KREKORIAN, SOMMERVILLE, and FORD: LOBSTER BEHAVIORAL INTERACTIONS 



3. There was a significant reduction in Homarus- 

 initiated actions with time as indicated by the 

 resuhs of a Spearman Rank Correlation Analysis 

 (r, = -0.66, P < 0.05; Siegel, 1956). Social 

 contact was excluded from the statistical analysis 

 of actor actions because it included and did 

 not differentiate H. americanus and P. inter- 

 rap^us- initiated interactions. Most social contact, 

 however, was initiated hy H. americanus. There 

 also was a significant decrease in behavioral 

 actions with time for P. interruptus responses 

 {r, = -0.82, P < 0.01). Only Panulirus walk 

 away and abdomen flex were considered. No 

 response was excluded from the statistical analy- 

 sis of reactor actions because it included both 

 H. americanus and P. interruptus responses. 



In the absence of shelter, some H. americanus 

 excavated a depression in the sand where they 

 remained when they were not roaming. When a 

 P. interruptus approached an H. americanus in 

 its sand depression, the likelihood of attack 

 increased, and the attacks appeared to last longer 

 and involve more pinching. 



Homarus vs. Panulirus with Shelter 



The addition of seven shelters reduced the 

 number of //omart/s-initiated interactions as 

 compared with the no shelter condition. A com- 

 parison of all Homari/s-initiated interactions 

 (both actor and reactor) between the shelter and 

 no shelter conditions indicated that Homarus- 

 initiated interactions for the shelter condition 

 were significantly reduced (P = 0.01, Wilcoxon 

 matched- pairs test; Siegel, 1956). There were a 

 total of 269 behavioral actions by actors and 177 

 by reactors (Table 2). Ninety percent (243) of 



the behavioral actions by actors and 86% (152) 

 of behavioral actions by the reactors occurred in 

 the 1510-1700 h observation period. 



Fourteen percent of the //omarus-initiated 

 interactions of actors were classed as social con- 

 tact, 42% as Homarus approach, 289c as Homarus 

 threat, and 169c as Homarus attack. The be- 

 havioral actions of the reactors were 38% no 

 response, 45% Panulirus walk away, and 16% 

 Panulirus abdomen flex. 



There was a total of 28 Pa/iw/i>us-initiated 

 behavioral actions for the five replicate experi- 

 ments. All were classed as Panulirus approach. 

 Thirty-four behavioral actions by H. americanus 

 (reactor) resulted. Of these, 1 was classed no 

 response, 2 Homarus walk away, 25 Homarus 

 threat, and 6 Homarus attack. Thus, 92% of 

 these responses of H. americanus to Panulirus 

 approach involved threat and attack. 



Most of the behavioral interactions that 

 occurred in the Homarus-Panulirus shelter 

 condition took place when the lobsters were out 

 of their shelters. On some occasions, however, 

 H. americanus attacked P. interruptus while they 

 were in shelters. When this occurred H. ameri- 

 canus entered the shelter through the front 

 entrance, the attack ensued, and P. interruptus 

 fled through the back entrance which was nearly 

 flush against the side of the tank. The amount of 

 time H. americanus remained in the shelter of 

 the displaced P. interruptus varied greatly. Some 

 H. americanus left the shelter within 1 min and 

 either roamed or displaced another P. interruptus 

 from its shelter. Others remained in the shelter 

 longer, and some for the duration of the observa- 

 tion period. Panulirus interruptus that ap- 

 proached//, americanus in a shelter were usually 



Table 3. — The total number of Homarus americanus -initiated behavioral interactions vnth Panulirus interruptus by day for the no 

 shelter condition {n = 5 groups). These totals include data from morning, noon, and evening observations. Social contact (SC) and no 

 response (NR) totals include both//, americanus and P. interruptus actions. However, the great majority of SC is Homarus initiated, 

 and the great majority of NR is derived from Panulirus. HA = Homarus approach; HT •= Homarus threat; HAT = Homarus attack; 

 PWA = Panulirus walk away; PAF = Panulirus abdomen flex. 



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