Professor, Graduate School of Engineering, Hiroshima University, Japan

Speech Title: Settlement of short neck clam larvae onto steel making slags

Abstract: Steel making slags were examined as sea sand alternatives for settlement of short neck clam larvae (Ruditapes philippinarum) to investigate the potential use for establishment or restoration of tidal flats. Petri dishes were filled up with blast-furnace (BF), decarburization (De-C), and dephosphorization (De-P) slags with a diameter from 0.85 mm to 2 mm and placed at the bottom of a tank filled with sand-filtered seawater containing full-grown larvae of R. philippinarum. In addition, the surface-roughed glass beads and the bilayer media consisting of mountain sand/De-P slag were also tested for the larval settlement to find the causes for the larval attraction. The settlers onto the De-P slag were about ten times higher than that onto the mountain and sea sands, indicating the larval attraction by the De-P slag. As for the BF and De-C slags, the larval settlement was not promoted. Since the De-P slag is the molten material, possible causes for the settlement traction were levelled surface by melting and/or eluted components. In the experiments using glass beads, the number of settlers decreased to about a half, as the surface got roughed to the same level of sea sand surface. Furthermore, a number of settlers onto the double layer basal media containing the De-P slag beneath the mountain sand were about 8 times greater than that onto the mountain sand. The results showed that together levelled surface and eluted components promoted the larval settlement.