Color profile and microstructure of the nacre shell of an invasive freshwater mussel, Sinanodonta woodiana, at different elevations in West Java, Indonesia

The Chinese pond mussel Sinanodonta woodiana is an invasive freshwater mussel in Indonesia but has economic potential owing to the production of hemispherical pearls in their nacreous shell. To our knowledge, this study is the first to report on the species' shell nacre color profile and correlate it with microstructure and environmental factors at different elevations, from sea level to more than 1500 m. Samples from Lowland, Midland, and Highland elevations in West Java Province were observed and analyzed using the scanning electron microscope for shell microstructure. In addition, the nacre color was analyzed using spectrophotometry and estimated using the CIE Yxy color space and yellowness index. The nacre color ranged from gold to yellow and silvery. The microstructure at five positions on the shell was observed with a scanning electron microscope. The nacre with gold color had a thicker whole nacre layer, thinner nacre tablet thickness, and narrower surface nacre tablet area. In contrast, the nacre with silver color had a thinner whole nacre layer, thicker nacre tablet thickness, and greater surface nacre tablet area. The posterior position of shell nacre had a strong gold color with a high yellowness index, whereas the anterior and dorsal positions had a yellow color, and the central and ventral positions had a silver color. Mussels from the Midland locations displayed strong gold-colored nacre with a high yellowness index and high brightness. Based on these results, Midland areas are considered to have optimum environmental conditions for hemispherical pearl culture. S. woodiana shell with a thicker nacre layer and thinner nacre tablet shows a strong gold color, whereas a thinner nacre layer and thicker tablet nacre has a silvery color. We surmise that environments with high chlorophyll-a concentrations and low concentrations of total suspended solids result in the thicker nacre layer and the stronger gold color in the inner shell of S. woodiana.