Vitamin B₁₂ as a Factor in the Environment of Bivalves-I

Seasonal and Environmental Variation of Vitamin B₁₂ Content in Tapes japonica and Meretrix mererix lusoria

Abstract

It has been reported that the vitamin B₁₂ content of bivalves, and of starfish which devour bivalves, is higher than that of fish or other aquatic animals. Recent studies have shown that vitamin B₁₂ will affect the growth of Porphyra tenera and relate to the development of “red tide”. In view of these facts, we made a study of vitamin B₁₂ as one of some means to analyze the environment of the shallow water clam bed.
In this experiment we measured the vitamin B₁₂ content of Tapes japonica and Meretrix meretrix lusoria, the bottom substances in which they lived, the fine deposits in the hollow of ripple marks and the plankton which are the food of clams.
Vitamin B₁₂ content was determind by Euglena method added 1mg/cc acid hydrolysed casein to H_UTNER's basal medium, and each sample were digested by trypsin before hot water extraction. Results obtained were as follows:
1. Vitamin B₁₂ content in the soft body of Tapes japonica and Meretrix meretrix Zusoria is high before and during spawning, and low after spawning. In Tapes japonica, there is a tendency for individuals that live off the coast to be higher in vitamin B₁₂ content than those that live near the coast; moreover individuals cultured by the hanging method are higher in vitamin B₁₂ content than those raised in the above-mentioned benthic environment. In Mere-trix meretrix Zusoria, however, the above described tendency is not clear. Further, vitamin B₁₂ content of Tapes japonica is higher than that of Meretrix meretrix lusoria during every month of the year (see Tables 1, 2, & Fig. 1).
2. Vitamin B₁₂ content of the sandy bottom in the offshore areas is higher than in the shallow coastal beds, and vitamin B₁₂ content of same substances divided into three vertical layers is higher in the upper and middle layers and poorer in lower layer. Fine deposits on the hollow of ripple mark are higher in Vitamin B₁₂ than in the sandy bottom areas mentioned above. Vitamin B₁₂ content in zooplankton (Copepoda) is higher than that of phytoplankton (Coscinodiscus sp. or Thalassiothrix sp.) (see Table 3).