Abstract.- Early juvenile (Stages 

 V-IX) American lobsters Homarus 

 arnericanus were fed diets of meso- 

 plankton in filtered seawater, meso/ 

 microplankton combination in fil- 

 tered seawater, and frozen brine 

 shrimp in both filtered and unfiltered 

 seawater to determine if mesoplank- 

 ton diets could sustain survival and 

 growth throughout most of the first 

 year of molts and if smaller zooplank- 

 ters and phytoplankton in the meso/ 

 microplankton diet could be utilized 

 as food and could sustain survival in 

 periods of low food supply. At the 

 beginning of the experiment, there 

 were no significant differences in 

 either carapace length or weight be- 

 tween the groups of sibling lobsters. 

 Lobsters fed mesoplankton had high 

 survival (80%) and significant in- 

 creases in both carapace length and 

 weight, although they weighed less 

 at Stage IX than those fed frozen 

 brine shrimp in unfiltered seawater. 

 Lobsters fed frozen brine shrimp in 

 filtered seawater had low survival 

 (15%), but did not differ significant- 

 ly at Stage IX from those fed meso- 

 plankton in terms of both carapace 

 length and weight. Lobsters fed 

 brine shrimp in unfiltered seawater 

 had high survival rates (95%) and 

 weighed nearly twice as much at 

 Stage IX than both the brine shrimp- 

 fed lobsters in filtered seawater and 

 the mesoplankton-fed lobsters; how- 

 ever, none of these three surviving 

 groups differed significantly in cara- 

 pace length at Stage IX. Intermolt 

 periods for the three surviving groups 

 were not significantly different until 

 the molt between Stage VIII and IX 

 when the mesoplankton-fed lobsters 

 took nearly twice as long to molt as 

 either of the brine shrimp-fed groups. 

 Lobsters fed meso/microplankton did 

 not molt out of Stage V and died 

 within 36 days of the 107-day experi- 

 ment. These results indicate that 

 mesoplankton diets promote growth 

 and survival of lobsters throughout 

 most of their first season of molting 

 and that larger planktonic organisms 

 may contain essential nutritional re- 

 quirements not met by brine shrimp 

 alone. However, the meso/microplank- 

 ton diet, consisting mostly of dia- 

 toms, does not provide sufficient 

 nutrition for survival during periods 

 of starvation. 



Manuscript accepted 6 August 1990. 

 Fishery Bulletin, U.S. 89:61-68 (1991). 



Survival and Growth of 

 Early-Juvenile American Lobsters 

 Homarus americanus Through Their 

 First Season While Fed Diets of 

 Mesoplankton, Microplankton, 

 and Frozen Brine Shrimp 



Kari L. Lavalli 



Boston University Marine Program, Marine Biological Laboratory 

 U/oods Hole, Massachusetts 02543 



Little is known of the natural forag- 

 ing activities of the settled postlarvae 

 (Stage IV) and early-juvenile (<1 

 year-old) stages of the American lob- 

 ster Homarus americanus, presum- 

 ably due to the inability of past inves- 

 tigators to locate them in the benthic 

 environment. Recently, Barshaw and 

 Bryant-Rich (1988) examined the be- 

 havior of the early-juvenile American 

 lobster in naturalistic settings in the 

 laboratory and found that they spent 

 a considerable amount of time pleo- 

 pod fanning (15% of the time) and 

 antennule flicking (15-40% of the 

 time) at the entrance of their bur- 

 rows. During their 8-month investi- 

 gation, Barshaw and Bryant-Rich 

 never observed an early-juvenile lob- 

 ster leave its burrow; of the several 

 instances where lobsters were seen 

 feeding, they captured amphipods 

 near the entrance of the burrow 

 twice while other observations in- 

 dicated that the lobsters were cap- 

 turing planktonic organisms via self- 

 generated currents which drew the 

 organisms toward the burrow en- 

 trance. Their observations are cor- 

 roborated by field cage studies of 

 Gregory Roach (Nova Scotia Dep. 

 Fish., Halifax, N.S., Canada B3J 

 3C4, pers. commun., Nov. 1989) 

 where he, too, never observed early- 

 juvenile American lobsters leave 

 their burrows during one year of 

 observations. 



While little is known about the nat- 

 ural diet of recently settled American 

 lobsters, Cobb et al. (1983) observed 

 presettlement Stage-IV American 

 lobsters capturing crab megalopae 

 and insects in the field. Stomach con- 

 tent analyses indicate that the Stage- 

 IV diet is similar to that of the larvae, 

 consisting of copepods, decapod lar- 

 vae, amphipods, algae, and diatoms 

 (Williams 1907, Herrick 1911, Tem- 

 pleman and Tibbo 1945). Although 

 most laboratory investigations have 

 used artificial feeds which wild early- 

 juvenile lobsters would never en- 

 counter, some studies have provided 

 information on naturalistic diets. 

 Emmel (1908) found that Stage-IV 

 American lobsters were capable of 

 surviving on planktonic organisms 

 obtained from the water alone. The 

 intermolt period for this group of 

 lobsters was significantly longer than 

 that for groups fed on beef, soft- 

 shelled clam, lobster muscle, or 

 shredded fish, but this result was 

 probably due to differences in the 

 overall amount of food available to 

 the groups, as unequal weights of 

 food were used. More recently, An- 

 drea (1975), D'Agostino (1980), and 

 Good et al. (1982) found that when 

 amphipods were used as a food 

 source, growth rates of larval, post- 

 larval, and early-juvenile American 

 lobsters improved significantly over 

 brine shrimp diets (both live and 



61 



