Behavioral responses of a larval crustacean to hydrostatic pressure: Rhithropanopeus harrisii (Brachyura: Xanthidae)

Responses of the four zoeal stages of the crab Rhithropanopeus harrisii (Gould) to step and continuous changes in hydrostatic pressure were analyzed with a video system. Crabs were collected from the Neuse River estuary (North Carolina, USA) from June to August, 1987. The lower thresholds for step increases and decreases in pressure were 3 and 8 to 10 mbar, respectively. There was little change in sensitivity with zoeal development. Tests of larval responses in a light field that simulated the underwater angular light distribution indicated positive phototaxis does not occur upon pressure changes. In darkness, rates of pressure increase at and above 0.175 mbar s^-1 induced high barokinesis and negative geotaxis in all but Stage IV zoeae, which had a threshold of 1.19 mbar s^-1. Since larval sinking and descent swimming speeds exceed these threshold rates, larvae can move rapidly enough to produce suprathreshold changes in pressure which evoke behavioral responses. Slow rates of pressure decrease induced passive sinking while rapid rates caused an active ascent. This ascent response upon a pressure decrease is unreported among crustaceans, and is hypothesized to function for avoidance of feeding and respiratory currents of benthic invertebrates. The descent response occurs in all zoeal stages, except IV, at rates of pressure decrease (0.4 to 0.71 mbar s^-1) that are within the range of ascent swimming speeds. These results support Sulkin's negative feedback depth regulation model. The absolute distances moved before corrective vertical responses to threshold rates of pressure change are initated delimit the depth regulatory window. In darkness, the asymmetry of the window would lead to an ascent. It is hypothesized that light is an additional component in depth regulation, and that the limits and symmetry of the depth regulatory window may be controlled by the level of light adaptation.     

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.     

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.     

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.     

A dispersal model for larvae of the deep sea red crab Geryon quinquedens based upon behavioral regulation of vertical migration in the hatching stage

Behavioral responses to gravity, hydrostatic pressure, and thermoclines are described for Stage I zoeae of the deep sea red crab Geryon quinquedens Smith. Survival and rate of development as a function of temperature is presented for all larval stages. Although temperatures between 10° and 25°C have no direct effect upon survival, development time is five times longer at 10°C than at 25°C. Stage I larvae show strong negative response to gravity. Swimming rate increases with an increase in pressure up to 20 atm above ambient at 11°C, but not at 15°C. Swimming rates at 15°C are higher than those measured at 11°C at each pressure tested. Stage I larvae readily penetrate sharp thermoclines. Potential dispersal ranges of G. quinquedens larvae in the Mid-Atlantic Bight are suggested based on larval behavior, development time, and coastal hydrography. A testable recruitment model is proposed for G. quinquedens.Contribution no. 1365 of the Center for Environmental and Estuarine Studies     

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.     

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.     

Locomotion,feeding, grooming and the behavioural responses to gravity,light and hydrostatic pressure in the stage I zoea larvae of Ebalia tuberosa (Crustacea: Decapoda: Leucosiidae)

The stage I zoeae of Ebalia tuberosa swam by sculling with the exopodites of the 1st and 2nd maxillipeds and flexed the abdomen to brake or change direction. The larvae gained depth by stopping all natatory movements and sinking passively at rates of 6 mm s^-1. The zoeae refused both living and dead nauplii of Artemia spp., as well as two species of diatoms, but fed readily on detritic material on the bottom which they scooped up using the endopodites of the maxillipeds and pressed against the mouthparts using the telson. The setae on the posterior border of the telson were used for grooming the maxillipeds and the anterior mouthparts. Day-old stage I zoeae were negatively geotactic, positively phototactic and responded to pressure increases by swimming upwards and by high barokinesis. By the third day some larvae had become positively geotactic but were photopositive, and the majority responded to pressure increases as in the day-old larvae. Five-day old larvae were still photopositive but the majority had become positively geotactic and fewer himbers responded to pressure. Seven-day old larvae failed to respond to any of the stimuli used and assumed a predominantly benthic lifestyle. It is suggested that this anomalous behaviour is related to the dispersal of the larvae and to the specialized habitat requirements of the adults while the rather unusual morphology of the larvae is related to their feeding behaviour and semi-benthic lifestyle.     

Effects of cadmium and mercury on the behavioral responses and development of Eurypanopeus depressus larvae

Larval stages of the estuarine mud crab Eurypanopeus depressus were exposed to either 10 ppb cadmium or 1.8 ppb mercury in a flow-through rearing system. Development time from the megalopa to juvenile crab was extended in the cadmium-exposed individuals. Cadmium elevated the swimming rates of the late zoeal stages, while mercury depressed swimming rates of the early stages. Increased mortality of Stage I zoeae was observed after 24 h exposure to cadmium; increased mortality was also noted for megalopa and early crab stages reared in cadmium.Contribution No. 212 of the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Circatidal swimming behavior of brachyuran crab zoea larvae: implications for ebb-tide transport

Larvae of the blue crab Callinectes sapidus and fiddler crab Uca pugilator are exported from estuaries and develop on the continental shelf. Previous studies have shown that the zoea-1 larvae of some crab species use selective tidal-stream transport (STST) to migrate from estuaries to coastal areas. The STST behavior of newly hatched larvae is characterized by upward vertical migration during ebb tide followed by a descent toward the bottom during flood. The objectives of the study were (1) to determine if newly hatched zoeae of U. pugilator and C. sapidus possess endogenous tidal rhythms in vertical migration that could underlie STST, (2) to determine if the rhythms persist in the absence of estuarine chemical cues, and (3) to characterize the photoresponses of zoeae to assess the impact of light on swimming behavior and vertical distribution. Ovigerous crabs with late-stage embryos were collected from June to August 2002 and maintained under constant laboratory conditions. Following hatching, swimming activity of zoeae was monitored in darkness for 72 h. U. pugilator zoeae displayed a circatidal rhythm in swimming with peaks in activity occurring near the expected times of ebb currents in the field. Conversely, C. sapidus zoeae exhibited no clear rhythmic migration patterns. When placed in a light field that simulated the underwater angular light distribution, C. sapidus larvae displayed a weak positive phototaxis at the highest light levels tested, while U. pugilator zoeae were unresponsive. Swimming behaviors and photoresponses of both species were not significantly influenced by the presence of chemical cues associated with offshore or estuarine water. These results are consistent with predictions based on species-specific differences in spawning and the proximity of hatching areas to the mouths of estuaries. U. pugilator larvae are released within estuaries near the adult habitat. Thus, ebb-phased STST behavior by zoeae is adaptive since it enhances export. Selective pressures for a tidal migration in C. sapidus larvae are likely weaker than for U. pugilator since ovigerous females migrate seaward prior to spawning and hatching occurs near inlets and in coastal waters.     

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.     

Patterns of growth and triacylglycerol content in snow crab Chionoecetes opilio (Brachyura: Majidae) zoeal stages reared in the laboratory

Snow carb Chionoecetes opilio zoea I and zoea II larvae, hatched from females in a controlled mating experiment, were reared in the laboratory at 10.1 °C and 28.0 salinity, to resolve the patterns of growth (dry weight [DW]) and change in energy reserves (triacylglycerols [TAG]) within a given moult cycle. The patterns of growth and change in TAG reserves were similar in each zoeal stage. Following hatching or a moult, the zoeae entered a phase of rapid size increase, i.e. high daily growth rates (5.5 to 12.8% DWd^-1), for 1/3 to 2/5 of the duration of the moult cycle. During the same period, the zoeae accumulated TAG reserves until a maximum (TAG DW^-1) was reached at the end of the phase of rapid growth. The period of high growth rates and of TAG accumulation is interpreted as the required time for the zoeae to reach a point in development [i.e. point of reserves saturation (PRS); Anger and Dawirs (1981)] where sufficient growth and energy reserves allow moulting to the next stage. Following the phase of rapid growth and TAG accumulation, the zoeae entered a phase of low daily growth rates (0 to 1% DWd^-1) during which the TAG reserves decreased to a minimum at the end of the phase. Prior to, and during the moult to zoea II, a phase of negative growth was observed in the zoea I larvae. We conclude that measurement of zoeal size and TAG content, along with morphometric criteria (e.g. epidermal retraction), can be used to assess growth and nutritional condition of C. opilio zoeal stages from the sea.     

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.     

Salinity and temperature tolerance of zoeae of the portunid crab Scylla serrata

The tolerances of the first zoeal stage of the crab Scylla serrata (Forskal) have been investigated in 64 different temperature-salinity combinations. Exposure to temperatures above 25°C or to salinities below 17.5 caused considerable mortality; therefore, zoeae are unsuited to estuarine conditions. The larvae can tolerate temperatures down to 5°C is they are inactive below 10°C. It is suggested that 10°C is probably a lower limit and that female crabs which migrate to sea to release their eggs do not enter water with a temperature below 12°C. Hydrological conditions along the south-east coast of Africa indicate that females would, therefore, migrate less than 10 km offshore.     

Depth regulation of larval marine decapod crustaceans: test of an hypothesis

This study tested the hypothesis that the dimensions and symmetry of the depth regulatory window of crustacean larvae are controlled by the level of light adaptation. Responses of first and last zoeal stages of the crab Rhithropanopeus harrisii (Gould) to different rates of pressure change were analyzed with a video system. Crabs were collected from the Neuse River estuary (North Carolina, USA) from May to September 1988. Responses were measured when larvae were adapted to light having an angular light distribution similar to that underwater at intensities ranging from one log unit above the lower phototaxis threshold to four log units higher. For both zoeal stages in darkness and at 10^-6 W m^-2, the distance larvae descend before responding to a pressure increase was much shorter than the distance they would ascend before responding to a pressure decrease. When adapted to a light level of 10^-4 W m^-2 both zoeal stages descended and ascended approximately equal distances before responding to an increase or decrease in pressure, respectively. Finally at the highest test light intensity (10^-2 W m^-2), the ascent distance was much shorter than the descent distance. These results support the hypothesis. The depth regulatory window dimensions predict an ascent in the water column upon adaptation to low light intensities and descent at high light levels. Thus Sulkin's negative feedback model provides the general mechanism of depth regulation. The effects of light adaptation on the limits of the depth regulatory window provide an additional component that negates the requirement for depth regulation at an absolute depth. The composite model can be termed the light-dependent negative feedback model of depth regulation.     

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.     

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.     

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     

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.     

Laboratory-reared larvae of Cancer anthonyi (Decapoda: Brachyura) with a brief description of the internal anatomy of the megalopa

The larval development of Cancer anthonyi Rathbun (Decapoda, Brachyura) is described from laboratory rearing experiments. The external anatomy of the various larval stages is illustrated. A prezoeal stage, 5 zoeal stages and 1 megalopa stage were identified. At 17.5°C it took an average of 32.5 days for the first-stage zoeae to develop through the fifth zoeal stage and molt to the megalopa stage. The general internal anatomy of C. anthonyi larvae is discussed, and a drawing of a parasagittal section of a megalopa-stage larva is included.