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Fishery Bulletin 89|1), 1991 



food abundance, but this type of diet does not support 

 molting or growth (McConaugha 1985). Post-larval 

 lobsters are known to contain diatoms and other algae 

 in their guts (Herrick 1895, Williams 1907, Herrick 

 1911) which suggests some nutritional role for these 

 items, but one not fully understood nor clarified by this 

 experiment. The smaller planktonic organisms in the 

 meso/microplankton combination diet may not have 

 been present in sufficient numbers to make up for the 

 small amount of nutrients derived. Because the meso/ 

 microplankton diet consisted mostly of diatoms which 

 have a high content of silicon-based ash, it is likely that 

 this diet had a greater percentage of non-digestible 

 fiber or bulk than that in the mesoplankton or brine 

 shrimp diets (John Castell, Dep. Fish. & Oceans, Hali- 

 fax, N.S., Canada B3J 2S7, pers. commun., May 1990). 

 Furthermore, these smaller organisms may have been 

 more easily flushed out of the containers when the 

 water flow resumed. 



The results presented here also clearly support those 

 of Barshaw (1989) and Daniel et al. (1985) in terms of 

 postlarval and early-juvenile lobsters being capable of 

 surviving on mesoplankton, and in demonstrating high 

 survival among the brine shrimp-fed (in filtered sea- 

 water) and mesoplankton-fed groups through Stage VI. 

 These studies differ, however, in that Barshaw (1989) 

 found molt delays in her plankton-fed group between 

 Stages V and VI, whereas no molt delays were found 

 in this study until Stage VIII. Barshaw's lobsters also 

 took longer to molt into Stage VI (34 days for the 

 plankton-fed lobsters and 23 days for the brine shrimp- 

 fed lobsters) than did the lobsters in this experiment 

 (10 and 11 days for the same groups), indicating that 

 they were not receiving enough food and thus took 

 longer to build up the reserves to molt. In addition, both 

 Daniel et al. (1985) and Barshaw (1989) found that 

 lobsters fed on frozen brine shrimp in filtered seawater 

 were significantly larger than the filtrate-fed or 

 plankton-fed lobsters. This study found no such dif- 

 ference between the similarly treated groups. 



The differences between the two groups of lobsters 

 fed on brine shrimp diets were striking. Lobsters fed 

 brine shrimp in the filtered seawater had pale blue col- 

 oration and poor survival, with the majority of deaths 

 occurring during molting. However, this difference in 

 survival was not present until after Stage VI where 

 Barshaw's (1989) experiment ended. Similar drops in 

 survival of brine shrimp-fed lobsters in filtered sea- 

 water after Stage VI have been observed by Colleen 

 Boggs (Edgerton Res. Lab. [in collaboration with the 

 Kravitz Lab., Harvard Medical School], New England 

 Aquarium, Boston 02110, pers. commun., summer 

 1990). Certain strains of brine shrimp promote better 

 growth than others (McConaugha 1985), and the suc- 

 cess of one strain versus another is linked to its fatty 



acid content (Fujita et al. 1980), the presence of which 

 is extremely important for the survival of postlarval 

 and early-juvenile American lobsters (D'Abramo et al. 

 1981). The San Francisco Bay brand used in this ex- 

 periment is intermediate in lipid content (McConaugha 

 1985), but even different lots of the same strain of brine 

 shrimp are known to be highly variable in quality 

 (Eagles et al. 1984, 1986). Thus, whatever nutritional 

 component was lacking in the lot of the brine shrimp 

 used in this experiment was compensated by the 

 planktonic organisms entering through the ambient 

 water supply, since the brine shrimp-fed group of 

 lobsters in unfiltered seawater showed high survival, 

 a greater weight increase compared with those in 

 filtered seawater, and wild-type coloration. What is 

 particularly interesting, though, is that while the lob- 

 sters fed brine shrimp in unfiltered seawater were 

 nearly twice as heavy at Stage IX as both those fed 

 brine shrimp in filtered seawater and mesoplankton, 

 there was no significant difference at Stage IX between 

 any of these groups in terms of carapace lengths. 

 Weight, therefore, might be a more important index of 

 growth in early-juvenile lobsters. The carapace lengths 

 achieved by the three surviving groups of lobsters at 

 Stage IX were shorter than those predicted by calcula- 

 tions of Hudon (1987) from early juveniles captured in 

 the field. This contradiction may have resulted from 

 the lobsters used in this experiment being hatchery- 

 and laboratory-reared and thus being typically smaller 

 than wild lobsters at Stage V (pers. observ.). 



The difference in weights at Stage IX between lob- 

 sters fed brine shrimp in unfiltered seawater and those 

 fed mesoplankton indicates that growth (as well as sur- 

 vival) might be significantly enhanced if the lobsters 

 have access to both a planktonic diet and a diet of small 

 benthic organisms. Andrea (1975) demonstrated that 

 lobster larvae (Stages I-IV) fed frozen copepods or 

 frozen amphipods had significantly higher survival 

 rates than those fed frozen brine shrimp. Furthermore, 

 those larvae fed live copepods had higher survival than 

 those fed both live and frozen adult brine shrimp when 

 held under the same rearing conditions. Andrea's data 

 also showed that the increase in carapace length and 

 the gain in weight by lobsters fed diets of live copepods 

 were comparable to the increases found in lobsters fed 

 live brine shrimp. 



Evidence to date indicates that early juveniles are 

 found in shallow subtidal areas (Cooper and Uzmann 

 1980, Hudon 1987, Able et al. 1988, Wahle 1990) where 

 they would have access to suprabenthic plankton and 

 epiplankton (Wieser 1960, Cornet et al. 1983) as well 

 as surface plankton that vertically migrate in response 

 to light/dark conditions (Hardy 1970). They would also 

 have access to the many benthic organisms found in 

 subtidal areas (Orth 1973, Reise 1977). In support of 



