Western Pacific Shore Crab, commonly known as Hemigrapsus sanguineus, is one of the most common species of crabs in the intertidal and subtidal zone on a depth of 10 m. It prefers sandy, rocky, and muddy bottoms. It is common in the coastal rocks. During quiet summer nights, they crawl in masses above the water’s edge, on the rocks, drying in the intertidal zone. The crab has a characteristic motley marble pattern of carapace and legs. The length of carapace is up to 6 cm. It lives around southern Sakhalin to Hawaii, Australia and New Zealand.
The crab has been introduced to other shores and is now an invasive species in North America and in Europe.
The belief that the invasive species is always harmful to ecosystems, have been challenged by recent studies. Andrew Altieri and his colleagues from America and the Netherlands examined the effects of invasive Asian crab Hemigrapsus sanguineus on the ecosystem of the beaches along the Atlantic coast of the United States and found that the presence of these arthropods had a favorable effect on the propagation of native shellfish.
Western Pacific shore crabs had probably been accidentally brought to the US waters by commercial ships more than 20 years ago. Since then, they have spread along the Atlantic coast as far north as Maine, and as far south as North Carolina.
The experts counted the number of crabs in the four areas of the bay Rhode Island and found that the highest density of settlement is observed in areas with thickets plants Cordgrass (Spartina A_lterniflora) and ribbed mussels Geukensia demissa. More than 100-fold difference is observed between regions with Cordgrass and mussels in areas without one or the other.
The experts suggest that Cordgrass attracts ribbed mussels, providing shade and shelter, as well as the appropriate substrate for their livelihoods. The presence of mussels in turn attracts crabs, which also receive protection from predators and exposure to the scorching sun.
Although it would be logical to assume that the high density of crabs in these areas will be at the expense of native species, but the authors of the study found that this is not so. In fact, the observations indicate the opposite phenomenon – the diversity of native species (for example, snails) is actually higher in areas where invasive crabs were found in most high-density.
According to lead author Andre Altieri, Cordgrass and ribbed mussels may contribute to the peaceful coexistence based on the absorption of new species of the ecosystem. Asian crabs have also invaded the coast of northern France, the Netherlands and the Channel Islands, where their presence could lead to significantly less favorable results.
Western Pacific Shore Crab, commonly known as Hemigrapsus sanguineus, is one of the most common species of crabs in the intertidal and subtidal zone on a depth of 10 m. It prefers sandy, rocky, and muddy bottoms. It is common in the coastal rocks. During quiet summer nights, they crawl in masses above the water’s edge, on the rocks, drying in the intertidal zone.