European green crab’s parasite

April 16, 2010

The European green crab (Carcinus maenas) poses a devastating problem to the ecosystem and fish economy on both the east and west coasts of the United States. It out-competes many local crab species for food resources, and as a result, reduces the local shellfish population that is crucial for the economy and ecosystem. There are currently many speculations of how the European green crab can be contained, but none of which have been empirically proven to be effective.

Jenna Barbee of Duke University proposes using Sacculina carcini, a parasitic barnacle, to control the green crab population. S. carcini prevents the green crab from developing reproductive organs, and ultimately kills the host organism. The parasite has been demonstrated to be relatively host-specific, in that it only targets a specific set of species of crab, which allows it to be a potential viable bio-control. However, there is little systematic research concerning whether the parasite attacks native US crab species. Barbee’s proposed project therefore targets the question of whether S. carcini is a feasible bio-control option for the invasion of the European green crab.

The project proposes to infect an equal number of five species of crabs native to the east and west coast of the United States. All crabs will be selected at similar developmental stage and size. They will be infected at various stages of development and be allowed to grow to full maturity. The crabs will be housed in separate aquarium tanks throughout over a course of two years.

Barbee expects that the S. carcini will infect all five species of crab that the study will test, but will exhibit a preference for the invasive European green crab. Therefore depending on how much S. carcini infects other species, S. carcini may or may not prove to be an effective bio-control for the European green crab.

Besides S. carcini, Barbee points out that there are other possible methods to eliminate green crab, such as through the use of the U.S.-native adult blue crab, which will prey on the smaller European green crab. However, Barbee explains that the “parasite is a more effective castrator of green crab.” Similarly, because the European green crabs “are so small, there is no market for using them as food.”

In terms of possible health issues that the parasite might pose on humans, Barbee assures that S. carcini cannot affect humans, because it manifests specifically in the fold of the crab’s underside.

Host Specificity in a Parasite

March 24, 2010

Armand Kuris and his team of researchers from the University of California conducted an experiment to examine host specificity of the barnacle Sacculina carcini, a parasite of the European green crab (Carcinus maenas).  Two main aspects of interactions between parasitic and host species, called “filters,” were referenced.  The encounter filter occurs first and refers to the parasite’s ability to reach the host in suitable conditions, i.e. temperature, time, etc.  If the parasite successfully passes through this filter, it then contends with the compatibility filter, or whether or not the host is nutritionally suitable for the parasite.  The parasite is only able to infect the host if it passes through both of these filters.

The researchers found that both the encounter and compatibility filters for S. carcini were closed in Pachygrapsus marmoratus (a crab not usually infected by this parasite) and is thus this crab is adequately protected from infection, even where the ranges of C. maenas and P. marmoratus overlap.

International Journal for Parasitology 37: 539-545 (2007).

Champion Fighter Crabs

February 8, 2010

Biological Invasions 9, 837-848 (2007)

Some invasive species, such as the European green crab, Carcinus maenas, are able to invade new environments because of brute strength.  In a study conducted by a team of researchers from Rutgers University and Bloomfield College, C. maenas was tested to see how it fared in physical competition with other crab species.

Upon comparing the feeding habits and defensive and agnostic behaviors of C. maenas, another invasive species of crab, and the native blue crab, researchers found that, in addition to finding and consuming food more quickly than either other species, C. maenas is able to steal food from other crabs. It is also more likely to win fights, regardless of the initiator.  Exceptions to these observations may be seen in the European green crab’s interactions with adult blue crab, the only group of crab possessing stronger carapaces than those of C. maenas. Established populations of adult blue crab may be able to contain the threat of C. maenas invasion.