Calanoid resting eggs in the Baltic Sea: implications for the population dynamics of Acartia bifilosa (Copepoda)

Resting eggs of Acartia spp. (presumably A. bifilosa Giesbr.) at densities between 65 and 125 eggs cm^-2 were found in sediment off the southern coast of Finland and represent the first observations of dormant calanoid eggs in the Baltic Sea. The highest egg densities were found at sediment depths between 4 and 8 cm. The hatching percentage varied between 0 and 90% in the different sediment layers and at different experimental temperatures (13, 16 and 19°C). Some nauplii emerged from the eggs extracted from sediment layers 9 to 10 cm beneath the surface layer and other nauplii emerged from eggs after 82 d of dark storage at 3°C. Light was not needed to trigger hatching; the nauplii were able to hatch in darkness when the eggs were resuspended in filtered seawater. Indirect evidence suggests that the marked spring peak of Acartia spp. nauplii seen in a monitoring data from the years 1973 to 1984 was derived from benthic eggs and not from spawning. The possible mechanisms for induction of hatching and the adaptive benefits of resting egg production for A. bifilosa are discussed.     

Escape responses of copepod nauplii in the flow field of the blue mussel,<Emphasis Type="Italic"> Mytilus edulis</Emphasis>

Bivalves are important grazers on phytoplankton in shallow waters. However, very little is known about their ability to capture actively moving zooplankton. We investigated the escape response and success of early and late nauplii of three copepod species (Acartia tonsa, Temora longicornis and Eurytemora affinis) in the flow field of a blue mussel, Mytilus edulis, using both video observations and incubation experiments. An empirical model was created to describe the spatial distribution of the fluid deformation rate. Nauplii responded with escape jumps at mean fluid deformation rates of 0.6-1.9 s^у. Escape success differed between taxa. T. longicornis was the poorest escaper, while A. tonsa and E. affinis were more efficient and similar to one another. Deformation rates differed in different parts of the flow field, which resulted in differences in escape success between the sectors. Nauplii were caught most often in the sector furthest away from the exhalent siphon, where the deformation rate was the weakest. There the nauplii were unable to detect an escape signal in time to react and flee.     

Viability of embryos of the winter flounder Pseudopleuronectes americanus exposed to combinations of cadmium and salinity at selected temperatures

Developing eggs of the winter flounder Pseudopleuronectes americanus (Walbaum) were exposed to 9 combinations of cadmium and salinity at 5° and 10°C. Overall mean times to 50% hatch ranged from 7.7 days at 10°C to 17.9 days at 5°C. Mean percentages of total hatches ranged from 50 to 100% for all treatment combinations. Response-surface analyses indicate percentages of viable hatches were generally lowest at 10% S and highest in the 25 to 30% S range. Regression analyses of viable hatch data show that at both temperatures cadmium significantly influenced viable hatch in all experiments. Viable hatch was also significantly influenced by the linear and quadratic effect of salinity in both tests at 5°C and in 2 of 3 tests at 10°C. The interaction between cadmium and salinity also significantly affected viable hatch at 10°C.     

Effects of anoxia and hypoxia on the dormancy and survival of subitaneous eggs of<Emphasis Type="Italic"> Acartia bifilosa</Emphasis> (Copepoda: Calanoida)

Subitaneous eggs of the copepod Acartia bifilosa were incubated at low oxygen concentrations and in anoxic conditions to study the induction of dormancy and the longevity of the resting eggs. Eggs were incubated in hypoxic conditions for 8 or 10 days, and also in anoxic conditions for 8–441 days. After the anoxic and hypoxic incubations, the unhatched eggs were subsequently incubated in normal oxygen conditions to reveal the viability of the eggs. Low oxygen concentrations (< 0.17 ml l^–1) induced dormancy in the eggs: they did not hatch at these concentrations in the hypox experiments but did hatch afterwards. Eggs survived well in anoxic conditions: after 10 months at 4°C, approximately 40% of the eggs still hatched, while some eggs survived in anoxic conditions for a year at 13°C, which is longer than hitherto reported for subitaneous eggs of any copepod species. Also, sediment that contained eggs of copepods was stored in the laboratory to reveal the long-term survival of the eggs. When incubated after 1.8 years storage, more than 40% of A. bifilosa eggs hatched. The study shows that subitaneous eggs may also be used as a survival strategy on seasonal time scales. This may partly explain why A. bifilosa does not produce diapause eggs in the present study area in the northern Baltic Sea.Communicated by M. Kühl, Helsingør     

Critical thermal maxima and upper lethal temperatures for the calanoid copepods Acartia tonsa and A. clausi

Determination of the critical thermal maxima and upper lethal temperatures for Acartia tonsa Dana and A. clausi Giesbrecht revealed the relative temperature tolerance of the two species. A. tonsa exhibited a wider range of acclimation temperatures compared to A. clausi. The response of A. tonsa is related to its ubiquity in Atlantic Ocean estuaries (temperate and tropical), and its capacity to live in temperate waters throughout most of the year. Differences between upper lethal temperatures and critical thermal maxima were very narrow for A. tonsa from tropical and subtropical areas. This suggests that, in warm climates, this copepod lives close to its upper lethal temperature limits.Based in part on a dissertation submitted in partial fulfillment for the Ph.D. degree at the University of Rhode Island.     

Neue ergebnisse über die aufzucht von Carcinus maenas im laboratorium

The shore crab Carcinus maenas was reared in the laboratory from egg deposition to sexual maturity. Special enclosures were developed for cultivation of the larvae. Food and temperature proved to be the most important exogenous factors for rearing success. Fresh Artemia salina nauplii were the only food suitable for all larval stages. The following rearing temperatures proved most successful during larval development: (1) embryonic development, 10°C; (2) zoea stages, 15°C; (3) megalopa stage, 17.5°C. The larvae hatch preferably in darkness when reared under short-day conditions.     

The effects of temperature and salinity on reproductive success of <Emphasis Type="Italic">Temora longicornis</Emphasis> in the Baltic Sea: a copepod coping with a tough situation

At specific locations within the Baltic Sea, thermoclines and haloclines can create rapid spatial and temporal changes in temperature (T) and salinity (S) exceeding 10°C and 9 psu with seasonal ranges in temperature exceeding 20°C. These wide ranges in abiotic factors affect the distribution and abundance of Baltic Sea copepods via species-specific, physiological-based impacts on vital rates. In this laboratory study, we characterized the influence of T and S on aspects of reproductive success and naupliar survival of a southwestern Baltic population of Temora longicornis (Copepoda: Calanoida). First, using ad libitum feeding conditions, we measured egg production (EP, no. of eggs female⁻¹ day⁻¹) at 12 different temperatures between 2.5 and 24°C, observing the highest mean EP at 16.9°C (12 eggs female⁻¹ day⁻¹). Next, the effect of S on EP and hatching success (HS, %) was quantified at 12°C for cohorts that had been acclimated to either 8, 14, 20 or 26 psu and tested at each of five salinities (8, 14, 20, 26 and 32 psu). The mean EP was highest for (and maximum EP similar among) 14, 20 and 26 psu cohorts when tested at their acclimation salinity whereas EP was lower at other salinities. For adults reared at 8 psu, a commonly encountered salinity in Baltic surface waters, EP was relatively low at all test salinities—a pattern indicative of osmotic stress. When incubated at 12°C and 15 different salinities between 0 and 34 psu, HS increased asymptotically with increasing S and was maximal (82.6–84.3%) between 24 and 26 psu. However, HS did depend upon the adult acclimation salinity. Finally, the 48-h survival of nauplii hatched and reared at 14 psu at one of six different temperatures (10, 12, 14, 16, 18 and 20°C) was measured after exposure to a novel salinity (either 7 or 20 psu). Upon exposure to 7 psu, 48-h naupliar mortality increased with increasing temperature, ranging from 26.7% at 10°C to 63.2% at 20°C. In contrast, after exposure to 20 psu, mortality was relatively low at all temperatures (1.7% at 10°C and ≤26.7% for all other temperatures). An intra-specific comparison of EP for three different T. longicornis populations revealed markedly different temperature optima and clearly demonstrated the negative impact of brackish (Baltic) salinities. Our results provide estimates of reproductive success and early survival of T. longicornis to the wide ranges of temperatures and salinities that will aid ongoing biophysical modeling examining climate impacts on this species within the Baltic Sea.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.     

Measurement of copepod predation on nauplii using qPCR of the cytochrome oxidase I gene

A method to directly measure predation rates by older stage copepods upon copepod nauplii using species-specific primers for the mitochondrial cytochrome oxidase subunit one gene (mtCOI) and real-time quantitative PCR (qPCR) was developed. The general approach is to determine the mtCOI gene copy number of an individual prey organism and the copy number of the same gene in the stomachs of predatory copepods collected in the field. From the knowledge of DNA disappearance rates in the stomachs, ingestion rates can be calculated. In October 2006, laboratory experiments were carried out with Acartia tonsa N1 and N2 as prey and adult female Centropages typicus as predator. The copepods were collected in Narragansett Bay, USA. A. tonsa mtCOI copy numbers copepod⁻¹ were determined for stages N1–C1 and for adults. A. tonsa DNA was detectable in the guts of the predators for as long as 3 h. Exponential rates of decline in prey DNA from the stomachs of the predators are similar to those measured for gut pigments. Because of the very small amount of DNA in an individual N1 or N2 nauplius, procedures were developed to maximize the quantitative extraction and recovery of DNA and to increase the sensitivity of the method. Two quite divergent haplotypes of A. tonsa were found in Narragansett Bay, which required separate qPCR primers; one was present in summer (July) and the other in fall and winter (October and February). With modification, the methods in this study can likely be applied to a range of predator–prey systems.     

Temperature,salinity, and prey effects on polyp versus medusa bud production by the invasive hydrozoan<Emphasis Type="Italic"> Moerisia lyonsi</Emphasis>

Hydrozoan species are renowned for flexible asexual reproduction, which may predispose them to be successful invaders. Polyps of the invasive hydrozoan Moerisia lyonsi (Boulenger, 1908) have very high rates of asexual production of both polyp and medusa buds. In order to determine how environmental factors affect asexual reproduction in M. lyonsi, the quantitative relationships between polyp bud and medusa bud production were studied in a 31-day laboratory experiment during August 2001. The combined effects of prey (4, 8, 12, 16 Acartia tonsa copepods polyp^–1 day^–1), temperature (20°C, 29°C), and salinity (5, 15, 25) were tested on the development times for polyp buds (DT_p) and medusa buds (DT_m), the total asexual reproduction rate (ARR, no. buds polyp^–1 day^–1), and the ratio of medusa bud to total bud production (R_m). Greater food consumption significantly and directly enhanced ARR and R_m and shortened DT_p and DT_m. A lower temperature (20°C) and higher salinity (25) reduced food consumption, lengthened development times, and decreased ARR and R_m, with opposite effects for the higher temperature (29°C) and lowest salinity (5). The patterns of variation of these reproductive parameters are more complex. DT_m was most sensitive and was significantly and directly affected by all three measured factors. In addition to food consumption, direct effects were seen by temperature on DT_p and by salinity on R_m. ARR was directly affected only by food consumption. Overall, DT_p, DT_m, and R_m were more sensitive to environmental differences than was ARR. More favorable conditions enhanced medusa bud production. The adaptive reproductive processes and their significance for the maintenance and dispersal of M. lyonsi are discussed.Communicated by J.P. Grassle, New Brunswick     

A continuous recirculating culture system for planktonic copepods

The calanoid copepods, Acartia clausi Giesbrecht and Acartia tonsa Dana, are maintained at high densities in continuous culture at 15°C. Synthetic sea-water medium is recirculated through filters and a foam tower which limits accumulation of dissolved wastes and various metabolites. The ciliate Euplotes vannus Müller is associated in culture with the copepods, and effectively controls bacterial population and accumulation of algal debris. The copepods graze upon the ciliates as well as upon the phytoflagellates Isochrysis galbana Parke and Rhodomonas baltica Korsten.Contribution No. 119 from the Institute of Marine and Atmospheric Sciences, University of Miami.     

Being young in a changing world: how temperature and salinity changes interactively modify the performance of larval stages of the barnacle <Emphasis Type="Italic">Amphibalanus improvisus</Emphasis>

The fate of key species, such as the barnacle Amphibalanus improvisus, in the course of global change is of particular interest since any change in their abundance and/or performance may entail community-wide effects. In the fluctuating Western Baltic, species typically experience a broad range of environmental conditions, which may preselect them to better cope with climate change. In this study, we examined the sensitivity of two crucial ontogenetic phases (naupliar, cypris) of the barnacle toward a range of temperature (12, 20, and 28°C) and salinity (5, 15, and 30 psu) combinations. Under all salinity treatments, nauplii developed faster at intermediate and high temperatures. Cyprid metamorphosis success, in contrast, was interactively impacted by temperature and salinity. Survival of nauplii decreased with increasing salinity under all temperature treatments. Highest settlement rates occurred at the intermediate temperature and salinity combination, i.e., 20°C and 15 psu. Settlement success of “naive” cyprids, i.e., when nauplii were raised in the absence of stress (20°C/15 psu), was less impacted by stressful temperature/salinity combinations than that of cyprids with a stress history. Here, settlement success was highest at 30 psu particularly at low and high temperatures. Surprisingly, larval survival was not highest under the conditions typical for the Kiel Fjord at the season of peak settlement (20°C/15 psu). The proportion of nauplii that ultimately transformed to attached juveniles was, however, highest under these “home” conditions. Overall, only particularly stressful combinations of temperature and salinity substantially reduced larval performance and development. Given more time for adaptation, the relatively smooth climate shifts predicted will probably not dramatically affect this species.     

Effects of temperature,salinity, and predators on mortality of and colonization by the invasive hydrozoan<Emphasis Type="Italic"> Moerisia lyonsi</Emphasis>

The successful invasion of non-indigeneous species depends on initial colonization as well as establishing a self-maintaining population. The invasive hydrozoan Moerisia lyonsi (Boulenger, 1908), possibly originating from low-salinity waters in the Black Sea and Middle East regions, has become established in low-salinity waters in several estuaries of North America, including Chesapeake Bay. The effects of temperature and salinity on mortality of M. lyonsi polyps were examined in the laboratory in February 2001 in the presence of abundant food. The polyps of M. lyonsi were directly transferred from 20°C and 10 salinity to one of 45 combinations of temperature (10–29°C) and salinity (1–40). Polyp mortality within 7 days occurred only in low-temperature treatments with salinities of 35–40. Surviving polyps reproduced asexually in salinities of 1–40 at 20–29°C, and in salinities of 1–25 at 15°C, but not in any salinities at 10°C. The greatest asexual reproduction rates, an index for population survival potential, occurred at salinities of 5–20. Survival and reproduction of M. lyonsi over such broad temperature and salinity ranges indicate that M. lyonsi may colonize and establish populations throughout the Chesapeake Bay; however, M. lyonsi medusae were reported only at salinities <9.3 there. This discrepancy may be due to the effects of predators. The scyphomedusan Chrysaora quinquecirrha (Desor, 1848), but not the ctenophore Mnemiopsis leidyi (A. Agassiz, 1865) consumed M. lyonsi medusae in laboratory experiments in August–September 2001. Populations of M. lyonsi do not appear to be limited by temperature and salinity conditions; however, their distribution in Chesapeake Bay may be restricted to low salinities not inhabited by predators.Communicated by J.P. Grassle, New Brunswick     

Combined effects of temperature and salinity on the complete development ofEurytemora velox (Crustacea: Calanoidea)

The calanoid copepodEurytemora velox was collected from rock pools at Castletown, Isle of Man, UK. Its optimum environmental requirements, particularly temperature and salinity, were determined, with a view to its possible future use as living food in intensive fish and shellfish farming. The species was cultured in 21 different temperature and salinity combinations. Investigations covered a period of two years from December 1983 to December 1985. Complete development from hatching to adult stage was followed in 21 temperature and salinity combinations. Nauplii suffered relatively high mortalities, indicating the sensitivity of this development stage to variations in temperature and salinity. Highest nauplii survival was observed in the combinations 15°C with 25 and 20 S and 20°C with 20 S, the highest copepodite survival at 10°C and 20 S. Lower salinities were tolerated better at higher temperatures and higher salinities at lower temperatures. Development time varied with the temperature and salinity combinations. Lower salinities at the lower temperatures of 10° and 15°C and both lower and higher salinities at 20°C prolonged development, particularly of the naupliar stage. Highest Q₅ values (i.e., rate of change of development with a 5 C° increase in temperature) were recorded for the naupliar stage. Statistical analysis indicated that salinity influences the survival of both nauplii and copepodites; however, this effect is not linear.     

Comparative study of the effects of temperature,salinity and oxygen tension on the rates of oxygen consumption of nauplii of different strains of Artemia

The effects of temperature, salinity and oxygen tension on the rates of oxygen consumption of three different strains of Artemia nauplii have been studied. When acclimated to a salinity of 30, nauplii from each of the three strains were able to maintain approximately constant rates of oxygen consumption over a wide range of oxygen tension. The ability to maintain respiratory independence during hypoxia was reduced, however, with an increase in either temperature or salinity. Nauplii of two of the strains (parthenogenetic diploid and tetraploid) showed a progressive increase in the rate of oxygen consumption with increasing temperature up to 35°C. Nauplii of the bisexual strain appeared to be less tolerant of exposure to temperatures >30°C, since at higher temperatures their oxygen consumption declined slightly. The differences between the nauplii of the different strains in their physiological responses to changing environmental conditions appear to correlate well with their seasonal occurrence in the field.     

Synergistic effects of cadmium and salinity combined with constant and cycling temperatures on the larval development of two estuarine crab species

The developmental stages from megalopa to third crab of the blue crab Callinectes sapidus Rathbun were tested in 12 combinations of cadmium (0, 50, and 150 ppb) and salinity (10, 20, 30, and 40) at 25°C. A reduction in survival and a significant delay in development from megalopa to third crab occurred within each salinity regime in 50 ppb compared with the control. Comparison of the delay in development within each salinity regime revealed that the sublethal effect of cadmium was most pronounced in the salinities normally preferred by C. sapidus. A similar comparison within each cadmium concentration, however, showed that the developmental time from megalopa to third crab was approximately the same irrespective of salinity. The developmental stages from hatch to first crab of the mud-crab Rhithropanopeus harrisii (Gould) were examined in 63 combinations of cadmium (0, 50, and 150 ppb), salinity (10, 20, and 30), constant temperature (20°, 25°, 30°, and 35°C) and cycling temperature (20° to 25°C, 25° to 30°C, and 30° to 35°C). The results indicated that cycling temperatures may have a stimulating effect on survival of the larvae compared to constant temperatures, both in the presence and in the absence of cadmium. Effects of cadmium and salinity and their interaction on the survival of the larvae from zoeae to megalopa were documented at most of the temperatures by analyses of variance. The zoeal larvae were more susceptible to cadmium than the megalopa. Effects of different combinations of cadmium and salinity on the duration of larval development were assessed by a t-test.     

Acquisition and loss of cold-tolerance in adult barnacles (Balanus balanoides) kept under laboratory conditions

In the laboratory, Balanus balanoides (L.) barnacles maintained without food at 5°C over the winter to summer period remained cold-tolerant. Winter animals maintained at 5°C and fed Artemia nauplii under a controlled light-dark regime until mid-summer lost this cold-tolerance. Summer animals, maintained without food at 5° or 15°C until midwinter, became cold-tolerant. Summer and winter animals subjected to increased (or decreased) ambient salinity for 48 h showed a small decrease (or increase) in their lower median lethal temperature (MLT—defined as the temperature at which 50% of the animals die after 18 h exposure to air). Summer animals subjected to desiccation for 48 h also showed a small decrease in their lower MLT. It is concluded that the seasonal changes in cold-tolerance of adult barnacles are probably induced by a combination of environmental factors including food availability, light intensity, day-length and changes in ambient sea-water temperatures. Development of cold-tolerance in the winter did not depend upon fertilisation. Changes in intra-cellular solute concentration which accompany adaptation to changes in ambient salinity or desiccation do not appear to be related to the seasonal changes in cold-tolerance.     

Overwintering strategies of dominant calanoid copepods in the German Bight, southern North Sea

Abundance, stage composition and reproductive parameters (egg production, egg viability, proportion of spawning females) of the four copepod species Acartia clausi, Centropages hamatus, C. typicus and Temora longicornis were measured at the long term sampling station Helgoland Roads (German Bight, southern North Sea) from September 2003 to May 2004 to study their overwintering strategies. A. clausi was overwintering as females with arrested reproduction from November to January. T. longicornis, which is known to produce resting eggs in the North Sea, had a pelagic population with all developmental stages present during winter and reproductive rates closely related to food concentrations. Although their females produced eggs in response to ambient food conditions, both C. hamatus and C. typicus were rare in the pelagic. The C. hamatus population returned in May, probably from resting eggs, whereas C. typicus depended on advection. The Centropages species seemed to be less adapted to pelagic life in winter than A. clausi and T. longicornis. Sporadic occurrence of large numbers of nauplii and young copepodids of A. clausi and Centropages spp. pointed to different overwintering strategies or more successful survival in adjacent regions and advection of them into the waters around Helgoland island. While A. clausi was decoupled from environmental conditions in late autumn and winter, the other species were able to respond to variations in the food environment. Thus, egg production of T. longicornis increased during an unusual autumn diatom bloom.     

Predation of calanoid copepods on their own and other copepods’ offspring

Predation of eggs and nauplii by adult copepods is often used to explain unexpected death rates in population dynamics studies, but the phenomenon has been rarely investigated or quantified. Therefore, we studied the predatory feeding of adult females (Acartia clausi, Centropages hamatus, Centropages typicus, and Temora longicornis) on their own and other species’ eggs and young nauplii with different densities of single animal-prey, mixtures of animal-prey and in the presence of diatoms. All species preyed on eggs and nauplii of their own and all other species. Maximal egg predation varied between 7 and 64 eggs fem^?1 day^?1. Ingestion of Centropages spp. eggs was lowest, potentially due to the spiny egg surface. Maximal feeding rates on nauplii ranged from 5 to 45 nauplii fem^?1 day^?1. T. longicornis preferred eggs, when eggs and nauplii were offered together at the same densities, and the other predators selected for nauplii. At a diatom concentration of 60 μg C l^?1 predation on eggs by C. typicus was higher than without algae, whereas A. clausi and T. longicornis did not change their uptake of eggs. Feeding on nauplii in the presence of diatoms was again enhanced in C. typicus, and unaffected in A. clausi and C. hamatus. T. longicornis reduced its feeding on nauplii in the presence of diatoms. Calculated predation rates, using field abundances of predators and prey, suggest that predation of copepods on their own young stages may account for ca. 30 % of total mortality of young stages in North Sea copepod populations.     

Individual effects and interactions of salinity,temperature, and zinc on larval development of the grass shrimp Palaemonetes pugio. I. Survival and developmental duration through metamorphosis

Larvae of the estuarine grass shrimp Palaemonetes pugio (Holthuis) were reared from hatch through successful completion of metamorphosis in 80 combinations of salinity (3 to 31%), temperature (20° to 35°C), and zinc (0.00 to 1.00 ppm Zn⁺⁺). Response-surface methodology was employed to depict the individual effects and interactions of the three factors on survival and developmental duration through total larval development. Outside the optimal salinity-temperature conditions of 17 to 27 S and 20° to 27°C, viability of larvae was reduced by both the individual effects of salinity and temperature and interactions between the two factors. Survival capacity of larvae and resistance adaptations to salinity and temperature were progresively reduced by zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺. Response-surface analysis of the data suggested that the duration of total larval development of P. pugio was least at salinities from 18 to 23 and at temperatures from 30° to 32°C. At both higher and lower salinity-temperature conditions and in increasing zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺, developmental rates were retarded. A significant zinc-temperature interaction existed, whereby increasing zinc concentrations reduced both survival and developmental rates of larvae more at suboptimal temperatures. Larval resistance to zinc toxicity was least at supraoptimal salinities, indicative of a significant zinc-salinity interaction. The reduced viability, restricted euryplasticity, and retarded developmental rates of P. pugio larvae developing in media with low-level zinc contamination would limit the distributive properties of the pelagic phase in the life cycle of the species and reduce recruitment both into and out of the parent estuarine population.