Abstract
Horseshoe crabs are found in coastal and estuarine areas and, when the tide is on the flow, the mature adults migrate shorewards to spawn on sandy beaches. The salinity measured was 18-33‰ in Tatara coast where Japanese horseshoe crabs were laying eggs. Therefore, eggs and embryos as well as adults of horseshoe crabs were expected to tolerate a moderate reduction in salinity. In this experiment, the eggs of four horseshoe crab species, Tachypleus tridentatus, T. gigas, Carcinoscorpius rotundicauda, and Limulus polyphemus, were artificially inseminated and reared until hatching in different salinities ranging from 5‰ to 35‰. The embryos of all the four species were considered adaptable to the salinity ranges of their natural localities. The viability of C. rotundicauda embryos in low salinity was the lowest of all horseshoe crabs, though only C. rotundicauda goes up a river to spawn on the muddy banks of the river below the highest tidal level.
