FISHERY BULLETIN: VOL, 86. NO. 4 



Table 3. — Average biomass (wet weight) and species list of organisms larger than 1 mm liv- 

 ing in the sediment of each treatment at the end of the expehment. 



Treatment 



Bivalve 



Polycheate 



Other 



Eeigrass: Mean biomass per tank 

 Mercenaha mercenaria 

 Yoldia (spp.) 



Rock: Mean biomass per tank = 



Andora oval is 

 Andora transversa 

 Mercenaria mercenaria 

 Mucoma (spp.) 

 Yoldia (spp.) 



8.2 ± 2.7 g 

 Capitella (spp.) 

 Clemenalla (spp.) 

 Glycera (spp.) 

 Lumbrineris (spp.) 

 Neris (spp.) 

 Spiondae (gen.) 

 Terebellida (gen.) 



3.28 ± 1.07 g 



Chrysopetalidae 



{Dysponetus pygmaeus) 

 Nephytidae (spp.) 

 Nereis (spp.) 

 Phyllodocdae (gen.) 

 Sapella (gen.) 

 Terebellida (gen.) 



Sipunculoidea 

 {Golfingia gouldi) 



Sipuculoidea 



{Golfingia gouldi) 

 Crustacea 



(Neopanope sayi) 



Mud: Mean biomass per tank = 4.4 + 1.07 g 



Geukendia demessus 

 Solemya velum 

 Yoldia (spp.) 



Glycera (spp.) 

 Nephtys (spp.) 

 Nereis (spp.) 

 Orbiniidae (spp.) 

 Terebelleda (gen.) 



The mud substrate appeared to be the least 

 suitable of the three tested since American lobsters 

 in eeigrass and rocks were without burrows for less 

 time than those in mud. However, even in the mud 

 habitat the lobsters had burrows for an average of 

 87.8% of the observations (Table 2B). The three 

 substrates used in this study were chosen partly 

 because of their differences, yet the lobsters man- 

 aged to build and maintain burrows in all three 

 substrates for eight months. This result clearly 

 shows that early juveniles have flexible behavior and 

 modify it to adapt to different substrates. 



The way that the American lobsters partitioned 

 the amount of time they spent on different activities 

 was also affected by the substrate in which they 

 lived. While lobsters in eeigrass and rock habitats 

 spent little time repairing their burrows, lobsters 

 in mud spent considerable time on repair (Fig. 1). 

 This result is consistent with the characteristics 

 of the three substrates. Eeigrass stabilizes the 

 underlying sediment (decreases erosion) by baffling 

 the water currents with its leaves and binding the 

 sediment with its roots (Scoffin 1970); rocks, al- 

 though usually found in areas of stronger currents, 

 provide a ready made solid roof; mud, however, is 

 more easily disturbed (Rhoads and Young 1970). If 

 one lobster did not have a burrow in the mud tanks, 

 its walking often destroyed the other lobsters' 

 burrows. 



The extra time that the American lobsters in mud 

 spent repairing their burrows was subtracted mainly 

 from investigation time (Fig. 1), perhaps because 

 there was not as much prey in the mud for the 

 lobsters to detect, so this activity was the most ex- 

 pendable. No significant differences were found 

 between the time budgets of the lobsters in eeigrass 

 and the lobsters in rocks; however, the lobsters in 

 eeigrass spent more time resting than investigating, 

 while the opposite was true of the lobsters in rock 

 substrate. 



The American lobsters in the eeigrass had a lower 

 mortality rate than those in either mud or rocks. 

 This result could have been due to the greater bio- 

 mass of possible prey animals living in the eeigrass 

 habitat, and/or the greater complexity of the eel- 

 grass habitat, which in essence separated the lob- 

 sters and ameliorated the effects of high density. 

 Seagrass beds in nature have also been shown to 

 have a greater biomass of species living in them than 

 the biomass of species living in less complex sub- 

 strates such as mud or sand (Orth 1973; Thayer et 

 al. 1984). 



The lower mortality rate of lobsters in eeigrass 

 led to a greater number of lobsters per tank in this 

 treatment. Higher concentrations of lobsters have 

 been shown to cause slower rates of growth in 

 lobster living in fairly unnatural substrates (Cobb 

 and Tamm 1974). In this study, the American 



794 



