Ecological investigations of the late-stage phyllosoma and puerulus larvae of the western rock lobster Panulirus longipes cygnus

The distribution and abundance of the late-stage phyllosoma larvae of Panulirus longipes cygnus George and the distribution and densities of the final larval stage, the puerulus, both in the plankton and at settlement along the coast, were investigated. A total of 3,617 late-stage phyllosoma (Stages VI to IX) and 301 puerulus larvae were caught at 187 plankton stations during the July to November periods 1974, 1975 and 1976 off the west coast of Australia between 29°00 to 32°30S and 113°30 to 115°00E. The depth range sampled was 0 to 35 m on the continental shelf and 0 to 90 m off the shelf. During onshore/offshore cruises with similar sampling effort on and off the shelf, 1,169 late-stage phyllosoma larvae were taken, of which only 9 were caught on the shelf, and these near the outer edge. A series of cruises sampling two areas beyond the shelf near 29°30 and 32°00S yielded 2448 late-stage phyllosoma, with greater densities of larvae in the northern location. The settlement of puerulus-stage larvae along the coast in the same geographical range was also greater in the north than in the south. The data from the onshore/offshore cruises showed a definite effect of moon phase on numbers of puerulus larvae caught on the shelf, with higher catches near new moon. The low numbers of puerulus larvae (usually 0, 1 or 2 individuals) caught at all stations showed that the puerulus stage is sparsely distributed in the plankton. Fewer puerulus larvae were present at the surface than at lower depths, but it was not possible to determine a depth preference for the puerulus between 10 m and the lowest depths sampled because of the low catch numbers. No relationships were found between puerulus larvae density and surface-water temperature, salinity, or plankton biomass at each station. Data on the larval distributions indicate that, near the end of their planktonic existence, the majority of the late-stage phyllosoma larvae of P. longipes cygnus are not carried onto the shelf, where mixing of oceanic and continental shelf waters occurs only on the outer third, but are transported southward by oceanic circulation beyond the shelf. The puerulus moults from the last phyllosoma stage beyond the shelf and completes the larval cycle by swimming across the shelf and settling in the shallow reef areas.     

Laboratory growth of early juveniles of the western rock lobster Panulirus longipes cygnus

Growth in the laboratory of early juvenile Panulirus longipes cygnus George from the last larval (puerulus) stage to approximately 3 years of age is described. Specimens were held either in isolation or in groups of 3 or 5 rock lobsters per tank, at constant temperatures of 20° or 23°C (both ± 0.5 C°) or at the temperatures of the incoming seawater, which ranged annually between 14.9° and 25.9°C. Metamorphosis from the planktonic puerulus to the settled juvenile existence involved a reduction in size and usually took about two moults to complete. By this time the sexes could be distinguished. Growth in aquaria from the 2nd moult after puerulus until the juveniles were approximately 3 years of age was adequately described by exponential (von Bertalanffy) functions, with the growth curves gradually tapering off after the rock lobsters had reached 40 to 42 mm carapace length. Young juveniles were not gregarious until 20 to 25 mm carapace length (approximately 1.5 years old), however, growth rates were not depressed in individuals held in isolation up to approximately 3 years of age. Temperature markedly affected growth; the fastest observed growth up to 450 days was at 23°C. Variations in temperature resulted in decreased growth rates in winter and the reverse in summer in individuals at ambient temperatures. There was an increase in the moult increment at successive moults corresponding to increased carapace length, but increased growth rates were achieved through shortening the intermoult duration. The period of development from the puerulus stage until approximately 1.5 years of age is a distinct phase of development both of behaviour and growth.     

Spatial and temporal variation in the size at maturity of the western rock lobster Panulirus cygnus George

The sizes at which female and male western rock lobster Panulirus cygnus become mature were examined over 32 years from records at six localities along the coast of Western Australia. The size of males at maturity was estimated from a subset of these data by a morphometric and a physiological method, with both producing statistically similar results. Males were larger at first maturity than females at the same sites. For both sexes, the sizes at first maturity at each location correlated (P<0.05) with the mean annual water temperature at that location, decreasing from south to north along the mainland coast and being smallest at the offshore Abrolhos Islands. Smaller sizes at maturity were recorded for both sexes than have been published previously. One certain explanation for these differences is that management measures protecting females with ovigerous setae have distorted size compositions and the ratio of immature to mature females, thereby increasing the likelihood of capturing small mature females. However, these fishing effects cannot fully account for the progressive decline in CL₅₀ observed over the past 20 years. Other possible hypotheses considered include increases in water temperature over this period, as well as whether this change could be consistent with a genotypic response caused by the selective removal of large lobsters combined with high exploitation rates.     

Temporal variation of recruits as a basis of ephemeral genetic heterogeneity in the western rock lobster Panulirus cygnus

Allozymes were examined in quantitative lunar monthly collections of larval recruits of the western rock lobster Panulirus cygnus George over three recruitment seasons at two sites nearly 350 km apart in Western Australia. At Alkimos, the southern site, recruitment occurs in a relatively narrow peak early in the spring, whereas at the northern Houtman Abrolhos Islands, recruitment extends into the summer months. In the 1995/1996 recruitment season, the frequency of the GPI ^* 100 allele increased from early to late in the season, but the frequencies were indistinguishable at the two sites in each monthly collection. The combination of this temporal variation in allelic frequencies with the contrasting patterns of recruitment at the Abrolhos Islands and Alkimos resulted in genetically different cohorts at the two sites. This pattern was ephemeral, as it was not repeated in the subsequent two years. Thus, ephemeral genetic patchiness in P. cygnus can be generated by the locally-specific genetic mix of recruits obtained from a common larval pool. This mechanism is the probable explanation of previously observed temporal and possible spatial genetic variation in adult P. cygnus, and highlights the importance of studying recruitment in order to understand the genetic structure of marine species. Received: 22 February 1999 / Accepted: 8 June 1999     

Biochemical evidence for absence of feeding in puerulus larvae of the Western rock lobster Panulirus cygnus (Decapoda: Palinuridae)

Changes in energy-reserves during the transition from phyllosoma through peurulus to juvenile in the Western rock lobster Panulirus cygnus (George, 1962) were studied by means of carbon: nitrogen analysis. Specimens were collected by means of plankton nets and puerulus collectors along the Western Australian coastline between July 1992 and January 1993. Reserves are accumulated during the last phyllosoma stage and are consumed during the puerulus stage. These observations support the hypothesis that the puerulus is a non-feeding stage. Based on basal metabolic rate and observed changes in reserves, the natant puerulus stage is calculated to last a maximum of 21.6d. When the estimated cost of swimming is taken into account, the duration is reduced to perhaps a week. The latter time-span corre-sponds with field observations that both abundance of planktonic pueruli in oceanic waters and inshore settlement of pueruli peak in the week around new moon. At 18°C, the puerulus metamorphoses to the first juvenile stage within 12.8 d after settlement; at 23°C this is reduced to 8.3 d. After settlement, puerulus larvae have an energetic advantage at elevated temperatures; the increased cost of metabolism is compensated by an accelerated development. The natant puerulus, however, appears to be slightly disadvantaged energetically at elevated temperatures; both C:N ratio and ash-free dry weight of pueruli just after settlement show a decreasing trend as the water temperature increases. The effect of water temperature and the distance from the edge of the continental shelf to the shore on consumption of energy reserves might provide a mechanism to partially explain temporal and spatial patterns in puerulus settlement.     

Factors affecting the distribution of rock-lobster larvae (Panulirus longipes cygnus), with reference to variability of plankton-net catches

One of the major problems in the quantitative study of the distribution of larvae of the western rock lobster Panulirus longipes cygnus George, is the high variability in planktonnet catches taken at night, even when replicate hauls are made at a single station. Some of the possible causes of this variability are considered. The density of early and late-stage phyllosoma larvae caught at the surface at night showed no direct relationship to either temperature or salinity. Early-stage phyllosoma larvae were equally well represented at the surface under all light conditions encountered at night. In contrast, the density of late-stage phyllosoma larvae at the surface was, on an average, four times greater on dark nights than on bright moonlight nights. The mean density for all phyllosoma stages decreased rapidly with depth, i.e., from 0.70/1000 m³ at the surface to 0.04/1000 m³ at 25 to 35 m, indicating that the vertical movements at night are not very extensive. The density of early-stage phyllosoma larvae in the surface at night showed no relationship to micronekton biomass (measured as wet weight). Density of late-stage phyllosoma larvae at the surface at night increased slightly, but significantly, with increase of micronekton biomass, possibly indicating similar behavioural responses to light or some other factor(s). The distribution of cast exuviae of final-stage phyllosoma larvae indicated that metamorphosis to the puerulus phase can occur more than 100 miles (161 km) from shore. Moreover, 80% of the puerulus larvae caught were within 80 miles (129 km) of the shore. Mean densities of puerulus larvae taken at and below the surface at night were 0.04/1000 m³ and 0.10/1000 m³, respectively, although total numbers were low. This evidence indicates that, after metamorphosis, the puerulus larvae return to the coastal environment at some subsurface depth.     

Diet quality and muscle tissue location influence consumer-diet discrimination in captive-reared rock lobsters (Panulirus cygnus)

Fundamental to the accuracy of stable isotope analysis in trophodynamic studies is the ability to predict discrimination between a consumer and its diet. Despite the widespread use of stable isotope analysis in trophic ecology, uncertainty still surrounds the factors affecting consumer-diet discrimination. Here we present evidence that diet quality and location of muscle tissue analysed affects the consumer-diet discrimination for the western rock lobster, Panulirus cygnus. Consumer-diet δ¹⁵N and δ¹³C discrimination for western rock lobster tail tissue were 1.67–2.97 and 2.92–3.60‰, respectively, with δ¹³C discrimination differing to values reported in the literature. Differences in nitrogen and carbon discrimination were observed between tail and leg tissue of lobsters of 1.22 and 1.13‰, respectively. Diet quality was also found to affect consumer-diet discrimination, with high protein pilchard diet leading to lower δ¹⁵N and higher δ¹³C discrimination. Diet quality should be considered as a factor that has the potential to affect consumer-diet discrimination when interpreting results from stable isotope studies.     

Distribution of final stage phyllosoma larvae and free-swimming pueruli of Panulirus japonicus around the Kuroshio Current off southern Kyusyu, Japan

The distribution of the phyllosoma larvae and free-swimming pueruli of the Japanese spiny lobster Panulirus japonicus (von Siebold, 1824) has been studied off the south coast of Kyusyu Island. From 1992 to 1995, four research cruises were conducted on board the R.V. “Yoko-maru”. Cruises were mainly carried out over the new moon period between June and August along transect lines that cross the Kuroshio Current. In total, 89 later stage Form F phyllosoma (body lengths ≥20 mm) and 43 free-swimming pueruli of P. japonicus were caught; 94.4% of the later stage phyllosoma larvae were in the final stage. The phyllosoma were distributed widely in and south of the Kuroshio Current, where high-salinity (34.8) water exists at depths below about 80 m. Highest densities of the final phyllosoma larvae were observed in or near the  Kuroshio Current, and molting to the puerulus stage also occurred in the same area. Free-swimming pueruli were mainly sampled in and north of the Current. It is suggested that the pueruli of P. japonicus swim across the Kuroshio Current to settle in coastal areas. Received: 9 December 1996 / Accepted: 25 September 1998     

Origin and nature of spermatophoric mass of the spiny lobster Panulirus homarus

In the spiny lobster Panulirus homarus (Linnaeus) the spermatophoric mass consists of a highly convoluted tube, containing the sperm mass and a gelatinous matrix. The spermatophoric components have their origin in the proximal vas deferens and the completed spermatophoric mass is stored within the distal dilated part of the vas deferens. In the proximal vas deferens the inner glandular epithelial cells give rise to leaf-like typhlosoles which gradually diminish in size and finally disappear in the distal vas deferens. The secretions originating from the typhlosole form the outer gelatinous matrix of the spermatophoric mass. Histochemical observations reveal that the wall of the spermatophore tube consists of neutral mucopolysaccharide, whereas the sperm mass and the gelatinous matrix are rich in acidic mucopolysaccharides. Both polyacrylamide gel electrophoresis and agarose gel electrophoresis were used to separate the acidic mucopolysaccharide (AMPS) complexed with the proteins and the simple proteins. In addition, AMPS have been isolated following the method of Rahemtulla and Lovtrup (1974) and used for electrophoresis. In both the polyacrylamide gel electrophoresis and agarose gel electrophoresis, the extracted acid mucopolysaccharides give only a single fraction which, in comparison with the standard acid mucopolysaccharides, corresponds to chondroitin sulphate. The functional significance of the chondroitin sulphate and neutral mucopolysaccharides in the spermatophoric components of P. homarus is discussed in relation to their functional role in spermatophore hardening and protection of the delicate spermatozoa during their prolonged storage on the sternum of the female.     

Diurnal vertical migration of Solmissus albescens (Hydromedusae) in the Southern Adriatic

During a study on diurnal vertical migration in the hydromedusa Solmissus albescens (Gegenbaur, 1856), 112 net samples were taken from a depth of 1000 m to the surface. Sampling was performed in July, August, and September, 1969, at a station located 20 miles SSW of Dubrovnik (Yugoslavia). S. albescens migrates vertical distances of over 300 m. No significant influences on migration were noticed due to environmental factors (temperature, salinity, vertical water currents, etc.). The hydromedusa was able to approach surface layers. The recording obtained at various water-depth levels are considered in relation to illumination, mechanisms of evolution, and feeding of S. albescens.     

Some aspects of the circulatory physiology of the spiny lobster Panulirus interruptus

The blood circulatory system and the circulatory dynamics of the spiny lobster Panulirus interruptus (Randall) have been examined in detail. A mean absolute blood pressure of 36.5 cm-H₂O and a mean pulse pressure of 27 cm-H₂O, show this species to have the highest pressure-driven circulation yet measured in decapod crustaceans. Mean blood velocities have been directly measured in intact animals for the first time. These velocities range from over 10 cm/sec in the large arteries to less than 1.0 cm/sec in the sinuses. Total blood volume is variable but averages near 30% of the wet weight, while heart volume averages 0.3% of the wet weight. The blood velocity and volume data are used to compute circulatory parameters such as cardiac output, stroke volume and turnover time. Comparisons with other animals suggest that the so-called “open-system” characteristic of crustaceans may be much more effective than previously supposed.     

Control and coordination of reproduction and molting in the spiny lobster Panulirus argus

Behavioral and physiological correlates of vernal reproduction and molting were investigated experimentally in laboratory-held spiny lobsters (Panulirus argus Latreille) from Florida to determine their control by photoperiod and temperature. Behavioral measures included courtship, copulation and aggression; physiological measures included the timing and frequency of ecdysis, spermatophore emplacement, oviposition, egg hatching, and setal (pleopod) and gonadal development. Behavior resembled that observed in nature, as evidenced in the expression of complete reproductive cycles. Long daylengths and warmer temperatures enhanced courtship, spawning frequencies, and female gonadal development, although gonadal recrudescence occurred in large females irrespective of photoperiod. A significant interaction effect between photoperiod and temperature indicated a need to examine joint, non-independent factor effects upon reproductive parameters. Photoperiod and temperature did not significantly influence aggression and male gonadal development. Photoperiod did not affect molting rates significantly. However, warm temperatures enhanced molting and growth such that sub-adult and young adult lobsters (both sexes) had highest molting rates, followed by large adult males, which in turn had higher rates than reproductively active females. Female setal development correlated positively with female size, and changed abruptly at ecdysis. Although setal lengths were highly variable, setae of 9 mm or more signified sexual maturity. Reproduction and molting were size-dependent: the largest adults mated or spawned, the smallest molted, and intermediate-sized ones either mated, or molted before mating. Spiny-lobster reproductive and molting patterns were influenced by photoperiod and temperature in a complex manner depending upon sex, season, size and developmental state.     

Mitochondrial DNA variation and population structure in the spiny lobster Panulirus argus

Adult spiny lobsters (Panulirus argus) were collected from nine locations throughout the tropical and subtropical northwest Atlantic Ocean and examined for mitochondrial DNA (mtDNA) variation. 187 different mtDNA haplotypes were observed among the 259 lobsters sampled. Haplotype diversity was calulated to be 0.986 and mean nucleotide sequence-diversity was estimated to be 1.44%; both of these values are among the highest reported values for a marine species. Analysis of molecular variance (AMOVA) and phenetic clustering both failed to reveal any evidence of genetic structure within and among populations of P. argus. The present data are consistent with high levels of gene flow among populations of P. argus resulting from an extended planktonic larval stage and strong prevailing ocean currents.     

Diel vertical migration and timing of metamorphosis of larvae of the Dungeness crab Cancer magister

Joint USA/USSR ichthyoplankton surveys off the coasts of Washington, Oregon and northern California during the years 1981 to 1985 sampled more than 120 stations each year, from 5 to 360 km offshore and between Latitude 40° and 48° N, providing information on ontogeny and diel migration of larvae of the Dungeness crab Cancer magister on a scale not studied previously. We developed a maximum likelihood method for estimating abundance and fraction in the neuston at each station from a neuston tow and an oblique bongo tow. Latestage megalopae migrate vertically on a diel basis, with the fraction in the neuston being (on average) 62% at night (19.00 to 08.00 hrs Pacific Standard Time, PST) and 8% during the day (08.00 to 19.00 hrs PST). The hourly pattern of this migration includes a peak in the early evening, possibly another in the early morning, and an intermediate level in the late afternoon. We detected no dependence of vertical migration on cloud cover or sea state. Early-stage megalopae were present in much lower fractions in the neuston, but weakly displayed the same diel pattern of migration. Zoeae appeared to be below the neuston at all times, except for 2 or 3 h in the evening. From an abrupt change in larval stage in samples from a north-south cruise, we concluded that the majority of the larvae metamorphose from zoeae to megalopae over a fairly short time span (2 to 4 wk) at a given latitude. In later cruises, 95% of the larvae were megalopae, indicating that metamorphosis over the study area either occurs at the same time or proceeds from south to north over a time span of less than a month in early spring.     

Diurnal vertical migration of Cochlodinium polykrikoides during the red tide in Korean coastal sea waters

The diurnal vertical migration of Cochlodinium polykrikoides (C. polykrikoides), which caused a red tide in the Korean coastal waters of the East Sea/Sea of Japan in September 2003, was examined by determining the time-dependent changes in the density of living cells in relation to the depth of the water column. The ascent of this species into the surface layer (depth of water 2 m) occurred during 1400-1500. The descent started at 1600 and a high distribution rate (86%) at 15-20 m was observed at 0300. During the ascent, the cells were widely distributed at each depth level from 0600 hr and at 0800-1100, the cells were primarily distributed in the middle layer (0-6 m). The concentration of dissolved inorganic nitrogen was generally < or = 2.86 micromol l(-1), but at 1400-1500, the concentration in the surface layer reduced to < or = 0.14 micromol l(-1). Moreover, the concentration gradually increased as the depth increased to > or = 5 m. These results showed that the nutrient-consumption rate associated with the proliferation of C. polykrikoides during a red tide is more influenced by the inorganic-nitrogen resources ratherthan the inorganic-phosphorus compounds.     

Diurnal vertical migration of an estuarine cladoceran,Podon polyphemoides,in the Chesapeake Bay

Populations of the marine cladoceran Podon polyphemoides (Leuckart) in the Chesapeake Bay (USA) zooplankton typically occur in large patches, extending the length of the estuary. These patches are characterized by well defined maxima, which do not move seaward during a given season. During the day, the bulk of the population is situated in the upper part of the two-layered estuarine circulation, where it is subjected to transport by net non-tidal seaward current. One mechanism for maintaining the population within the estuary is provided by the diurnal behavior of the podonids, which migrate to deeper water during the night. The landward advection of the deeper currents, thus, helps to counterbalance seaward population loss during the day. The extent of the vertical movement of the population can be modified by various environmental factors, but a suggestive correlation with light was found. It is thought that the downward component of the migration is due to passive sinking.     

Determining the diet of larvae of the red rock lobster (Jasus edwardsii) using high-throughput DNA sequencing techniques

The diet of Jasus edwardsii during its ~2-year larval (phyllosoma) phase is largely unknown. High mortalities experienced during larviculture might be reduced if their diet were nutritionally modelled on the natural diet. Here, prey species were identified from phyllosoma midgut glands using 454 pyrosequencing of 18S rDNA. We found that gelatinous zooplankton, particularly Siphonophora and Ctenophora, occurred frequently in the midgut glands of phyllosomas, resolving previous conjecture that these animals are in the diet of J. edwardsii phyllosomas. A high occurrence of sequencing reads from unicellular microbes may also reflect a reliance on scavenging detritus.     

Bimodal vertical distribution and diel migration of the copepods Metridia pacifica,M. okhotensis and Pleuromamma scutullata in the western North Pacific Ocean

Diel changes in fine-scale vertical distributions of three calanoid copepods Metridia pacifica, M. okhotensis and Pleuromamma scutullata in the subarctic waters of the western North Pacific were examined. Sampling was carried out in June and August 1983, at two stations in Oyashio water using a Longhurst-Hardy Plankton Recorder (LHPR). Sampling, down to about 1 000 m, was repeated four to five times at intervals of several hours. Vertical resolution was 5 to 40 m. Copepods were concentrated in two strata, the surface (0 to 60 m) and the mesopelagic (200 to 300 m) layers, throughout the day at both stations. Younger M. pacifica (C III and C IV) were dominant in both strata. Although most female C V and adult females demonstrated diel vertical migration at 20 to 30 m h^-1, a significant number of females did not migrate upward but remained in the deep stratum at night. The same trend was evident in M. ohkotensis and P. scutullata. Foregut content observations indicated that feeding activities of the deep mode populations were as high as those of the surface mode, though food of deep individuals was different. Such a bimodal distribution may increase intraspecific diversity of copepod populations and is possibly why metridiid copepods dominate during late summer to winter in the relatively simple ecosystems of high latitudes.     

Vertical distribution of eggs and larvae ofEngraulis encrasicolus in stratified waters of the western Mediterranean

The vertical distribution of the eggs and larvae of the European anchovy (Engraulis encrasicolus) in the western Mediterranean Sea in June 1984 and Agust 1985 was analyzed based on multiple plankton tows carried out at varying depths and using nets equipped with opening and closing mechanisms. Hydrographic parameters such as temperature, salinity, and chlorophylla were recorded simultaneously. Maximum abundance of anchovy eggs and larvae always occurred above the thermocline, even when maximum chlorophylla concentrations were located below the thermocline. Larval distribution appeared to be associated with the availability of suitable food organisms. As in other clupeoid species, the anchovy larvae carried out vertical migrations related to the photoperiod.