Occurrence of Chaceon Larvae in Plankton Samples from Slope Waters of the Northeastern Gulf of Mexico

Abstract

Geographic, seasonal, and bathymetric distributions of Chaceon larvae are described for the northeastem Gulf of Mexico. INTRODUCTION From 1986 to 1988 a cooperative research project to define geographic, seasonal and bathymetric distribution and abundance of geryonid crabs in the northeastem Gulf of Mexico was carried out by personnel of the University of Florida, the University of South Florida, and the Gulf Coast Research Laboratory (Lockhart et al. 1990). Four seasonal cruises (May 1987, August 1987, December, 1987, and February 1988) were conducted in five distinct geographic sampling areas (Figure 1). Three depth contours (311, 494, and 677 m) were sampled in each area. MATERIALS AND METHODS Plankton tows were made at each depth contour in Areas 1 through 5. Oblique tows were taken with closing nets (1 meter diameter, 333 micron mesh) equipped with Niskin double-trip devices. Deployment rate was approximately 8 meters per minute. Tow depth and duration varied with station depth. The upper 200 meters of the water column were sampled at all depth contours (this was the only portion of the water column sampled at the 311 meter stations). At the 494 and 677 depth contours, bottom tow depth range was 200 to 400 meters and 200 to 500 meters, respectively. Samples were preserved in the field in 5% formalin and taken to Gulf Coast Research Laboratory for analysis. Samples in May, August, November/December 1987 Manuscript received November 5 , 1990; accepted November 21, 1990. and February 1988 were taken aboard the Gulf Coast Research Laboratory vessel R/V TOMMY MUNRO . An additional set of samples was taken in Area 5 in March 1988 by personnel of the University of South Florida aboard the R/V SUNCOASTER (Florida Institute of Oceanography). RESULTS Chaceon larvae occurred infrequently and in small numbers. Larvae of the red crab, Chaceon quinquedens, occurred in samples in February. Zoeal stages I, 11, and III were identified from samples taken in the upper 200 meters of the water column (Table 1). Zoeae occurred in all areas except Area 4. The fourth zoeal stage and the megalopal stage were not collected. Zoeae of Chaceon fenneri (Stuck et al. In manuscript) were more limited in distribution. Seven stage I1 zoeae were collected in a surface tow in Area 2 in February. All other occurrences were in Area 5 in March 1988; a single stage I zoea and two stage II zoeae were identified from surface samples, and one stage I1 zoea was taken in a bottom tow. TABLE 1 Number of zoeae of Chaceon quinquedens by area and developmental stage. Area Zoea I Zoea JI Zoea IU 5 1 3 3 4 3 2 6 6 1 1 9 4 1