Particles in the eruption cloud from st. Augustine volcano.

rate of seaward transport. Although the rate of transport out of the estuary depends on the pattern of vertical migration of developing larvae and on the variance and magnitude of residual drift and tidal currents, many larvae are probably displaced seaward during development, each stage moving further toward the mouth of the estuary (14). Any behavior that would increase the magnitude of the up-estuary transport of the megalopae when they are ready to settle would be strongly favored. Female Uca pugilator are releasing their larvae at a time in the semimonthly cycle of tidal amplitude and current velocity such that the megalopae experience maximum up-estuary transport when they are ready to colonize adult habitats. Laboratory-reared Uca pugilator take about 18 days at 28° to 30°C to reach the megalops stage, and molt to the first crab after spending 3 to 15 days as megalopae (15). On the assumption that the megalopae will first be ready to settle after about 4 days, megalopae from clutches released 7 days before a spring tide would be ready to settle about 22 days later, during the next spring tides. If megalopae show the same patterns of vertical migration relative to the tide currents as stage one Uca larvae, then these megalopae would experience maximum up-estuary transport. Megalopae released near or during the spring tides would be ready to settle at the time of the neap tides. They would have a decreased probability of being carried to suitable substrates because of the smaller magnitude of their horizontal displacement by the neap tide currents. This hypothesized behavioral adaptation of adults, which may be a general characteristic of the genus, should be viewed as complementary to behavioral adaptations of larvae that reduce transport out of the estuary. Both should increase the probability that larvae will reach substrates suitable for settlement. JOHN H. CHRISTY Ecology and Systematics, 110 Insectary, Cornell University, Ithaca, New York 14853