Cnales et al.: Variability m supply and cross-shelf transport of Foi fantepenaeus duorarum postlarvae into Florida Bay 



69 



-40 



and 86% of larvae reached 80 km. The aver- 

 age eastward distance traveled in Simula- 60 

 tions was 66 km. The maximum distances 

 traveled in the alongshore direction was 25 40  

 km northward (70% of larvae) and 10 km 

 southward (30%). The maximum distance 20 

 traveled was recorded in March-April and 

 June 2000 (Fig. 6, A and B). 



Offshore mooring The maximum displace- 

 ment of larvae in the cross-shelf direction -20 

 was 90 km eastward and 85% of larvae 

 reached 80 km. Distance traveled in the 

 alongshore direction reached 20 km north- 

 ward (86% of larvae) and 5 km southward 

 (14%) (Fig. 6, C and D). 



Discussion 



The monthly influx of pink shrimp postlar- 

 vae entering Florida Bay through its north- 

 western border showed a strong seasonal 

 pattern of annual high peaks in summer 

 over the 3-year period. Postlarval concentra- 

 tions were correlated with alongshore winds 

 and sea surface temperature. Alongshore 

 winds were seasonal, with a weak northward 

 constituent in spring-summer of each year 

 changing to a strong southward in fall and 

 winter. This seasonal pattern agrees with 

 the general circulation described for the SW 

 Florida shelf, highly dependent on synoptic- 

 scale winds, coupled with a strong seasonal- 

 ity and strong tidal currents (e.g., Weisberg 

 et al.. 1996; Wang, 1998; Smith, 2000; Lee 

 et al., 2001). Although tidal currents seem 

 to be the main vehicle of eastward transport 

 for planktonic stages, alongshore winds may 

 be fundamental for moving larvae northward 

 along the SW Florida shelf by avoiding a 

 drift with the Florida Current or with the 

 cyclonic circulation of the gyres that form 

 southwest of the Dry Tortugas (Lee et al., 

 1994; Fratantoni et al., 1998). Under these 

 circumstances larvae may reach Florida Bay 

 by the shortest route in summer using tidal 

 currents and winds across the shallow SW 

 Florida shelf and entering Florida Bay by 

 its northwestern border. The summer sea- 

 sonality of postlarval immigration may also 

 be amplified by the seasonality of spawning 

 because higher temperatures induce higher 

 spawning activity (Cripe, 1994) and conse- 

 quently more recruits to enter the Bay during 

 favorable onshore conditions. 



Another alternative explanation for the summer lar- 

 val immigration is that larvae may take advantage of 

 a distinct annual tidal cycle produced in summer every 

 year as a result of the interaction of the periods of the 

 diel vertical migration and the tidal constituent (S.,, 



- 1 



- -1 



19h 20h 21ti 22ti 23h 24ti 



n 



Figure 5 



Hourly concentration of pink shrimp (Farfantepenaeus duorarum) 

 postlarvae at Sandy Key station (SK) during a complete dark (night) 

 tidal cycle conducted during (A) new moon, 9-10 July 2002, (B) full 

 moon, 23-24 July 2002, and (C) new moon, 8-9 August 2002. Right 

 y-axis indicates concentration of postlarvae/m''; lefty-axis is tidal 

 current speed (cm/sec) measured by acoustic Doppler velocity meter 

 (filled circle and solid line) and by flowmeter (empty circles and 

 interrupted line). Positive values in they-axes indicate transport into 

 Florida Bay (flood), and negative values transport out of the Bay (ebb). 

 Horizontal bars on the bottom indicate hours of darkness versus light. 



K,) with the annual cycle of the length of the night 

 (Criales et al., 2005). Larvae moving vertically in the 

 water column with a diel behavior can be transported 

 up to 70 km onshore in summer because the eastward 

 current of the tidal constituents matches the diel cycle 

 over extended intervals in the shorter summer nights 



