301 

 30' 



obile 

 Bay 



^o 3-^Cedar Point 



Mississippi Sound 



Little Daup h i n 



2 ^iS\ Island 

 6 



GULF OF MEXICO 



-+- 



88°10' 



Figure 1. — Section of the northern Gulf of Mexico 

 showing southwestern Mobile Bay and eastern Mis- 

 sissippi Sound with indicated prominent physical 

 features and location of numbered sampling stations 

 discussed in text. Station substrate types: unmarked 

 = intertidal rubble and shell beach; underscored = 

 undercut marsh; overscored = mud bank; encircled 

 = jetty. 



containing Juncus and Spartina roots and marsh 

 mussel (Geukensia) shells, generally about 1 ft (30 

 cm) in depth from top of marsh surface to bottom of 

 silty mud along tidal creeks at stations 9, 10, 11, 12); 

 from burrows 2-4 ft (61-122 cm) longX 2-3 in (50-75 

 mm) in diameter; crabs captured at mouths of 

 burrows, trapped near openings by inserting shovel 

 behind crabs and breaking burrow open, or taken by 

 hand from depths of burrows. 4) Jetty (among 

 boulders and stones at stations 13, 14); crabs cap- 

 tured by hand intertidally, and subtidally with aid of 

 mask and snorkel. 



Physical and biological factors, along with color and 

 behavior of mud crabs, were noted at each collection 

 site. Mud crabs were preserved in the field for 

 morphological studies or transported alive to the 

 laboratory and maintained in seawater aquaria until 



886 



used in feeding experiments. Three kinds of prey — 

 oysters, snails, and crabs — associated with the crabs 

 in nature were presented to both species in the 

 aquaria. 



Seven morphological characters were measured 

 with a metric vernier caliper for statistical analysis 

 (Fig. 2): Carapace, length in midline and greatest 

 width; body depth; third maxilliped, length of merus 

 and ischium; major chela, length and height of palm. 

 Third maxillipeds of crabs with carapace lengths of 

 <9 mm were not measured, nor were newly regen- 

 erated chelae. Male gonopods were examined with 

 the aid of a light microscope and scanning electron 

 microscope. 



Statistical analyses were performed at the Com- 

 puter Center of the University of Alabama, Mobile, 

 using the MUSIC STATPAK program (Jarvis 1974), 





