BULLETIN OF MARINE SCIENCE, 49(3): 699-714,1991 DIFFERENCES IN INSHORE-OFFSHORE AND VERTICAL DISTRIBUTION OF PHYLLOSOMA LARVAE OF PANULIRUS, SCYLLARUS AND SCYLLARIDES IN THE FLORIDA KEYS IN MAY-JUNE, 1989 Cynthia Yeung and Michael F. McGowan ABSTRACT As part of a multidisciplinary study of recruitment to South Florida reefs, lobster phyl- losoma larvae were sampled with a MOCNESS to describe their vertical and horizontal distribution in relation to coastal oceanography. A total of 850 phyllosomata of the genus Panulirus. 200 of the genus Scyllarus. and 43 of the genus Scyllarides were caught at 26 stations. The phyllosomata of Scyllarus spp. were more abundant near shore, while those of Panulirus spp. phyllosomata were distinctly more abundant at offshore stations. All stages of Scyllarus were present in comparable proportions, but 60% of Panulirus were stage-I larvae. Scyllarides phyllosomata were similar to Panu/irus in distribution and stage composition, Limited data from three additional anchor stations showed small range of diel vertical mi- gration in the upper 75 m by Panu/irus stages IV-VIII. Vertical migration crossed the ther- mocline but did not go below the 24° C isotherm. These preliminary data support the hy- pothesis that Scyllarus is locally recruited while Panu/irus and Scyllarides are recruited from upstream populations. The phyllosoma larvae of the spiny lobsters (Palinuridae) have an extended planktonic life estimated to last 6 to 12 months (Lewis, 1951; Sims, 1966; Chit- tleborough and Thomas, 1969; Phillips et a1., 1979; Kittaka, 1988; Kittaka and Ikegami, 1988; Kittaka and Kimura, 1989). During this larval period they are susceptible to long-distance transport by local and oceanic circulation, and their survival is critically affected by physical oceanographic processes, Studying the larval distribution of these species in the oceanographic context assists in the de- duction of linkages between the variability of the physical and the biological regimes, and constitutes a key aspect of recruitment research. Although the long planktonic duration favors long-distance dispersal (Thorson, 1961), local oceanographic features such as gyres and countercurrents have been implicated in the entrainment and retention of phyllosomata in South Africa (Lazarus, 1967), California (Johnson, 1960a, 1960b, 1971a, 1974), and Australia (Phillips et a1., 1978) for different palinurid species of the genus Panulirus. Some active control over advection is believed to be exercised through diurnal vertical migration of the phyllosomata, by which they encounter currents flowing in op- posite directions at different depths and achieve a horizontal distribution con- ducive to retention (Johnson, 1971a; Rimmer and Phillips, 1979; Phillips, 1981). In the Florida Keys, near the northern and down-current limit of the range of Panulirus argus, gyres and countercurrents have also been observed (Brooks and Niiler, 1975; Lee, 1975; Lee and Mayer, 1977) which might promote the retention and, ultimately, the recruitment oflocally-spawned phyllosomata to maintain the large adult populations. Previous studies of the distribution of phyllosomata in the southern Straits of Florida (Lewis, 1951; Ingle et a1., 1963; Robinson and Dimitriou, 1963b; Sims and Ingle, 1966; Richards and Potthoff, 1980) have not treated the phyllosomata of the slipper lobster genera Scyllarus and Scyllarides (Scyllaridae) though they are common in the plankton in this area (Robinson and Dimitriou, 1963b; Robertson, 1968a; 1968b; Little, 1977; Lyons, 1980). As was suggested for larval fish species (Miller et al., 1988), description and comparison 699 700 BULLETINOFMARINESCIENCE,VOL.49, NO.3, 1991 25.5 • 1 .2 25.0 .3 .5 .7 24.5 .22 .20 • 18 24.0 w 82.5 82.0 81.5 81.0 80.5 80.0 C 25.5 ;:) l- S 25.0 z...;:~.. ./ .51 .,..fi •?29 " .":':'~'; .~ DavlIR_ .42 ,,~ ".- ~ .30 .44 24.5 .23 '. ~ ..39.40 • 4~ 48 .25 • .35 Sombrero Roe' .27 Cosgrove Shoal Looe Key 24.0 I 82.5 82.0 81.5 81.0 80.5 80.0 LONGITUDE Figure 1. Map showing locations of the MOCNESS and CTD stations during SEFCAR cruise CA8906 Leg 1, 26-29 May 1989 (upper) and Leg 2,30 May-5 June 1989 (lower). XBT stations, not shown, account for out of sequence station numbers. of the spatial distribution across genera might reveal how the interaction of bi- ological and hydrographic mechanisms affect the recruitment process. In this study we quantitatively describe and compare the horizonta1.distribution and abundance of phyllosomata of Scyllarus and Scyllarides, as well as Panulirus, in the Florida Keys during 26 May-5 June 1989. We present data on vertical distribution and preliminary observations of vertical migration. We describe the distributions of larvae with regard to advective loss or retention in countercurrents. Finally, we discuss the implications of the observed distributions to contrasting recruitment strategies among Panulirus and Scyllarus in the Florida Keys. METHODS This study is part of the initial phase of the multidisciplinary Southeastern Florida and Caribbean Recruitment (SEFCAR) project investigating the ecological factors affecting the recruitment of reef organisms to this area. Field sampling was conducted in the Florida Keys from the R/V CALANUS during SEFCAR cruise CA8906 26 May-5 June 1989. The study area (Fig. 1) stretched alongshore from Carysfort Reef in the northeast to Cosgrove Shoal in the southwest. Sampling stations were placed 5 to 10 km apart along transects which extended normal to the shoreline from the edge of the YEUNG AND McGOWAN: DISTRIBUTION OF PHYLLOSOMATA IN THE FLORIDA KEYS 701 10.0 9.0 8.0 ~ N 7.0 E o 0 o '-.. 6.0 '0 I o U I- 5.0 <t: ~U 4.0 C --l 3.0 2.0 o 1.0 0.0 DAY (n=!?) NIGHT (n=9) Figure 2. Day versus night comparison ofln-transformed standardized catch ofphyllosomata (catch ·10 m-2); n = number of samples. reef tract (2-4 kIn offshore) to the approximate edge of the shelf (30 km offshore, or less). The cruise was divided into two legs. During the first leg (26-29 May) four transects running offshore from Carysfort Reef, Tennessee Reef, Looe Key, and Key West, were sampled. During the second leg (30 May-5 June) five transects were sampled: Cosgrove Shoal, Looe Key, Sombrero Reef, Davis Reef, and Carysfort Reef. Sampling was carried out continuously day and night, depending on the time the ship arrived on station (Table I). The means of the abundance of total phyllosomata (natural-log transformed) caught at day (N = 17) versus night (N = 9) stations (Fig. 2) were not significantly different (t.J.O'.24= 0.475, Pob",rved= 0.639, t-test, Sokal and Rohlf, 1981), therefore no adjustments in catch were made for day- night sampling bias. In addition to the 26 standard stations, 3 stations were made at the same location (stations 38-40) at Looe Key on 2 June (Fig. 1), consecutively sampling at 0245, 0805, and 1818 Universal Time (UT) to investigate the diet vertical migration pattern ofthe plankters. Local time was 4 h earlier than Universal Time. Due to equipment failure, samples were not collected during the entire 24-h cycle, but samples from these three samples were examined for preliminary indications of a diel vertical migration. A l_m2 MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System, Wiebe et aI., 1976) was employed in sampling. It has nine nets of 0.333-mm mesh-size which can be opened and closed sequentially at the desired depth by electronic signals sent through a conducting cable from the surface. A flowmeter and conductivity-temperature depth (CTD) sensors are attached to the net frame. Data from these devices are transmitted back up the towing wire to a shipboard computer for recording and real-time plotting. For our sampling, the first in the set of nine nets was fished obliquely from the surface down to 200 m or to the closest multiple of25 m, if the depth of water at the station was less than 200 m. Each subsequent net fished approximately 250 m3 within 25 m strata as the MOCNESS was towed to the surface at a vertical ascent rate of approximately 5 m· min-I. The depth- stratified samples of the upward tow were used in our data analysis. Plankton samples were preserved in formalin and seawater, and were later transferred to 70% ethanol. Phyllosomata were sorted from the samples, and then identified to the lowest taxonomic level possible and assigned stages using literature references (Lewis, 1951; Robertson, 1968a, 1968b, 1968c, 1969a, 1969b, 1969c, 1971, 1979; Baisre and Ruiz de Quivedo, 1982) for confirmation or elimination of the possible species present. Following Lewis (1951), 11 stages for the entire larval development were assigned to Panu/irus, 9 stages to Scyllarus based on the maximum number of stages assigned to Western Atlantic Scyllarus species by Robertson (1968b), and 11 stages to Scyllarides based on Robertson (1969c). The catch of each net was standardized to numbers per 1,000 m3 of seawater (no. of phyllosomata per 1,000 m3 = catch x 1,000 -;- volume filtered). This concentration ofphyllosomata was assigned to the mean depth that each net fished to illustrate the vertical distribution. The catch per unit volume was converted to abundance (catch under an area) by multiplying by the depth fished by the net. The 702 BULLETIN OF MARINE SCIENCE, VOL. 49, NO.3, 1991 Table I. Station data and catch ofpalinurid and scyllarid phyllosomata on cruise CA8906, 26 May- 5 June 1989 (Catch from the 24h anchor stations 38, 39, 40 are excluded from the total) Latitude Longitude Number of phyllosomala caught Distance N W offshore Time Depth