The American horseshoe crab Limulus polyphemus
typically spawns in the upper intertidal zone, where
the developing embryos are exposed to large variations in
abiotic factors such as temperature, humidity, salinity, and
oxygen, which affect the rate of development. It has been
shown that embryonic development is slowed at both high
and low salinities and temperatures, and that late embryos
close to hatching tolerate periodic hypoxia. In this study we
investigated the influence of hypoxia on both early and late
embryonic development in L. polyphemus under controlled
laboratory conditions. Embryos were exposed to four different
oxygen levels and their developmental stage was
scored every second day. Embryos developed more slowly
at both 5% O2 and 10% O2 than at the 21% O2 treatment;
late development was arrested when oxygen was reduced to
2%. Our study confims that L. polyphemus not only tolerates
pronounced hypoxia in later embryonic developmental
stages, but also in earlier, previously unexplored, developmental
stages.