Microalgal feeding preference of Mytilus coruscus and its effects on fatty acid composition and microbes of the digestive gland

Microalgae are the primary source of food and energy for marine bivalves, and hence play a vital role in their development and growth. To characterize the microalgal feeding preference and the effects of fatty acid composition and digestive gland microorganisms on Mytilus, four microalgal species (Chlorella vulgaris, Chaetoceros muelleri, Isochrysis zhanjiangensis and Platymonas helgolandica) were used in a mix and single feeding experiments. The feeding preference in the mix feeding was determined using quantitative PCR analysis of water samples obtained at various time periods from biodeposits. The results demonstrated that C. muelleri and I. zhanjiangensis were selectively filtered by M. coruscus, while C. vulgaris and P. helgolandica were preferentially rejected. Individuals of M. coruscus fed with C. muelleri and I. zhanjiangensis had higher levels of fatty acids contents, particularly some unsaturated fatty acids like eicosapentaenoic acid (EPA), which rose by 63.6% after 28 days feeding with C. muelleri. In the digestive glands of M. coruscus fed these two microalgae diets, the relative abundance of digestion-related bacteria such as Polaribacter was also dramatically enhanced, indicating that they had a greater ability to degrade and metabolize microalgal polysaccharides. The metabolic pathway may also play a dominant role as a feedback reaction to microalgal diet feeding, according to potential function prediction. In comparison to C. vulgaris and P. helgolandica, our findings showed that C. muelleri and I. zhanjiangensis had a better nutritional value and could be utilized more efficiently by M. coruscus, implying that C. muelleri and I. zhanjiangensis may be employed to boost M. coruscus growth and output.