Stoner et al : Reproduction and larval abundance in queen conch 



163 



Table 1 



Numbers and (percentages) of queen conch engaged in repro- 

 ductive activity on three substratum types near Lee Stock- 

 ing Island, Bahamas, 1988. Values for pairing and copulating 

 represent number of male/female pairs. 



Behavioral type 



Substratum 



Pairing Copulating Egg-laying 



Sand 



Rubble 



Hardground 



51 (94.4) 

 (0.0) 

 3 (5.6) 



28 (84.4) 



2 (6.1) 



3 (9.1) 



148 (99.3) 



(0.0) 



1 (0.7) 



(transects Sl-1 and Sl-2; Fig. 2) were examined each 

 survey period. Tiie transect surveys were made by a 

 scuba diver who counted all adult conch within a known 

 range while being towed 5 m above the sediment. High 

 water transparency resulted in a mean transect width 

 of 29 m (SD 6; range 20-40 m), which was measured 

 with a tape on each survey date. The total survey area 

 for each transect was calculated on the basis of horizon- 

 tal visibOity and the fixed distance of each transect line. 

 For additional information on the abundance of queen 

 conch on sand during the reproductive season, all adult 

 conch were counted in circles of 20 m radii at locations 

 of highest conch density in August 1987 (n 7 circles), 

 and in June (n 2) and July 1988 (n 2). 



Each individual conch was classified in one of the 

 following reproductive categories. (1) Pairing: Two 

 conch were aligned, with the anterior part of the shell 

 of one animal overlapping the posterior part of the shell 

 of the other; but copulation was not observed. (2) 

 Copulating: Animals were engaged in copulation, with 

 the verge of the male beneath the mantle of the female. 

 (3) Egg-laying: A female was actively laying an egg 

 mass. (4) Non-reproductive: Conch was not engaged 

 in reproductive behavior. 



Seasonality in reproductive behavior was quantified 

 by recording the percentage of total animals on sand 

 in each behavioral category. Notes were made on the 

 locations and substratum types (sand, rubble, hard- 

 ground) where pairing, copulating, and egg-laying 

 conch were found. Conch were measured for total shell 

 length (spire to siphonal groove) and greatest shell lip 

 thickness (approximately two-thirds of the distance 

 posterior from the siphonal groove). Shell measure- 

 ments were made to the nearest mm. 



To estimate seasonal abundance of conch on sand, 

 two quantitative transects across the SI sand area 



Physical measurements 



To provide information on sediment grain-size and 

 organic content in the spawning habitat, sediment 

 samples were taken from the surface adjacent to 

 females laying eggs in August. Only eight samples were 

 collected; however, the sediment in sand areas SI and 

 S2 appeared to be of uniform grain size. An effort was 

 made to collect sediment samples from throughout the 

 study site. Sediments were frozen until laboratory 

 analysis. Organic content was determined by drying 

 a subsample (~100g wet wt) at 80 °C to constant 

 weight and incinerating at 500°C for 4 hours. Organic 

 content was quantified as the percent difference be- 

 tween dry weight and ash-free dry weight. Another 

 subsample (~50g wet wt) was examined for granulo- 

 metric properties. The sample was washed to remove 

 salts and extract the silt-clay fraction (<62^m). Silt- 

 clay was analyzed with standard pipette procedures 

 (Galehouse 1971), and the sand fraction with standard 

 dry sieve procedures (Folk 1966). 



Bottom-water temperature was recorded with a 

 Ryan Instruments Temp Mentor placed at 17 m depth, 

 near the base of the coral ledge. The thermograph 

 recorded temperature with a precision of 0.2° C every 



