Hydromineral Regulation in the Hydrothermal Vent Crab Bythograea thermydron

8 Pages·2001·3.6 MB·

by  Anne-Sophie Martinez

Reference: Hiol. Bull. 201: 167-174. (October 2001)
Hydromineral Regulation in the Hydrothermal Vent
Crab
Bythograea thermydron
ANNE-SOPHIE MARTINEZ1 JEAN-YVES TOULLEC2 BRUCE SHILLITO1
, , ,
MIREILLE CHARMANTIER-DAURES1 AND GUY CHARMANTIER1 *
,
1Lahoratoire d'Ecophysiologie des Invertebres, EA 3009 Adaptation Ecophysiologique an cours de
I'Ontogenese, Universite Montpellier II, PI E. Butaillon, 34095 Monipellier cedex 05, France;
UMR
Laboratoire Biogenese des Peptides Isomeres, Physiologic el Physiopathologie, Universite P. et
M. Curie, 7 Quai Saint-Bernard, 75252 Paris cedex 05, France; and Laboratoire de Biologic
Cellulaire et Moleculaire du Developpement, UMR 7622, Croupe Biologie Marine, UPMC.
7 Quai Saint-Bernard, 75252 Paris cedex 05, France
Abstract. This study investigates the salinity tolerance acterized by variable and extreme conditions ofsome phys-
and the pattern of osmotic and ionic regulation of Bytho- icochemical parameters, in particular by high temperature,
graea thermydron Williams, 1980, a brachyuran crab en- high sulfide and metal content, high level ofcarbon dioxide,
demic to the deep-sea hydrothermal vent habitat. Salinities low level ofoxygen and low pH (Truchot and Lallier, 1998;
of 33%cr-35%c were measured in the seawater surrounding Sarradin et ai, 1998, 1999). To live in this environment,
the captured specimens. B. thermydron is a marine steno- biological communities associated with the vents have de-
haline osmoconformer, which tolerates salinities ranging veloped behavioral, physiological, morphological, and re-
between about 31"/cc and 42%c. The time of osmotic adap- productive adaptations such as symbiosis (Fisher, 1990),
tation after a sudden decrease in external salinity is about physiological and biochemical systems for sulfide detoxifi-
15-24 h. which is relatively short for a brachyuran crab. In cation (Powell and Somero, 1986; Cosson and Vivier, 1997;
the range of tolerable salinities, it exhibits an iso-osmotic Geret et ai, 1998; Truchet et ai, 1998). behavioral and
hprKerege+muslsoaucltroyieno,mcnpe,anhntwdrChaaiatcni2ho+inscioso-ininscooentnislctairfgrafhetetgicluotylenadthiisbyopysnelricf-ghohhratynlpNygoae-hsr+yepigaenunrl-dharyteCdegrlduo,lsa.ttaTaethndied,c ym1eo9rl9ee1s;cuelDtairaxior,nes1ept9o9na8si;e,sFi1ts9oh9e2hr;i.gSh1e9gt9oe8m)n,pzearacantdeutrseapie,(ciDaa1lh9il9zh3e;odffDseeesntbsroauri-,y
Mg2+ concentration isstronglyhypo-regulated.These findings orgAamnsontgo ltohciastveenhtotfacuhniamnleivyese(nJdienmksicetbraia,chy19u9r8a)n.decapod
probably reflect a high permeability ofthe teguments to water
and ions. In addition to limited information about salinity crustaceans (superfamily: Bythograeoidea Williams, 1980;
aroundhydrothermal vents,theseresults leadtothe hypothesis family: B\thograeidae Williams, 1980; genera: Bythograea
Williams, 1980: Cyanagraea de Saint Laurent, 1984; Seg-
that B. thermydron lives in a habitat of stable seawater
salinity. The osmoconformity of this species is briefly dis- onzacia Guinot, 1989; Aitstinograea Hessler and Martin,
cussed in relation to its potential phylogeny. 1989) (Tudge et ai. 1998). They have been found in all the
known hydrothermal vents Bythograea and Cyanagraea
in the East Pacific, Austinograea in the West Pacific, Seg-
Introduction
onzacia in the mid-Atlantic (Tunnicliffe et ai, 1998). In-
Hydrothermal vents, first discovered in 1977 on the Ga- formation published on these brachyurans includes studies
lapagos Ridge, are unique deep-sea habitats. They are char- on their biogeography and evolution (Hessler and Wilson,
1983; Newman, 1985: Tunnicliffe. 1988). reproductive bi-
ology and larval development (Van Dover et ai, 1984.
Received 2 January 2001; accepted 9June 2001.
*Towhomcorrespondence shouldbeaddressed. E-mail: charmantierw 1985; Epifanio et ai, 1999), and ecology and distribution
univ-montp2.fr (Van Dover, 1995; Guinot and Segonzac, 1997). Probably
167
168 A.-S. MARTINEZ ET AL.
due to the difficulty ofgetting live specimens, physiological 1 X 0.5 X 0.5 m). on the East Pacific Rise (EPR) on the
studies are scarcerandhave addressed aspects ofrespiration 13N and 9N sites [1246-50'N, 10357'W and 950'N,
(Lallier et ill., 1998), sulfide detoxification (Vetter el <;/., 10417'W (Tunnicliffe et al., 1998)]. at a depth of about
1987), and temperature or pressure effects on the mitochon- 2500 m. during the HOPE 99 mission in May 1999. Only a
dria, heart rate, or oxygen consumption rate (Mickel and small numberofcrabs were available, which resulted in 3 to
Childress, 1982a,b; Dahlhoff et /., 1991) of these crabs. 10 individuals for each experimental condition. As this
To our knowledge, no information is available on the hy- species seems incapable of long-term survival outside the
dromineral metabolism ofthe hydrothermal vent animals and high-pressure environment of the deep sea (Mickel and
particularly of the brachyuran crustaceans. Salinity is one of Childress. 1982a; Airries and Childress. 1994). most ofthe
themainenvironmental factorsexertingaselectionpressureon crabs were transferred into aquaria with running aerated
aquatic organisms, and the successful establishment ofa spe- Pacific surface seawater as soon as they reached the ship
cies in a given habitat depends on the ability ofthe organisms Atalante, and they were used in the following hours for
toadaptto.amongotherfactors,thetypicallevelandvariations experimentsconductedon board, at atmospheric pressure, at
in salinity (Charmantier, 1998). This majoradaptive process is a water temperature of 13C. Some of them were also
achieved through different behavioral or physiological mech- exposed to high pressure (see below). Crab cephalothoracic
anisms. Osmoregulation is one ofthe most important ofthese widths were 6-8 cm. Their molt stages (Drach, 1939) were
mechanisms in some animal groups, including crustaceans. It not checked, but soft (post-molt) crabs were not used in
hasbeenexplored intheadultsofnumerouscrustacean species experiments.
(reviews in Mantel and Fanner. 1983: Pequeux. 1995).
The present study hasbeen conducted with one speciesof Ambient
salinity
bythograeid crab from hydrothermal vents. Bythograea
t/ienuyilron Williams. 1980. This crab is the most fre- Water samples from the depth of the Riftia pachyptila
quently observed [density about 20 individuals pernr (Gui- ring on the 13N and 9N EPR sites were collected in
not and Segonzac, 1997)] and captured species among 750-ml titanium syringes manipulated by the Nantile. The
brachyuran crustaceans on the East Pacific sites (Guinot, waterosmolality in mosm/kg was measuredonan automatic
1989). It is found predominantly in the warm water micro-osmometer (WescorVarro 5520). The corresponding
(>20C) suiTounding mussels and vestimentiferans on values of salinity in parts per thousand were calculated by
which it feeds, and also at the periphery of the vent areas interpolation of data according to Weast (1969).
2C
where temperature is about (Grassle, 1986. cited by
Epifanio et a!., 1999). These habitats, influenced by the Preparation ofmedia
spatially and temporally variable input of hydrothermal
fluid, are greatly variable over short time and distance. Dilute media were prepared by adding fresh water to
Information on their salinity does not exist or is unpub- Pacific surface seawater (1002 2 mosm/kg: approxi-
lished. It is thus unclear whether the salinity of the water mately 34.6%p), and high-salinity media were prepared by
surrounding the vents is as stable as the deep-sea water adding ocean salts (Wimex, Germany) to seawater. Salini-
environment or is variable under the influence of the hy- ties were expressed as osmolality (in mosm/kg) and salt
drothermal fluid. Physiological studies have indicated that concentration (in parts per thousand). The osmolality ofthe
adults of B. thermydron are tolerant of wide variations in media was measured with a Wescor Varro 5520 micro-
temperature, dissolved oxygen, and hydrogen sulfide osmometer. Media with the following osmolalities and cor-
(Mickel and Childress, 1982a,b; Vetter et al.. 1987; Airries responding salinities were prepared: 740 mosm/kg (25.4%c>),
and Childress. 1994). but their ability to tolerate salinity 800 (27.5). 900 (31.0). 1002 (34.6). 1100 (38.2), 1200
variation and to osmoregulate is not known. The objectives of (41.9), 1300 (45.7). Experiments were conducted at 13C in
the present study were thus to evaluate the salinity tolerance 40-1 aerated aquaria that were kept in the dark except at the
and the pattern of osmoregulation of B. thennydron. The time of sampling, when light was briefly necessary.
salinityofthe natural habitatofthecrabwasalsomeasured. As
bthyeihneomrgoalnyicmpihonossm(eoslsaelnittiyalolfycNraus+taacnedanCslis)mo(sPtelqyueeusxt,abl1i99s5h)e,d Salinity tolerance
the ionic regulation ofthis crab was also studied. The objective of the experiment was to estimate the
survival time of the crabs at different salinities. The crabs
Materials and Methods were transferred directly from seawater to the experimental
media. Observations were made and dead individuals were
Animals
removed 1, 2. 3, 5. 6. 12. 15, and 24 h after the beginning
Adults of Bvthograea tliennvilron were collected by the of the tests. The absence ofbody movement after repeated
submarine Nuntilc. using resin watertight containers (about touches with a probe was considered as a proof of death.
OSMOCONFORMITY IN ft THERMYDRON 169
Hydnmineral regulation of a 10-ju.l sample of hemolymph was immediately mea-
Acclimation lime. To estimate the time necessary for sured on the Wescor Varro 5520 micro-osmometer.
mshaoelsimnmoi/tlkyy,gm)tp,hheicnortsaomboasla7wl4ei0rte-ymfsoitrsastmbi/tlrkiagznastmfieeordnriefudomlf.lroowHmienmsgeoaalwydaemtceprrhea(ss1ea0m0i-2n EwpapsIoennqiduciocrrkfelgytuulbdaeitsli,uotnae.nddHtkoeemp2ot5l%aytmi-pn8hd0eCif.ornoiAmzfettdehrewtasrtaeanrms,eposrtstoarmteopdltehisen
ples were taken from surviving animals after0, 2.45, 5, and Montpellier laboratory in liquid nitrogen, the hemolymph
15 h in the dilute medium. As 75% ofthe animals weredead and media samples were dissolved in deionized waterto the
at 15 h and 100% shortly afterward, a second experiment appropriate volume, and their ionic contents were deter-
wasconductedinan 800-mosm/kgmedium.Survival was60% mined using an amperometric Aminco-Cotlove chloridime-
tatheO12ssumhrovatinivdcin1gre7cg%rualabatts2ioa4fnth.e.rTH0he,em1oh.l2e,ymmo3p,lhy6,mspa1m2h.plo2es4sm.owlaeanrldeit4ty8akohef.nsformoem tfteiorornfNoparh+otth,eoKmte+itt,reCartaiof2no+r,ofMangCdl2~+a,.VaanriEapnpeAnAd-or1f27f5laamteompihcotaobmseotrep-r
crabs was measured as soon as they were brought on board.
The crabs were then transferred to the different media, and Statistical analysis
their hemolymph osmolality was remeasured after a period Statistical comparisons of experimental data were per-
ofosmotic stabilization in each medium; the length of this formed by one-way analysis of variance (ANOVA) (Sokal
period was determined from the results on adaptation time. and Rohlf, 1981) by using the software StatView 4.02
A similarexperiment was conducted under high pressure, at (Abacus Concept, Inc.).
15C. The crabs were immersed in an 800-mosm/kg me-
dium, in individual 400-ml containers set in a 19-1 pressur- Results
ized tank called "Incubateur Pressurise pour 1'Observation
en Culture d'Animaux Marins Profonds" (IPOCAMP) Ambient sal/nitv
sp(iSrtheeislsoluiftroec,aopuftnu2pr6ueb0..)bTa.hrseT,hhweehmiccorahlbyasmpppwrehorxewiamssautbtejhseecntthesedapmfroperlses1ud3reahnatdtotihteas m99oT6sh-me1/0ks0gal7iantimttyohesmme9a/sNkugrEePdatRfrtsohitmee.bo1t3tNom sEePawRatesrites,amapnleds w9a5s0
osmolality was measured.
For sampling, the crabs were rinsed with deionized water
and dried with absorbent paper. Hemolymph was sampled Salinity tolerance
with a hypodermic needle mounted on a syringe and in- The survival rates ofadults ofBythograea thermydron in
serted at the basis of a posterior pereiopod. The osmolality Figure 1 were different according to salinity and decreased
100 -
Bythograea
80 -
thermydron
, s
~
60 -
-
740 mosm/kg 25.4 %o
I -0800 " 27.5 "
40- a- 900 " 31.0 "
-A- 1002 " 34.6 "
- 1100 " 38.2 "
20 - --
1200 " 41.9 "
-o-- 1300 " 45.7 "
6 12 18 24
Time
(h)
Figure 1. Bythograea thermydron. Survival rate (in %) at different salinities according to the time of
exposure. Numberofcrabs percondition at the start ofthe experiment: 3 to 10.
170 A.-S. MARTINEZ ET AL.
with the time ofexposure (Fig. 1). They decreased sharply 3A). The hemolymph osmotic concentration was close to
to less than 25% within 15-24 h at the highest (1300 that of the medium, different from it by only 9 to 22
mosm/kg) and lowest (740. 800 mosin/kg) salinities. Sur- mosm/kg, 15 mosm/kg on average.
vival was higher in seawater (1002 mosm/kg) and in salin- The hemolymph osmolality was also measured in crabs
ities ranging from 900 to 1200 mosm/kg. maintained in the 800-mosm/kg medium, under a pressure
of 260 bars. The mean value of hemolymph osmolality
following this treatment for 13 h was 860 9 mosm/kg
Hydromineral regulation =
(;/ 3), not significantly different from the value of856
=
Acclimation time. The time of adaptation after a sudden 6 mosm/kg (/; 3) in control crabs kept in the same
change in salinity was evaluated at two low salinities (Fig. medium for 13 h under atmospheric pressure.
2). In both media, the hemolymph osmolality decreased Ionic regulation. The results concerning hemolymph ion
dsihaurmp,lyhewmitohliynmp1h2 ho.smAofltaelrity15hahdindetchreea7s4e0d-tmoo8s0m5/kmgosmme/- c3oBn-cFe.ntIrnatsieoanwsatienr,thNead+ifafnedreCntPmewdeirae tahreemgaiivnenosimnoeFfifgeucr-e
kg that is, to about 65 mosm/kg above the medium osmo- tors in hemolymph since they accounted for about 95% of
lality. As all crabs had died before 24 h, it was not possible the total hemolymph osmolality, and this trend was retained
to determine whether hemolymph osmolality had entirely in all media. The hemolymph Cl~ concentration followed
stabilized at 15 h. After a transfer to the 800-mosm/kg that ofthe medium in the whole range oftolerable salinities.
medium, the hemolymph osmolality stabilized within 24 h. It tended to be slightly hypo-regulated in most media (Fig.
Its mean values were respectively 817 and 808 mosm/kg (no 3B). Na+ regulation was iso-ionic; hemolymph Na+ con-
significant difference) after24 h and48 h in this medium. In centration constantly remained slightly above that of the
subsequent experiments, the time of exposure to different medium, by 8 to 23 mEq Na+/F ' (Fig. 3C). K+ was
media was based on these results and was kept in general at slightly hypo-regulated (by approximately 2.5 mEq K+/
15-24 h. I"1) in the media in which concentrations were above 10.5
Osmotic regulation. Upon the arrival of the crabs on mEq K+/l~' (900 mosm/kg). and it was slightly hyper-
boardthe ship following theirtransferfrom thebottom, their regulated (by approximately 3.5 mEq K+/r') in the lowest
hemolymph osmolality was 1025 4 mosm/kg (n = 18) salinity (800 mosm/kg, 9.3 mEq K+/r') (Fig. 3D). Hemo-
and 984 12 mosm/kg (/i = 29) at the 13N EPR and 9N lymph Ca2+ concentration was slightly hyper-regulated (by
EPR sites respectively. The ability of the crabs to osmo- 1.2 to 3.6 mEq Ca2+/r' ) at most tested salinities (Fig. 3E).
regulate was then evaluated in the range of tolerable salin- Hemolymph Mg2+ concentration was strongly hypo-regu-
2+
ities between 900 mosm/kg and 1200 mosm/kg. The crabs lated (by about 33 to 57 mEq Mg /r') over the entire
osmoconformed in the whole range oftested salinities (Fig. ransje of salinities (Fis. 3F).
1100
M
Bythograea thermydron
=*1000
oOa
E
800mosm/kg
900 -
-740mosm/kg
E
_>
"o
800 -
Ol
700
12 24 36 48
Time
(h)
Figure 2. Bythogrueu thermydron. Change in hemolymph osmolality according to the time after rapid
transferfrom Pacific surface seawater(1002 2 mosm/kg) todilute mediaat740mosm/kg and800mosm/kg.
Error bars: mean SD; ;;: 4 to 6 individuals.
OSMOCONFORMITY IN . THERMYDRON 171
about 15 to 24 h. This is short fora brachyurancrab, similar
1300
O.P. ci to the 15 h required for osmotic equilibration in osmocon-
1200 formers such as the Majidae Maja sp. and Hyas sp. trans-
1100 ferred to 75% seawater(Prosserand Brown, 1965). Osmotic-
11100 adaptation requires longer times in strongly osmoregulating
100 species, such as 48 h in osmoregulating crabs (Charmantier,
1998) and up to 96 h in crayfish (Susanto and Charmantier,
2000). The short acclimation time found in B. thennvdron
700 800 100 1000 1100 1200 1300 400 500 600
Medium(mosm/kg) i Medium(mEq/1) probably indicates a relatively high exchange of water and
ions between the organism and the external medium and a
high permeability ofthe body surface in this species; it also
reflects the weak salinity stress applied.
Na
Hydromineral regulation
B. thermydron osmoconformed over the narrow range of
tolerable salinities. When salinity varied, the hemolymph
osmolality tended to follow the external osmolality, with a
300 400 500 600 slight positive difference ofonly about 15 mosm/kg. This is
Medium(mEq/1) i Medium(mEq/1) probably due to the colloid osmotic pressure of plasma
proteins. B. thermydron is therefore an osmoconformer like
the Majidae Libinia emarginatu, Pugettiaproducta (Mantel
and Farmer, 1983), Maja sp. (Potts and Parry, 1963). and
Ca'
Chionoecetes sp. (Mantel and Farmer, 1983; Hardy et ai,
1994); the Cancridae Cancer antennarius (Jones, 1941;
Gross, 1964) and C. pagurus (Pequeux, 1995); and the
Calappidae Calappa hepatica (Kamemoto and Kato. 1969).
As already noted by different authors (reviewed in Mantel
and Farmer, 1983; Pequeux. 1995), osmoconformity does
not permit survival at salinities widely different from sea-
Medium(mEq/1) E Medium(mEq/1) water, and these osmoconformers are marine stenohaline
species. As in other crustaceans, the osmolality of the he-
Figure3. Byihnitnu'ci thermydron. Variations in hemolymph osmola-
tliot\F)(A(:inOm.EP.q) (1o~sm'o)taiftcerprheesmsuorleyminphmoossmmo/lkagl)itaynsdtaiboinliiczactoionnce(natbroauttio1n5s-2(B4 mioonls,ymespshentoifalBl.y Nthae+rmaynddroCnl~wa(sPemqousetulxy. d1u99e5)t,owihniocrhganaicc-
h),inrelationtotheosmolalityorionicconcentrationofthemedium.Time counted for about 95% of the total hemolymph osmolality.
ofexposuretothedifferent mediawas24h(A)or 15-24h(B toF). Error The regulation of these ions was almost iso-ionic. In these
bars: mean SD;;;: 3 to 12 individuals; isoconcentration linesaredrawn. crabs, hemolymph Cl ~ and Na+ concentrations respectively
represented about 93% and 102% of the same ion concen-
Discussion trations in the medium. There is thus a slight excess ofNa+
Salinity tolerance and a slight deficit of Cl~ in the hemolymph compared to
The limited numberofavailable animals and lack oftime the medium, as is noted in other osmoconformers such as
and space on board the ship prevented long-term tolerance the Majidae Libinia emarginata (Gilles. 1970), Maja sp.
experiments. Specimens of Bythograen thermydron sur- (Potts and Parry, 1963). and Chionoecetes opilio (Hardy et
vived for 24 h in a narrow range of salinities ranging from ai. 1994); the Cancridae Cancerantennarius (Gross, 1964);
about 3\7(( to427cc. Thesecrabs,unable to withstand agreat and the Calappidae Calappahepatica (Spenceretai, 1979).
2+
extent ofsalinity fluctuations, are thus stenohaline animals. In B. thermydron, the hemolymph Ca concentration
They share this feature with other species of decapods was slightly hyper-regulated, as noted by Prosser (1973) in
whose habitat is most often restricted to seawater, for ex- marine crustaceans. K+ concentration was slightly hyper-
ample, the Majidae. the Cancridae. and the Calappidae hypo-regulated. However, among crustaceans, K+ is often
(review in Mantel and Farmer, 1983: Pequeux, 1995). found in higher concentration in the hemolymph than in the
medium (Mantel and Farmer, 1983).
Acclimation time In B. thermydron, Mg~+ concentration was strongly
In B. thermydron, the time required to reach an osmotic hypo-regulated. The concentration of this ion was about 44%
steady-state after a sudden decrease in external salinity was of that found in the medium, a percentage included in the
172 A.-S. MARTINEZ ET AL.
standard range of hemolymph Mg2+ concentration for dron confirms that these crabs live in an environment where
brachyurans, that is, between 20% and 80% ofthe medium salinity is stable and close to 33%o-35%c. In addition, these
concentration (Prosser, 1973). As in several species of values of salinity add to the knowledge of the ambient
crabs, Mg2+ might be excreted through the antennal glands parameters of the deep-sea hydrothermal environment
M(MaojraristtquainndadSopiocrerH,ya1s99s8p)... wOthhiecrhoarsemorceloantfivoerlmye"rusnrseuscphona-s M(Mgid2-+A,tlCaln~t,icPOR4i3d~g.eNoOr2Ea,sNtHP/a,cifNicOR3i~s,e)andwhNerOe2~Caco2n+-,
sive" (slow-moving) species, have higher hemolymph centrations have been measured (Truchot and Lallier, 1998;
Mg2+ concentration (about 80% ofthat of seawater) (Rob- Sarradin et al., 1998. 1999).
ertson, 1960; Frederich etai, 2000). B. thermydron exhibits
+
n hemolymph Mg" concentration closer to that of more Phytogeny and osmoregiilatory adaptation
"active" crabs such as Carcinus nmenas and Pachygrapsits
mannoratus, in which the ion concentration is below 50% The phylogenetic origin ofthe Bythograeidae is disputed
ofthat found in the medium (Robertson, 1960; Frederich et (Delamare Deboutteville and Guinot, 1981; Guinot, 1988,
a/., 2000). This fact can be related to the active locomotor 1990). According to Williams ( 1980). Tudge et al. (1998),
and Steinberg et al. (1999), Bythograea thermydron
behavior of B. thermydron (Williams. 1980; Guinot. 1988;
exhibits some similarities to Potamoidea (Potamidae),
Guinot and Segonzac, 1997), which is evident in visual
observations and video monitoring (Jean-Yves Toullec, Portunoidea (Portunidae), and Xanthoidea (Goneplacidae;
npeeryss.,oibns.a)ntdhaotutshoofwtthheewcararbms afrreeaqsu,enatnldy maomvoinnggtohne cvhesitmi-- fXaonrtmheirdaB.e;thTrearpmeyzdiriodnae)m.ayThtehumsarhianvee sdteerniovheadlifnreomosfmaomicloine-s
mentiferans or mussels on which they feed. In addition, consisting mainly of crab species that are able to strongly
ttohehsyeproe-sruelgtuslsahteowMtgha2t+tihnetchreaibrshheamdorleytmaipnhedafatesrtrtohneigratbrialnisty- oBaslmloarredgualnatdeA(bJboontets,, 11994619;;SKhaawm,em1o9t59o; aRnobderKtastoon,, 11996690;;
fer to the surface and one or two days of exposure to Harris and Micallef, 1971; Taylor et al., 1977; Birchard et
different media. Thus, their osmoconformity and their Na+ al., 1982; Blasco and Forward, 1988; review in Mantel and
and Cl iso-regulation most probably result from a specific Farmer, 1983). During its evolution, B. thermydron would
pattern and not from damage to the integument or serious have lost its ancestor's osmoregulatory ability, which had
stthreescsradbusetotothtehesuprrfeascseu.re change associated with bringing bsteacbloem.eAsuspimeirlfalru,ouisf niont aindenetnicvailr,onpamtetnetrnwohfereevolsuatliinointyhaiss
been reported in some freshwater caridean shrimps for
Exposure to high pressure did not affect the hemolymph
osmolality ofB. thermydron exposed to low salinity, when example, Palaemonetes paludosus (Dobkin and Manning.
1964) and P. argentinus (Charmantier and Anger, 1999).
compared to crabs kept at atmospheric pressure. In these
deep-sea hydrothermal crabs, osmoconformity thus appears These species, which live in fresh water or in low-salinity
to be unaffected by a change in hydrostatic pressure. This habitats, have lost the useless function of hypo-regulation
contrasts with the few tested epibenthic crabs in which usually present in osmoregulatory caridean shrimps and
osmotic and ionic regulation may vary in relation to pres- have retained only the capacity to hyper-regulate.
sure. For instance, short-term exposure (1-3 h) to pressure
of 50-100 bars significantly affected the concentration of Acknowledgments
the inorganic ions (Na+, K+, Cl~, Ca2+, Mg2+) in hemo- The authors warmly thank Prof. Daniele Guinot, who
lymph ofCarcinus maenas (Pequeux and Gilles, 1984). but provided useful ideas on crab phylogeny and reviewed a
changed only the Ca2+ content of the hemolymph in Erio- draft of the manuscript. They also thank Dr. F. Lallier, the
cheir sinensis (Sebert et ai, 1997). chiefscientist ofthe HOPE99cruise. Dr. P.-M. Sarradin for
the supply ofbottom seawater, and Dr. L. Nonnotte for the
Ecological implications loan of the osmometer used aboard ship.
Because B. thermydron is a marine stenohaline osmocon- Literature Cited
former, we may hypothesize that this species occupies a
deep hydrothermal habitat where salinity is stable and close Airriimepsl,icCa.teNd.b,yatnhdeiJn.terJ.actCihvieledfrfeescst.so1f9p9r4e.ssuHreomaenodvtiesmcpoeursatuprreopoerntitehes
to that ofseawater. This hypothesis has been verified in the hydrothermal ventcrabBvthograeathermydron. Biol. Bull. 187: 208-
present study through direct measurements of the ambient 214.
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