Development of growth-promoting substances for diatoms (Navicula sp.)

Abalone production in Korea has reached 5000 metric tonnes (MT) since 2000 and has been consistently increasing to reach 10,000 MT in 2015. Abalone fisheries are mainly seen in Wando on the south coast of Korea, where seaweed aquaculture has been majorly conducted. Mass mortality of abalone spats is considered a major problem in abalone fisheries and is caused by changes in environmental factors and food availability (including availability of benthic diatoms). However, it is difficult to supply sufficient quantities of benthic diatoms to post-larvae abalone. Therefore, we explored the development of growth-promoting substances for diatoms Navicula sp. and experimentally mixed several substances to enhance the growth of diatoms. In this study, we used alginic acid, fucoidan, Scytosiphon lomentaria, Ecklonia cava, Ecklonia cava processing byproduct (i.e., Ecklonia cava–boiled extracts, EBE), and Porphyra tenera. In addition, EBE, phosphate fertilizer (PF), nitrogenous manure (NM), and sodium silicate (SS) were mixed to determine the optimal composition of growth substances. The growth of diatoms significantly increased under EBE exposure, compared with other substances. During this study, attempts were made to identify the optimal composition of mixtures of PF, NM, and SS with that of EBE (1:1:1:1). The Navicula sp. growth-promoting substance (NGPS) mixture enhanced Navicula sp. growth by 150% compared with existing market products. We were therefore able to develop a substance that promotes the growth of diatoms, thereby facilitating the cultivation of healthy abalone with reduced mortality.