Optimum survival conditions for egg develop- 

 ment and hatching success for M. mercenaria (30° 

 C and 34%o salinity) were determined by Ong and 

 Costlow ( 1970). Salinity in the present study var- 

 ied between 32.0 and 36.0%o and averaged 34.4"/oi) 

 in all experiments. Air and water temperatures in 

 the control room fluctuated from 27° to 33° C with 

 water temperature generally 0.5°-1.0° C lower. 

 Dissolved oxygen levels were measured twice 

 monthly. Nitrites and ammonia levels were 

 evaluated weekly and never exceeded 0.089 and 

 0.073%o, respectively. Lighting was regulated for 

 16 h light: 8 h dark and utilized Vita-Lite- bulbs 

 which simulated the natural spectrum of sunlight 

 (Dugan et al. 1975). 



Experiment 1(13 April-31 July) 



Crabs were divided into three test groups, with 

 similar ranges of animal size and egg mass color 

 (maturity) and were acclimated to tanks for at 

 least 18 h. Initially, individual crabs were exposed 

 to ambient indoor air conditions in separate cages. 

 This procedure was modified after the first series 

 to simulate commercial holding techniques more 

 closely by placing crabs from a single group into 

 loosely covered wooden slat boxes located in direct 

 sunlight. After desiccation, crabs were returned to 

 holding tanks and observed every 24 h until all 

 eggs hatched. Group I (control) crabs remained in 

 water throughout the experiment. Group II and 

 Group III crabs were desiccated for 2 and 5 h, 

 respectively. Total number of crabs for each group 

 was: 35-Group I, 34-Group II, 33-Group III. 



Experiment II (S August-21 September) 



Desiccation procedures were identical to mod- 

 ified procedures in Experiment I; added stress 

 from claw removal was introduced after desicca- 

 tion. Claws were removed using commercial har- 

 vesting methods by inducing autospasy (loss of 

 appendage through externally applied pressure). 

 In this technique, claws were grasped firmly and 

 ventral pressure applied until the fused basis- 

 chium stopped against the coxa. Further flexion 

 strained the autotomizer muscle, and separation 

 of the limb occurred at a natural fracture plane. 

 Excessive hemorrhaging is prevented by swelling 



^Reference to trade names does not imply endorsement by the 

 Marme Research Laboratory, FDNR or the National Marine 

 Fisheries Service, NOAA. 



of a hypodermal diaphragm located at the fracture 

 plane. 



Group IV (control) crabs remained in water 

 throughout the experiment and had similar 

 treatment as Group I. Group V and Group VI crabs 

 were desiccated for 2 and 5 h, respectively, then 

 declawed. Declawed crabs were placed im- 

 mediatedly into holding tanks and observed every 

 24 h as in Experiment I. Total number of crabs for 

 each group was: 30-Group IV: 34-Group V; and 

 35-Group VI. 



Crabs continuously discarded eggs from egg 

 masses. Single eggs were shed when females 

 raised their bodies on claws and legs and preened 

 (combed) egg masses with rear legs. Egg stalks 

 containing up to several hundred eggs (clumps) 

 were also frequently shed. Aeration of eggs by 

 rapid abdominal movement also occurred at this 

 time. Detached eggs, larvae, and other egg mass 

 products retained in individual glass tanks were 

 removed daily and preserved in 10*"^ Formalin 

 prior to counting. 



.\nalysis 



Hatching occurred from to 9 days after day of 

 experimental stress. Complete hatching generally 

 required 24-48 h, and organic matter retained in 

 glass tanks after that time was principally dead 

 eggs, deformed larvae, or empty egg cases cleaned 

 from pleopods. 



The day with highest number of normal first- 

 stage larvae was called major hatch. Days before 

 and following major hatch were called prehatch 

 and posthatch. 



Eggs from a single ovigerous female were ob- 

 served microscopically to determine normal 

 hatching process and identify normal first-stage 

 larvae. Initial breaking of the chorion enabled 

 larvae to emerge head first from the egg. Vigorous 

 abdominal flexing by the larvae cast off the egg 

 case and induced shedding of the prezoeal cuticle 

 and full extension of the rostral and lateral spines. 

 In a few instances, spinular extension was delayed 

 until complete seperation from the egg, but all 

 prezoea yielded normal, active free-swimming 

 first-stage larvae within minutes of initial hatch. 

 Eggs removed from the same female after desicca- 

 tion were observed for comparison. Increased 

 numbers of inviable eggs and partial hatches were 

 evident. Numerous prezoea, unable to cast off pre- 

 zoeal cuticles, died after continued struggle. Suc- 

 cessful first-stage development was reduced, and 



696 



