Abstract
The present study examined the influence of algal vegetation and hydrographic conditions on the growth and survival of the young topshells. These were artificially incubated and cultured in tank until growing up to 8-10mm in shell height during about one year, and then were released to several shallow and rocky coastal areas of Kyoto Prefecture.
Favorable algae for growth of the topshells were Gelidiaceae, Ulva and microalgae such as Ceramium sp. and Herposiphonia subdisticha which were growing on the Corallinoideae. However, Corallinoideae and Sargassum spp. were unfavorable algae for the young topshells. For example, in the case of Port Niizaki, the topshell released in the patch of Pterocladia capillacea grew up to 28.5mm in mean shell height in 124 days, whereas the topshell released in the area where only Corallinoideae and Dictyota dichotoma grew up to 21.0mm only.
The survival rates of the topshell in the experimental areas exposed to relatively little wave action were 53.6-93.8%. On the other hand, the rate was only 12.1% in Aoshima exposed to the oceanic swell and wave action.
According to the above results, it is suggested that favorable areas for the topshell of 8-10mm in shell height were under conditions covered with Gelidiaceae and Ulva, and without oceanic swell and strong wave action.
