Early development and larval survival of Psammechinus miliaris under deep-sea temperature and pressure conditions

The aim of this study was to analyse the tolerance of the planktonic stages of Psammechinus miliaris to hydrostatic pressure and temperature. Embryos of Psammechinus miliaris were subjected to different combinations of pressure and temperature for 3, 6 and 12 h. The percentage of embryos at each stage and the percentage of embryos developing abnormally were measured. Larvae at the gastrula and prism stages were subjected to pressure and temperature combinations for 24 h and the larval survival was calculated measuring the percentage of swimming larvae. Both embryos and larvae could survive at greater pressures than the known adult depth limits. Larvae showed a much greater potential than embryos for surviving deeper, with approximately 100% of both gastrulae and prisms surviving up to 200 atm at 5 degrees C. These results are similar to other shallow-water species of Echinoida. Thus larval tolerance of high pressure and low temperature may have been important for the success of this group in colonizing the deep-sea.