Crabs were maintained in a recirculating aquarium in conditions that reflected those of their collection site in the fall (temperature: 13 degrees C and salinity: 33–34 ppt). Each crab was maintained in an individual experimental chamber that was submerged in the recirculating aquarium. Experimental chambers were individually plumbed so that each had a constant flow of water. Crabs were initially weighed and these initial weights were used to determine the amount of food that they would receive. Crabs were randomly assigned to food treatments which crossed four levels of food amount (1, 2, 4, 8 % of body weight per day) and five levels of proportion of that food that was animal tissue or algae (all animal, 0.25 animal and 0.75 plant, 0.5 of each, 0.75 animal and 0.25 plant, all animal). The red alga Chondrus crispus was the plant material offered to crabs in this experiment and the animal tissue was Tilapia filets.
Crabs were fed twice per week (Monday and Thursday), and uneaten food was removed after 48 h, dried at 70 degrees C for 48 h, and weighed. At the conclusion of the experiment we dissected each crab and removed the ovaries and the hepatopancreas. We calculated the gonadosomatic index (GSI), or the proportion of body weight allocated to the ovaries, and the hepatosomatic index (HSI), or the proportion of body weight allocated to the hepatopancreas.
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