SERFLING and FORD: ECOLOGICAL STUDIES OF PANULIRUS INTERRUPTUS 



neuston nets was initiated late in the study, dur- 

 ing the period 3 September to 12 October 1969 

 (Table 4). The results of the habitat trap collec- 

 tions (Table 2) suggest that these towing opera- 

 tions were conducted during a period of very low 

 puerulus abundance, yet two pueruli were collect- 

 ed during two separate towing efforts. Unfor- 

 tunately, it was not possible to complete the 

 development of these nets and begin sampling 

 operations during the summer period of peak 

 puerulus abundance. 



Concurrent studies of the distribution and 

 abundance of the phyllosoma larval stage of P. 

 interruptus in the same inshore areas, using 

 standard 1 m and larger conical nets in surface and 

 oblique towing patterns, failed to catch any 

 pueruli (W. E. Hazen and J. H. Rutherford, pers. 

 commun.). In addition, considering that Johnson 

 (1956, 1960) obtained only a few pueruli during 7 yr 

 of extensive sampling with surface and oblique 

 hauls of a 1-m conical net, our preliminary results 

 suggest that use of this neuston net system 

 probably is a more effective sampling technique 

 and should be thoroughly evaluated in future 

 studies. These results also strengthen the ar- 

 gument that the puerulus is pelagic, occurs at the 

 surface, and is a temporary member of the neuston 

 community. 



Relationship of Puerulus Settlement 

 to Environmental Factors 



Efforts to relate the influx of pueruli in major 

 environmental factors, such as temperature, 

 salinity, and lunar phase, were complicated by lack 

 of information concerning other unmea-sured or 

 unknown variables which may have subtle effects 

 on the settlement of pueruli in the habitat traps. 

 These may include specific wave characteristics, 

 current velocity and direction, and water tur- 

 bidity. Therefore, the apparent low abundance of 

 pueruli during some periods might be due to their 

 failure to settle in the habitat traps, rather than 

 their absence from coastal waters. Variations in 

 surface salinity levels of water masses along the 

 open coast when our sampling was conducted were 

 very slight. Consequently, the influence of this 

 factor probably was negligible and showed no ob- 

 vious relationship to puerulus settlement, based on 

 data available for the area of the Scripps Institu- 

 tion pier. Variations in wave heights and surf 

 conditions occurring at the Scripps Institution 

 pier during the summer also were relatively small. 



Table 4.-Results of puerulus sampling with paired neuston 



nets. 



'Estimated from average boat speed and duration of tow. 



The range in height of swells recorded at the pier 

 was 0.3-0.9 m (1-3 feet), and showed no obvious 

 pattern in relation to puerulus settlement. 

 However, the following general relationships 

 between puerulus settlement and environmental 

 conditions seem apparent. 



Seasonal Periodicity 



The results of night-lighting during 1969 (Table 

 1), and habitat trap sampling conducted in 1969 

 (Table 2) are presented together in Figure 7. These 

 data indicate that the pueruli of P. interruptus 

 began to appear in nearshore San Diego waters 

 during late May, and occurred there continuously 

 until mid-September, apparently reaching their 

 greatest abundance during the first week of 

 August. The habitat traps could not be maintained 

 during rough winter surf conditions, and oc- 

 casional night-light efforts during the winter 

 were unsuccessful, so we were not able to establish 

 conclusively that pueruli are absent from 

 nearshore waters between October and May. 

 However, evidence presented by Johnson (1960) on 

 the seasonal periodicity of the later phyllosoma 

 stages of P. interruptus, which are abundant only 

 during the period from January to June, suggests 

 that there would be no major influx of pueruli 

 during the winter months, although a small 

 number of individuals might be present 

 throughout the year. 



Relationship to Water Temperature 



A comparison between surface water tempera- 

 tures and puerulus trap catches obtained at the 

 Scripps Institution pier indicates that the 



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