Wednesday, April 6, 2011

Invasive Species Battle

In New England the European crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus) are two invasive species that are causing a lot of harm... to each other. Ecologists had first expected to see that the two species would cause double the harm to the area and its organisms but really they are cancelling each other out.

The European crab came to New England by ship in the 1800s, ate through the American soft-shell clam industry, and spread rapidly into Canada and the southeastern United States. The Asian shore crab came over from Asia by ship in the 1980s. It was attracted to the same rocky holes and habitats as the European crab but it mostly fed on algae.

Upon being studied, the crabs do not do much harm to native plant and animal species. Most of the focus is on each other. The Asian shore crab would often drive the European crab from its rocky homes. Also, when the Asian shore crab was in the presence of the European crab, this caused the European crab to eat less shellfish and less food overall. The European crab's population grew slowly due to the bullying from the Asian shore crab but it is known to often get its revenge because the European crab was sometimes observed feasting on the Asian shore crab.

From this information, ecologists have drawn the conclusion that when there are two similar invasives living in one area, they often mutually attack one another. This information can better help conservationalists control invasive species. Previously a species may have purposely been introduced to kill the invasive but now it is known that if there is an invasive that a species that needs the same habitat and food as the invasive should be introduced. This creates competition and keeps either species from harming natives.



  1. It's definately interesting to find that there is an invasive crab that is causing harm to natives because they don't seem like they would be an aggressive species. Very interesting!

  2. Interesting post, particularly that an Asian species and European species can limit each others growth. I wonder if this might work better for certain animals for which habitat needs can be better determined. There is also the danger of habitat shift when presented with new environment, so it would be interesting to see whether any similar interactions have been observed in other cases of multiple introduction of similar species.