SERFLING and FORD: ECOLOGICAL STUDIES OF PANULIRUS INTERRUPTUS 



per trap), when all were in continuous use during 

 the same 90-day time period from June through 

 September 1969 (Table 2). Comparison of these 

 catch figures by a chi-square test for equality in- 

 dicates that the mean catch of the seaweed traps 

 was significantly higher than that of the Witham 

 traps (P < 0.05). The Witham habitat trap was 

 not effective, either when new or moderately 

 fouled with a variety of sessile organisms, yet the 

 natural seaweed habitat traps appeared to catch 

 well regardless of the condition of the plant 

 material. Variations in the abundance of pueruli 

 throughout the summer and differences in 

 settlement in the different habitat positions, as 

 discussed in subsequent sections, did not allow 

 specific comparisons to be made between results of 

 the habitat trap designs listed in Table 2. Yet 

 general comparisons indicate that there were no 

 major differences in catch between these trap 

 designs that are not attributable to the environ- 

 mental causes discussed in subsequent sections 

 below. However, the nylon bag habitat trap 

 (Figure 2E) proved to be the best in terms of cost, 

 ease of use, and durability. It also appeared to 

 catch as well as the other types, although tests 

 were begun too late in the final puerulus 

 settlement season during which we sampled to 

 verify this. Thus, the bag trap design is recom- 

 mended for future studies of this nature, and was 

 used by Parker (1972) in a later study. 



Habitat Trap Success in Relation 

 to Position on the Pier 



A comparison of the catch results of the "dou- 

 ble" and "single" frame seaweed habitat traps, as 

 shown in Table 2, indicates that more pueruli were 

 consistently collected from the B than the A posi- 

 tion on the Scripps Institution pier (Figure 1), 



when either type of trap was placed there. A com- 

 bined total of 65 larvae was collected in the B 

 position, versus only 24 in the A position by these 

 two traps during the same 82-day period from 2 

 July to 19 September. A comparison of these catch 

 figures by a chi-square test for equality indicates 

 that the catch at position B was significantly 

 greater than at position A (P < 0.05). No 

 explanation for this difference is apparent at the 

 present time, but it seems to indicate that there 

 may be subtle environmental effects which 

 influence puerulus settlement in habitat traps to a 

 greater extent than do variations in trap design. 



Significance of Nocturnal Illumination 

 of Traps in the Attraction of Pueruli 



The strongly positive phototactic response 

 exhibited by the puerulus stage during night- 

 lighting observations suggested that nocturnal 

 illumination may play an important role in the 

 successful operation of habitat traps. To evaluate 

 this, additional traps were maintained in an 

 unlighted area of the Scripps Institution pier (area 

 C in Figure 1). 



The results, summarized in Table 3, indicate 

 that during the period from 10 August to 29 Sep- 

 tember 1969, when each trap design was main- 

 tained at both the lighted (positions A and B) and 

 nonlighted (position C) pier locations, all traps 

 caught more larvae in the lighted positions. A total 

 of 38 larvae were collected over 132 "trap-days" (1 

 trap in place for a 24-h period = 1 trap-day) in the 

 lighted position, versus only 4 per 132 trap-days in 

 the nonlighted position. Comparison of these total 

 catch values by means of a chi-square test for 

 equality indicates that the value for the lighted 

 positions was significantly greater than for the 

 unlighted one {P < 0.05). This suggests that noc- 



Table 3.-A comparison of the number of pueruli caught in lighted and nonlighted habitat traps. For detailed 

 descriptions of trap types, and lighted and nonlighted pier positions, see text and Figures 1 and 2. 



Lighted (positions A and B) 



Nonlighted (position C) 



Type of 



habitat 



trap 



No. individuals 



collected 



per trap 



Sampling 

 period ' 

 (days)' 



Catch 



per 20 



trap-days 



No. individuals 

 collected 

 per trap 



Sampling 

 period 

 (days)' 



'Number of trap days during the period of 10 August to 29 September only (see Table 1). 

 ^Habitat trap not in place. 



Catch 



per 20 



trap-days 



367 



