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Asian & European Invasive Crab Species of Cape Cod Research Paper

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Updated: May 2nd, 2022

Introduction to Cape Cod

Nature and science have provided us with some of the best and most beautiful sceneries on the face of the earth. People are always fascinated by the complex features that are to be found on the surface of the earth since ancient times. Cape Cod is one such feature that nature has given mankind. The feature is to be found on the shores of the Atlantic Ocean.

The cape stretches for approximately 60 miles into the Atlantic Ocean. The feature takes up an area of about 44, 600 acres of land made up of different ecosystems which are home to different species of organisms. The ecosystem around Cape Cod is characterized by among others robust marine life, an estuarine, inlets where freshwater from the hinterland comes into contact with saltwater from the ocean and terrestrial land among other features.

The ecosystem is unique in the world as it forms the habitat for different organisms that attract tourists from all over the world as well as scientific studies. Cape Cod is characterized by ever-changing geomorphic actions giving it distinct scenery which is unique and which favors the life of different aquatic and non-aquatic organisms.

The change can be attributed to various phenomena such as the rise and fall of tidal waves which shape the surrounding environment forming a very distinct ecosystem. Cape Cod’s freshwater ecosystem consists of kettle ponds, swamps and such other features. The terrestrial ecosystem is unique and plays host to different species that draw attention from different parts of the world.

Invasive Species in Cape Cod

As already indicated earlier in this paper, Cape Cod is inhabited by different organisms representing different species. Some of these species are invasive while others are not. In this section, the author will dwell on the invasive species of Cape Cod.

Asian Shore Crab and European Green Crab


There are several invasive species that are to be found in the Cape Cod ecosystem. Some of them have caused a lot of havoc in the area. The species include the Asian Shore Crab and the European Green Crab. They are scientifically referred to as Hemigraspus sanguineus and Carcinus maenas respectively. They are considered to be among the 100 most invasive species in the world (Cohen and Carlton 230).

The Asian Shore Crab (Hemigraspus sanguineus)


The species has three teeth or spines that are triangular in shape and which are located on either side of the body. These organs are used for feeding. The species has a carapace that gives the body a rigid structure which is strong and massive. It is on this rigid structure where all parts of the body are attached.

The carapace is hard with different colors ranging from green, red, and purple and in some cases brown. Scientists have examined the variations in color and they have concluded that the differences are genetic. They are also brought about by different environments within which the species thrives (Yamada and Hauck 907).

The males can be differentiated from the females given that they have pincers with fleshy, bulb-like features. They are less active as compared to the female crabs. Their sizes are smaller ranging between 35 and 42 millimeters of carapace width. They are smaller than their European Green crab counterparts (Bourdeau and O’Connor 320).

Hemigraspus Sanguineus: Habitat

The species dominates the shallow waters with hard bottoms. It thrives well in intertidal as well as the sub tidal areas. It thrives in rock crevices and it usually populates areas where certain organisms cannot survive. Artificial substrates can also serve as a good environment for this species. Saline environment is not a threat to these organisms as they can venture into moderate and high salinity waters. The crabs are adapted to different range of temperature and that is why they have successfully invaded different coasts in the world. This trait enables them to travel long distances without being affected negatively by the change in environment (Bourdeau and O’Connor 324).

Having discussed the characteristics as well as the features of this species, the author will now focus on its invasion history. Here the author will discuss how the species spread from its native location to Cape Cod which is the reference location for this paper. Its consequences in the area will also be put into perspective.

Invasion History

The species was discovered in the western part of the Pacific Ocean in 1817. The native location for the species is thought to be Russian, Japanese, Korean and Chinese coasts. In 1988, the species was sighted in New Jersey in the United States of America through ballast water that was ejected from the ships being cleaned. A few decades later, the species was found in abundance on the coast of the Atlantic Ocean where Cape Code is located (Lohrer and Whitlatch 209)

The species was estimated to move at an average speed of 750 kilometers in ten years. As a result of its invasive nature, it is a threat to the ecosystem. Efforts have been made to stop or minimize its distribution in the world’s coasts. Cape Cod is one of the world’s coasts with a unique ecosystem hosting different and equally unique organisms. But with the invasion of the species, the organisms are moving away (Lohrer and Whitlatch 212). At this juncture, it is important to discuss the impacts of the species in the Cape Cod ecosystem.

Impacts of the Invasion

The species has a great impact on the ecosystem. It is noted that Hemigraspus Sanguineus is omnivorous as it feeds on quite a number of organisms and plants creating competition and stress in the available food web. Due to the wide range of foods forming part of its diet, the food web is altered and the environment niche changes significantly posing a danger to the other organisms. The Asian Crab feeds on other crabs such as the Rock Crab scientifically known as the Cancer irroratus.

The Asian species has also been identified as the most dangerous species as compared to the European crab since in spite of its relatively small size, it can feed on the European Green crab (Ledesma and O’Connor 66).

Other organisms found in the ecosystem (such as oysters and lobsters) are being affected since the Asian crabs feed on them. When food is scarce, the invasive species preys on the few remaining organisms creating an imbalance in the ecosystem (Ledesma and O’Connor 69).

The species dominates almost all the habitats occupied by the other organisms. For example the mud crab’s habitat is invaded by this species which preys on these organisms. The great impact is as a result of direct predation that gives the species an advantage over the others. This is seen when the species effectively competes with other large organisms in the ecosystem (organisms such as the blue and rock crabs) without exhausting its food. This is given that almost the entire ecosystem provides a preying ground for the species (McDermott 325).

Statistics show that native organisms especially the shore crabs are decreasing in number while the population of the invasive species is rising. This is a threat to the Cape Cod ecosystem as the environment is prone to changes from the current state to one that may not support the organisms that completes it (McDermott 327).

For the past few years, the marsh grassland has decreased as large swathes of marshland are mysteriously disappearing leaving behind a muddy bare land. It has been noted that the Asian crabs are the cause of this menace. Many aquatic animals breed in the marshland and this supports future generations. However the invasive species are feeding on the young organisms which make reproduction among aquatic animals difficult. Such impacts have raised concerns in some governmental departments such as the Fish and Wildlife Departments. The authorities in Cape Cod have made efforts to control the situation (McDermott 233).

Control of the Asian Crab

Some short term measures were taken to control the situation. Some of the measures are analyzed in subsequent sections of the paper.

Departments were formed to monitor the presence of the Asian crab along the entire coast. Guidelines have been put in place such that if anyone spots the Asian crab (including tourists) they are advised to report to the authorities who will take action and get rid of the organism. In addition to this, the species has been declared harmful to the ecosystem and a law has been enacted to proscribe the possession of an Asian crab. Local tourists are being educated on the danger of the species and how to curb the menace (Lohrer and Whitlatch 215).

Laws have also been enacted to check the spread of the species by prohibiting people from carrying shells around and any such things that may transport the species from one place to the other. These were thought to be some of the practices encouraging the spread of the species.

The Green Crab (Carcinus Maenas)


Another invasive crab species in the region is the European Green Crab. It is believed to have originated from Europe in the Atlantic coasts and also from the Northern parts of Africa. It is known under different names around the world and it is recognized as one of the most dangerous and invasive species. It is scientifically known as the Carcinus maenas (Jare and Rock 49).


The organism acquires different colors as it undergoes molting. The color is not necessarily green but it ranges from red to orange depending on the stage of molting. Unlike the Asian Crab, the European Green Crab has five spines on every side of the body which makes it larger than the Asian species. Its size ranges from 65mm to 80mm with extremely flat legs (Greccon 259)

The crab has been noted to be a great forager as it has the capability of adopting different styles to capture food. Its diet is made up of a wide range of foods that gives it an advantage over other organisms in the ecosystem. It has a bivalve shell that can take different shapes which enables it to capture different types of foods in different ways (Greccon 261).

The species is an omnivorous feeding on different types of food that include many aquatic organisms such as oysters, mussels and even juvenile crabs making reproduction among other aquatic life difficult (Jare and Rock 48).


The species dominates different kinds of environments ranging from rocky and flat shores. The European Green crab also thrives in the tidal marshes and the changing environment conditions is not a threat to it. The organisms can tolerate different levels of salinity ranging from low to high (4 to 52 range of salinity). A wide range of temperature (including temperatures below the freezing point) favors the organism (Grosholz and Ruiz 49).

Invasion History

The species originated from Europe and has invaded many coasts around the world. In 1817, the species found its way into the United States (in New Jersey and New York) and it has expanded to other coasts in the world. Like the Asian crab, the species is also estimated to travel at a speed of 750 kilometers in ten years. It has also reached the South African (Cohen and Carlton 235).

Impact of the European Green Crab

This organism is a voracious predator since it can feed on a wide range of organisms in the ecosystem. Various species living in the ecosystem risk being wiped out by this organism. Since its arrival in Cape Cod, it has been noted that native organisms have decreased at a very high rate. For example the shore crab has reduced in number after the European green crab showed up in the ecosystem (Jare and Rock 49).

Different feeding habits as well as the ability to tolerate different environments has given the species an upper hand. It preys on almost all species in the ecosystem. This inhibits the growth of other organisms suppressing their distribution in the ecosystem (Grosholz and Ruiz 63)

Management and Control

Different strategies have been adopted in attempts to control and manage this invasive species. Like in the case of the Asian crab, there is regular monitoring to manage the spread of this organism.

Rules have been put in place to regulate individuals carrying equipments around the shoreline since this can transport the species from one place to the other. This is for example moving shells along the shoreline. Ships which are believed to be the major transporters of crabs along the coast are inspected thoroughly to make sure that they do not introduce ballast carrying crabs into the Cape Cod coast (Bedini 710).

Another effective method to manage and control the menace is through the introduction of another parasite feeding on this invasive crab. The Sacculina carcini has been tested and found to suppress this organism at different stages. This is for example by feeding on the molting crab and even altering the development of the males. This method is effective but scientists are still assessing its impact on the ecosystem before introducing the parasites (Bedini 709).


Different species are important in any given ecosystem. They create a natural balance that is needed to sustain the ecosystem. Using emerging scientific knowledge, invasive species can be controlled effectively without affecting the others in the ecosystem. This is for example through the introduction of parasites. It is important to monitor the invasion rate and respond appropriately to protect native species.

Works Cited

Bedini, Brian. “Color Change and Mimicry from Juvenile to Adult: Carcinus Maenas.”Crustaceana 75.5 (2008): 703–710. Print.

Bourdeau, Paul and O’Connor, John. “Predation by the Nonindigenous Asian Shore Crab Hemigrapsus sanguineus on Macroalgae and Molluscs.” Northeastern Naturalist 10.2 (2010): 319-334. Print.

Cohen, Andrew and Carlton, Jerald. “Introduction, Dispersal and Potential Impacts of the Green Crabs in San Francisco Bay, California.” Marine Biology 122.2 (2011): 225–237. Print.

Greccon, Jensen. “East Meets West: Competitive Interactions between Green Crab Carcinus Maenas and Native and Introduced Shore Crab Hemigrapsus spp.” Marine Ecology Progress Series 225.6 (2008): 251-262. Print.

Grosholz, Edwin and Ruiz, Michael. “Predicting the Impact of Introduced Marine Species: Lessons from the Multiple Invasions of the European Green Crab Carcinus Maenas.Biological Conservation 78.12 (2009): 59–66. Print.

Jare, Brian and Rock, Fernandes. “Patterns of Morphological and Genetic Variability and Populations of the Shore Crab: Carcinus Maenas.Journal of the Experimental Marine Biology 329.1 (2005): 47–54. Print.

Ledesma, Ellison and O’Connor, John. “Habitat and diet of the Non-native Crab Hemigrapsus sanguineus in Southeastern New England.” Northeastern Naturalist 8.3 (2009): 63-78. Print.

Lohrer, Allan and Whitlatch, James. “Structural Complexity and Verticalzonation of Intertidal Crabs with Focus on Habitat Requirements of the Invasive Asian Shore Crab Hemigrapsus Sanguineus.” Journal of Experimental Marine Biology and Ecology 244.17 (2011): 203–217. Print.

McDermott, Jackson. “A Breeding Population of the Western Pacific Crab Hemigrapsus.” Journal of Experimental Marine Biology and Ecology 12.2 (2003): 23-24.

Yamada, Susan and Hauck, Luke. “Field Identification of the European Green Crab Species Carcinus Maenas.” Journal of Selfish Research 20.3 (2010): 905–909. Print.

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