Distribution of Diatom Resting Stages in Sediment near Artificial Reefs Deployed in the Dysphotic Zone: Exploration of New Artificial Reef Function

Artificial reefs (ARs) have multiple beneficial effects involved in increased fishery production. The present study investigated diatom resting stages in the sediments near ARs at a depth of about 90 m by the combined use of direct microscopic observation and the MPN method, seeking a novel function of AR deployment that potentially increases biological production. Although the concentration of diatom resting stages at A2 (north end station of the AR area), composed mainly of Chaetoceros, was ten times the concentration at A5 (non-reef station), the concentration at A1 (south end station of the AR area) was the same level as at A5. These results suggest that the AR contributes to the accumulation of diatom resting stages while the degree of accumulation is attributed to the arrangement of ARs and their physical environment such as flow directions. Interestingly, live pennate diatoms possessing photosynthetic pigments were constantly observed in all samples despite the low light intensity (≤1.2 µmol photons m−2 s−1), which provides new ecological insight into their biological and physiological characteristics. In this study, the distribution of viable diatom resting stages and live pennate diatoms in the sediment around ARs in a dysphotic zone was revealed for the first time, casting a light on the novel function of ARs potentially enhancing primary production around them.