Population-related toxicity responses to two butyltin compounds by zoeae of the mud crab Rhithropanopeus harrisii

We exposed zoeae of the mud crab Rhithropanopeus harrisii to either bis(tri-n-butyltin) oxide (TBT) or di-n-butyltin dichloride (DBT). Experiments were repeated with zoeae from females collected from the Petaluma River, California in June–August 1983 and 1984 or from Sykes Creek, Florida (USA) in February 1985. Using probit analysis, we calculated LC₅₀ values for exposure lasting the duration of zoeal development. Tributyltin was 54 to 65 times more toxic than dibutyltin, the lower value characterizing the response of Florida zoeae. Increases in duration of zoeal development and reduction of dry weights of megalops, both sublethal responses, were dose-dependent for the two populations. However, zoeae from Florida consistently had shorter duration of zoeal development and higher megalopal weights at metamorphosis, indicating less sensitivity to an identical exposure to either organotin compound. The results of these experiments show that dibutyltin, a putative degradation product of tributyltin, is less toxic than the parent compound. In addition, early life-history stages of two populations may have significantly different responses to xenobiotic stress which, in the case of brachyuran larvae, is evident in a differential reduction of survival and growth and an increase in duration of zoeal development.     

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.     

Larval development of the hermit crab Clibanarius albidigitus (Crustacea: Anomura: Diogenidae) reared under laboratory conditions

The larval development of Clibanarius albidigitus Nobili is described and illustrated from laboratory-reared specimens. At 30°C, this species passes through four zoeal stages before molting to the megalopa. Of the 120 individual larvae reared, survival was high, with 88% reaching the megalopal stage. Zoeal stage durations varied from 3 to 18 d. Rearing was terminated after 45 d, and at that time no megalopae had molted to the firstcrab stage. Among known larvae of Clibanarius species, C. albidigitus is immediately distinguished by the presence of dorsomedial and dorsolateral carapace keels.     

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.     

Larval development of the crabCancer magister in temperature regimes simulating outer-coast and inland-water habitats

Postlarval megalopae of the Dungeness crabCancer magister inhabiting offshore coastal waters along the west toast of North America are larger and settle earlier than do those occupying the inland waters of the Puget Sound basin (Washington, USA, and British Columbia, Canada). The Puget Sound habitat is characterized by low initial temperatures that steadily increase during the course of zoeal development, while offshore temperatures are more moderate and stable. Larvae were raised in the laboratory from hatching to megalopa in three temperature treatments: (1) constant 10 °C (CO), (2) a regime that temporally simulated temperatures found off the central California coast during the larval season (CA); and (3) a regime simulating temperatures found within the Puget Sound basin (PS). Zoeal duration was 44% longer in the PS treatment than in the other two, at least partially accounting for observed differentes between outer-toast and inland-water settlement times. Although differentes were measured in megalopal weights and carapace lengths among treatments, results do not explain differences in megalopal size observed between outer-toast and inland-water individuals. Survival to megalopa was highest in the PS treatment, with the difference due to significantly lower mortality than in CO and CA treatments during the terminal zoeal stage. Daily instantaneous mortality rates were lower in the PS than in CO or CA treatments, indicating Chat extended larval duration will not necessarily result in reduced settlement success.     

Settlement cues in successive developmental stages of the ghost shrimps Callichirus major and C. islagrande (Crustacea: Decapoda: Thalassinidea)

Larvae of Callichirus major (Say) and C. islagrande (Schmitt) were given unconditioned water with sand, water conditioned by previous exposure to adults (AW) without sand, or the combination of both AW and sand to determine if these factors served as settlement cues. Shrimp were first given stimuli upon reaching the last zoeal stage (ZIV), the decapodid stage (D), or the first juvenile stage (J1). Once initiated, exposure of shrimp to stimuli was maintained until termination of␣the experiment. Stage duration, burrowing activity of decapodids and early juveniles and location of exuviae were observed daily. Exposure to sand and AW did not decrease duration of the decapodid stage in either species. However duration of ZIV in C. major appeared to decrease when these stimuli were offered at this stage; this suggests that molting to Stage D may be delayed without such cues. When stimuli were examined separately, AW was found to have a significant effect on the duration of ZIV, while the effect of sand with unconditioned water and effects of simultaneously offered stimuli were not significant. Shrimp that received stimuli at ZIV subsequently burrowed more at D and J1 than individuals that did not receive stimuli at ZIV. Location of exuviae was recorded as on top of sand (not burrowed during molt) or within sand (burrowed during molt) for each shrimp's molt from Stages D to J1 (D molt), and from J1 to J2 (J1 molt). In C. major, the percentage of D exuviae and J1 exuviae found within sand as opposed to on top of sand was significantly higher in individuals which received stimuli at ZIV than for those that first received them at D or J1. When stimuli were examined separately in C. major, the effect of sand on burrowing activity was highly significant, while AW and the stimuli in combination had weaker effects. For C. major, AW appeared to accelerate development to D, while sand triggered settlement. Neither stimulus altered stage duration or burrowing activity of C. islagrande. Received: 7 December 1997 / Accepted: 24 July 1998     

Effects of dieldrin in seawater on the development of two species of crab larvae,Leptodius floridanus and Panopeus herbstii

Some of the effets of dieldrin on the development of two species of crabs, Leptodius floridanus (Rathbun) and Panopeus herbstii (Milne-Edwards), were studied. It was found that the larvae of neither species were able to complete their development at 10 ppb dieldrin or higher in seawater. Groups of L. floridanus larvae reared in 1 ppb dieldrin in seawater had a 15 to 27% higher mortality during development to the postlarval stage than controls. The highest mortality occurred during the first zoeal stage. The time of development to the megalopal stage was as much as 11.4% longer among larvae reared in 1 ppb than among controls. The survival of L. floridanus larvae was not affected by 0.5 ppb dieldrin in seawater. The survival of P. herbstii larvae to the first crab stage was not affected by 1 ppb dieldrin in seawater at 28.5 °C, 30%.S. It was concluded that a comprehensive study of the toxicity of a given pesticide to all stages in the life cycle of a species is necessary to give even an incomplete idea of how the pesticide might affect the animal in its natural environment.     

Facultative lecithotrophy during larval development of the burrowing shrimp Callianassa tyrrhena (Decapoda: Callianassidae)

Survival, developmental and consumption rate (Artemia nauplii ingested per day) as well as predation efficiency (ingested per available Artemia nauplii) were studied during the larval development of the shallow-water burrowing thalassinid Callianassa tyrrhena (Petagna, 1792), which exhibits an abbreviated type of development with only two zoeal stages and a megalopa. The larvae, hatched from berried females from S. Euboikos Bay (Aegean Sea, Greece), were reared at 10 temperature–food density combinations (19 and 24 °C; 0, 2, 4, 8 and 16 Artemia nauplii d⁻¹). Enhanced starvation resistance was evident: 92 and 58% of starved zoeas I molted to zoea II, while metamorphosis to megalopa was achieved by 76 and 42% of the hatched zoeas at 19 and 24 °C, respectively. The duration of both zoeal stages was affected by temperature, food density and their interaction. Nevertheless, starvation showed different effects at the two temperatures: compared to the fed shrimp, the starved zoeae exhibited accelerated development at 19 °C (8.4 d) but delayed metamorphosis at 24 °C (5.9 d). On the other hand, both zoeal stages were able to consume food at an increased rate as food density and temperature increased. Predation efficiency also increased with temperature, but never exceeded 0.6. Facultative lecithotrophy, more pronounced during the first zoeal stage of C.tyrrhena, can be regarded as an adaptation of a species whose larvae can respond physiologically to the different temperature–food density combinations encountered in the wide geographical range of their natural habitat. Received: 28 February 1998 / Accepted: 21 October 1998     

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.     

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.     

Laboratory study of survival and duration of individual zoeal stages as a function of temperature in the brachyuran crab Cancer magister

Larvae were hatched from ovigerous Dungeness crabs, Cancer magister, collected from Puget Sound Basin, Washington, USA, in April, 1986, and the effects of temperature on rates of survival and development were studied for each of the five zoeal stages both in small batch-culture and in individual culture. Culture method had little effect on the results at 10°, 15°, and 20°C. Increased mortality was measured at all stages at 20°C, with 100% mortality occurring during the terminal fifth stage. Fifth stage larvae may also show higher mortality at 15°C than at 10°C. Stage duration varied inversely with temperature at all stages, although differences between 10° and 15°C were greater than between 15° and 20°C. The results indicate that survival and stage duration are independent of the values for the previous and subsequent stages, that variability among larvae in instar duration increases with temperature, and that the terminal fifth zoeal stage is the most sensitive to temperature stress. Duration of a late zoeal instar is not related to its earlier development rate nor can early development rates be used to predict whether individual zoeae will successfully develop to the megalopa. Measurements of megalopa dry weights indicate no differences due either to previous culture temperatures or to total time to the megalopa. Predictive models of larval transport that require estimates of larval duration should account for both changes in temperature response that can affect individual stage duration, and variability among individuals in stage duration that can influence the degree of larval dispersion.     

Effects on larval crabs of exposure to algal toxin via ingestion of heterotrophic prey

We tested whether ingesting toxic algae by heterotrophic prey affected their nutritional value to crab larval predators, using toxic algal strains that are either ingested directly by larval crabs or rejected by them. Ingestion of toxic strains of the dinoflagellates Alexandrium andersoni and A. fundyense by the rotifer Brachionus plicatilis was confirmed. Rotifers having ingested either algal type for five days were fed to freshly hatched larvae of three crab species, with larval survival and stage durations determined. For both algal/rotifer treatments in all three crab species, larvae fed algae directly died during the first zoeal stage, while those fed rotifers that had been fed either algal strain survived to the experiment’s end (zoeal stage 3). Survival was lower, and stage duration longer, for larvae fed rotifers cultured on toxic algae when compared to those fed non-toxic algae. The role of toxic algae in the planktonic food web may be influenced by its direct or indirect ingestion by larval crabs.     

Biochemical changes during larval development of the xanthid crab Rhithropanopeus harrisii. I. Protein,total lipid,alkaline phosphatase,and glutamic oxaloacetic transaminase

Protein, total lipid, and the activities of the enzymes alkaline phosphatase (AP) and glutamic oxaloacetic transaminase (GOT) were measured daily during larval development of the xanthid crab Rhithropanopeus harrisii (Gould). Percent increase in fresh weight was greatest on the first day after each molt. Protein and total lipid per larva increased during the second, third, and fourth zoeal stages, with the most marked increase during the third. When calculated as percent fresh weight, marked accumulation of both protein and total lipid occurred during the third zoeal stage. GOT activity remained stable during the third zoeal stage, but increased significantly during the fourth zoeal stage. AP showed a 4-day cycle of activity apparently related to the molt cycle. It is suggested that increased protein and total lipid content during the third zoeal stage indicate nutritional requirements prior to metamorphosis. Biochemical change may be a more relevant indicator of growth during larval development than either size increase or molt frequency when assessing the value of various diets in the culture of crabs.     

Larval development of the spider crab Pisoides edwardsi (Decapoda,Brachyura) under laboratory conditions

Larvae of Pisoides edwardsi (Bell, 1835) have been reared in the laboratory at 2 different temperatures (13.8° and 18.5°C), from hatching to megalops stage. The two zoeal stages and the megalops, as well as the setation of the functional appendages are described and illustrated. The main characteristics useful to differentiate the larvae of P. edwardsi from those of Libidoclaea granaria, the other Chilean species belonging to the same sub-family, are discussed. Data on duration of zoeal development, length of moulting intervals, and mortality at the 2 test temperatures, are also given.This study was financially supported, in part, by the Chilean Ministry of Agriculture.     

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.     

Effects of the insect growth regulator Dimilin® (TH 6040) on larval development of two estuarine crabs

Effects of Dimilin^® (TH 6040), an insect growth regulator which interferes with the formation of the insect cuticle, were studied on the larval development of Rhithropanopeus harrisii (Gould) and Sesarma reticulatum (Say) (Crustacea: Brachyura). When larvae were exposed to 0.5 (R. harrisii only), 1, 3, 5, 7, and 10 ppb Dimilin from hatching to the first crab stage, survival in both species decreased in relation to increased concentrations of Dimilin. Survival of R. harrisii larvae wa significantly lower at 1 ppb and higher levels compared with control experiments, and in S. reticulatum a significant decrease in survival began at the 3 ppb level. At 10 ppb Dimilin, no larvae survived to the megalopa stage in either of the two species. The results indicate that early stage larvae of R. harrisii are more sensitive to Dimilin than those of S. reticulatum. When R. harrisii larvae were treated with 10 ppb Dimilin during the intermolt period of each of the 4 zoeal stages, nearly all larvae died during molting to the succeeding stage. First zoeal larvae of R. harrisii exposed to 10 ppb Dimilin at various days during the intermolt period were more sensitive to the compound late than early in the period. It is suggested that Dimilin also may interfere with the formation of the cuticle in crab larvae.     

Larval development of Ocypode quadrata (Brachyura: Crustacea) under laboratory conditions

The larvae of Ocypode quadrata (Fabricius) have been reared in the laboratory, from hatching to megalopa stage, at 35 S, 25°C. The five zoeal stages and the megalopa are described, including functional appendages of each stage. On the basis of morphological characteristics, the first zoeal and megalopa stages of O. quadrata can be distinguished from similar stages of closely related Ocypodinae. At 25°C, the megalopa appeared in a minimum of 34 days following hatching.     

Response of mud crab (Panopeus herbstii) megalopae to cues from adult habitat

During the summer of 1995, we investigated the response of mud crab megalopae (Panopeus herbstii Milne-Edwards) to cues associated with adult habitat. Natural rock/shell substratum and the rock-associated seaweed, Fucus vesiculosus L., both induced metamorphosis of competent megalopae; natural sand substratum did not induce metamorphosis. Structural mimics of preferred substrata induced metamorphosis only when covered with natural biofilm. Clean mimics did not induce metamorphosis. Water-soluble exudates from preferred substrata showed weak induction of metamorphosis. Exudates from adult P. herbstii elicited a similar weak response. Exudates from another species of crab and from two fish predators did not induce metamorphosis. We conclude that water-soluble cues associated with major components of preferred adult habitat induce the metamorphic molt of P. herbstii megalopae. The three-dimensional structure of the substratum is not important in induction of metamorphosis, but the biofilm associated with preferred substratum plays a critical role. It is not clear whether the biofilm produces the water-soluble cue or simply provides a tactile stimulus that works in conjunction with the soluble cue.