FISHERY BULLETIN: VOL. 73, NO. 2 



DISCUSSION 

 Mode of Life of the Puerulus Stage 



Johnson (1960) and Lindberg (1955) speculated 

 that the puerulus of P. interruptua is a benthic 

 form, largely because it occurs so infrequently in 

 standard net tows. However, the results of this 

 study strongly suggest that it is a pelagic form, 

 and in particular a member of the surface- 

 dwelling neuston. Several lines of evidence sup- 

 port this conclusion. Our observations of many 

 free-swimming pueruli which were attracted to 

 night-lights revealed that the pueruli always 

 swam in the top few centimeters of surface water, 

 and no individuals were ever observed moving 

 toward the light from deeper water. Pueruli were 

 readily collected in habitat traps floating at the 

 surface. However, the occurrence of pueruli at 

 greater depths cannot be ruled out on the basis of 

 habitat trap evidence alone because the traps were 

 not maintained at greater depths. Although 

 preliminary and very limited, our surface 

 sampling with neuston nets yielded a much higher 

 catch per unit effort than did standard near-sur- 

 face and oblique tow sampling methods employed 

 by previous investigators. 



The puerulus stage of P. interruptus also has 

 specialized physical characteristics which suggest 

 that it is adapted to a pelagic existence. These 

 include: 1) heavily setose pleopods and a 

 streamlined body for efficient, forward swimming; 

 2) a transparent body completely devoid of pig- 

 mentation; and 3) extremely long, delicate anten- 

 nae which appear unsuitable for a benthic exis- 

 tence because they quickly break off upon 

 settlement. In addition, at the time the puerulus 

 moults into the first postpuerulus stage, it loses the 

 setose pleopods and acquires stronger antennae, 

 an expanded cephalothorax, and walking ability 

 typical of later demersal stages. In fact, pueruli we 

 collected and held in aquaria were never observed 

 walking upon the substrate, instead only clinging 

 to algae or crevices in rocks and shells. A more 

 detailed description of this transformation process 

 from puerulus to postpuerulus was developed in a 

 subsequent study by Parker (1972). 



Both Witham et al. (1968) and Phillips (1972) 

 reported that, in comparative tests between habi- 

 tat traps maintained on the surface and traps 

 anchored 1-4 m below the surface, all but a few 

 pueruli of P. argus and P. longipes cygnus were 

 collected in those at the surface. Phillips collected 



only 1 out of 38 pueruli in traps at 4-m depth, and 

 Witham collected 12 from one trap anchored on the 

 bottom in water 1 m deep, as compared to an 

 average of 27 pueruli in surface traps located 

 nearby. 



Sweat (1968) utilized a multiple plankton net 

 array for studying the depth preference of P. ar- 

 gus pueruli in the Florida Keys area. This system 

 consisted of three conical plankton nets mounted 

 from a bridge across a shallow channel connecting 

 Florida Bay with the Atlantic Ocean. The nets 

 were suspended at the surface, at mid-depth (1 m), 

 and on the bottom (2.3 m), and were operated for 

 2-h periods within the new moon phase during 

 evening flood tides. The largest proportion of the 

 pueruli were collected by the mid-depth net (116 

 at the surface, 418 at 1 m, 61 at 2.3 m depth). 

 However, this may have been due to the particular 

 conditions in the channel, including its shallow 

 depth, water turbulence, and the possibility that 

 the pueruli were in the process of settlement at the 

 time of sampling. 



In general, these observations by Sweat (1968), 

 Witham et al. (1968), and Phillips (1972) agree with 

 ours on P. interruptus. The pueruli of these species 

 seem to be restricted primarily to the ocean sur- 

 face, at least just prior to settlement. 



The Functional Significance of 

 the Puerulus Stage 



On the basis of morphology and our observations 

 of its behavior, the puerulus stage of P. interrup- 

 tus appears to be well adapted for directed, for- 

 ward swimming, as shown in Figure 5, rather than 

 for the passive, pelagic existence apparently 

 exhibited by all phyllosoma larval stages of spiny 

 lobsters. What, then, is the purpose of this directed 

 swimming? A possible answer is suggested by 

 considering the early life history of the scyllarid 

 lobster, Scyllarus americanus, which also has a 

 phyllosoma larval stage but no transitional 

 puerulus stage, moulting instead directly into a 

 nonswimming, benthic juvenile (Robertson 1968). 

 Some other scyllarid species have a transitional 

 form called a puerulus or, more properly, a nesto 

 stage. The phyllosoma larval period of S. 

 americanus is quite short (4-5 wk), thereby allow- 

 ing the larvae a much greater chance of remaining 

 near the shallow coastal areas suitable for later 

 demersal life. In contrast, the phyllosomes of 

 palinurid lobsters and other species of scyllarids 

 may be carried several hundred kilometers out to 



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