Genetic heterogeneity in a single year-class from a panmictic population of adult blue rockfish (<Emphasis Type="Italic">Sebastes mystinus</Emphasis>)

We used microsatellite genetic markers to investigate adult population structure and the formation of a new year-class in Sebastes mystinus (blue rockfish). Since S. mystinus may live as long as 45 years and reach reproductive age at approximately 5 years, the adult population may contain as many as eight generations of reproductive adults. We investigated whether the juveniles of the 2000 year-class and the adult population were genetically homogeneous along the California coast. We sampled approximately 100 juveniles from three sites, two sites along the Monterey Peninsula (Carmel and Monterey) in central California and one at Fort Ross in northern California, and approximately 50 adult S. mystinus from five sites throughout the population center. The adult sampling spanned approximately 700 km from the northern Channel Islands to Fort Bragg. The juveniles showed significant heterogeneity in allele frequencies among distant locations and genetic homogeneity among adjacent locations. In contrast, the adults showed genetic homogeneity over large distances (San Miguel Island to Fort Bragg), indicating little limitation of gene flow in this region. Allele frequencies of juveniles differed from adult samples and in some cases reduced genetic diversity indicative of sweepstakes recruitment (small sample of the adult reproductive potential). The genetic structure of the 2000 year-class suggests that despite a genetically homogenous adult population, settled juveniles can be genetically heterogeneous along the California coast. The results also suggest that the adults, with several year-classes, are capable of maintaining a panmictic population despite the genetic distinctiveness of individual year-classes.     

Growth and population structure of Lepidochitona cinereus (Mollusca: Polyplacophora) infected with Minchinia chitonis (Protozoa: Sporozoa) at Easthaven,Scotland

Growth and population structure of Lepidochitona cinereus was studied at Easthaven in Scotland. Length was isometrically related to height and breadth, while tissue dry weight was negatively allometric. Length-shell weight relationships were variable with the time of year. Periods of differential growth were associated with the onset of growth in spring and gonad development in July. The use of growth-check lines to age individuals is described. Population structure and growth was investigated using a combination of winter growth-check line and length-frequency analyses. Infection with the protozoan Minchinia chitonis is shown to cause enhanced growth and deviation from the normal growth curve. Individuals survived for a maximum of 5 winters and length-frequency data could be interpreted only after growth-check line analysis due to extensive overlap of year-class size ranges. Year-class success was variable, and the present population was dominated by older year-classes.     

Population dynamics and reproduction of Mysella bidentata (Bivalvia: Galeommatacea) in Galway Bay,Irish west coast

Mysella bidentata (Montagu) is found in high densities in an Amphiura filiformis (O. F. Müller) community in Inner Galway Bay, west coast of Ireland. As part of an ongoing investigation at one station within this community, the population dynamics and reproductive pattern of this bivalve were investigated during the period November 1978-December 1981. Monthly sampling over the 3 yr period revealed a mean population density of 745±672 individuals m^-2. Recruitment occurred during August-October and three year-classes were identified. Growth rates were assessed by analysis of length-frequency histograms and winter growth checks. Individuals from the Y1 and Y2 year-classes functioned as hermaphrodites during the 1980 and 1981 reproductive seasons. The Y0 year-class contained both males and hermaphrodites. Results are compared with available information on the same species from other locations.Contribution No. 225 from the School of Marine Sciences, University College, Galway Ireland     

Temporal stability of gene frequencies within genetically heterogeneous populations of the queen scallop Aequipecten (Chlamys) opercularis

The widely held assumption that gene frequencies within samples of multi-aged organisms are temporally stable has rarely been tested. In order to test this assumption in the commercially exploited bivalve scallop Aequipecten (Chlamys) opercularis (L.), 12 populations were sampled from around the UK over the period 1988–1990 and each was assayed at four putative polymorphic enzyme loci. Most populations were comprised of 3 to 4 year-classes, distinguishable by annual rings laid down on the shell. Three alleles from each locus were used as discriminant-function variables. Discriminant-function analysis based on allele frequencies averaged for each inividual year-class (45 demes) revealed highly significant inter-site heterogeneity. A posteriori classification of individual year-classes based on the discriminant analysis resulted in assignment of year-classes to the correct home site in 80% of cases. If allozyme neutrality is assumed, the phenomenon of predominant local allele frequency-stability through time within populations which are genetically heterogeneous from one site to another raises the possibility that queen scallop populations may be self-recruiting. Despite a planktonic larval phase lasting up to several weeks, this possibility is not excluded by the available hydrographic data.     

A biochemical genetic study of population structure in queen scallop (Chlamys opercularis) stocks in the Northern Irish Sea

Electrophoresis was used to survey a number of enzymes for loci of potential value as stock markers in Chlamys opercularis (L.). Two loci, Pgi and Pgd, were then studied in larger samples from each of two localities around the Isle of Man. One Pgi allele was found to be restricted to a particular year-class in both populations. This was confirmed by subsequent studies of three further populations, in each of which the same allele occurred only in the one year-class. Otherwise, no significant differences in allele frequencies were found between year-classes or between populations in any of the samples used. From the results it is concluded that there is temporal variation in the sources of recruitment of C. opercularis stocks around the Isle of Man. Possible origins of larvae contributing to these stocks are discussed in the light of what is known of current circulation patterns in the northern Irish Sea.     

Hatching and viability of copepod eggs at two stages of embryological development: anoxic/hypoxic effect

The effects of low oxygen concentrations on the hatching and viability of copepod eggs at two stages of embryological development were investigated. Fully developed eggs from Acartia tonsa (Dana) and Labidocera aestiva (Wheeler) collected between July and September 1991 at Turkey Point, Florida, USA, hatched at lower oxygen concentrations than newly spawned eggs given the same incubation periods. Since many of the newly spawned eggs subsequently hatched when exposed to normoxic conditions, it is likely that the exposure to low oxygen delayed embryonic development. At oxygen concentrations where no initial hatching occurred, the subsequent hatching success of fully developed eggs of A. tonsa was higher than that of newly spawned eggs, indicating that newly spawned eggs were more sensitive to low oxygen concentrations. No such difference was observed for the eggs of L. aestiva.     

Infection dynamics of an oyster parasite in its newly expanded range

Over a 2-year period in 1990 and 1991, coincident with a pronounced warming episode, Dermo disease outbreaks in the oyster, Crassostrea virginica, caused by the parasite Perkinsus marinus, occurred over a 500-km range from Delaware Bay to Cape Cod, in the northeastern United States. The parasite had not previously been recorded or known to cause mortalities in this region. To document infection patterns and levels in this region several years after the initial outbreaks, and to compare them with those in the parasite’s historic southern range, we deployed and sampled oysters from 1996 to 1998 at multiple sites spanning the expanded range. During this 2-year period, the parasite was documented to occur in oysters at high prevalences throughout the new range, in sites varying from small, enclosed embayments to large estuaries, and in both cultured and wild-set oysters. Infection and mortality patterns, and levels were similar to those in southern locations where the parasite has been enzootic for at least decades. The persistence of high P. marinus infection levels in the new range after the initial expansion is probably due to several factors: (1) winter temperatures continued to increase during the 1990s and early 2000s, albeit at a slower rate than in 1990–1991, facilitating overwinter survival of the parasite; (2) many oyster-growing sites in the northeast are in relatively shallow water in which summer temperatures offer ample time for the parasite to proliferate and spread; and (3) the combination of high parasite burdens and high host densities in oyster farms results in an abundance of parasites and high transmission rates. Colder winters and high rainfall after 2002 reduced prevalences in some regions, but P. marinus can survive low temperatures and low salinities, and epizootic conditions are likely to return if temperatures rise again, as predicted by climate-change models.     

Effects of El Niño/Southern Oscillation on the population dynamics of a Gari solida population (Bivalvia: Psammobiidae) from Bahía Independencia,Peru

Population dynamics of a Gari solida (Gray, 1828) population from Bahía Independencia, Peru (14°S) was studied between November 1989 and February 1995 (except for 1991) in order to investigate the effects of the climate phenomenon El Niño/Southern Oscillation (ENSO) which occurred in 1992/93. Results indicate that ENSO had negative effects on gonad production in 1992, when temperatures were very high, and positive effects in 1993, when temperatures were lower, but the warm period lasted longer than in 1992. Higher reproductive output in 1993 was achieved by several spawning events in addition to the normal pattern. Growth rate in 1990 was higher (K=0.495) than in 1993/94 (K=0.346). A possible explanation could be that more energy was allocated to reproduction, and thus less surplus energy remained for growth. The negative effect of ENSO on production in 1992 is indicated by the low P/B ratio (0.298); in all other years P/B was consistently higher (1990: 0.570; 1993: 0.597; 1994: 0.597). From 1990 to 1994 a reduction of mean annual biomass from 189.3 to 14.4 g ash-free dry weight m^-2 was also observed which may be related to fishery activities. The consistency of P/B ratio is best explained by the higher somatic production of the smaller individuals remaining after the larger individuals had been removed selectively by fishermen. Based on the results presented in this study and from the literature, a model is proposed depicting how ENSO may negatively affect bivalve populations. Two main factors are mentioned, increased temperature and reduction of assimilated energy.Contribution No. 991 of the Alfred-Wegener-Institut für Polar- und Meeresforschung, Germany     

Growth and mortality of subtidal red sea urchins (Strongylocentrotus franciscanus) at San Nicolas Island,California, USA: problems with models

Red sea urchins, Strongylocentrotus franciscanus, were tagged with tetracycline in 1990 at subtidal sites off San Nicolas Island, California, USA. After one year in the field, the sea urchins were collected and growth increments were measured based on tetracycline marks, which indicated initial slow growth, a maximum rate, and finally a prolonged period of very slow growth. Small red sea urchins (4 cm diam) were estimated to be 3 to 4 yr old, which is much older than has previously been reported. It is estimated that about 12 yr would be required to attain 10 cm diam. Survival has previously been modeled assuming a constant rate. If the population of red sea urchins is assumed to be stable and stationary, annual survival rate was between 71 and 77% yr^-1. Census data for the two years of study have permitted annual survival to be estimated without assuming stable and stationary population structure. Under these conditions, annual survival rate was between 79 and 86% yr^-1. Analysis of transitions in the size distributions from 1990 to 1991 suggested that annual survival may have been sizespecific: 91% yr^-1 for individuals 1.1 to 4.0 cm diam, 82% yr^-1 for individuals 4.1 to 7.0 cm diam, and 63% yr^-1 for those of 7.1 to 10.0 cm diam. An alternative explanation to size-specific survival in our study is sizespecific immigration.     

Spatial and temporal variability of phytoplankton biomass and taxonomic composition around Elephant Island,Antarctica, during the summers of 1990–1993

During the austral summers of 1990–1993, phytoplankton studies were conducted in the vicinity of Elephant Island, Antarctica, to investigate the spatial and temporal variability of phytoplankton biomass and taxonomic composition. There was much intraannual variability, with a trend for increasing biomass from January–February (Leg I) to February–March (Leg II), except in the 1993 studies. There was also a change in phytoplankton composition between the two legs. During 1990–1991 the increase was due mostly to diatoms, during 1992 mostly to an increase of flagellates; during 1993 there was a decrease in total biomass between the two legs, with diatoms decreasing, so that dinoflagellates, which increased slightly in numbers, dominated the biomass during the second leg. There was also much inter-annual variability, with the summers of 1990–1991 having greater biomass and higher proportions of microplanktonic diatoms than that of 1992–1993, which had a higher proportion of flagellates. Cluster analyses revealed the presence of four major phytoplankton assemblages, with varying geographical distributions. The northwestern portion of the grid (Drake Passage waters), was characterized by nanoplanktonic diatoms during 1990–1991 and 1993, but by nanoplanktonic flagellates during 1992. The central area (Drake-Bransfield confluence) was characterized by microplanktonic diatoms in 1990–1991, but by cryptophytes or flagellates in 1992–1993. The south and southeastern portion of the area (Bransfield Strait waters) was characterized mainly by either cryptophytes or other flagellates during all 4 yr. The spatial and temporal variability of phytoplankton could not be ascribed specifically to the geographical extent of the different water masses found in the study area, but appears to be due to changing growth conditions in the upper water column as influenced by physical mixing and meteorological conditions, as well as to effects of differential grazing.     

Food and feeding dynamics of the larval Antarctic fishNototheniops larseni

The feeding dynamics of larvae of the Antarctic fishNototheniops larseni were analyzed from data collected over three years in Bransfield Strait and adjacent waters (Antarctica). Seasonal feeding was examined from 1977/1978 (November–March). The diel feeding cycle was investigated during a 96 h station established in February 1976, while food selection was analyzed using larvae and zooplankton samples collected in February 1982. Hatching occurs in early spring, and larvae fed on eggs of calanoid copepods and on cyclopoid copepods. Copepod eggs were the principal food near the pack ice, and cyclopoids in open waters. Cyclopoids were the staple food in summer. Eggs of the Antarctic krillEuphausia superba were ingested selectively and formed major portions of the larval summer diet in neritic (Joinville Island) and oceanic (Elephant Island) spawning areas ofE. superba. In the fall, copepods predominated in the diets. Most abundant and most frequently ingested prey in summer and fall wereOncaea spp. Feeding commenced at dawn and continued at least until dusk. Krill eggs were taken chiefly during morning hours and egg incidence declined during the day, suggesting that eggs were ingested soon after spawning. Prey size at the onset of feeding was estimated as 0.130 to 0.330 mm. Size-selective feeding was evident in small larvae, while in larger larvae median prey length remained constant. High feeding incidence among yolk-sac larvae in spring, high overall feeding incidence in summer, and size-selective foraging of small larvae suggested favorable feeding conditions in the 1977/1978 season. Yolk-absorption times in Antarctic fish larvae vary on a scale of weeks and may be further retarded due to early feeding. Hence, year-to-year variability of yolk incidence inN. larseni indicated variable biotic environments of early feeding larvae rather than temporal shifts of hatching periods. As hatching periods are constant between years in contrast to the variable retreat of the pack ice and subsequent onset of the production cycle in space and time, maternal yolk reserves are probably utilized to compensate for such variations.     

Larval supply of shorefishes to nursery habitats around Lee Stocking Island,Bahamas. II. Lunar and oceanographic influences

Plankton nets were moored in tidal channels around Lee Stocking Island to monitor larval supply of fishes to nursery habitats that fringe Exuma Sound, Bahamas. Sampling was conducted continuously through two consecutive winters of 1990–1991 and 1991–1992. Meteorological and hydrographic data were also recorded during these periods. Three of the six most abundant taxa (leptocephali, Bothidae and Ophidiidae) showed strong lunar associations, with periodicities between 28 and 30 d. Labrids were the only family to show evidence of any semi-lunar activity. The time series for the families Clupeidae and Tetraodontidae appeared to be stochastic. Cross-correlation analyses were used to examine coupling of larval replenishment and physical processes. Four of six taxa examined showed significant relationships between larval supply and onshore winds at short time lags during 1990–1991. In 1991–1992, however, taxa showed stronger associations with the northwest, long-shore wind component than with onshore winds. Coherency in larval supply among several taxa was remarkably strong. This implies either that the magnitude of spawning is linked among taxa, or that planktonic processes are affecting a number of taxa in very similar ways. The similarities in the magnitude of supply events among taxa found here may be related to complex interactions between larval behavior and the physical environment.     

Vertical distributions and photosynthetic action spectre of two oceanic picophytopianlcters,Prochlorococcus marinus andSynechococcus sp.

Two picophytoplankters,Prochlorococcus marinus andSynechococcus sp., were isolated from the bottom of the euphotic zone (150 m depth) in the western Pacifie Ocean. The concentration ofP. marinus at this depth was more than 10⁴ cells ml^–1 while that ofSynechococcus sp. was less than 10² cells ml^–1. TheP. marinus isolate has a high divinyl-chlorophylla:b ratio similar to that of the Mediterranean strain, while theSynechococcus sp. isolate is of the phycourobilinrich type. The growth rate ofP. marinus was higher thanSynechococcus sp. when both were cultured under weak blue-green to blue-violet light (ca. 2 E m^–2 s^–1). While the chlorophyll-specific absorption spectra showed higher values inSynechococcus sp., the photosynthetic action spectre revealed thatP. marinus was able to use blue-violet light, whereasSynechococcus sp. was able to use blue-green light, more efficiently for photosynthesis. The photosynthetic quantum yield ofP. marinus was higher than that ofSynechococcus sp. at any wavelength between 400 and 700 nm. The calculated in situ photosynthesis rates per Gell volume forP. marinus were estimated to be higher than forSynechococcus sp. at 50 and 150 m depth. These results indicate thatP. marinus photosynthetically surpassesSynechococcus sp. in the blue-light-rieh environment of the oceanic euphotic zone. This may be why the former predominates at depths in temperate to tropical open ocean waters.     

Physiologische anpassungen eines marinen insekts. I. Die zeitliche steuerung der entwicklung

The Baltic populations of Clunio marinus (Chironomidae, Diptera) differ from their Atlantic counterparts in three ways: they neither pupate nor hatch in synchrony with a lunar rhythm; they live in a permanently submersed habitat; the structures of their gelatinous egg-masses are different. C. marinus produces two generations each year. The spring generation, which hibernates in the 4th larval stage, hatches in May; the summer generation hatches at the end of July or beginning of August; hatching periods last only a few days. In the laboratory, a permanent short-day period (8 h light, 16 h dark; LD 8:16) induces larval quiescence (oligopause), which can be terminated by long-day conditions (ca. LD 16:8). If larval populations are exposed to continuous light (LL) for 4 days every 30 days, particularly large numbers of imagos hatch about the time of the next LL-period. Increased illumination may influence the time of hatching. Raising the temperature for a few days does not affect hatching. The roles of photoperiod, illumination and temperature are discussed with regard to the temporal programming of development and the start of mass hatching in the natural habitat.

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Herrn Professor Dr. D. Neumann danke ich für die Anregung und Betreuung dieser Arbeit, die Teil einer Dissertation ist.

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Communicated by O. Kinne, Hamburg     

Critical threshold size for overwintering sandeels (<Emphasis Type="Italic">Ammodytes marinus</Emphasis>)

Several ecologically and commercially important fish species spend the winter in a state of minimum feeding activity and at lower risk of predation. To enable this overwintering behaviour, energetic reserves are generated prior to winter to support winter metabolism. Maintenance metabolism in fish scales with body size and increases with temperature, and the two factors together determine a critical threshold size for passive overwintering below which the organism is unlikely to survive without feeding. This is because the energetic cost of metabolism exceeds maximum energy reserves. In the present study, we estimated the energetic cost of overwintering from a bioenergetic model. The model was parameterised using respirometry-based measurements of standard metabolic rate in buried A. tobianus (a close relative to A. marinus) at temperatures from 5.3 to 18.3°C and validated with two independent long-term overwintering experiments. Maximum attainable energy reserves were estimated from published data on A. marinus in the North Sea. The critical threshold size in terms of length (L _th) for A. marinus in the North Sea was estimated to be 9.5 cm. We then investigated two general predictions: (1) Fish smaller than L _th display winter feeding activity, and (2) size at maturation of iteroparous species is larger than L _th to ensure sufficient energy reserves to accommodate both the metabolic cost of passive overwintering and reproductive investments. Both predictions were found to be consistent with data on size at maturation and total body energy in December and February.     

Distribution and abundance of juvenile Loligo gahi in Falkland Island waters

Four research surveys of Falkland Island waters were carried out to determine the distribution and abundance of the early life-history stages of Loligo gahi (d'Orbigny, 1835) in the austral winter of 1988 and the austral springs of 1990, 1991 and 1992. Juveniles were caught during three of the four surveys in both Bongo nets and an RMT8 net. In each case, greatest numbers were consistently caught in waters of 100 m to the south and east of East Falkland. The use of an opening/closing net in 1992 showed that most L. gahi juveniles aggregate close to the sea floor and are more available to the sampling gear by night than by day. Limited temperature data for the 1991 and 1992 surveys suggest that distribution on the coastal shelf may be associated with water-column structure. In 1992 when temperature data implied a mixed water column, juveniles were caught in deeper water than in 1991 when the water column was stratified. The results suggest that the spawning grounds of L. gahi are probably situated to the south and east of the Falkland Islands, at least for squid hatched in the austral winter/spring.     

Relationship between growth rate and age at recruitment ofAnguilla japonica elvers in a Taiwan estuary as inferred from otolith growth increments

The growth history and recruitment dynamics of eel (Anguilla japonica) elvers were studied. Observations were based on growth increments in sagittal otoliths of elvers collected from Shuang-Chi River estuary off northeastern Taiwan, from November 1985 to February 1986. Total lengths of elvers upon arrival at the estuary were similar in most case; mean total lengths were from 55.99 to 59.06 mm. Daily ages of elvers at arrival ranged from 112.8±9.4 (±SD) to 156.5±13.5 d, indicating that migration of eel larvae from their oceanic spawning ground to the estuary requires 4 to 5 mo. Elver hatching dates, back-calculated from estimated daily ages, indicated that the spawning season lasted 5 mo (from late June to early October). Furthermore, the earlier eels spawned, the earlier elvers reached the estuary. The transition in growth history during the larval stage was obvious, as indicated from the change in increment width in elver otoliths. The inverse correlation between daily age and mean daily growth rates of fish length and otolith indicated that the age of elvers upon arrival at the estuary was susceptible to larval growth rate. In other words, the time taken on migration from oceanic spawning ground to the estuary was shorter for fast-growing larvae than for slowgrowing ones.     

Temporal life history plasticity of the Southern Ocean squid <Emphasis Type="Italic">Todarodes filippovae</Emphasis> from waters off Tasmania,Australia

Population dynamics and maturity parameters were analysed for seasonal samples of the oceanic ommastrephid squid Todarodes filippovae from off the coast of Tasmania Australia from 2002 to 2004. Based on assumed daily periodicity in statolith increments, T. filippovae had a life cycle of about a year with the sexually dimorphic females reaching their larger size by predominantly growing faster than males. Due to the small sample size of males, analysis was undertaken on female individuals only. Growth in all samples was best described by a power curve and varied annually, with significantly faster growth in 2001 compared to the subsequent 2 years. Seasonal growth rates also varied with autumn- and winter-hatched squid significantly faster than summer-hatched squid. Spring growth rates were intermediate but not significantly different to the other three seasons. Peak hatching periods occurred in late autumn and early winter. ANOVA revealed a season × year interaction for mantle length and total body weight. Pairwise comparisons showed that the annual differences were likely driven by smaller squid in autumn 2002 compared to autumn samples in the other 2 years. Pairwise comparisons also revealed seasonal differences with winter-caught squid smaller than those from the majority of other samples. There were no seasonal effects on mature female gonad weights but females caught in 2002 had significantly lighter gonad weights than females from the following 2 years. There were no consistent trends among seasons or years in the age structure of mature females. This study revealed the plasticity and flexibility in growth and maturity parameters in this species, with a preference for faster growth during cooler periods.     

Spatio-temporal population dynamics of the sand snail Umbonium costatum: importance of ontogenetic migration and annual recruitment variability

The spatio-temporal population dynamics of the subtidal snail Umbonium costatum (Kiener) in Hakodate Bay, northern Japan, are described over a 9-yr period (1982 to 1988, 1992). Annual variations in recruitment success not only caused the highly variable age structure of the population, but also affected its distribution pattern. In heavy recruitment years (1982, 1984 and 1988), location of the densest population differed from the other years, and the areas with 0 yr old individuals were larger. Every year, the distribution of 0 yr olds was mostly restricted to inshore (within 320 m from shore), while the distribution of adults (>0 yr) was mostly restricted to offshore (>320 m from shore). Such patterns may be generated by ontogenetic migration of cohorts to offshore areas. Ontogenetic migration also could have buffered the large annual variation in spat distribution and maintained the small variation in the distribution of adults. (Prince et al. 1988). Density-related migration has also been reported in Acmaea digitalis (Frank 1965), Patella cochlear (Branch 1974) and Patelloida alticostata (Black 1977).Dense populations of the gastropod Umbonium costatum are found in some clean subtidal sandy-bottoms in Japan, e.g. inner part of Hakodate Bay. In the bay, the age structure of U. costatum revealed predominant year-classes. The 0 yr olds were restricted to the shallowest zone (<4 m depth) and most adult (<0 yr) cohorts were restricted to 6 to 7 m depths (Noda 1991a).This paper describes the temporal variability of population structure and distributional patterns of Umbonium costatum, and examines the distribution-regulating processes.     

Growth and production of the inshore marine copepod Pseudodiaptomus marinus in the central part of the Inland Sea of Japan

The growth and production of the inshore marine copepod Pseudodiaptomus marinus was studied in the central part of the Inland Sea of Japan. The stage-specific growth rate was determined under controlled laboratory conditions by examining the length-weight relationship and development rates at various temperatures. The stage duration was short and constant from NII to CII, beyond which development was retarded. Males developed faster than females in CIV and CV. The specific growth rate was highest in copepodite stages followed by the nauplii and adult females (=egg production rate). The daily production of P. marinus was estimated from the stage-specific growth rate and stage-specific abundance in nature as the sum of the individual stages. The production changed seasonally with water temperature and population biomass. Daily production and biomass (P/B) ratios increased linearly with temperature. Total annual production was 20.7 mg C m^-3 yr^-1.