Carbon stable isotope ratios of new leaves of Zostera marina in the mid-latitude region: Implications of seasonal variation in productivity

The morphological characteristics, primary productivity, and carbon stable isotope ratios of the shoots of Zostera marina were investigated in order to compare environmental habitat factors between Dongdae Bay and Ojiri, Korea. The Z. marina samples collected over twelve months at both sampling sites from March 2004 to February 2005 were separated into four fractions (new and adult leaves, sheath, and rhizome). When the new leaf productivity of Z. marina is maximized in the summer, δ13C becomes heavier. However, when the new leaf productivity of Z. marina is at its lowest, δ13C becomes lighter. The new leaf productivity and δ13C of Z. marina are closely correlated with environmental factors such as irradiance, temperature and dissolved inorganic nitrogen. However, the correlation rate between the new leaf productivity and δ13C values of Z. marina in each habitat varied. At Dongdae Bay, the δ13C value of Z. marina new leaf had a high correlation with productivity, water temperature, and DIN. In contrast, the δ13C value of Z. marina new leaf was affected by productivity, water temperature, and irradiance at the Ojiri site. Therefore, carbon stable isotope ratio could be used as a good indicator for relationships among environmental factors, morphological characteristics and productivity of Z. marina.