抄録
Glass plates were immersed in the surface layer (1 m) in Gokasho Bay during a 7 day period every month over an annual cycle to allow periodic collection of epilithic microalgae and to analyze their year-round stable carbon and nitrogen isotope ratios. The bulk of the attached material was diatoms throughout the year. The δ13C and δ15N of epilithic microalgae varied seasonally, ranging from −22.0 to −14.6‰ and from 3.6 to 10.2‰, respectively. The δ13C increased during a period from August to November when large microalgal biomasses were found, while the δ15N decreased after November through January in the next year. Such seasonal variations are discussed from the viewpoints of the algal growth and ambient nutrient concentrations. Comparison of the δ13C (yearly mean=−19.8‰) and δ15N (7.7‰) for epilithic microalgae with the previously reported values for primary producers and organic matter in Gokasho Bay shows that the overlap of the δ13C with marine phytoplankton (−20.4‰), which will result in poor resolution of sources.
