Shell growth and reproductive cycle of the Mediterranean mussel Mytilus galloprovincialis in Tokyo Bay, Japan: relationship with environmental conditions

This study investigates shell growth patterns and the reproductive cycle of the Mediterranean mussel Mytilus galloprovincialis in Tokyo Bay, central Japan. A follow-up study of marked mussels within the intertidal zone from July 2007 to September 2008 indicates a remarkably fast annual shell-growth rate and a short life span, reaching the maximum shell length (ca. 70 mm) at age 3 or 4 years. Histological examinations of mussel gonads collected fort- nightly revealed that the Tokyo Bay population has a spawning season between late autumn and spring, and attains sex- ual maturation several months after recruitment. Shell growth patterns for individual mussels show seasonal variations, with high shell-growth rates during spring and summer, and minimal growth from late autumn to early spring. Slow shell growth during winter is possibly controlled by combined environmental (lower air and seawater temperatures, and scarce phytoplankton) and physiological (the reproductive effort expended in gametogenesis and spawning) factors.