Glycogen Concentration in the Mantle Tissue of Freshwater Mussels (Bivalvia : Unionidae) During Starvation and Controlled Feeding

4 Pages·1999·1.8 MB·English

by  M A Patterson

Glycogen concentration in the mantle tissue of freshwater mussels
(Bivalvia: Unionidae) during starvation and controlled feeding
Matthew A. Patterson1, Bruce C. Parker1, and Richard J. Neves2
1 DepartmentofBiology, VirginiaPolytechnic InstituteandState University,Blacksburg,Virginia24061,U. S. A.
2VirginiaCooperativeFish andWildlifeResearch Unit, DepartmentofFisheriesandWildlifeSciences, VirginiaPolytechnic Institute and
StateUniversity, Blacksburg, Virginia 24061, U. S. A.
Abstract: The effects ofcontrolled feeding versus starvation during quarantine on mantle tissue glycogen concentration (represented as milligrams
glycogenpergramofmantletissue±SD)oftwofreshwatermussel species were compared. Starvedindividuals were notprovided with supplemental food
duringquarantine,whilefedspecimenswereprovidedwith 105algalcells/ml,twiceperday. InitialmeanglycogenlevelsforAmblema plicata (Say, 1817)
(9.4±2.4mg/g)andQuadrula pustulosa (I.Lea, 1831)(7.9± 1.8mg/g)collectedfromOhioRiverMile(ORM) 175.5inJuly 1997 were notsignificantly
different(p>0.3) frommean glycogen levels ofA.plicata (8.1 ±4.2 mg/g) and Q.pustulosa (6.2±2.9 mg/g) collected fromthe same site inJuly 1996.
Initialglycogenconcentrationsofquarantinedmussels, therefore, weresimilarinboththestarvedandfedgroups. Aftersevendaysoffeedinginquarantine,
meanglycogenlevelsofA.plicata (12.3±2.3mg/g)andQ.pustulosa (7.1 ±3.7 mg/g)didnotchangesignificantly(p>0.1)relativetowild-caughtspeci-
mens,andweresignificantlylarger(p<0.05)thanmeanglycogenlevelsofstarvedindividuals(3.6± 1.8mg/gand3.5±2.3 mg/g,respectively). Similarly,
meanglycogenlevelsofA.plicata and Q.pustulosa after 14days(8.1 ±3.3 mg/gand7.7±3.3mg/g, respectively)and30days(9.9±4.8 mg/gand 8.4±
2.7 mg/g,respectively)offeeding weresignificantly larger(p<0.01)than meanglycogen levels ofstarvedspecimens after 14days (3.27± 1.74mg/gand
5.37 +3.06 mg/g, respectively) and 30 days (1.2 ± 0.5 mg/g and 1.9 ± 1.4 mg/g, respectively). Adequate feedingofunionids in quarantine is essential to
maintainanimalsinaconditionthatwillincreasethelikelihoodofsurvivalfollowingrelocation.
Key Words: glycogen, zebramussels,OhioRiver,quarantine,Dreissenidae
Relocation has been used widely as a management relocation.
tool to re-establish or assist in the recovery of declining Condition, as defined by Mann (1978: 490), is the
populations ofterrestrial and aquatic organisms (Griffith et "ability ofan animal to withstand an adverse environmental
al, 1989; Cope and Waller, 1995). In response to recent stress, be this physical, chemical or biological." Glycogen
declines in the unionid fauna of North America (Williams is the primary energy store in bivalves (Bayne, 1976;
et al, 1993), relocation is being tested as a management Gabbott, 1983), and the relative amount ofglycogen stored
technique to (1) re-introduce extirpated populations, (2) in bivalve tissues is considered a good indicator of body
remove unionids from project construction zones, (3) aug- condition (Galtsoff, 1964; Walne, 1970). Significant reduc-
ment populations to increase genetic diversity, and (4) sal- tions in unionid glycogen stores prior to and during reloca-
vage unionids from zebra mussel-infested areas (Cope and tion, therefore, could greatly reduce their ability to cope
Waller, 1995). The ultimate goal ofany relocation projectis with natural stressors present in the new environment.
to establish a self-sustaining population ofthe target organ- Collection, handling, aerial exposure, abrupt tem-
ism, and several authors have developed a list of factors perature changes, holding, and transport ofunionids during
that should extend population persistence after relocation, relocation can result in varying degrees ofstress, depending
including (1) the presence of suitable habitat and refugia, on the length ofexposure, that can in turn adversely affect
(2) the release of large founder groups with high genetic body condition (Cope and Waller, 1995). Relocation of
diversity, (3) low levels of competition, and (4) high rates unionids to avoid the adverse effects ofbridge construction,
of population growth (Griffith et al, 1989; Cope and for example, could have little or no effect on condition if
Waller, 1995). Little attention, however, has been given to individual specimens are removed from their natural habitat
the biochemical andphysiological condition ofan organism for short time periods (several hours or days). The presence
priortorelocation and its influence on survival and the abil- of zebra mussels, however, has been shown to cause
ity to develop reproductively viable populations after decreased glycogen reserves in unionids (Haag et al.,
AmericanMalacologicalBulletin,Vol. 15(1)(1999):47-50
47
48 AMER. MALAC. BULL. 15(1) (1999)
1993). In addition, zebra mussel-infested unionids presently tures of N. oleoabundans were grown in Bold's Basal
require a 30-day quarantine period to ensure that zebra Medium (Nichols, 1973) under continuous cool white fluo-
mussel adults andjuveniles are removed prior to relocation rescent light (photon flux: 60-100 uE/m2/s) at 20°C. Stock
(J. Clayton, pers. comm.). In addition to the stress ofrelo- cultures were then transferred to the quarantine facility and
cation, unionids can experience nutritive stress in quaran- used to inoculate a 20 1 carboy containing Fritz F2 algal
tine because little or no information exists on their nutri- medium (Fritz Aquaculture, Mesquite, Texas). When cell
tional requirements (Gatenby et al., 1997). Under laborato- densities in the carboy reached 106 cells/ml, 7 1 aliquots
ry or hatchery conditions, bivalve energy stores have been were used to inoculate three 250 1 algal culture tanks
shown to decline without proper feeding (Calvin, 1931; (Aquatic Ecosystems, Inc., Apopka, Florida), thatalso were
Pora etai, 1969; Bayne and Thompson, 1970; Gabbott and fertilized with Fritz F2 algal medium, aerated, and placed
Walker, 1971), and recent studies reveal that unionid glyco- outside the quarantine facility in direct sunlight. Culture
gen stores can decline as much as 80% after only 30 days tanks were placed outside because algal cultures continual-
of starvation in quarantine (Patterson et al., 1997). ly failed inside the quarantine facility, possibly due to
Consequently, the development of a feeding regime for insufficient light or high water temperatures. Algal cell
mussels held in quarantine could be a critical link in the densities in the 250 1 culture tanks reached 106 cells/ml in
success of future relocation projects. The objectives ofthis ca. 4 days. Water samples from the culture tanks were col-
experiment were to (1) monitor the glycogen levels of lected daily and fixed with acid Lugol's solution (Saraceni
unionids during controlled feeding in quarantine, and (2) and Ruggiu, 1969) forenumeration and identification ofthe
compare these results to reported changes in unionid glyco- algae. Water samples from the Ohio River in 1996 and
gen levels during starvation in quarantine, as reported by 1997 showed that algal cell densities ranged from 104
Patterson etal. (1997). - 105/cells/ml during the summer (Parker etai, 1998), thus
unionids in quarantine were fed ca. 10 cells/ml twice per
day, at 8:00 AM and 5:00 PM. Each day, 75% ofthe water
METHODS
in the quarantine tanks was drained; fresh water and food
were added, and vigorous aeration was applied to maintain
On 20 July 1997, ten specimens each of Amblema algal cells in suspension.
plicata (Say, 1817) and Quadrula pustulosa (I. Lea, The glycogen content of all preserved specimens
1831) were collected from Ohio River Mile (ORM) 175.5 was determined from mantle tissue using the technique of
near Parkersburg, West Virginia. Mussels were removed Keppler and Decker (1974) as described in Patterson et al.
from the shell and placed in 95% ethanol forthe determina- (1997). Mean glycogen levels were expressed in milligrams
tion of initial glycogen levels. Additional specimens ofA. ofglycogen per gram ofpreserved mantle tissue ± standard
plicata and Q. pustulosa (N = 200 and 80, respectively) deviation (SD). It should be noted that preserved tissue
ORM
were collected from 175.5 for placement in individ- weights overestimate dry weights and underestimate wet
ual quarantine tanks. Unionids salvaged from zebra mussel- tissue weights because 95% ethanol dehydrates tissue.
infested waters were thoroughly scrubbed to remove zebra Dehydration by 95% ethanol also reduces error that can
mussels. Cleaned unionids were then hand-inspected before result from changes in tissue water levels during stress.
being placed in aerated quarantine tanks without substra- Mean glycogen levels were compared using ANOVA and,
tum for a minimum of 30 days. During this 30-day period, if significant differences were detected, the Scheffe F-test
water temperatures were maintained around 20°C to allow was used to determine the statistical significance ofindivid-
juvenile zebra mussels missed during the scrubbing proce- ual treatments.
dure to become visible. At the end of 30 days, individual
unionids were inspected under 10X magnification to ensure
the absence ofzebra mussels prior to relocation. Ten speci- RESULTS AND DISCUSSION
mens of A. plicata and Q. pustulosa were sacrificed after
seven, 14, and 30 days ofquarantine, and preserved in 95% During the first 14 d of quarantine, Neochloris
ethanol for subsequent glycogen analysis. After the experi- oleoabundans comprised > 95% of the algae in the 250-1
ment, all remaining specimens were returned to the Ohio culture containers. Because culture tanks were maintained
River. outside the quarantine facility, cultures were contaminated
In 1997, unionids were fed cultures of the chloro- with low densities oftwo green algae, Scenedesmus sp. and
phyte, Neochloris oleoabundans Chantanachat and Bold, Ankistrodesmus sp. Once cultures were contaminated, den-
1962. This species was chosen because previous experi- sities of these contaminants continued to increase. After
ments indicated that juvenile unionids readily ingest and 30 d, the algal community in the culture containers
assimilate this alga (Gatenby etal., 1997). Initial stockcul- had changed significantly, with Scenedesmus and
PATTERSON ETAL. GLYCOGEN LEVELS IN UNIONIDS 49
:
Ankistrodesmus comprising ca. 40% ofthe available algae, ± 3.06 mg/g, respectively) and 30 days (1.2 ± 0.5 mg/g and
and N. oleoabundans comprising the remaining 60%. 1.9 ± 1.4mg/g, respectively).
Despite changes in the algal community, cell densities Glycogen, the primary energy reserve in bivalves,
remained at 106 cells/ml throughout the experiment. drives many important physiological processes and can be
Both the fed and starved treatments had some intial used to endure short-term exposure to anoxia, emersion, or
mortality likely as a result ofcollection and handling, how- reduced food supplies (Bayne, 1976; Gabbott, 1983; Bayne
ever, no mortality occurred during the remainder of the et al, 1985; Hummel et al, 1988). Although exposure to
quarantine period. Mean glycogen levels ofAmblemaplica- anoxia and emersion can be limited if unionids are relocat-
ta and Quadrula pustulosa during controlled feeding in ed to suitable habitat, unionids will likely experience short-
quarantine remained the same, whereas mean glycogen lev- term, localized shifts in food abundance and long-term food
els declined in a previous starvation experiment by shortages during the winter months. Normally, by accumu-
Patterson etal. (1997) (Fig. 1). Initial mean glycogen levels lating glycogen when food is abundant, bivalves are able to
forA. plicata (9.4 ± 2.4 mg/g) and Q. pustulosa (7.9 ± 1.8 withstand these food shortages (Gabbott, 1983; Hummel et
ORM
mg/g) collected from 175.5 in July 1997 were not al, 1988). However, unionid survival after relocation could
significantly different (p > 0.3) from the mean glycogen be greatly reduced if glycogen stores are depleted in quar-
levels ofA. plicata (8.1 ± 4.2 mg/g) and Q. pustulosa (6.2 antine and do not recover prior to the onset of winter.
± 2.9 mg/g) collected from the same site in July 1996 Regardless ofeffects on survival, decreased glycogen levels
(Patterson etal, 1997). Glycogen stores ofunionids enter- in adult bivalves also can have sublethal effects including
ing quarantine, therefore, were similar in both the starvation reduced fecundity and reduced growth rates of developing
and controlled feeding experiments. After seven days of offspring (Bayne, 1972; Helm et al, 1973; Bayne et al,
feeding in quarantine, mean glycogen levels of A. plicata 1975). Thus, the provision of adequate food resources for
(12.3 ± 2.3 mg/g) and Q. pustulosa (7.1 ± 3.7 mg/g) did unionids in quarantine is pertinent to maintaining glycogen
not change significantly (p > 0.1) relative to wild-caught levels and enabling mussels to develop reproductively
specimens, and were significantly larger (p < 0.05) than viable populations afterrelocation.
mean glycogen levels ofstarved individuals (3.6 ± 1.8 mg/g Results from this study indicate that relatively high
and 3.5 ± 2.3 mg/g, respectively). Similarly, mean glycogen cell densities of the green alga, Neochloris oleoabundans,
levels ofA. plicata and Q. pustulosa after 14 days (8.1 ± 3.3 in combination with Scenedesmus and Ankistrodesmus, is
mg/g and 7.7 ± 3.3 mg/g, respectively) and 30 days (9.9 ± an adequate food resource for the maintenance of unionid
4.8 mg/g and 8.4 ± 2.7 mg/g, respectively) of feeding were glycogen stores in the short term (30 d). Currently, no infor-
significantly larger (p < 0.01) than mean glycogen levels of mation exists on the ability ofunionids to digest and assim-
starved specimens after 14 days (3.27 ± 1.74 mg/g and 5.37 ilate Scenedesmus and Ankistrodesmus, but recent studies
show that unionids assimilate Neochloris oleoabundans
with relatively high efficiency (> 50%, M. Patterson, unpub.
A.plicata(starved)
1I Q.pustulosa(starved) data). Additional studies to determine which algal species
!IAQ.ppluisctautlaos(faed()fed) are readily digested and assimilated by unionids are critical,
because some algal species might not be readily digested
and assimilated by certain bivalve species (Peirson, 1983).
Regardless of the digestibility of a particular algal food
resource, large amounts ofalgae will be required ifmanage-
ment agencies hope to relocate large numbers of native
oo 10 - mussels away from zebra mussel-infested areas. In this
study, the quarantine of 300 mussels required constant cul-
ture of 750 1 of living algae. Discovering ways to shorten
6 the quarantine period would make the production of algae
more feasible and decrease the time that unionids must be
1 maintained in captivity, outside their natural habitat.
Studies dealing with more efficient methods of removing
zebra mussels from the shells ofunionids could prove to be
0 7 14 30 the best avenue for reducing the quarantine period.
Time(days) Ultimately, a short quarantine period along with the provi-
Fig. 1.Glycogen levels ofAmblemaplicata and Quadrulapustulosaat0, sion of food will improve the body condition of unionids
7, 14, and 30 d ofstarvation and controlled feeding in quarantine (N = and improve the success offuture relocations.
10/samplingperiod).
.
50 AMER. MALAC. BULL. 15(1) (1999)
ACKNOWLEDGMENTS
Unionidae), reared on algal diets and sediment. American
MalacologicalBulletin 14(l):57-66.
We would like to thank Patty Morrison, Mitch Ellis, and every- Griffith,B.,J.M.Scott,J.W.Carpenter,andC.Reed. 1989.Translocation
one else at the Ohio River Islands National Wildlife Refuge Office, as as a species conservation tool: status and strategy. Science
wellasDr. Andrew MillerandtheUnitedStatesArmyCorpsofEngineers 245:477-480.
fortheir help in collecting mussels fromthe Ohio River. We would also Haag,W. R„ D. L. Berg, D. W. Garton, andJ. L. Farris. 1993. Reduced
liketothankthemanyvolunteersthatassistedwithcollectionandprocess- survivaland fitness in native bivalves in response to fouling by
ingofmussels in the field. ThanksalsogotoLi-Yen Chen forassistance the introduced zebra mussel (Dreissena polymorpha) in western
in developing the glycogen assay and Catherine Gatenby forbuilding the LakeErie. Canadian Journal of Fisheries andAquaticSciences
quarantine facilityand assistingwith field work, algaeculture, and manu- 50(1):13-19.
scriptrevisions. Finally, very special thanks go toJim Dotson forensur- Helm, M. M., D. L. Holland, and R. R. Stephenson. 1973. The effect of
ingthatmusselsreceivedplentyoffoodandforhisincredibleabilitytofix supplementary algal feeding of a hatchery breeding stock of
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