The Life History Cycle of Limulus polyphemus in the Great Bay Estuary, New Hampshire U.S.A.

The overall goal of this chapter is to provide an overview of the life history cycle of the American horseshoe crabs (Limulus polyphemus) that reside in the Great Bay Estuary, New Hampshire, U.S.A. Great Bay horseshoe crabs generally spawn during high tides in the spring. Based on recent work and studies, spawning appeared to be triggered by increases in water temperature, and animals seemed to prefer to spawn in the warmest sections of the estuary. However, in contrast to horseshoe crabs in some other areas of the U.S.A., peaks of spawning activity did not necessarily correspond with the new and full moons, or with the highest tides, and similar numbers of animals were observed spawning during day and night high tides. Once the eggs hatch, it is hypothesized that their planktonic larvae are likely transported to the upper regions of the estuary where they settle on the expansive mudflats that characterize most of the Great Bay Estuary. At ~9 years (about the 17th instar stage), males appear to reach sexual maturity, while it appears that females molt one more time before reaching sexual maturity. This difference, along with a tendency for males to approach mating beaches more often than females, may contribute to a sex ratio that is skewed towards males at most spawning beaches in the estuary