L�PEZ-DUARTE, P.C.*; TANKERSLEY, R.A.; Florida Institute of Technology; Florida Institute of Technology: Endogenous Swimming Rhythms of Fiddler Crab Zoeae from Different Tidal Regimes

Larvae of the fiddler crab Uca pugilator are released near the time of high tide and are exported to shelf waters to undergo development. Previous studies indicate that newly hatched zoeae use selective tidal-stream transport (STST) to migrate from estuaries to coastal areas. In areas with semi-diurnal tides, the STST behavior of larvae is mediated by a circatidal activity rhythm that is characterized by upward vertical migration into the water column during ebb tide followed by a descent toward the bottom during flood tide. We tested the hypothesis that U. pugilator zoeae from different tidal regimes possess endogenous activity rhythms that match local tidal patterns. Ovigerous crabs with late-stage embryos were collected from locations lacking tides (microtidal) and from areas with diurnal and mixed tides. Following hatching, larvae were placed in constant conditions and swimming activity was monitored continuously for 96 h. Zoeae from the diurnal regime exhibited a rhythm with a periodicity of ≈24.2 h, consistent with the tides at the collection site. Crabs from areas with mixed tides displayed activity rhythms with two dominant periodicities at 12.6 h and 23.5 h, reflecting the main semi-diurnal and diurnal components of this tidal pattern. At both locations, peaks in larval activity occurred during the time of expected ebb currents, which is consistent with STST behavior favoring seaward transport (i.e., ebb-tide transport). Finally, zoeae from microtidal areas exhibited circatidal rhythms similar to those observed in crabs from areas with semi-diurnal tides. Differences in the activity patterns of zoeae from the three tidal regimes suggest that STST behaviors are controlled by multiple endogenous clocks or multiple couplers linked to a single clock.