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Fishery Bulletin 88(3). 1990 



Between 27 September and 28 October 1988 three 

 conch size-classes were tested for their preferences for 

 habitat type. The classes included animals between 75 

 and 100 mm shell length (~1 year old), conch between 

 125 and 150 mm (2 and 3 years old), and adults with 

 the fully developed flare of the shell lip (~4 years or 

 more). All were collected from the seagrass beds 

 aroimd the experimental enclosiu'es. To provide a conch 

 density similar to that in nature, 10 juveniles of a size- 

 class were added to each enclosure (1.0 conch/m-) 

 after removal of all large invertebrates such as urchins, 

 hermit crabs, and conch. For runs with the adults, 8 

 animals were placed in an enclosure. 



Preliminary experiments showed that the distribu- 

 tion of conch in both Moderate/Low and Moderate/Sand 

 treatments did not change significantly between 1 and 

 5 days; therefore, all runs were terminated at 3 days. 

 At the end of a run, the numbers of conch found on 

 each side of the cage were recorded, and the animals 

 were removed. Because the animals touching the 

 screen may have been moving around the periphery of 

 the enclosure, they were not included in the counts. 

 Three or four runs were made for each size-class and 

 treatment, except those in the High/Moderate en- 

 closures where two runs were made in each cage. No 

 significant differences were found in the distribution 

 of animals in a size-class in any of the pairs of cages 

 providing similar combinations of macrophytes 

 (Fisher's Exact Test, p>0.05); therefore, the paired 

 cages were considered to be replicates. 



Results 



Station characteristics 



Average depths for the five stations at CBC increased 

 from station 1 (1.0 m) to station 5 (3.4 m). Average sta- 

 tion depths for SR increased from .station 1 (1.6 m) to 

 station 6 (3.3 m) and then decreased slightly at station 

 7 (3.2 m). Thalassia shoot density, biomass, and 

 detritus biomass all increased with increasing station 



number and depth, with a few exceptions (see Table 

 1). At CBC shoot density ranged from 0.0 to 864 

 shoots/m-, Thalassia biomass from 0.0 to 80 g dry 

 wt/m^, and detritus biomass from 0.0 to 125 g dry 

 wt/m^. At SR shoot density ranged from 0.0 to 765 

 shoots/m-, Thalassia biomass from 0.0 to 115 g dry 

 wt/m^, and detritus biomass from 0.0 to 309 g dry 

 wt/m^. 



Sediment grain-size at the CBC transects was rela- 

 tively constant (1.38-1.83 0) between stations 1 and 

 4, but finer at station 5 (2.44 0). Sediment organic 

 content increased slightly over the transects from low- 

 biomass to high-biomass stations. At the SR transects 

 mean grain diameter decreased (increasing 0) from 

 stations 1-6, while stations 6 and 7 had nearly equal 

 grain size (2.57 and 2.53 0). Organic content was high- 

 est at SR station 6, but values ranged only from 2.33 

 to 3.50% of dry sediment weight. 



Children's Bay Cay and the Shark Rock site showed 

 highly significant correlations among all of the vari- 

 ables: water depth, seagrass shoot density, above- 

 ground seagrass biomass, and standing crop of macro- 

 detritus (Table 3). Weakest correlations (r = 0.586 to 

 0.631) occurred between detritus and the other vari- 

 ables at Shark Rock in February, when abundance of 

 detritus was low. Correlations between macrophyte 

 and depth characteristics remained highly significant 

 when all sites, stations, and dates were included in 

 regression models (Table 3) suggesting that the rela- 

 tionships are relatively universal in the study area. The 

 highest correlation occurred between seagrass shoot 

 density and water depth (?• = 0.930), and weakest cor- 

 relations were found between detritus biomass and the 

 other variables. 



Concin density patterns 



At CBC there was an increase in conch density in both 

 July and February along the transects from station 

 1-5, except for a small decrease in February from sta- 

 tion 4 to station 5 (Fig. 1 ). Densities in July were similar 



