BARSHAW and BRYANT-RICH: EARLY JUVENILE AMERICAN LOBSTER 



Mortality 



There was an initial mortality of the American 

 lobsters in all habitats followed by no deaths in the 

 winter and another die-off in the spring (Fig. 2). The 

 mortality rate for American lobsters in eelgrass was 

 significantly lower than those in the mud or in the 

 rocks (arcsine transformation, linear, least-square 

 regression, r^ = 0.75 eelgrass, 0.86 rock, 0.94 

 mud, comparison of slopes, P < 0.001). 



Molting and Size 



At the end of the experiment there was no signif- 

 icant difference in the size of the lobsters between 

 habitats, although the American lobsters in eelgrass 

 tended to be larger (Table 2C). There was also no 

 significant difference in the number of observed 

 molts between treatments. We observed molting by 

 six lobsters during the coldest part of the year when 

 the water temperature was between 1° and 2°C. 



Possible Prey 



The biomass of American lobsters (>1 mm) was 

 not significantly different among treatments, but 



the biomass of American lobsters in eelgrass tended 

 to be higher (ANOVA, Newman-Keuls test, P < 

 0.01, Table 3). There were fewer different genera 

 residing in the mud habitats, with the greatest diver- 

 sity in rock. 



DISCUSSION 



Initial observations showed that stage IV Ameri- 

 can lobsters started to burrow more quickly in eel- 

 grass and rock habitats. While several investigators 

 have shown that American lobsters choose rocks 

 over mud (Howard and Bennett 1979; Pottle and 

 Elner 1982; Botero andAtema 1982), no choice ex- 

 periments have used eelgrass as a substrate. Like- 

 wise, in this experiment we have not directly shown 

 that the lobsters prefer the eelgrass substrate 

 because they were not offered a choice. Speed of 

 settling would be indicative of a preference, how- 

 ever, if the method that lobsters use to choose a 

 substrate is to keep swimming if the habitat is un- 

 suitable, but settle if it is suitable. Such behavior 

 was observed in laboratory experiments by Botero 

 and Atema (1982). Indications that lobsters keep 

 swimming over unsuitable substrates was also ob- 

 served by Cobb et al. (1983) in the field. 



Q 

 < 

 LU 

 Q 



H 

 Z 

 LU 

 O 

 QC 

 LU 

 Q. 



NOV 



DEC 



JAN 



FEB 



MAR 



APR 



MAY 



Figure 2.— The cumulative percent of American lobsters that died in the three treatments, each 

 point represents a day when a lobster died. Fifteen lobsters per treatment were present at the begin- 

 ning of the experiment. Eelgrass vs. mud and eelgrass vs. rock, P < 0.001. 



793 



