Biochemical changes during larval development of the xanthid crab Rhithropanopeus harrisii. III. Isozyme changes during ontogeny

Isozyme changes in the xanthid crab Rhithropanopeus harrisii (Gould) are described for 6 enzyme systems through all four zoeal stages, megalopa stage, and juveniles. There is considerable variation in the number of isozymes and their expression during the ontogeny of R. harrisii.Contribution No. 806 of the Chesapeake Biological Laboratory, Center for Environmental and Estuarine Studies, University of Maryland, USA.     

Biochemical changes during larval development of the xanthid crab Rhithro panopeus harrisii. II. Nucleic acids

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) contents were measured daily during the zoeal development of the crab Rhithropanopeus harrisii (Gould). DNA concentration (per unit protein) decreased as larvae increased in size. Total DNA content per larva showed an abrupt increase at the second molt and increased steadily during the third and fourth zoeal stages. Ratios of fresh weight to DNA were highest during the first two zoeal stages, dropped sharply at the second molt, then increased during the third and fourth zoeal stages. RNA:DNA ratios showed cyclical activity apparently related to the molt cycle. Assuming that fresh weight: DNA ratio reflects cell size and that DNA content reflects cell number, growth during the first two stages is due primarily to increase in cell size and during the last two stages to a combination of increase in cell size and number. Assuming further that RNA:DNA ratios reflect protein-synthesis activity, such activity in these larvae follows a rhythm related to the molt cycle.     

Biology and ecology of the crab Rhithropanopeus harrisii ssp. tridentatus

Data are presented on the geographic and local distributions as well as on the life cycle of the crab Rhithropanopeus harrisii (Gould) ssp. tridentatus (Maitland). Extensive studies on this subspecies were carried out in its natural habitat (an abandoned arm of the Vistula, Poland), and under laboratory conditions. The effects of some environmental factors on distribution, life cycles, and abundance of the crab are discussed. The results obtained are compared with those reported by other investigators.     

Interactions between temperature and salinity during brooding on subsequent zoeal development of the mud crab Rhithropanopeus harrisii

Female mud crabs, Rhithropanopeus harrisii, carrying newly extruded eggs, were collected from the Petaluma River (San Francisco Bay Estuarine System, California, USA) in summer 1985, and exposed to factorial combinations of temperature (20°, 25° or 30°C) and salinity (2, 5, 15, 25, or 32%.). Upon hatching, dry weights of 12 to 15 h-old zoeae were determined. Subgroups of the remaining zoeae were transferred from hatching salinities to the salinities listed above and raised until metamorphosis to megalopa. Low salinities reduced zoeal dry weights by as much as 25%. Temperature played a secondary role in reduction of hatching weight of zoeae. Survival of larvae through zoeal development was best when hatching and rearing salinities were the same; in this case, overall survival increased with temperature. Both duration of zoeal development and megalopal dry weights were strongly influenced by temperature and rearing salinity, with only a small contribution from hatching salinity. The influence of hatching salinity was most obvious at extremes of the range tested. These studies indicate that physical conditions during embryogenesis profoundly influence subsequent larval development. Interpretation of experimental approaches to study ecophysiological adaptations of larval stages should not neglect the role of physical conditions during embryogenesis.     

Entrainment of the larval release rhythm of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) by cycles in salinity change

Influences of salinity, Na, K, Ca and Mg on Na–K-ATPase activity in the posterior gills of Carcinus maenas (L.) have been investigated with respect to the role of the enzyme in hyperosmotic regulation. K and Mg ions were obligatory for enzyme activity. The dependence on the K concentration can be seen in a saturation curve of the Michaelis-Menten type. Low concentrations of Ca (0.2–3 mM) in the incubation medium strongly inhibited Na–K-ATPase activity. Activities inhibited by Ca could be reactivated to non-inhibited values by the addition of higher amounts of Mg (25 mM). Activity increased along with the salinity of the sea water used as incubation medium up to about 10 S. Here, maximum activity was observed. Further salinity increases of the incubating sea water were inhibitory. Salinity dependence is assumed to be based on Na dependence of the Na-pump. Comparative investigations of the Na–K-ATPase activity and its affinity to sodium in five species of decapod crustaceans indicated that levels of Na–K-ATPase differed in the posterior gills of stenohaline and euryhaline species. The results obtained confirm previous assumptions of a central role of the branchial Na–K-ATPase in hyperosmotic regulation. Properties of the Na–K-ATPase, such as affinity for substrates or dependence on ionic sea water constituents, are kept constant with respect to salinity changes. Modifications due to salinity only concern enzyme amounts especially in the posterior gills. The finding that the Na-pump is localized in basolateral parts of ion-transporting epithelial cells confirms the aforementioned results.     

Absence of sterol synthesis in larvae of the mud crab Rhithropanopeus harrisii and of the spider crab Libinia emarginata

A dietary requirement for sterols in crustacean larvae was established by the use of isotopic tracer techniques. Larvae of the mud crab Rhithropanopeus harrisii and larvae of the spider crab Libinia emarginata were exposed to acetate-¹⁴C or mevalonate-¹⁴C. Radioanalysis of the fatty acids of each species indicated sufficient incorporation of acetate for lipid synthesis. No radioactivity was detected in the sterols of animals exposed to either acetate-¹⁴C or mevalonate-¹⁴C. It was concluded that R. harrisii and L. emarginata larvae are unable to synthesize sterols from acetate or mevalonate and, therefore, require them in their diet.     

Behavioral responses of larvae of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) during diel vertical migration

Larval Rhithropanopeus harrisii (Gould) show nocturnal vertical migration. Larval behavioral responses to different rates of increase and decrease in light intensity were measured in an apparatus with a natural angular light distribution. A central objective was to establish whether phototaxis actually participates in vertical migration. At sunset the level of light adaptation controlled the readiness of the larvae to migrate, while an ascent was initiated by a preductable relative decrease in intensity (e.g. 4.0x10^-3s^-1). Rates of relative decrease around sunset would evoke continuous upward swimming. Gravity was the orienting cue and there was no change in swimming speed during the ascent. At sunrise, the larval descent was initiated by exposure to an absolute light intensity of about 0.23 log unit above the lower visual threshold. Light served as an orienting cue, as larvae descended by a negative phototaxis. Thus, phototaxis is not a laboratory artifact and does participate in vertical migration. A consideration of behavioral responses of other crustacean zooplankton indicates there is considerable variation in the initiating and directing cues for vertical movements. The variety of behavioral responses of R. harrisii suggests that a synthesis of hypotheses about migration may provide the proper basis for explaining the mechanisms underlying diel vertical migration.     

A long-term study of the effects of water-soluble fractions of No. 2 fuel oil on the survival,development rate,and growth of the mud crab Rhithropanopeus harrisii

Mud crabs, Rhithropanopeus harrisii (Gould), were exposed continuously for 6 months after hatching to water-soluble fractions (WSF) of No. 2 fuel oil. Survival, growth and development rate were monitored during this time. The zoeal stages were the most sensitive to fuel oil. A 20% WSF (0.36 ppm total naphthalenes, 1.26 ppm total hydrocarbons) was acutely toxic to these stages. Of the zoeal stages, the first stage appeared to be the most sensitive. The combined duration of the 4 zoeal stages was significantly increased by increasing WSF exposure concentrations. The megalopa and crab stages were not particularly sensitive to continued petroleum hydrocarbon exposure, particularly when compared to zoeal stages. However, mean duration of the megalopa and first crab stages was significantly affected by oil exposure. Individuals which survived the highest exposure concentrations as larvae appeared to grow larger during the crab stages, so that at the end of 6 months comparably staged crabs were equal to or larger than both control crabs and those exposed to low WSF concentrations. Stage distributions at the end of 6 months showed no differences due to WSF exposure. Sex ratios, which could be determined at the end of 6 months, were approximately 1, indicating no sex-related differential sensitivity to WSF exposure, at least as larvae or juveniles. The data indicate that these crabs possess considerable ability to recover from the effects of chronic sublethal exposure to petroleum hydrocarbons. The most deleterious effects of oil pollution on this species may be due to its impact on larval recruitment into the adult population.     

Laboratory study of effects of temperature and salinity on survival and larval development of a population of Rhithropanopeus harrisii from the Mondego River estuary,Portugal

Rhithropanopeus harrisii (Gould) is an introduced species in the estuary of the Mondego River (Portugal): it was first recorded from the Iberian Peninsula in 1989. The larval development of this population was studied under laboratory conditions at different temperatures and salinities, and showed a larval development pattern very similar to that reported for American estuarine populations of this species. Larval development was negatively correlated with temperature. Time to megalopa varied between 7 and 35 d; the first crab (C₁) was reached after a maximum of 11 to 43 d. Larval development was optimum at 25°C and 15S. Larval survival was maximum at 10, 15 and 20S at all three temperatures studied (20, 25 and 30°C). The percentage of abnormal megalopae increased with increasing salinity to a maximum (100%) at 30S; incidence of abnormality was not affected by temperature.     

Effects of the juvenile hormone mimic ZR-512 (Altozar®) on larval development of the mud-crab Rhithropanopeus harrisii at various cyclic temperatures

Effects of the juvenile hormone (JH) mimic hydroprene (Altozar^®: ZR-512), which exhibits high activity against Lepidoptera, were studied on the larval development of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae). Larvae reared in 20 S at 3 cycles of temperature of 20° to 25°C, 25° to 30°C and 30° to 35°C, were exposed to 0.01, 0.1 and 0.5 ppm hydroprene from hatching to the first crab stage. Larvae were also exposed to 0.1 and 0.5 ppm hydroprene only from the megalopa stage to the first crab stage. When larvae were treated with hydroprene throughout larval life, survival was significantly reduced with increasing concentrations of the compound at all temperature cycles. Synergistic effect between hydroprene and temperature on survival of zoeal larvae was not observed. On the average there was 11% less survival in the zoeal stages at the 0.01 ppm concentration. of hydroprene than in the control, an additional reduction of 13% occurred at 0.1 ppm, and finally there was a further decrease of 46% at 0.5 ppm hydroprene. Significant decrease in survival in the megalopa stage occurred only in the 0.5 ppm concentration of hydroprene at the lowest temperature cycle when larvae were exposed to the compound from hatching. When larvae were treated with hydroprene only within the megalopa stage, a significant reduction in survival was not observed. First-stage zoeae were the most sensitive of the larval stages to hydroprene. Duration of zoeal development was significantly delayed at 0.5 ppm hydroprene at the two lower temperature cycles, whereas in the megalopa stage the delay began at the 0.1 ppm level at all 3 temperature cycles when larvae were exposed to hydroprene from hatching. A significant delay was also observed at 0.1 ppm hydroprene at the two lower cycles when larvae were exposed to hydroprene only in the megalopa stage; at 30° to 35°C a significant delay was observed only at the 0.5 ppm level. The results show that metamorphosis to the first crab stage was not inhibited at the 0.5 ppm level of hydroprene or lower. Reduction in survival and increase in duration of larval development were presumably related to stress conditions caused by hydroprene. The results also suggest an interaction between temperature and hydroprene on survival of megalopa larvae and duration of larval development.     

The effect of salinity and cyclic temperature on larval development of the mud-crab Rhithropanopeus harrisii (Brachyura: Xanthidae) reared in the laboratory

Larvae of Rhithropanopeus harrisii (Gould) were reared from hatching to the first or second crab stages in 11 combinations of salinities and cyclic temperatures (5, 20, and 35 S at 20° to 25°C, 25° to 30°C, and 30° to 35°C; 25 S at 20° to 25°C and 30° to 35°C). The larvae survived to the megalops and first crab stages in all salinities and cycles of temperature other than 5 S at 30° to 35°C. The best survival to the megalops (94%) and first crab (90%) stages occurred in 20 S, 20° to 25°C. In all other combinations of salinities and temperatures there was a reduction in survival to the first crab stage. The duration of the larval stages was affected significantly by temperature, whereas the effect of salinity on the mean days from hatching to the first crab stage was not consistent at the different temperature cycles. Development to the first crab stage required the shortest time in 20 S, 30° to 35°C (mean 12.3 days), and the longest time in 5 and 35 S, 20° to 25°C (mean 22.6 days and 21.6 days, respectively). Megalops larvae reared in 35 S at all cycles of temperature, as well as larvae in 20 and 25 S, 30° to 35°C, showed a high percentage of abnormality, with the highest percentage occurring in 35 S, 30° to 35°C. It appears that larval development of R. harrisii is strongly influenced by environmental factors and not solely related to genetic differences.This research was supported by grants from the Nordic Council for Marine Biology and the U.S. Atomic Energy Commission [Grant No. At-(40-1)-4377].Contribution No. 116, Zoological Museum, University of Oslo, Norway.     

Effects of the juvenile hormone mimic ZR-515 (Altosid®) on larval development of the mud-crab Rhithropanopeus harrisii in various salinities and cyclic temperatures

Effects of 0.01, 0.1 and 1.0 ppm methoprene (Altosid^®: ZR-515), a juvenile hormone (JH) mimic which shows high activity against some economically important insect pests, especially Diptera, were tested on larvae of the mud-crab Rhithropanopeus harrisii (Gould) (Brachyura: Xanthidae) from hatching to the first crab stage under optimum and stress conditions of a number of salinities and cyclic temperatures. There was a significant reduction in survival of zoeal larvae with increasing concentrations of methoprene in nearly all combinations of salinity and temperature. On the average there was 9% less survival in the 0.01 ppm concentration of methoprene than in the control, and in the 0.1 ppm concentration the survival was further reduced by another 16%. At 1.0 ppm methoprene no larvae survived beyond the first zoeal stage under optimum conditions or under stressful combinations of salinity and temperature. Except at 0.2 ppm in 27.5% S, survival of the megalopa was not significantly reduced in 0.01 or 0.1 ppm methoprene in any salinity or temperature, although the percentage of abnormal megalopa increased under stress conditions. The first zoeal stage was the most sensitive of the larval stages to methoprene as well as to salinity and temperature stress. The duration of zoeal development was significantly lengthened with an increase in concentration of methoprene under nearly all conditions of salinity and temperature. The JH mimic had, however, no significant effect on the duration of megalopa development. A significant synergism between methoprene, salinity and temperature was not observed. It can be concluded from the results that methoprene does not inhibit metamophosis of R. harrisii larvae at the 0.1 ppm level or lower. Reduction in survival of zoeal stages and increased duration of zoeal development with increasing concentrations of methoprene are presumably related to stress.     

Ultrastructural study of the exoskeleton of the estuarine crab Rhithropanopeus harrisii: Effect of the insect growth regulator Dimilin® (diflubenzuron) on the formation of the larval cuticle

Ultrastructure of larval cuticle during the molt cycle of the estuarine crab Rhitropanopeus harrisii (Gould) (Crustacea: Brachyura) was studied in control larvae as well as in larvae exposed to 10 ppb of the insect growth regulator Dimilin^® (diflubenzuron). First zoeal larvae were used as test organisms. It has earlier been shown that 10 ppb Dimilin is lethal to zoeal larvae of R. harrisii, and nearly all exposed larvae died during molting to the next stage (Christiansen et al., 1978). Distinct differences in structure of the cuticle were found between the two groups of larvae. Both endocuticle and exocuticle appear to be deformed in Dimilin-treated larvae, whereas formation of epicuticle did not seem to be affected. The results indicate that Dimilin probably inhibits chitin synthesis in crab larvae as shown earlier by several authors for insect larvae.     

Differences in responses to factorial combinations of temperature and salinity by zoeae from two geographically isolated populations of the mud crab Rhithropanopeus harrisii

Ovigerous mud crabs, Rhithropanopeus harrisii, were collected from the Petaluma River (San Francisco Bay Estuarine System, California, USA) and from Sykes Creek (Indian River Lagoon System, Florida, USA) during the summer of 1984 and during February 1985, respectively. Their zoeae were reared in factorial combinations of temperature (20°, 25° or 30°C) and salinity (2, 5, 10, 15, 20, 25, or 30%.). Survival and megalopal dry weight were maximal over a far larger range of temperature-salinity combinations for the Florida population. Absolute values of the two parameters were also greater for this group. Temperature dominated effects on duration of zoeal development in both populations. California zoeae developed more slowly at any of the temperatures tested compared with those from Florida. The pattern of all three indices was markedly different under non-optimal conditions. Putatively adaptive modification of survival, development rate and growth of zoeae is evident in response to prevailing environmental conditions which are, in part, a function of latitudinal position. Even though populations in the Petaluma River, California, are less capable of reaching maximal performance under the prevailing physical regimes than the Florida population, they still can live in habitats where physical conditions exclude competitors and predators.     

Physiological and biochemical changes during lecithotrophic larval development and early juvenile growth in the northern stone crab,Lithodes maja (Decapoda: Anomura)

Larvae of the northern stone crab, Lithodes maja L., were reared in the laboratory from hatching to the second crab stage. complete larval development (at constant 9°C) lasted about 7 wk, invariably consisting of three pelagic zoeal stages and a semibenthic Megalopa; only two zoeal stages have been described in the literature. All larval stages are lecithotrophic. First feeding was consistently observed only after metamorphosis, in the first juvenile crab stage. In short intervals (every 1 to 5 d), developmental changes in biomass, B (expressed as: dry weight, W; carbon, C; nitrogen, N; hydrogen, H) and oxygen consumption (respiration, R) were measured in larvae and early juveniles; additionally, protein and carbohydrates were measured, but only in the zoeal stages and early Megalopa. Unusually high C contents (varying between 56 and 61% of W in eggs and freshly hatched Zoea I larvae from 12 different females) and high C:N weight ratios (8 to 11) indicate enhanced initial lipid stores, which are utilized as the major metabolic substrate during both embryonic and lecithotrophic larval development. Predominant degradation of lipids is shown indirectly; the C:N ratio decreased significantly, from 10 (at hatching) to 6 (at metamorphosis), while larval protein decreased only little, from ca. 55% of W (at hatching) to 48% (in the Megalopa). From hatching to metamorphosis, about 27% of the initially present W, 48% of C, 18% of N, and 52% of H were lost. This decrease in larval biomass can be described as an exponential function of development time. The major part of these losses were associated with metabolic energy requirements, while exuvial losses were comparably small. In each of the zoeal stages, only about 1 to 2% of late premoult (LPM) B was shed with the exuvia. The Megalopa, which produces a much thicker, calcified exoskeleton, lost 20% of LPM W, but only 5 to 8% of organic constituents (C, N, H). Much higher exuvial losses were measured in the Crab I stage (51% in W, 21% in C, 5% in N, and 7% in H). Maximum respiration was found in the actively swimming zoeal stages, a minimum in the predominantly benthic, mostly inactive Megalopa. The Crab I stage exhibits also a sluggish behaviour and low R, in spite of beginning food uptake and growth. Immediately after metamorphosis, the juvenile crab gained rapidly in W, in particular in its C fraction. A transitorily steep increase in the C:N ratio indicates a replenishment of partially depleted lipid stores, but also a rapid initial increase of inorganic C in the heavily calcified exoskeleton. Instantaneous rates of growth, assimilation, and net growth efficiency (K ₂) were high during the initial (postmoult) phase in the first juvenile crab stage (C-specific growth rate: 6% d^-1; K ₂:70%), but decreased towards zero values during laterstages of the moulting cycle; metabolism remained practically constant during the Crab I stage. Entirely lecithotrophic larval development from hatching to metamorphosis in L. maja is considered an adaptation to seasonally short and limited planktonic food production in subarctic regions of the northern Atlantic.     

Larval growth in the estuarine crab Chasmagnathus granulata: the importance of salinity experienced during embryonic development, and the initial larval biomass

The importance of salinity experienced during embryonic development and initial larval biomass on larval growth was studied in the South American estuarine crab Chasmagnathus granulata. Ovigerous females were maintained at three salinities (15, 20, and 32‰) from egg laying to hatching of zoea l. Larvae from all treatments were reared under constant conditions of photoperiod (12∶12), temperature (18°C), and salinity (first instar at 20‰, subsequent instars at 32‰). Biomass was measured as dry weight, carbon, and nitrogen content per individual at egg laying, hatching of zoea l, premoult zoea l, and zoea 4, and in 8-day-old megalopa. From hatching to premoult zoea 4, biomass was higher for larvae from prehatching salinities of 15 and 32‰. There was a significant positive correlation between biomass at hatching and at premoult zoea l and zoea 4. Accumulated biomass during zoeal stages tended to be higher for larvae from broods with higher biomass at hatching, although this trend was not always significant. Zoea 4 either directly metamorphosed to megalopa or moulted to zoea 5, following, respectively, a short or long developmental pathway. The proportion of zoea 4 that followed the long pathway was negatively correlated with biomass of zoeal stages. Biomass at hatching was correlated with biomass of megalopae developed through the short pathway, although it was not correlated with the accumulated biomass at this stage. Megalopae developed through the long pathway (i.e. metamorphosed from zoeae 5) had higher biomass than those from the short pathway. The present results suggest that prehatching salinity and initial egg and larval biomass can be very important for larval growth. Published online: 9 August 2002     

Differential utilization of biochemical components during larval development of the spider crab Maja brachydactyla (Decapoda: Majidae)

Changes in lipid class, fatty acid, fat-soluble vitamins, amino acid and minerals were studied during larval development of Maja brachydactyla Balss, 1922 in order to provide information of its ontogeny and evaluate possible dietary deficiencies and constraints. Four different batches were analyzed from hatching to metamorphosis using enriched Artemia as food. Cultured larvae were in a good nutritional condition as confirmed by the continuous lipid accumulation throughout ontogeny. A regulation of polyunsaturated fatty acids (PUFA) occurred during development in order to maintain adequate basal levels of ω-3 fatty acids (likely through a retro conversion of C₂₀ and C₂₂ into C₁₈ PUFA). Variations in the tocopherol levels indicated its possible role in PUFA protection against oxidation. Essential amino acid balance during development was not correlated with the Artemia feeding regime, but rather reflected inherent variations of the own species ontogeny. Larval requirements in essential minerals were fully supplied by the enriched Artemia.     

Long-term effects of water-soluble fractions of Kuwait crude oil on the larval and juvenile development of the mud crab Eurypanopeus depressus

Larvae of the mud crab Eurypanopeus depressus (Smith) were reared in various concentrations of the water-soluble fraction of Kuwait crude oil. The 48-h TL_m (median tolerance limit) for Zoea Stage I was approximately 10 ppm total dissolved hydrocarbons and that for Zoea Stage II approximately 17 ppm. Chronic toxicity of more dilute solutions (4.3 and 8.7 ppm) was assessed independently for each larval stage and for subsequent developmental stages through Crab Stage 5. In the group continuously exposed to oil from hatching, there was differential mortality relative to controls in every larval stage and increased duration of intermolt periods was observed at every stage through Crab Stage 5. Mortality in groups not exposed until larvae had reached Zoea Stages III or IV was not greater than controls, suggesting that toxicity to advanced larval stages may be related to accumulation of toxic compounds by the larvae. Neither concentration (4.3 or 8.7 ppm) of crude oil caused increased mortality among juvenile crab stages regardless of the time of initial exposure. Increased occurrence of an extra and morphologically abnormal megalopa stage was associated with exposure to the crude oil. This has not been reported before.Communicated by I. Morris, West Boothbay Harbor     

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.     

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.