of Asian shore crabs has increased in Massachusetts in recent years with simultaneous decreases in green crab and blue mussel populations 2. Asian shore crabs directly consume and outcompete native crab species, contributing to their declines. This is just one example of the negative impacts invasive species can have on native species.

Climate Impacts
Crabs are vulnerable to various aspects of climate change because they rely on salt marsh and beach habitats for survival, which are highly vulnerable to the impacts of sea level rise, storms, increased sea and air temperatures, and altered salinity 13,22. Crabs are benthic (live on the bottom of coastal habitats) and bury themselves in the sediment for protection and overwintering. Therefore, climate-induced changes in water quality and sediments affect crabs. For example, the combination of increasing temperature, precipitation, and terrestrial runoff alters shallow and bottom habitats that crabs use. Seasonal changes in these factors may disrupt crab populations, and changes in sediment distribution can lead to higher mortality (especially for eggs, which are vulnerable to suffocation in stagnant water) 10.

Projected increases in temperature and changes in salinity will also impact crab populations, particularly during early life stages. Larval crab development has already been shown to vary with both these factors 4,19. However, crab populations may benefit from some climate changes. Overwinter crab mortality is highest in colder areas of estuaries and lowest during mild winters 19; spawning season duration is also reduced by long periods of cold temperatures 6. Therefore, warming temperatures, particularly during winter and spawning seasons, could lead to increased survival. Unfortunately, non-native invasive species typically respond faster and have a greater ability to take advantage of improved conditions and may out-compete native species as these changes occur.

Similar to fiddler crabs, blue crabs have also begun to expand their range northward to coastal Massachusetts, New Hampshire, Maine, and even Nova Scotia 12. The combination of increasing temperatures and ocean acidification, however, has generally been found to have negative impacts on crustaceans 9. In addition, crabs are highly vulnerable to parasites, which are expected to become more widespread with additional climate change impacts. Crab vulnerability to climate change and the resulting changes in crab populations is expected to affect the ecology and economy of Massachusetts.

Assessment reference label: 
Assessment reference text: 

1. Altieri, A.H., M.D. Bertness, T.C. Coverdale, N.C. Herrmann, C. Angelini. 2012. A trophic cascade triggers collapse of a salt-marsh ecosystem with intensive recreational fishing. Ecology 93:1402–1410

2. Bloch, C.P., K.D. Curry, and J.C. Jahoda. 2015. Long-term Effects of an invasive Shore Crab on Cape Cod, Massachusetts. Northeast Naturalist 22:178-191.

3. Bourdeau, P.E., and N.J. O’Connor. 2003. Predation by the Nonindigenous Asian Shore Crab Hemigrapsus Sanguineus on Macroalgae and Molluscs. Northeast Naturalist 10:319-334.

4. Costlow, J.D., Jr., and C. G. Bookhout. 1959. The larval development of Callinectes sapidus Rathbun reared in the laboratory. Biol. Bull. (Woods Hole) 116:373-396.

5. Crothers, J.H. 1967. The biology of the shore crab Carcinus maenas (L.). I. The background: anatomy, growth and life history. Field Studies 2:407–434.

6. Daugherty, F.M., Jr. 1952. The blue crab investigation, 1949-1950. Tex. J. Sci. 4:77-84.

7. Grosholz, E., S. Lovell, E. Besedin, and M. Katz. 2011. Modeling the impacts of the European green crab on commercial shellfisheries. Ecological Applications 21:915-924.

8. Hare J.A., W.E. Morrison, M.W. Nelson, N.M. Stachura, E.J. Teeters, R.B Griffis, et al. 2016. A Vulnerability Assessment of Fish and Invertebrates to Climate Change on the Northeast U.S. Continental Shelf. PLoS ONE 11: e0146756. doi:10.1371/ journal.pone.0146756

9. Harvey, B.P., D. Gwynn-Jones, and P.J. Moore. 2013. Meta-analysis reveals complex marine biological responses to the interactive effects of ocean acidification and warming. Ecology and Evolution 3:1016-1030.

10. Hill, J., D.L. Fowler, and M.J. Van Den Avyle. 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic)-Blue crab. U.S. Fish Wildl. Serv. Biol. Rep. 82(11.100). U.S. Army Corps of Engineers, TR EL-82-4. 18 pp.

11. Johnson, S.D. 2014. Fiddler on the roof: a northern range extension for the marsh fiddler crab Uca pugnax. Journal of Crustacean Biology 34: 671 DOI:10.1163/1937240X-00002268

12. Johnson, D.S. 2015.The savory swimmer swims north: a northern range extension of the blue crab Callinectes sapidus? J Crust Biol. 35:105-110. DOI: 10.1163/1937240X-00002293

13. MA CCVA: Manomet Center for Conservation Science (Manomet) and Massachusetts Division of Fisheries and Wildlife (MA DFW). 2010. Climate change and Massachusetts fish and wildlife: Volume 2 habitat.

14. National Marine Fisheries Service (NMFS). 2013. Fisheries and the United States. Current Fishery Statistics No. 2013, Silver Spring, MD. pp. 129.

15. National Park Service (NPS). Cape Cod National Seashore: Crab driven vegetation losses. Accessed 06/08/2016.

16. Perry, H. 2016a. Carcinus maenas. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Revision Date: 9/13/2011

17. Harriet Perry. 2016b. Rhithropanopeus harrisii. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Revision Date: 9/14/2011

18. Robichaud, D.A., C. Frail. 2006. Development of Jonah crab, Cancer borealis, and rock crab, Cancer irroratus, fisheries in the Bay of Fundy (LFAs 35-38) and off southwest Nova Scotia (LFA 34): from exploratory to commercial status (1995-2004). Can Manuscr Rep Fish Aquat Sci. 2775: 48 pp.

19. Rome, M.S., A.C. Young-Williams, G.R. Davis, and A.H. Hines. 2005. Linking temperature and salinity tolerance to winter mortality of Chesapeake Bay blue crabs (Callinectes sapidus). J Exp Mar Biol Ecol.  319:129-145. DOI: 10.1016/j.jembe.2004.06.014

20. Ropes, J. W. 1969. The feeding habits of the green crab, Carcinus maenas (L.). Fishery Bulletin 67:183–203.

21. Smith, S.M., M.C. Tyrell, and M. Congretel. 2013. Palatability of salt marsh forbs and grasses to the purple marsh crab (Sesarma reticulatum) and the potential for re-vegetation of herbivory-induced salt marsh dieback areas in cape cod (Massachusetts, USA). Wetlands Ecol Manage 21:263-275.

22. Whitman, A., A. Cutko, P. De Maynadier, S. Walker, B. Vickery, S. Stockwell, and R. Houston. 2013. Climate change and biodiversity in Maine: vulnerability of habitats and priority species. Report SEI-2013-03. Manomet Center for Conservation Sciences (in collaboration with Maine Beginning with Habitat Climate Change Working Group), Brunswick, ME.

23. Williams, A.B., and J.J. McDermott. 1990. An eastern United States record for the western Indo-Pacific crab Hemigrapsus sanguineus (Crustacea: Decapoda: Grapsidae). Proceedings of the Biological Society of Washington 103:108-109.

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