SERFLING and FORD: ECOLOGICAL STUDIES OF PANULIRUS INTERRUPTUS 



sea during their typical 5-10 mo larval existence. 

 Obviously, the larvae must return not only to the 

 coastal area, but also to very shallow nearshore 

 zones if they are to transform and become es- 

 tablished as demersal juveniles. 



Previous investigators (Lindberg 1955; Johnson 

 1956, 1960, 1971; Saisho 1966; Sims and Ingle 1966; 

 Lazarus 1967; Chittleborough and Thomas 1969; 

 Chittleborough 1970) have postulated for several 

 species that this recruitment in nearshore waters 

 takes place during the phyllosoma stage, possibly 

 through the action of countercurrents, upwelling, 

 and eddies. Several studies, particularly those of 

 Johnson (1960) and Chittleborough (1970), have 

 shown clearly that large numbers of late stage 

 phyllosoma larvae do remain well within the coast- 

 al areas in which the earlier larval stages occur. 

 Evidence presented by Johnson (1960) also has 

 shown that hydrography plays a major role in re- 

 taining a supply of late stage phyllosomes, and 

 presumably pueruli, within reasonable distances 

 from the coast. The presence, within one net haul, 

 of several different phyllosome stages that must 

 have been produced months apart, and the 

 presence of late stage phyllosomes at the same 

 locality, is good evidence that mixing processes 

 and retaining eddies prevent wholesale flushing of 

 these larvae from the coastal area. However, the 

 late stage phyllosomes seem to be concentrated 

 primarily in areas 50-250 km offshore, and the 

 specific mechanism of onshore movement and 

 recruitment has not been demonstrated. 



If there were major active or passive 

 movements of late stage phyllosomes toward 

 shore, then one would expect to find relatively 

 large numbers of them in shallow, inshore waters 

 as well, or at least a trend in this direction. Most of 

 the sampling reported by Johnson (1956, 1960) was 

 conducted in waters 8 or more kilometers ( > 5 

 miles) offshore. However, studies of the distribu- 

 tion and abundance of phyllosoma larvae of P. in- 

 terruptus in San Diego waters much closer inshore 

 by W. E. Hazen and J. H. Rutherford (pers. com- 

 mun.) during the summer months of 1969-1970, 

 employing surface and oblique net tows, failed to 

 collect any individuals older than stage 2. This 

 suggests that the later stages occur either many 

 kilometers offshore, as observed by Johnson (1956, 

 1960), or are concentrated in unknown areas. 



For lack of evidence to the contrary, it has also 

 been suggested that these phyllosoma larvae oc- 

 curring far offshore are lost to the population and 

 must perish. For similar reasons, Lindberg (1955) 



and Johnson (1960) have speculated that when 

 these phyllosomes moult into the puerulus stage, 

 the puerulus quickly settles to the bottom while 

 still in deep water. Presumably, some of these are 

 then able to migrate onshore to the shallow coastal 

 nursery areas as benthic puerulus or postpuerulus 

 forms. 



However, in light of our behavioral observations 

 on both pueruli and juveniles, another more likely 

 explanation is that the puerulus stage may have 

 evolved specifically for this purpose of recruit- 

 ment. These observations suggest to us that the 

 puerulus is a transitional, pelagic stage specifically 

 adapted for directional swimming, and that it is 

 capable of returning by active means to nearshore 

 nursery areas suitable for settlement, thereby 

 fulfilling the key role in recruitment. During this 

 process, the surface-swimming and associated 

 positive phototactic behavior of the puerulus stage 

 probably aid it in locating the shallow nearshore 

 areas which our related observations suggest are 

 required as nursery grounds for the early juvenile 

 stages. 



Exactly how important a role the puerulus stage 

 plays in the recruitment of the demersal popula- 

 tion probably depends on three factors: 1) the 

 degree of "assistance" contributed previously by 

 the late phyllosoma stages which may move ac- 

 tively, e.g., by vertical migrations, into 

 shoreward-directed currents or eddies; 2) how ef- 

 fective the puerulus is in travelling over long dis- 

 tances, with regard to both swimming speed and 

 endurance; and 3) how well the puerulus can 

 navigate, considering the fact that aimless wan- 

 dering or swimming away from the coast would 

 markedly reduce its probability of survival. 



It seems reasonable to expect that the puerulus 

 can swim nearly continuously, as other nektonic 

 crustaceans, such as euphausiids, apparently do. If 

 so, our estimate of an 8 cm /sec average swimming 

 speed for the puerulus indicates it has the poten- 

 tial to travel approximately 7 km (4.3 miles) per 

 day, or about 500 km (350 miles) during the period 

 of 80 days estimated as the approximate average 

 duration of this stage. Thus, the 160-320 km 

 (100-200 mile) distance from shore at which John- 

 son (1960) found most late stage P. interruptus 

 phyllosomes (Figure 9) could be within the basic 

 swimming capabilities of the puerulus stage, even 

 if part of the time was spent swimming against 

 surface currents or in an inactive state. 



The current patterns off the southern California 

 and Baja California coasts are complex, and have 



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