Abstract
The green mussel, Perna viridis, is an invasive species, that has been expanding its geographic range in warmer Japanese waters recently. To elucidate its habitat use pattern, its distribution was investigated in Uranouchi Inlet, Kochi Prefecture, Japan (33º 26' N, 133º 25' E), from March to May, 2008. Intertidal surveys revealed that P. viridis uses natural rocky shores and cobble shores as well as artificial vertical seawalls and block seawalls. No difference in its abundance was detected among the four habitat types. Green mussels were more abundant in the inner bay and middle bay than in the outer bay. They were also found on floats of fish-farming rafts. The total abundance of P. viridis in Uranouchi Inlet was estimated 240,000 individuals on floats and 50,000 on intertidal shores. The distribution of another invasive mussel, Xenostrobus securis, was also surveyed in Uranouchi Inlet, along with the Japanese native mussels X. atratus, Hormomya mutabilis, Septifer bilocularis, and S. virgatus. Perna viridis overlapped with H. mutabilis and S. bilocularis. The high abundance of P. viridis and its invasion of natural shores possibly represents a threat to the indigenous mussel species community, but further ecological research is needed to evaluate the scale of this threat.
