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The results showed that early embryos were able to tolerate pressures up to
150 atm at 15 o C and 100 atm at 10 o C. Generally, survivorship of Asterias rubens
swimming bipinnaria remained high (> 70%) after incubation at all the
pressure/temperature combinations. The highest number of swimming larvae was
100% at 10 o C/50 atm and the lowest was 72% at 15 o C/200 atm.
In Marthasterias glacialis the highest survival of swimming larvae was 100%
at 1 atm/5, 15 and 20 o C and 50 atm/15 and 20 o C and the lowest was 57 % at 5 o C/200
atm. In general, survivorship decreased as the pressure increased; nevertheless the
larvae of both species generally tolerated pressures of 200 atm. Furthermore, data for
the temperature and pressure effects on the later stages of development suggest that all
the larval stages are more temperature/pressure tolerant than the early embryos and
survivorship becomes greater with larval age.
All the developmental stages demonstrated to have a potentially wider depth
distribution than their respective adults. Comparison of these data with those of
shallow water and deep-sea Atlantic echinoids suggests that the early embryos of
echinoids are more tolerant of pressure/temperature changes, but that the later larval
stages of asteroids tolerate change more readily than the larval stages of echinoids.
Therefore, the larvae of the shallow water species Asterias rubens and Marthasterias
glacialis could survive transport to deeper waters and these species may be capable of
sending colonists to the deep sea. The plasticity on the early-life history stages, and
thus their ability to tolerate increasing pressure, may be cumulative over many
generations, until an individual species has successfully adapted to the deep-sea
environment. It is possible that this adaptation may have been rapid as a number of
deep-sea invertebrate species retain the seasonal growth and reproductive patterns
seen in shallow water congeners (Young 2003).
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