The horseshoe crab, Limulus polyphemus, has been used extensively as a model system for laboratory investigations of immune system function, visual physiology, and neuronal oscillators. It plays a crucial ecological role for many migratory bird species and its importance as a fishery and to human health is well documented. Limulus has also been the subject of many field studies concerning its annual migrations inshore to mate during high tides in the spring and early summer. Interestingly, while we know a great deal about the physiological basis of the horseshoe crab's circadian rhythm of visual sensitivity, we know little about how this relates to their normal daily patterns of activity. Similarly, we have a reasonable understanding of their mating behavior but we don't know what environmental factors they use to synchronize their mating with the tides or if they express these tidal rhythms at other times of year.
The overall goal of our research is to carry out complementary laboratory and field studies of Limulus biological rhythms so that we can unify our understanding of how endogenous rhythms and environmental factors work together to determine the patterns of behavior exhibited normally in their natural habitat. Despite the economic, ecological, and medical importance of this species, many aspects of the behavior of Limulus are unknown. While they are easily observed while they mate at the edge of the high-water mark in the spring, very little is known about their behavior during the majority of the year when they are subtidal. The work outlined in this proposal will provide insight into some aspects of these subtidal behaviors and thus contribute to our understanding of this important marine resource. This knowledge may, in turn, help managers and other scientists develop management practices that do not cause any further decline in their populations.