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Fishery Bulletin 89(1), 1991 



frozen) and artificially prepared compound 

 diets. Daniel et al. (1985) demonstrated 

 that Stage-IV and early-juvenile American 

 lobsters were capable of surviving and 

 growing on a frozen filtrate diet consisting 

 of 99% barnacle larvae and 1% calanoid 

 copepods; however, these filtrate-fed 

 lobsters were significantly smaller (by 17%) 

 than lobsters fed on frozen adult brine _. 

 shrimp. Similarly, Barshaw (1989) found 

 that Stage-IV American lobsters were 

 also capable of surviving and growing 

 through two molts on a diet of live, uniden- 

 tified plankton (size 152-1000/um), al- 

 though the plankton-fed lobsters were 

 smaller and had a greater intermolt period 

 from Stage V to VI than those fed on 

 frozen brine shrimp. In all of the above 

 studies, there were no differences in mor- 

 tality between the different groups of fed 

 lobsters. 



This study examined the survival and 

 growth of early-juvenile (Stages V-IX) 

 American lobsters fed on diets of meso- 

 plankton (95-lOOO^m) and a meso/micro- 

 plankton combination (25-95 ^m) while 

 using frozen brine shrimp diets for reference. Studies 

 with other crustaceans indicate that phytoplankton 

 may be used as a supplement when zooplankton abun- 

 dance is low and its presence may extend the period 

 of survival over that observed for starved animals 

 (McConaugha 1985). However, the nutritional value 

 of phytoplankton is highly dependent on its content 

 of essential fatty acids which can vary in response 

 to temperature, dissolved nutrients, light, and age 

 (Castell and Kean 1986). While American lobsters 

 have not been classified as algal feeders (Lebour 

 1922), stomach content analyses of the larvae and 

 postlarvae indicate that diatoms and other algae 

 form part of their diet (Herrick 1895, Williams 1907, 

 Herrick 1911). Recently, Lavalli and Barshaw (1989) 

 have shown that Stage-IV and -V American lobsters 

 are capable of removing particles from the water 

 column to at least a size of 70^m, indicating that early- 

 juvenile lobsters may be able to utilize small organ- 

 isms in the mesoplankton and microplankton. This 

 study was designed, in particular, to determine two 

 things: (1) Whether early juveniles could utilize 

 an already-proven diet (mesoplankton) for Stage-IV 

 and -V lobsters throughout much of their first season 

 of molting activity, and (2) whether early juveniles 

 could extend survival by utilizing the organisms found 

 in the smaller range of mesoplankton and in the 

 microplankton. 



Brine Shnmp/Unlillered Seawater 

 Brine Shrimp/Filtered Seawater 

 Mesoplankton 

 D " Meso/microplankton 



Figure 1 



Mean number of original 20 lobsters surviving through the 107 days of the 

 experiment (molt stages V-IX) on each of the diet regimes: brine shrimp 

 in unfiltered seawater, brine shrimp in filtered seawater, mesoplankton 

 (95-1000 /jm) in filtered seawater, meso/microplankton combination (25-95 

 fim) in filtered seawater, and starved. 



Materials and methods 



Prior to the beginning of the experiment, Stage-IV 

 American lobster siblings Homarus americanus were 

 held collectively in a seawater table supplied with am- 

 bient, unfiltered seawater and were fed ad libitum on 

 frozen adult Artemia (San Francisco Bay type). Sib- 

 lings were used for the experiment, since genetic dif- 

 ferences between females can produce significant dif- 

 ferences in weight among similarly raised juvenile 

 lobsters (Conklin et al. 1975, Hedgecock and Nelson 

 1978). The lobsters were then randomly assigned to one 

 of four groups of 20 animals: a mesoplankton-fed group 

 (95-1000^m), a meso/microplankton combination-fed 

 group (25-95 ^m), a frozen brine shrimp-fed group, and 

 a starved group. Upon assignment, individual lobsters 

 were placed into plastic trays (Rubbermaid Drawer 

 Organizers, No. 2915) with dimensions 224 mm long x 

 75 mm wide x 50mm deep, and volume of ~750 mL. 

 Each tray was modified to include a sidewall screen for 

 water flow and a dark -grey PVC tube (10 mm diameter) 

 glued to the bottom which could act as a shelter. The 

 trays were provided with ambient seawater which was 

 filtered with a dual-cartridge filtering system (a 50-^m 

 honeycomb filter followed by a 5-^m nominal filter). 

 They were arranged in a Latin square design to inter- 

 sperse the treatments and were kept in darkness, ex- 

 cept during cleaning and feeding periods, as previous 

 investigations demonstrated that juvenile lobsters 



