110 



Fishery Bulletin 103(1) 



32°0'N - 



31 ON 



31°0'W 

 I 



80°0'W 



South Carolina 



| Gray's Reef National Marine Sanctuary 

 Ichthyoplankton station 

 Depth contour (m) 



25 50 



Kilometers 



- 32°0'N 



Georgia 



- - 



20 m 



30 m 



40 m 



[Brunswick 



2-+ 23/ • 



50 m 



200m 



• 5 



7.' 



• 



1 



81°0'W 



1 



80°0'W 



- 31°0N 



Figure 1 



Map of the study area and the cross-shelf transect used for sampling larval abundance 

 and environmental data bimonthly from April 2000 to February 2002 (see Table 1). 

 Four stations (stations 2.1-2.4) were located around Gray's Reef National Marine 

 Sanctuary. 



tions were placed immediately adjacent to the four sides 

 of Gray's Reef National Marine Sanctuary. At each 

 station, temperature, salinity, density, and water depth 

 were measured from the water's surface to one meter 

 above the bottom with a Seabird conductivity-tempera- 

 ture-depth (CTD probe (SBE19, Seabird Electronics, Inc., 

 Bellevue, WA). Ichthyoplankton was collected at each sta- 

 tion with a five-minute single oblique net tow to within 

 one meter of the bottom. For all but one cruise (August 

 2000), a 61-cm paired bongo frame fitted with 333-fim 

 or 505-/xm mesh nets was used. During the remain- 

 ing cruise, a 1-m ichthyoplankton sled with 333-|um 

 mesh net was used because of the smaller size of the 

 research vessel. A flow meter (General Oceanica) was 

 used to measure the volume of water filtered. 



A gear comparison study, conducted during October 

 2000, showed that ichthyoplankton samples collected 

 with the two gear types (61-cm bongo versus 1-m 2 ich- 

 thyoplankton sled) were similar. An analysis of variance 

 (ANOVA) on the mean larval concentration revealed no 

 significant differences between the two gear types (one- 

 way ANOVA: F=0.489; df=l; P>0.5). Also, an analysis 

 of similarities (ANOSIM, Clarke and Warwick, 2001) 

 determined that the community structure varied more 

 within than between gear types (ANOSIM: i? = -0.11; 

 S=77.57). Similarly, preliminary analysis of the effect 



of gear selectivity due to mesh size indicated that the 

 larval communities collected by 333-f<m mesh and by 

 505-f<m mesh nets were similar. Thus, data from all 

 cruises were combined in the subsequent analyses (see 

 Marancik, 2003, for more details). 



Preparation of ichthyoplankton data 



All ichthyoplankton samples were sorted and larval fish 

 were identified to the lowest possible taxonomic level 

 by using previously published descriptions (e.g., Fahay, 

 1983; Johnson and Keener, 1984; Richards, 2001) and 

 descriptions developed as part of this study. Identifica- 

 tion to species was not easy given the diversity of spe- 

 cies along the southeast United States continental shelf 

 (see Kendall and Matarese, 1994), yet every effort was 

 made to identify larvae to species-level (46.3% to species, 

 27.4% to genus, 6.7% unidentified). Larval concentra- 

 tions were calculated as number of larvae/100 m 3 . 



Two data sets were used for statistical analyses, dif- 

 fering in the inclusion of rare taxa. Rare taxa pose a 

 problem in community analyses. Some rare taxa occur 

 because of transport anomalies (Cowen et al., 1993), 

 and their inclusion in data analyses can confound the 

 definition of larval assemblages. However, rare taxa can 

 also be indicative of consistent, but low larval abun- 



