Ion Transport in the Freshwater Zebra Mussel, Dreissena polymorpha

7 Pages·1992·2.8 MB·English

by  J Horohov

Reference: ;<>/. Bull 183: 297-303. (October.
Ion Transport in the Freshwater Zebra Mussel,
Dreissena polymorpha
JANICE HOROHOV. HAROLD SILVERMAN. JOHN W. LYNN,
AND THOMAS H. DIETZ*
Department ofZoologyandPhysiology, Louisiana State University. Baton Rouge, Louisiana, 70803
Abstract. Theblood soluteconcentration (36 mosm)of and there is extensive European literature on the ecology
pondwater acclimated zebra mussels isamong the lowest and gross morphology (Stanczykowska, 1977; Morton,
found in freshwater bivalves. Blood ion concentrations 1979; Mackie et al.. 1989). However, there are few os-
were Na (11-14 m.U) and Cl (12-15 m.U). with lesser moregulatory studiesand most physiological studies have
amounts ofCa (4-5 m.U). HCO3 (about 2-4 m.1/). and focusedon methodsforcontrolorextermination (Morton,
K (0.5 m,U). Sodium. Ca and Cl transport rateswere 20- 1979; Mackie et al.. 1989).
30 jueq (gdry tissue h) ' for pondwater acclimated mus- In a study by Fisher et al. (1991), a buffered artificial
sels. The influx ofboth Na and Cl was stimulated by ex- soft water was found to be lethal to Dreissena. Some ar-
ogenous serotonin (0.1 m.U). Sodium transport in zebra tificial freshwater solutions are buffered with up to 30
mussels was not inhibitmedMby amiloride. Zebra mussels mMKH2PO4 and 19 m.UNaOH to maintain neutral pH
became isosmotic in 30 NaCl solutions and did not (Porcella, 1981). Thisconcentration ofpotassium and so-
survive beyond a week in 45 m,U NaCl. Zebra mussels dium and the ionic ratio are exceptional for an artificial
arewell adapted to theirdilute freshwater habitat, but are freshwaterbut theprimary soluteresponsible forthemor-
more stenohaline than other freshwater bivalves as re- talityinDreissenaispotassium (Fisheretal., 1991). Others
flected bytheirintoleranceofelevated ion concentrations have noted that zebra mussel distribution is restricted by
in the bathing solution. salinity (see Morton. 1979; Deaton andGreenberg, 1991).
Studies demonstrating that zebra mussels are sensitive to
Introduction ionic concentration have opened avenues for possible
The zebra mussel (Dreissena polymorpha) is the most methodsofcontrollingtheirpopulations. However, other
recentfreshwaterbivalveintroduced intothe UnitedStates studies have demonstrated that many fresh-waterbivalves
from Europe(Mackieela!., 1989). Unlikeotherfreshwater are killed by low concentrations ofpotassium (see Dietz
bivalves, adult zebra mussels attach to solid substrate with and Byrne, 1990).
byssal threadsand may reach densitiesexceeding 105/m3. Thisreportdescribessomeofthecharacteristicsofionic
In addition, reproduction involves gametes that are dis- and osmotic regulation in the zebra mussel and some
charged into the water column and develop into free- conditions limiting theirsurvival. Because ofthe potential
swimming veliger larvae that may remain planktonic for similarities with indigenous bivalves, the basic biology of
weeks or months, allowing them to move considerable zebramussels mustbe understood tobeabletoselectively
distances before settling (Mackie et a/., 1989; Morton. control their numbers or distribution.
1979).
Dreissena hasbeen documented asa seriouseconomic Materials and Methods
pest because ofits propensity to foul raw-water systems. Animals
Zebra mussels (Dreissena polymorpha) were collected
Received 26 March 1992; accepted 20July 1992.
* Addresscorrespondence to: T. H. Dietz. Dept. Zoology and Phys- from Lake Erie near Cleveland, Ohio, and acclimated to
iology. LouisianaState University. Baton Rouge. LA 70803. artificial pondwater for a minimum of 5 days (Dietz,
297
298 J. HOROHOV ET AL
1979). Mu2sCsels were tored unfed in aerated pondwater dium. Un=idire-ctional efflux (J ) was calculated by differ-
at 22 b ;. Zebra mussels usually survived ence (J J, Jn).
6-8 weeks at ~" ;i no mortality. Forlonger mainte- The effectsofexogenousbiogenicamines on ion trans-
nance, mu?? \1 in pondwater at 16 1C and port were determined by the addition ofmonoamines to
subseque" sferredto room temperature forat least bringthe bathing medium concentration to0.1 mA/. Sev-
24-48 1 illy 5 days) before use in experiments. eral biogenic amines (dopamine, epinephrine, norepi-
We nor .elected larger specimens for study (2-3.5 nephrine, octopamine, and serotonin) were tested. All
cm length) with a dry tissue mass of 15-40 mg. monoamine neurotransmitters were obtained from Sigma
Toavoidcontaminating local watersystemswithzebra Chemical Company (St. Louis, MO).
musselsorveligerlarvae, all acclimation waterand animal Data are expressed as mean one standard error. The
containers were treated with 1% chlorine bleach for 24 h Student's /-test was used to compare means with equal
before being discarded. Mussels were dissected from the variances, and differences were considered significant if
shell and dried at 95C, and weighed before being dis- P < 0.05. Time-course studies and the effects ofion con-
carded. centrations on mussel blood, where variances were un-
equal, were analyzed by ANOVA and Scheffe's f-test on
Bloodanalyses log transformed data.
Bloodwascollected by heart puncture(Fyhn andCost-
low, 1975) and centrifuged 8000 g-min before use. We Results
could routinely collect blood volume equal to 10% ofthe The blood composition ofD. polymorpha acclimated
animal weight. However, the mantle cavity retains more to pondwater (PW) is shown in Table I. Zebra mussels
pondwater than other freshwater bivalves and was more were hyperionic to PW with sodium and chloride being
difficult todrain. Failure todrain the mantle cavity water the principal solutes. The measured solutes account for
insmallerzebra musselswill likelycontaminatetheblood 88% ofthetotal solute but thereisan ion deficit("other")
sample ifthesyringe needle passesbeyond the pericardia! of5.1 m.\/. From anothergroupofanimals, we measured
ddrbCcTmeeeaeyhigpnrtneirtlaeeoreetrbnasdom.aitsmniciibaiaonoTlyncrneoy.btdtieoaainlnbclSbetaasyoclhtostdeerfogripllbaocutauslmoitmmeonceoetochnrdaerewinnmsowcatdpimasrestasacsiptdtttimoorieroetagoonttaarsn,eissacsorsuonapmi.wprnhiuyeednT.mr(deBhecdoCaceaushnoltlobnCicbotcyliiOreicur:ienamfordtrruueraewbtsaeoiaiwtznnansaiiieagno,sltagnayes-1dsHpm9ewcao8ateeoyi5ecarne)nrh-e-d.t- t(pWaaoBthb"nryeseaoo2r.etb,nt3nrhaoeooCetbRbtar.l,cil"etycdBtsat3yiohillt.lnur.lh7,usnyattet1e9hf,,9e5rm90Sa%o1of.l)Umsl7o.oNtrozfYmfmBeot-bMlthfForohe;trafeoChedmeHCmOduaop,CmOsjniHsOow2sierosal23oiu.s)fian6l.otag7dnc.nssc4eeolx5a0ulii.tnushm4rttdaaaesatmltse(oMbdtt7Heao,0tleC%oanb)nOlplkmwoo3a=enaol(adisdu6snwn)CCeuap(rtuOOpsebeeH22.dre,.
suredbutwereestimated fromaliquotsofbloodthatwere The blood solute in D. polymorpha is among the
equilibrated in air. From previous studies, 95-98% ofthe lowest recorded for freshwater mussels (see Dietz, 1979).
COi would be in the form of bicarbonate over the pH To test their ability to osmoregulate, we challenged the
range 7.5-8.1 (Byrne ct ai. 1991). mussels with NaCl added to pondwater and measured
Ionfluxes twhaesbalosoidgniifoincacnotnc(ePnt<ra0t.i0o1n)s a1f1t.e8rm96Mh r(iTsaebline bIIl).ooTdheNrae
Unidirectional ion influxes (J,) were calculated by
monitoring the disappearance ofisotope from the bathing
medium usingpreviouslydescribed methods(Gravesand Table I
Dietz, 1982). The animals were removed from theirstor- liloojandpondwaterioncomposition inpondwateracclimated
age containers by cutting the byssal thread with scissors Dreissena polymorpha
or scraping the thread from the container, not by pulling
the thread from the animal. The mussels were rinsed in Ion
deionized water for about 30 min and transferred to a
small containerwiththeappropriate bathingsolution. The
animals ordinarily did not reattach with byssal threads
during the briefperiod ofstudy. Bath samples were col-
lected at timed intervals and radioactivity determined by
liquid scintillation counting. Net flux (Jn) was calculated
from the change in ion concentration in the bathing me-
IONIC AND OSMOTIC REGULATION IN ZEBRA MUSSELS 299
Table II
ilc<>iicenti'titiii 111 Dreissena polymorpha after4 duy\ acclimation inpondwalercuiiiaiiuiit; additional \'ui I
300 J. HOROHOV ET AL.
Table IV
'inhlood" "' '" Dreissena polymorphafollowingacutetransfertopondwatercontaining45 rriMNaCl
mosm
IONIC AND OSMOTIC REGULATION IN ZEBRA MUSSELS 301
unionid bivalve sodium transport system is inhibited by Table VII
amiloride. In contrast, corbiculid Na transport is not. So- Effectsotaniilondc(0,5 mM) addition topondwateron unidirectional
dium transport in D. polymorpha was not inhibited by sodium fluxes inpondwalcracclimatedDreissena polymorpha
0.5 m.U amiloride (Table VII). Some mussels were slow
to open their valvesand initiate siphoningand this raised (gdry tissue h)
the variabilityofthe measured fluxes. However, theamil- Treatment Influx Efflux Net flux
oride-treated mussels that were observed to be open and
siphoning had transport rates that equalled or exceeded Control 22.22 + 4.24 25.04 + 2.34 -2.92 4.12
the controls. Amiloride 19.00 5.96 30.34 + 7.33 -11.34 2.29
Discussion Mean SEM. n = 8.
Dreissenapolymorphaexhibited several characteristics
that were significantly different from the other freshwater pondwater. However, storage of zebra mussels in PW,
bivalvesthat havebeenstudied. TheCl transport ratewas withoutfood, beyond 2 monthsledtoan increase in mor-
higherthan observed in other freshwater mussels and the tality. Coincidentally, mussels maintained in the labora-
rateofNatransport isequaled only bythe fingernail clam tory tended to lose solutes and ion fluxes became more
Miiscitliiim (= Sphaeriiim) transversum (Dietz. 1979). variable, but this phenomenon has not been studied sys-
Chloride transport was double the transport rate of fin- tematically.
gernail clams and 10-20X that of unionids. This is the Sodium transport in zebra mussels was the same in
first report in a freshwater mussel of chloride transport solutions of either NaCl or Na2SO4 indicating an inde-
being dependent on Na and Cl uptake being stimulated pendence from chloridetransport. Unionidandcorbiculid
by exogenous serotonin. Preliminary data indicate that Natransport are also independent ofCl, using instead an
both Na and Cl transport also may be stimulated by se- apparent Na/H exchange component (Dietz, 1978;
rotonin in corbiculids (unpub. obs.). Serotonin has been McCorkle and Dietz, 1980). We have not examined the
reported to stimulate only sodium transport in unionid exchange mechanism in zebra mussels. Recent studies
bivalves (Dietz et a!., 1982). have indicated that Na flux across amphibian skin is
The blood ofPW acclimated zebra mussels has signif- largely regulated by availability of intracellular protons
icantly less total solute than other mussels and was com- rather than a directly coupled exchange mechanism
posed primarily ofNaCl with onlyabout 2-4 m.UHCO3. (Harvey and Ehrenfeld, 1988; Kirschner, 1988).
Organic solutescontribute littletothetotal solute offresh- This isthe first evidence that Cl transport isdependent
watermussels(Hanson and Dietz, 1976). The ionic com- on Na in a freshwater mussel. These data indicate that
position in zebra mussel blood is similar to a Canadian there may be a NaCl co-transport system in D. polymor-
unionid,Anodontagrandissimpsoniana, butdiffers from pha. This inference was further supported by the stimu-
most other unionids in that they contain a combination lation ofboth Na and Cl uptake by exogenous serotonin.
ofNa, Cl, and HCO, (Dietz, 1979; Byrneand McMahon, Because we have not measured transepithelial electrical
1991). Corbiculid blood composition is largely NaCl at characteristics in zebra mussels, it is premature to spec-
about twice the concentration found in D. polymorpha. ulate on primary or secondary transport mechanisms.
Corbiculaflumineaalso hastwicethecalcium concentra- Both Dreissena and Corbicula have elevated Na trans-
tion asthe zebra mussel (Dietz, 1979; Byrne et at.. 1989). portratescompared to unionids. Zebra musselssharewith
mM
Acutetransferofzebramusselsto45 NaCl resulted Corbicula the unusual property that sodium transport is
in an elevated blood NaCl concentration within 8 h, but insensitivetoamiloride(McCorkleandDietz, 1980). Since
48 h was required for acclimation. Corhicula fluminea Corbicula displays a substantial Na/Na exchange com-
rapidly adjust blood total solutes within 12 h after being ponent not found in unionids, it is tempting to speculate
transferred from freshwater to 5%o (172 mosm), but vol- that zebramusselsalso may havealargeNa/Naexchange
ume regulation is incomplete even after 120 h (Gainey, mechanism contributingtothehigh isotopeturnover,but
1978). Zebra musselsbecame isosmoticand suffered con- this has not been measured. It is possible that these Na/
siderable mortality when acutely transferred to NaCl so- Naexchangepathwayspresentinsomefreshwaterbivalves
lutionsabove 30 mM. In contrast, unionids become isos- are insensitive to amiloride inhibition.
motic above 50 mMNaCl and survive 75 mM NaCl and Alternatively, the large Na exchange diffusion com-
corbiculidscan tolerateeven highersoluteconcentrations ponent may be a characteristic ofrecent brackish-water
(Dietz and Branton. 1975; Gainey, 1978). ancestry ofCorhicula and Dreissena. Although they have
Although D. polymorpha displayed high ion turnover invaded freshwater independently, both genera contain
rates, they were able to maintain a steady state in dilute species that inhabit brackish-water (for review see
302 J. HOROHOV ET AL
McMahon. 1983: ,' al.. 1989; Deaton and be useful in controlling zebra mussels in a specific case
Greenberg, 199: such as freshwater ballast in trans-oceanic vessels. The
Freshwat s :ire capable hyper-regulators and addition of 5-10% seawater, in this example, would be
usually ar> : crate hyperosmotic conditions that lethal to adult zebra mussels.
would more iouble their normal total solute con-
centration iton and Greenberg. 1991; Kirschner, Acknowledgments
1991). >n..-i 'in is uniquely stenohaline in showingmelMe- Wethank Drs. Robert McMahon and Roger Byrne for
vated mortality at low solute concentrations (30 providingthezebra musselscollected from Lake Erieand
tNoaC4l5),maMndNabeCilngbeiynocnapdaablweeeokf.suWrevivhianvgeannotaecdutperetvriaonussfleyr afonrdtDheiomndainyLessusgagredstpiroonvsidaenddtcecohmnmiecanltsa.ssiJsutlaineceC.heTrhriys
that Corbicula subjected to a loss ofbody waterwill shift workwassupported, inpart,bythe LSUCenterforEnergy
Na and Cl out of the blood compartment presumably Studies grant 91-01-1 1 and NSF grant DCB90-17461.
intotheintracellularfluid(Byrneelal., 1989). Itispossible
that thechanges in intracellular ioniccomposition due to Literature Cited
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