ECOLOGICAL STUDIES OF THE PUERULUS LARVAL STAGE OF THE CALIFORNIA SPINY LOBSTER , PANULIRUS INTERRUPTUSI

Ecological and related behaviorai studies of the puerulus larval stage of the California spiny lobster, Panulirus interruptus, involved the development and use of artificial and natural seaweed habitat traps, special paired neuston nets, and underwater night-lights for collecting and observing pucruli in nature. The results obtained indicate that pueruli first enter the coastal waters off San Diego, Calif. , during May, and continue to appear regularly through September, but with no apparent relationship to lunar or temperature cycles. Pueruli exhibit a strong attraction to floating habitat traps containing the surfgrass Phyllospadix torreyi and to bright lights at night. The results also suggest that the puerulus is a surface-swimming, pelagic form which may actively seek out specific nearshore areas for settlement, and thereby serve the important function of returning larval stages to areas suitable for demersal life of the young juveniles. Previous studies of the California spiny lobster, Panulirus interruptus (Randall), and other spiny lobster species have concentrated primarily on either the adult or phyllosoma larval stages, leaving the biology of the intermediate, yet very important, puerulus and juvenile stages relatively unknown. This is particularly true for P. interruptus. Prior to the present study, essentially nothing was known about the ecological requirements or behavior of the puerulus or early juvenile stages, which together represent a period of 2-3 yr in the life history of this species. This is an unfortunate situation for an animal as heavily exploited by a commercial fishery as the California spiny lobster because, as Thorson (1950) has indicated, the abundance of any adult population is primarily dependent on the recruitment, survival, and growth of its larval and juvenile stages. Consequently, attempts to improve fishery yields through a better understanding of adult behavior and population ecology alone provide only a partial and temporary solution to the problem. Increasing fishing pressure on the steadily declining stocks of P. interruptus and other spiny lobster species urges more than an academic interest in the ecological requirements of their puerulus and juvenile stages. On the basis of this 'Contribution No.3 from the San Diego State University Center for Marine Studies. 'Center for Marine Studies, San Diego State University, San Diego, CA 92182. Manuscript accepted June 1974. FISHERY BULLETIN: VOL. 73, NO.2, 1975. 360 information, for example, it may be possible to protect their natural habitats or to develop supplementary artificial habitats for them in nature. Techniques for culturing these stages under artificial conditions, as a means of supplementing natural stocks, must also be given serious consideration for the following reasons. Evidence concerning P. interruptus (Johnson 1956, 1960, 1971) and other palinurid species (see, for example, Chittleborough and Thomas 1969) suggests that a majority of the phyllosoma and puerulus larvae may be lost from the population due to their long larval life (5-10 mol, during which they may be swept hundreds of kilometers offshore. Because of their small size, the surviving postpuerulus and early juvenile stages probably experience much higher predation mortality rates than do the adults (Winget 1968). In addition, evidence from limited studies of other spiny lobster species, including P. argus, P. longipes cygnus, and Jasus edwardsii, suggests that the nursery grounds of their postpuerulus and early juvenile stages are located in protected bays or estuaries (Sheard 1949; Lewis et al. 1952; Witham et al. 1964, 1968; Sweat 1968; C. B. Kensler, pers. commun.). If such estuarine nursery grounds are required by the early benthic stages of P. interruptus, reduction of this type of natural habitat as the result of commercial developments and water pollution may create a "weak link" in the life history of this species, at least within part of its geographical range. SERFLING and FORD: ECOLOGICAL STUDIES OF PANULIRUS INTERRUPTUS Aquaculture of P. interruptus or other palinurid lobsters, starting with the egg, has been attempted by several investigators as a means of bypassing what appears to be an inefficient recruitment process in nature. Yet all attempts to culture the phyllosoma larval stages from the egg through to the puerulus stage have been unsuccessful (for example, see Dexter 1972). This approach does not appear to be feasible at the present time, particularly on a mass culture basis, due to the long duration (5-10 mo in nature) and the poorly understood requirements of the delicate phyllosoma larval stages. In contrast, the succeeding puerulus and juvenile stages of spiny lobsters respond well to laboratory culture (Kensler 1967; Witham et al. 1968; Serfling and Ford in press a, b). Thus, if the puerulus stage of P. Interruptus proves to be abundant and relatively easy to collect in large numbers, particularly in certain offshore waters where these individuals might otherwise be swept away from coastal nursery grounds, it may be advantageous to supplement natural stocks by collecting pueruli and holding them in mass culture under controlled, optimal conditions through at least the early juvenile stages. These pueruli could either be reared directly to a marketable size under artificial conditions, or returned to the oceim, after passing the potentially critical early juvenile stages, for final growth and maturation. This approach to spiny lobster culture has also been proposed for P. argus by Ingle and Witham (1969). The lack of ecological information on the puerulus stage of any spiny lobster species is due largely to the fact that investigators usually have been unable to collect more than a few individuals, despite extensive sampling in areas where they might be expected to occur. Consequently, the central question precluding further research has concerned the mode of life of the puerulus stage, i.e., whether it is primarily a benthic or pelagic form. Evidence presented in the literature thus far supports about equally each side of the issue. Investigators who have failed to collect more than a few isolated pueruli, even after years of extensive sampling by conventional methods (Lewis et al. 1952; Johnson 1956, 1960, 1971; Harada 1957; Saisho 1966; Sims and Ingle 1966; Lazarus 1967), have concluded that the puerulus stage of their respective species is either primarily benthic, or concentrated in unknown pelagic areas. On the other hand, Gurney (1942), Sheard (1949), George and Cawthorn (1962), Chittleborough and Thomas (1969), and Chittleborough (1970) were able to collect small numbers of individuals in net hauls far out to sea, and thus suggested that the puerulus is a free-swimming stage. Harada (1957) and Johnson (1960) reported collecting a few pueruli which were attracted to bright lights over shallow water at night, but both authors apparently believed they were lured from the bottom. Yet Lindberg (1955) reported that University of Hawaii personnel collected several pueruli of a Panulirus species which were attracted to surface night-lights in water several hundred meters deep, thereby eliminating the possibility that they were attracted from the bottom. Witham et al. (1968), Sweat (1968), Phillips (1972), and we have successfully attracted large numbers of pueruli to artificial habitat traps floating at the surface, thereby offering the first strong evidence that the puerulus is primarily a pelagic, surface-dwelling form. Preliminary observations made originally by J. C. Van Olst (pers. commun.) in the spring of 1968, demonstrated that puerulus larvae of P. interruptus occurring in local coastal waters could be attracted to bright lights suspended underwater near the surface at night. This discovery prompted the following investigation into several aspects of puerulus behavior and ecology. The specific objectives of this study were: 1) to determine the mode of life of the puerulus stage of this species, e;g. , whether it is primarily benthic or pelagic; and, having done so, 2) to develop and apply suitable field sampling techniques to study the general dynamics of puerulus recruitment with regard to seasonal, lunar, and daily periodicity, area of settlement, specific habitat preferences, and migratory behavior; and 3) to estimate the general abundance and possibility of collecting large numbers of this stage for use in aquaculture. Closely related studies were also conducted concurrently to investigate the habitat preferences and the natural growth rates of the early juvenile stages in nature, as well as the growth and survival of the juvenile stages at elevated temperatures in recirculating culture systems (Serfling 1972; Serfling and Ford in press a, b). MATERIALS AND METHODS The failure of standard sampling methods used by previous investigators to collect the puerulus