Silicon Dioxide (SiO2) Is the Most Important Component of Spots on the Inner Surface of Mactra veneriformis Shells

Cheng He,Qiuyun Jiang,Wen Guo,Xiaona Wang,Baolu Zhang,Xiaotong Wang,Lei Wei,Wenchao Yu

doi:10.3389/fmars.2019.00651

Abstract

Yellow-brown spots are often observed on the inner shell surface of the clam Mactra veneriformis sampled in Binhai New Area, Lijin County, Shandong Province, China, negatively impacting its commercial value. In this study, SEM-EDS, X-ray diffraction (X-rd), laser Raman spectrum, and Fourier infrared spectrum scanning (FT-IR) were used to detect and analyze the composition of spots on the inner shell surface of these clams. Compared with shells without spots, the shells with spots showed significant differences in their silicon contents but no differences in the content of other basic elements; Laser Raman spectroscopy and X- rd examination revealed that, in addition to calcium carbonate particles, there were traces of silica bonds; after the removal of calcium carbonate by using hydrochloric acid, the spectral trend of particles was similar to that of sea sand, which was consistent with the spectral characteristics of SiO2. Therefore, the spots on the inner shell surface of M. veneriformis are sea sand. These are likely to result from the increased sand content in seawater in the Yellow River Delta, whereby the grains of sand have fallen into the gap between the mantle and shell; thus, the sand becomes encased in the shells as they grow.

Highlights

Mactra veneriformis (Lamellibranchia, Venerida, Mactridae), commonly known as the white clam, is a bivalve mollusk that lives in the tidal flats, subtidal zones, and shallow seas off the coasts of China, South Korea, and Japan
M. veneriformis in certain locations often have a large number of yellow-brown spots attached to their white inner shell surface (Figure 1), the cause of which is unclear
The curve characteristics were similar to those of sand, with an obvious absorption peak at 1080∼1100 cm−1, belonging to the Si-O tensile and Si-O-Si bending vibration peak (Chen et al, 2011), which was consistent with the recognized characteristic peak of SiO2 (Lippincott et al, 1958; Boyd and Wilson, 1982). These results indicated that the main component of shell spots treated with hydrochloric acid was similar to that of sand

Summary

Introduction

Mactra veneriformis (Lamellibranchia, Venerida, Mactridae), commonly known as the white clam, is a bivalve mollusk that lives in the tidal flats, subtidal zones, and shallow seas off the coasts of China, South Korea, and Japan It has a high nutritional value, tender meat, and delicious taste, rendering it an economically important species (Fang et al, 2010). M. veneriformis in certain locations often have a large number of yellow-brown spots attached to their white inner shell surface (Figure 1), the cause of which is unclear. The occurrence of such spots can negatively impact the economic return received from M. veneriformis.

Methods

Discussion

Conclusion