Lavalli: Survival and growth of Homarus amencanus fed plankton diets 



67 



this hypothesis, postlarvae and early juveniles in labor- 

 atory settings have been observed to lunge out of their 

 burrows to grab at food (amphipods) passing by (Ber- 

 rill 1974 with//, gammarus; Barshaw and Bryant-Rich 

 1988) or to stalk swimming amphipods (Good et al. 

 1982). Also, Crnkovic (1968) suggested that the crea- 

 tion of new openings in existing Nephrons norvegicus 

 burrows may be linked to searching for food within the 

 sediment. 



The intermolt periods, with the exception of that for 

 the mesoplankton-fed group between Stages VIII and 

 IX, were consistent with or shorter than previous 

 studies at the same average temperature (19°C) (Tem- 

 pleman 1948, as reported in Wilder 1953) and were 

 close to the values predicted by Hudon (1987) for the 

 same stages. These results show that early-juvenile 

 lobsters fed on mesoplankton are able to capture it ef- 

 fectively enough to keep pace with the brine shrimp- 

 fed lobsters in terms of intermolt periods until Stage 

 VIII. At that time, the mesoplankton-fed lobsters spend 

 nearly twice as much time in intermolt than either of 

 the brine shrimp-fed groups. This result could be in- 

 dicative of one of three conditions or some combina- 

 tion of all of them: (1) Either the lobsters became less 

 efficient at capturing the plankton, (2) the planktonic 

 organisms were not present in sufficient numbers in 

 this study to compete with a brine shrimp diet at later 

 stages, or (3) dietary requirements change with later 

 molt stages. 



In support of the first hypothesis is the fact that the 

 claws of the postlarvae are small and symmetrical prior 

 to Stage VIII. The claws slowly develop into the 

 crusher and seizer claws during the early-juvenile 

 stages; concomitant with this gradual development is 

 a change in the posture of the lobster from one that 

 is completely defensive (withdrawing or tail-flipping) 

 to one that is more aggressive (Lang et al. 1977), and 

 a change in the muscle fiber pattern and innervation 

 of the two types of claws (Govind 1984). At Stage VIII 

 the claw asymmetry is well established and the fiber 

 composition and innervation are nearly the same as 

 that found in the adult (Govind and Pearce 1986). These 

 changes may indicate a shift in the feeding strategies 

 used by the lobster, where capture of small benthic 

 organisms becomes more important than the capture 

 of planktonic organisms at or near Stage VIII. 



As for the second hypothesis, Bordner and Conklin 

 (1981) determined that older juvenile lobsters could 

 consume up to 10% of their body weight per day. Dur- 

 ing this entire experiment, each group of lobsters was 

 fed more than 10% of their body weight per day. There- 

 fore, it seems unlikely that the later stages of lobsters 

 were underfed on the mesoplankton diet. Finally, diet- 

 ary requirements might indeed change as the lobster 

 becomes more able to defend itself and thereby forage, 



and as the claws develop the ability to crush small 

 molluscs; however, this experiment was not designed 

 to answer such a question. 



In conclusion, the results from this experiment con- 

 tradict those of Barshaw (1989) and Daniel et al. (1985) 

 in that they show no difference in growth and survival 

 of early-juvenile lobsters (Stages V and VI) fed on a 

 diet of mesoplankton versus a diet of frozen brine 

 shrimp in filtered seawater. Stage VI-VIII lobsters are 

 able to survive and grow on planktonic diets, but after 

 Stage VIII they experience molt delays when compared 

 with lobsters fed frozen brine shrimp diets. Despite this 

 delay, the mesoplankton diet allows the early juveniles 

 the opportunity to reach the predicted (Hudon 1987) 

 winter stages of Stage VI (for late-fall settlers) to IX 

 or X (for August settlers) without the need for other 

 benthic food. Diets composed of smaller members of 

 the mesoplankton plus microplankton do not provide 

 sufficient nutrition to support survival in periods of low 

 food abundance. 



Acknowledgments 



I thank Mike Syslo and Kevin Johnson of the Massa- 

 chusetts State Lobster Hatchery for supplying me with 

 Stage IV lobsters, and Dr. Harold Edgerton for in- 

 struction in the technique of silhouette photography. 

 I also would like to thank Dr. Joe Costa (formerly of 

 BUMP) for getting the boat up and running, and Paula 

 Dolan (formerly of University of Tampa), Leslie Sam- 

 mon (formerly of Mt. Holyoke College), and Lee 

 Kefauver for their help in running the experiments and 

 their willingness to go on plankton tows during the 

 early hours of the morning in rain or shine. Drs. Jelle 

 Atema, Stanley Cobb, Diana Barshaw, John Castell, 

 and three anonymous reviewers provided helpful com- 

 ments on the manuscript for which I am grateful. 



Citations 



Able, K.W., K.L. Heck, M.P. Fahay, and C.T. Roman 



1988 Use of salt-marsh peat reefs by small juvenile lobsters 

 on Cape Cod, Massachusetts. Estuaries 11:83-86. 



Andrea, J.J. 



1975 The nutritional adequacy and acceptability of several 

 natural prey species for larval Homarus americanus (Milne- 

 Edwards) in culture. M.S. thesis, Mar. Sci. Res. Cent., State 

 Univ. New York, Stony Brook, 53 p. 



Barshaw, D.E. 



1989 Growth and survival of post-larval lobsters, Homarus 

 americanus, on a diet of plankton. Fish. Bull., U.S. 87: 

 366-370. 



Barshaw, D.E., and D.R. Bryant-Rich 



1988 Long-term survival and behavior of early juvenile lob- 

 sters, Homarus americanus, in the three naturalistic sub- 

 strates: Mud, rock, and eelgrass. Fish. Bull., U.S. 86:789-796. 



