Vent Crab Bythograea Thermydron Research Articles

Morphological adaptations to chronic hypoxia in deep-sea decapod crustaceans from hydrothermal vents and cold seeps

Animals inhabiting hydrothermal vents and cold seeps face conditions that are challenging for survival. In particular, these two habitats are characterized by chronic hypoxia, sometimes reaching complete anoxia. The characteristics of the scaphognathite and gills were studied in four species of shrimp and three species of crabs from hydrothermal vents and cold seeps, in order to highlight potential adaptations that could enhance oxygen acquisition in comparison with shallow-water relatives. All the vent and seep species studied here exhibit significantly larger scaphognathites, likely allowing more water to flow over their gills per stroke of this appendage. This is probably more energetically efficient that prolonged hyperventilation. In contrast to annelids, vent and seep decapods usually do not possess enlarged gills, a phenomenon likely due to the physical limitations imposed by the size of the gill chamber. In the vent shrimp Rimicaris exoculata and the vent crab Bythograea thermydron, however, there is a significantly higher specific gill surface area linked to a higher number of lamellae per gram of gill. Again in contrast to annelids, the diffusion distance through the gills is not strikingly different between the vent shrimp Alvinocaris komaii and the shallow-water species Palaemon spp. This may indicate that the epithelium and cuticle of the decapod gills are already optimized for oxygen uptake and that reducing the thickness of these compartments is not physically possible without affecting the physical integrity of the gills.

Biology of the Vent Crab Bythograea thermydron: A Brief Review

This paper provides a review of relevant literature concerning the vent crab Bythograea thermydron. This body of work describes a crab species that shares fundamental biological characteristics with typical shallow-water brachyuran crabs, yet possesses a suite of highly evolved traits specific for life at hydrothermal vents. Bythograea thermydron is one of only six known species of Bythograea and is very abundant at vent sites along the East Pacific Rise. Because of the large amount of scientific work at this location, almost everything known about bythograeid vent crabs is based on studies of this single species. This review specifically deals with biogeography, systematics, and evolution; morphology, physiology and special adaptations; ovarian development; mating, brooding, and hatching; and larval biology and dispersal. The various sections emphasize comparisons with shallow-water crabs and highlight characteristics such as: (1) the unique eye structure in the adult stage, which is adapted for sensing the exceptionally dim light that is generated by the vents themselves; (2) the extreme tolerance of adults and juveniles to conditions of low oxygen and high sulfides; (3) the exceptional eurythermal character of juvenile and adult physiology; and (4) the seasonality of ovarian development and subsequent reproductive activity. Discussion of larval biology presents various scenarios of larval dispersal and recruitment back to the vent sites.

Food sources for the early life history stages of the hydrothermal vent crab Bythograea thermydron: a stable isotope approach

We used stable isotope analysis to examine food sources for early life-history stages of the vent crab Bythograea thermydron. During two cruises to a hydrothermal vent site along the East Pacific Rise, we collected a variety of endemic organisms, including approximately 300 specimens of B. thermydron. The crab collection consisted mainly of megalopae and early juveniles, but also included adults and a single zoea. As expected, the carbon-isotope composition of newly released zoeae (−12.2%) was similar to the female (−11.1%) and clearly different from megalopae (21.7%). Because we were unsuccessful in culturing the zoea larvae, we were not able to conduct experiments to determine the effect of diet on isotopic composition. The tissue of megalopae was depleted in 13C (−21.7%) when compared to indigenous prey species, but was similar to that expected for carnivorous zooplankton dependent on surface primary production. The nitrogen-isotope composition of megalopae was enriched in 15N (10%) relative to potential prey species, again suggesting a photosynthetic source of primary production. The mean carbon-isotope composition of newly metamorphosed juvenile crabs (−19.9%) resembled megalopae, while tissue from subsequent juvenile stages was enriched in 13C (−10.9%) with values similar to those measured in co-occurring prey species. These results imply that megalopae are dependent on a source of primary production exogenous to the vents, but switch to a vent-based food web soon after metamorphosis to the juvenile stage.

Spatial and temporal patterns in development of eggs in the vent crab Bythograea thermydron

In this paper we describe results of a study on the reproductive biology of the hydrother- mal vent crab Bythograea thermydron. At vent sites along the East Pacific Rise, histological analyses of gonads from adult female crabs collected in November 1997, May 1999 and May 2000 provide strong evidence that B. thermydron undergoes a seasonal cycle of reproductive activity, with egg hatching peaking in April-May. Females undergo a synchronous pattern of oocyte development, whereby one cohort of oocytes undergoes vitellogenesis, while a second cohort is present and remains immature until the initial cohort reaches full maturity and is extruded onto the pleopods. When mean oocyte-size-frequency distributions were compared across months, the 2 May samples were similar to each other, with a dominance of previtellogenic oocytes and a second, smaller group of vitellogenic oocytes also present. In contrast, the November sample exhibited a wide variety of oocyte sizes, with no one size class predominating. In addition, May samples from the vent periphery contained a high proportion of females that showed evidence of recent egg hatching, while females collected from the region near the vent orifice exhibited a wide range of the intermediate stages of gonadal development. This set of data suggests an annual cycle whereby a given cohort of oocytes is in a previtellogenic state in early spring (April-May), but has begun vitellogenesis by late autumn (November) and has developed to maximum maturity by the time the eggs are extruded the follow- ing spring. While the current clutch of eggs is being brooded, a second cohort of previtellogenic oocytes begins to develop in the ovary and the cycle is repeated. Superimposed on this annual cycle is a pattern of behavior whereby females with mature gonads migrate to the vent periphery where fertilized eggs are extruded, brooded, and hatched.

Adaptive visual metamorphosis in a deep-sea hydrothermal vent crab.

Hydrothermal vents along the mid-ocean ridges host ephemeral ecosystems of diverse endemic fauna including several crustacean species, some of which undergo planktonic development as larvae up to 1,000 m above and 100 km away from the vents. Little is known about the role of vision in the life history of vent fauna. Here we report that planktonic zoea larvae of the vent crab Bythograea thermydron possess image-forming compound eyes with a visual pigment sensitive to the blue light of mesopelagic waters. As they metamorphose and begin to descend to and settle at the vents, they lose their image-forming optics and develop high-sensitivity naked-retina eyes. The spectral absorbance of the visual pigment in these eyes shifts towards longer wavelengths from larva to postlarva to adult. This progressive visual metamorphosis trades imaging for increased sensitivity, and changes spectral sensitivity from the blue wavelengths of the larval environment towards the dim, longer wavelengths produced in the deeper bathypelagic vent environment of the adults. As hydrothermal vents produce light, vision may supplement thermal and chemical senses to orient postlarval settlement at vent sites.

Structure and phylogeny of the crustacean hyperglycemic hormone and its precursor from a hydrothermal vent crustacean: the crab Bythograea thermydron

The structure of a well-known neurohormone involved in homeostasis regulation and stress response, the crustacean hyperglycemic hormone, was investigated in the deep-sea hydrothermal vent crab Bythograea thermydron. The neuropeptide was isolated from neurohemal organs (sinus glands) and its biological activity checked using an homologous bioassay. Partial amino acid sequence was established by a combination of Edman chemistry and mass spectrometry. Then, the sequence of the cDNA encoding the hormone precursor was determined. The preprohormone 1 is composed of a 29 amino acid signal peptide, followed by a 41 amino acid associated peptide flanking the 72 amino acid hyperglycemic hormone. Comparison of these data with other known crab hyperglycemic hormone and prohormone sequences was performed using phylogenetic analysis methods.

Hydromineral regulation in the hydrothermal vent crab Bythograea thermydron.

This study investigates the salinity tolerance and the pattern of osmotic and ionic regulation of Bythograea thermydron Williams, 1980, a brachyuran crab endemic to the deep-sea hydrothermal vent habitat. Salinities of 33 per thousand-35 per thousand were measured in the seawater surrounding the captured specimens. B. thermydron is a marine stenohaline osmoconformer, which tolerates salinities ranging between about 31 per thousand and 42 per thousand. The time of osmotic adaptation after a sudden decrease in external salinity is about 15-24 h, which is relatively short for a brachyuran crab. In the range of tolerable salinities, it exhibits an iso-osmotic regulation, which is not affected by changes in hydrostatic pressure, and an iso-ionic regulation for Na(+) and Cl(-). The hemolymph Ca(2+) concentration is slightly hyper-regulated, K(+) concentration is slightly hyper-hypo-regulated, and Mg(2+) concentration is strongly hypo-regulated. These findings probably reflect a high permeability of the teguments to water and ions. In addition to limited information about salinity around hydrothermal vents, these results lead to the hypothesis that B. thermydron lives in a habitat of stable seawater salinity. The osmoconformity of this species is briefly discussed in relation to its potential phylogeny.

Development and behavior of megalopa larvae and juveniles of the hydrothermal vent crab Bythograea thermydron

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 185:147-154 (1999) - doi:10.3354/meps185147 Development and behavior of megalopa larvae and juveniles of the hydrothermal vent crab Bythograea thermydron C. E. Epifanio*, G. Perovich, A. I. Dittel, S. C. Cary Graduate College of Marine Studies, University of Delaware, Lewes, Delaware 19958, USA *E-mail: epi@udel.edu ABSTRACT: We collected megalopa larvae and early juveniles of the crab Bythograea thermydron from a depth of 2500 to 2600 m at a hydrothermal vent field along the East Pacific Rise (ca 9° to 10° N, 104° W). Taxonomic identification of the megalopa larvae was accomplished through the use of morphological characteristics corroborated by molecular genetic analysis of an amplified portion of DNA from the mitochondrial 16s rRNA gene. We successfully reared megalopa larvae through metamorphosis and through subsequent juvenile molts at atmospheric pressure in the laboratory. This is the first time that this has been reported for any vent species. Laboratory data were combined with measurements of field-caught juveniles to allow estimation of carapace width, dry weight, and stage duration of the first 5 juvenile stages. Results of behavioral experiments indicated that B. thermydron megalopae swim actively over the range of temperature expected near the vents (2 to 25°C). Swimming speed varied with temperature (4 to 10 cm s-1), but generally exceeded the speed of bottom currents at the vent fields. Moreover, the propensity to swim was inversely related to temperature. These results suggest that swimming behavior may be an important component of locating warm vent settlement sites in the otherwise cold waters surrounding a vent field. KEY WORDS: Hydrothermal vents · Crab · Megalopa · Juvenile · Behavior · Development Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 185. Publication date: August 20, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi

Oxygen transport by the hemocyanin of the protobranch mollusc Solemya reidi Bernard was studied in native hemolymph samples. Clams were collected from two different reducing environments, beneath log booms in Alberni Inlet, British Columbia, Canada, and from the sewage effulent in Santa Monica Bay, California, USA. The hemocyanin concentration in a pooled hemolymph sample (n = 10 individuals) was 33.5 mg ml−1. The mean hemolymph pH of five Alberni clams maintained for 3 wk in mud was 7.96 ± 0.06. No significant variation in hemocyanin oxygen-affinity or cooperativity was found for hemocyanin in whole hemolymph samples from these five individually studied clams. There was a significant difference only at 15 °C in the oxygen affinity of hemocyanin in pooled whole-hemolymph samples from S. reidi collected from Alberni Inlet compared with clams collected from Santa Monica Bay. Little effect of temperature on hemocyanin oxygen-affinity was found for temperatures below 20 °C; above 20 °C, the oxygen affinity was reduced for clams from both sites. Temperature and pH had no apparent affect on hemocyanin cooperativity. Moderate Bohr shifts were found at all temperatures examined. The presence of physiologically relevant concentrations of thiosulphate in hemocyanin samples resulted in a decrease in hemocyanin oxygen-affinity, opposite to the effect on hemocyanin found for the hydrothermal vent crab Byth-ograea thermydron, but thiosulphate had no effect on hemocyanin cooperativity.

Homeoviscous Properties Implicated by the Interactive Effects of Pressure and Temperature on the Hydrothermal Vent Crab Bythograea thermydron.

Specimens of the hydrothermal vent crab Bythograea thermydron, collected from 13° N on the East Pacific Rise, were exposed to pressures greater than those in their natural habitat over a range of temperatures to assess how increased hydrostatic pressure affects a species that requires high pressure to survive. We measured heart beat frequency and contraction waveform at pressures ranging from 28 MPa (normal environmental pressure for this species) to 62 MPa at 5°, 10°, and 20°C. At 5°C, increased hydrostatic pressure induced bradycardia or acardia in conjunction with marked disruption of the ventricular contraction waveform. The animals did not survive following decompression. The effects of increased pressure were less pronounced at 10°C and almost negligible at 20°C. Our results support previous findings at subambient pressures which suggest that the lipid bilayers of cell and organelle membranes are the primary sites affected by short-term pressure variation in deep-sea organisms. We also found evidence of an adaptive mechanism of pressure temperature interaction in these animals from the eurythermic habitat of the hydrothermal vents.

Effects of sulfide exposure history and hemolymph thiosulfate on oxygen-consumption rates and regulation in the hydrothermal vent crab Bythograea thermydron

The hydrothermal vent crab Bythograea thermydron is exposed to high environmental concentrations of sulfide and low levels of oxygen for extended periods of time. It has previously been shown that hydrogen sulfide is oxidized to the relatively non-toxic thiosulfate (S2O 3 2− ), which accumulates in the hemolymph. Hemolymph thiosulfate levels in freshly captured crabs vary significantly among crabs from different hydrothermal vent sites as well as between crabs from different microhabitats within the same site. Hemolymph thiosulfate concentrations were not significantly different between crabs captured at the same site 6 mo apart. Hemolymph thiosulfate concentrations ranged from 66 μmol 1−1 in a crab captured at a site with relatively low sulfide venting, to 3206 μmol 1−1 in an individual that was netted from an active “smoker” vent with much higher sulfide exposure. The differences in hemolymph thiosulfate between sites and the stability of hemolymph thiosulfate in crabs captured at the same site at different times suggest that sulfide exposure is significantly different between sites and that this exposure may not vary significantly over the course of a few months. B. thermydron experimentally exposed to sulfide had high levels of thiosulfate in their hemolymph and increased abilities to regulate oxygen consumption in conditions of low oxygen. This enhancement of regulatory abilities suggests that the previously demonstrated increased hemocyaninoxygen (Hc−O2) affinity due to elevated thiosulfate may be adaptive in vivo. Average oxygen-consumption rates were much higher in crabs experimentally exposed to sulfide than in unexposed crabs. Crabs injected with isosmotic thiosulfate did not have increased oxygen-consumption rates as did the sulfide-exposed individuals, but did show a similar reduction in Pc (the critical partial pressure of oxygen at which crabs can no longer regulate oxygen consumption). This suggests that it is the sulfide exposure and/or detoxification rather than the elimination of thiosulfate that causes the increase in metabolic rate. Thiosulfate diffuses into dead crabs and into live crabs exposed to 15 mmol S2O 3 2- l−1, indicating substantial permeability, and yet live crabs are able to eliminate thiosulfate when incubated in sea water containing 1.5 mmol S2O 3 2- l−1, suggesting a process that has an active component.

Specific effects of thiosulphate and L-lactate on hemocyanin-O2 affinity in a brachyuran hydrothermal vent crab

The hydrothermal vent crab Bythograea thermydron Williams (Brachyura: Bythograeidae) is exposed to high environmental concentrations of hydrogen sulphide. Hydrogen sulphide has previously been shown to be oxidized to a non-toxic form, thiosulphate (S2O3 2-), that accumulates in the hemolymph (to concentrations>1 mmoll-1). Hemocyanin-oxygen (Hc-O2) affinity was determined in dialysed, fresh or frozen hemolymph samples from B. thermydron. Although freezing is known to alter the affinity or cooperativity of some decapod crustacean hemocyanins, neither Hc-O2 affinity nor cooperativity was significantly altered in B. thermydron hemolymph samples that had been frozen, consistent with previous findings. Oxygen affinity of B. thermydron hemocyanin was significantly increased by the presence of L-lactate. Likewise, Hc-O2 affinity was significantly increased by the presence of 1.5 mmol S2O3 2- I-1. The magnitude of this effect was the same as for similar concentrations of L-lactate. This specific effect of S2O3 2- does not appear to be a general property of crustacean hemocyanins, as there was no significant effect of S2O3 2- on Hc-O2 affinity or cooperativity in dialysed hemolymph samples from the brachyuran crabs Cancer anthonyi Rathbun and C. antennarius Stimpson, or the thalassinid ghost shrimp Callianassa californiensis Dana. In the context of high environmental sulphide concentrations coupled with low PO 2, and the subsequent accumulation of S2O3 2- in crab hemolymph, the increase in Hc-O2 affinity due to thiosulphate appears to be an adaptive response in B. thermydron.

Sulfide Detoxification by the Hydrothermal Vent Crab Bythograea thermydron and Other Decapod Crustaceans

Bythograea thermydron, a brachyuran crab endemic to the deep-sea hydrothermal vent habitats, encounters concentrations of hydrogen sulfide of up to 318 μM. To determine how B. thermydron avoids the potentially lethal effects of these high concentrations of sulfide, we examined several physiological and biochemical systems to determine, first, this species' sensitivity to sulfide, and, second, how sulfide entering the body is detoxified. The heart rate of B. thermydron was unaffected by ambient sulfide concentrations of up to 1,400 μM. The toxic effects of sulfide were not avoided by exclusion of sulfide from the body. Protection from sulfide poisoning appears to be achieved by a sulfide detoxification system located in the hepatopancreas. The initial step in this process was the oxidation of sulfide by a sulfide oxidase enzyme. The hepatopancreas of B. thermydron produced thiosulfate and sulfate as the major products of sulfide oxidation. Thiosulfate accumulated to >1 mM in the blood. The toxicity of sulfide, sulfide-oxidizing activities, and products of sulfide metabolism were compared in three nonvent crabs, Cancer antennarius, Pachygrapsus crassipes, and Portunis xantusii. These species exhibited qualitatively similar adaptations. However, the nonvent species were significantly more sensitive to sulfide poisoning than was the vent crab.

Effects of Temperature, Pressure, and Oxygen Concentration on the Oxygen Consumption Rate of the Hydrothermal Vent Crab Bythograea thermydron (Brachyura)

Oxygen consumption rates of the brachyuran crab, Bythograea thermydron, from the Galapagos hydrothermal vents were measured at temperatures of 2, 8, 12, 18, and 25 C; pressures of 272, 136, and 1 atm; and varying oxygen concentrations. The oxygen consumption rates were comparable to those of both shallow-living and deep-sea benthic decapods. Temperature had a minimal effect on oxygen consumption over the range of 8-18 C, and its effects increased at temperatures outside this range. Decompression of the crabs from their environmental pressure (272 atm) to 136 atm had no significant effect on oxygen consumption. Further decompression to 1 atm led to increased oxygen consumption. Vent crabs are able to regulate their rate of oxygen consumption down to an oxygen partial pressure of 13 mm Hg; this is unaffected by temperatures from 2 to 25 C and pressures from 1 to 272 atm. The crabs have an anaerobic capability exceeding 12 h. The results provide insight into the relative role of ecological factors (predation, competition) as opposed to environmental conditions (temperature, pressure, food) in selecting the characteristics of deep-sea species. The importance of temperature, pressure, and food availability in influencing metabolic rates in the deep sea are discussed. Habits and physiological capabilities of the crabs in the unusual vent environment are suggested on the basis of the crabs' physiological tolerances.