CONCHOLOGIT VOLUME XXXV, No. 2 ISSN 0885-1263 APR 12 2000 LIBRARIES JUNE, 1999 The Texas Conchologist is the official publication of the Houston Conchology Society, Inc., and is published occasionally at Houston, Texas. It is distributed as part of the dues to all its members. The Society holds regular meetings the fourth Wednesday in each of the follow- - ing months: August, September, October, January, February, March, April, and May. In November, the meeting is held the third Wednesday. An annual auction is held in place of the March or April Meeting Meetings are held at Southside Place Club House, 3743 Gamet, Houston, Texas. Meetings begin at 8:00 p. m. | The Texas Conchologist is published October, and May. Itis mailed postpaid to regular members in U.S. postal zones. Overseas members will be charged ad- ditional postage. Only one copy will be mailed to a family membership. ' Dues extend from the beginning of the fiscal year of June 1 through May 31. However, the May issue of the Texas Conchologist each year is the second issue due on the regular dues year beginning June 1 of the previous year. Member- ships will be accepted throughout the year but will receive issues of that fiscal year. Members receive meeting Newsletters and have all other privileges pro- vided by the Society's by-laws. Rates and Dues Family membership $12.00 Single Membership $10.00 Student membership $ 6.00 Single issues $ 2.50 Extra sets mailed to members $10.00 (Postage for overseas members required) Subscription $12.00 (Seamail $5.00, Airmail outside U.S. $8.00) Co- Editor Co-Editor Editorial Advisor Darwin Alder Constance E. Boone Dr. Helmer Odé 5415 Dickson St. 3706 Rice Blvd. 3319 Big Bend Dr. Houston, TX 77007 Houston, TX 77005 Austin, TX 78731 (713) 880-5946 (713) 668-8252 (512) 452-7799 Scientific Advisor Dr. John Wise Houston Museum of Natural Science Houston, TX 77030 (713) 639-4677 The Texas Conchologist accepts contributions for publication from amateurs, students, and professionals, subject to approval by the Editors. Manuscripts should be typed and double spaced, and should be in the hands of the Editors the first day of the month preceding eae tai dates. Photos acco | articles are welcomed. TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 Recent Harold W. Harry Memorial Award Winners The Houston Conchology Society, Inc. continues to present awards to students doing graduate research in malacology, at both private and public Texas institutions. In this issue of Texas Conchologist we present papers offered by three recent winners. The application forms for 2000 will be mailed to interested institutions in the fall of 1999. Inquiries may be sent to President Cheryl Hood 7406 Pierrepont Houston, TX 77040 (713) 937-4818 e-mail cheryl.hood@inteq.com In response to the Editors' request, we present some background infor- mation from the winners. 1999 Winner Christine Ritter Mary Christine Ritter was born in Austin, Texas on July 7, 1966, the daughter of Mary Catherine Johnson Ritter and Timothy Henderson Ritter. She has two younger siblings, John Timothy Ritter and Catherine Ann Ritter. After completing Stephen F. Austin High School, she went to Trinity University, San Antonio, Texas. While at Trinity she attended summer school at the University of Texas, and the Bermuda Biological Station. She also attended field based courses offered by Boston Uni- versity and Northeastern University. After graduating from Trinity with a Bachelor of Arts degree in Biology, May, 1988, she attended Texas A. & M. University where she received a Masters of Science in Wildlife and Fisheries Sciences in May, 1991. During the following years she worked for the Texas General Land Office and Congressman Greg Laughlin. In June, 1994, she entered the Graduate School of the Uni- versity of Texas at Austin to pursue a Ph.D. in Marine Science. Her advisor is Dr. Paul A. Montagna. She hopes to defend her dissertation this summer and graduate in August. There are several options for her to choose from for the future. She hopes to continue research to develop her scientific understanding of estuarine succession and her policy background. Permanent Address: 404 Mercer, Port Aransas, Texas 78373. 89 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 1999 Winner David Wayne Hicks David Hicks will be completing his Ph.D. in August, 1999 at the Univer- sity of Texas at Arlington, Texas. His advisor is Dr. Robert F. McMahon. He has accepted the position of Assistant Professor of Marine Biology at Lamar University in Beaumont, Texas. He will teach and will be di- recting their marine laboratory facility on Pleasure Island which has not been in use for some time. , Hicks received his B.S. in Marine Biology at the Texas A & M University at Galveston, Texas in 1989. He was awarded his M.S. in Biology at Texas A. & M. University at Corpus Christi, Texas in 1993, with Dr. J. W. Tunnell, Jr. as his thesis supervisor. He has had a varied professional experience as research assistant, graduate teaching assistant and is presently associate professor at Colin County Community College at Plano, Texas. His list of publication is varied and large. In the last few years he has several papers published with others on the brown mussel, Perna pema. He has received support from the Texas A. & M. University Sea Grant College Program. Current Research Activities: "My dissertation research details the resistance adaptations of nonindigenous Pema perma to the major physio-chemical parameters likely to influence its capacity to colonize estuarine and coastal waters of North America. The physio-chemical parameters being examined include upper thermal limit (acute and chronic), lower thermal limit (chronic and freeze resistant), salinity tolerance, desiccation resistance, and tolerance of anoxia/hypoxia. Regulation of respiratory responses in each of the aforementioned physiology stressor experiments are also being examined. Aside from detailing the basic physiology of P. perna, the results of my research can be utilized in developing habitat risk assessment for predicting the spread of this species and to estimate efficacy of physiological treatments for use as nonchemical control strategies for mussel fouling in raw water systems," writes Hicks. With his wife Kim and daughter Savannah, David will move to Beau- mont, sometime in August. — 90 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 1998 Winner Daniel E. Webb Department of Science, Paint Rock Schools Paint Rock, Texas 76866 (915) 732-4487 e mail cwebb@wcc.net Dan Webb grew up near Crosby, Texas. He completed his Master's Degree at San Angelo University, with Dr. Ned Strength his advisor. He has enjoyed teaching science at Paint Rock this last year and has signed a contract to teach there the 1999-2000 school year. He plans to continue his research at San Angelo State as that university is close to Paint Rock. Webb has published several papers on varied research interests and received many honors and grants to support his unique study involving mollusks. His wife also teaches at Paint Rock. All your winners have expressed appreciation for the Harry awards and mentioned them in publications. 9] TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 Estaurine Macrobenthic Community Succession: The influence of hypoxia, salinity fluctuations, sediment resuspension and disturbance frequency Christine Ritter University of Texas Marine Science Institute — Port Aransas, Texas Succession theory describes community changes over time in the absence of disturbance. The theory was initially developed for terrestrial systems where the progress of succession was character- ized by increasing community diversity, abundance, and biomass, and by changing species composition from species capable of rapid population growth (opportunists) to larger, more rare and slow growing species (Clements 1918; Cooper 1939). The application of succes- sion theory to estuarine ecosystems is comparatively new (Pearson and Rosenberg 1976; Rhoads et a/. 1978; Dauer 1993) and is problematic due to the great amount of environmental heterogeneity (e.g., salinity, oxygen, temperature) that affect organisms present. Macrobenthic succession models focus on defining the characteris- tics of early succession versus climax (e.g., late succession) commu- nities. A key characteristic of early succession communities is dominance by opportunistic species (e.g., the bivalve Mulinia lateralis; Dauer 1993). Other characteristics include lower biomass and diversity compared with that of a climax community (Dauer 1993). Larger infauna (e.g., Ophiuroida, Enteropneusta), often associated with climax communities, may facilitate oxygenation of deeper sedi- ments by bioturbation (Flint and Kalke 1986). The oxygenation of deeper sediments allows infauna (e.g., bivalves) to become more deeply distributed, enhancing colonization by still other infaunal species (Flint and Kalke 1986), facilitating an increase in diversity and promoting the progression of succession. The benthic estuarine environments of south Texas bays appear to be in a state of perpetual early succession (Montagna et al, 1998). Benthic communities in this area are characterized by low diversity and opportunistic species. There are three possible explanations for this observation. First, present sampling methods may not adequately sample larger deep dwelling species typically characteristic of late succession communities. Second, benthic communities of south Texas may be in a state of constant disturbance due to sediment resuspension (natural and anthropogenic), broad salinity variations, 92 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 and seasonal hypoxia (low oxygen). Third, estuarine succession models developed for application in other areas may not be suitable for south Texas estuaries due to physical (e.g., depth, tides) and climatological (e.g., rainfall, wind speed) differences. To determine why Texas estuarine benthic communities appear to be in a state of'constant disturbance, | conducted three experiments. The climax community study determined the adequacy of the present sampling effort and characterized a late succession estuarine com- munity for Corpus Christi Bay. The hypoxia study determined the effect of hypoxia on benthic communities, proposed models describ- ing how community characteristics respond to declining oxygen levels, and examined the present definition of hypoxia. The flow- resuspension experiment determined the effect of three flow/turbidity regimes on natural bottom and colonization of trays filled with defaunated sediment. In addition, the macrobenthic effects of frequency of physical disturbance and flooding were determined in the context of flow/turbidity disturbance. Based on these investiga- tions, a theoretical model is being developed to describe the roles of disturbance frequency and intensity in the temporal context of estua- rine benthic succession Summary of Findings Pertinent to Mollusks Climax Community Study Macrobenthic communities of station C and E in Corpus Christi Bay (Figure 1) were markedly different with station E having much higher diversity, abundance and biomass than station C. This trend is reflected in the mollusk fauna of these stations (Table. 1). No gastro- pods, and very few bivalves (10 m/sec) is achieved by a byssus composed of numerous collagenous threads secreted by the mussels foot. The entire structure is linked to the byssus retractor muscles by the root. The stem which extends from the root supports each of the byssal threads. This research proposes to investigate the biology and mechanical properties of byssal thread production in P. perna. The effects of high temperature, low salinity, and low oxygen tensions on the produc- tion and strength of byssal threads will be examined. Application of 96 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 thermal, hypoosmotic, and oxygen stress are potentially highly economical, environmentally acceptable, nonchemical tools for inhibiting and or eliminating mussel fouling. Prior to each experiment, 20 mussels will be randomly assigned to acclimation groups of varying temperatures, salinity, or oxygen tension. Following the acclimation periods, all byssal threads will be severed at the byssal gape with a razor blade. Mussels then will be allowed to byssally reattach and thereafter, the cumulative number of threads produced will be re- corded over the course of 21 days. Tensile strength and strain of byssal threads of five randomly selected threads from each individual will be determined using a Chatillon-DFGS2 digital force gauge at an extension rate of< 10 mm/min. Both thread thickness and mussel size will be considered in thread strength determinations. To evaluate the susceptibility of different structures to mussel fouling, whole mussel attachment strength to various substrates including steel, concrete, and plastic will be tested, on both field and laboratory animals. Studies of the mechanism of byssal attachment in bivalve molluscs have focused almost exclusively with the blue mussel, Mytilus edulis, with nothing Known about the biology and mechanical properties of byssal threads in Perna perna. Preliminary tests indicate that the threads of Perna perna are as much as four times the strength values reported for Mytilus spp. 97 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 A Comparison of Arsenic and Lead Concentrations in the fresh- water bivalves Corbicula fluminea (Corbiculidae) and Quadrula apiculata (Unionidae) from the Concho River, Texas using Energy Dispersive X-ray Fluorescence. Daniel E . Webb Department of Science Paint Rock Schools Paint Rock, Texas 76886 Abstract Asian clams (Corbicula fluminea) and southern mapleleaf clam (Quadrula apiculala) were collected from a mussel sanctuary on the Concho River approximately one kilometer west of Paint Rock, Concho County, Texas. Gill tissue from seventeen individuals of each species was analyzed for concentrations of arsenic (As) and lead (Pb) using energy dispersive x-ray fluorescence spectroscopy (EDXRF). Gill tissue from Corbicula fluminea contained significantly greater levels of As and Pb than did gill tissue from Quadrula apiculata. INTRODUCTION Asian clams, Corbicula fluminea, have often been used to determine whether elemental pollutants are present and bioavailable in aquatic systems. They are able to concentrate many elements to several orders of magnitude greater than the concentrations of those same elements in the environment. The southern mapleleaf, Quadrula apiculata, has never been used as a bioindicator of elemental pollut- ants. The fact that it does not occur in all U.S. surface waters and is more difficult to identify than Corbicula fluminea may have caused others to dismiss it as a potential bioindicator. This study was under- taken to compare the relative abilities of these two bivalve species to concentrate As and Pb because both species are two of the most common bivalve species in Texas and both occur in large numbers in the Concho River. Additionally, this study confirms the presence of As and Pb in the Concho River in a chemical form that can be incorporated into tissue. Energy dispersive x-ray fluorescence was used because it is accu- rate and relatively easy to use with samples in organic matrices. Moreover, the concentration of many elements can be determined from a single spectrum, thereby reducing sample-handling time. 98 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 xDetection and/or quantification of elemental pollutants often present several problems. Little information is available concerning the presence of elements in any but the most polluted of industrialized surface water (Heit et a/., 1980), and qualitative studies by most methods are expensive and time consuming (Webb & Dawkins, 1998). Additionally, many contaminants occur in such low quantities in surface waters and their substrates that they must be concentrated by appropriate methods in order to be detected and quantified by instrumental methods of analysis (Buhrke et a/., 1998). The fact that bioaccumulation occurs in this group of organisms alleviates the need to perform time consuming and, possibly, expensive concentration procedures in the laboratory. METHODS AND MATERIALS Sample Collection Site The collection site was a 10 m x 10 m area in the Concho River approximately one km west of Paint Rock, Concho County, Texas. The United States Geological Survey (USGS) has had a water sam- pling and field testing station (USGS Site 08136500) one kilometer east of the sample collection site since 1967. The Texas Natural Resource Conservation Committee (TNRCC) considers the sample collection site to be a part of Section 1421 of the Colorado River drainage system. The TNRCC considers the water to be safe for contact recreation with the following average annual physical and chemical parameters: sulfate, 425 mg/L; chloride, 775 mg/L; total dissolved solids, 1600 mg/L; dissolved oxygen, 5.0 mg/L; pH range, 6.5-9.0; temperature, 32° C (Lower Colorado River Authority et al., 1996). The mussel fauna at the site contains many individuals from at least seven species. One reason mussel populations are relatively healthy and stable here is that the shorelines of the Concho River are heavily vegetated for more than two km upstream of the site. This vegetation prevents excessive siltation due to runoff. In addition to the species in this study, the site is inhabited by paper pondshell, Anodonta imbecillis; giant floater, Anodonta grandis; bleufer, Potamilus purpuratus; fragile papershell, Leptodea fragilis; and the largest known population of the endangered and protected Texas pimpleback, Quadrula petrina. The population density of Corbicula fluminea at the site is > than 2200 individuals/m? (Howells et al., 1996) . The 99 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 Quadrula apiculata population has not been quantitatively described by Texas Parks and Wildlife but it is large. A semi-quantitative, timed search has produced as many as 77 individuals per hour in a recent survey. Sample Collection Thirty five Corbicula fluminea and 30 Quadrula apiculata were collected by wading in water approximately 0.5 m deep. Live animals were placed on ice overnight then frozen at -65° C until processed for analysis. The weights of the animals that were used for EDXRF are recorded on Table 1. It is not necessary to know the weight of a sample to calculate elemental concentrations with EDXRF, but the animals were weighed for several reasons. Dare & Edwards (1975) found that tissue weight and composition was seasonally variable in Mytilus edulis. Although the age of a bivalve is difficult to assess (Neves & Moyer, 1988), weight is generally relative to age for a given population. This study used only adult bivalves of similar age in each species so that contact time with contaminants would be the same. Tissue Preparation: EDXRF Seventeen individuals of each species were prepared for x-ray analysis. All tissue was prepared according to Webb and Dawkins (1998). Triplicate samples from a single gill were prepared by using a micropipette to transfer five L of macerated gill material to each of three Formvar (Ladd Research Industries, Inc., Burlington, Vermont) films. The films were prepared by making a weight/weight solution of 2% Formvar in 1,2-dichloroethane.(Webb and Dawkins,1998). The samples dried at indoor ambient temperature before being irradiated. Samples were routinely placed in the instrument's sample chamber within 90 minutes of being prepared. This precaution minimized the chance that airborne contaminants might corrupt or otherwise affect the organic matrix and subsequent size of the Compton scatter peak. Instrumentation and Experimental Procedure: EDXRF Both elements were analyzed with a Philips Electronics Instruments PV9550HP energy dispersive x-ray fluorescence spectrometer coupled to an EDAX PV9800 analyzer system. Continuous spectrum, primary, x-rays were generated at a Rh target and filtered with a thin- foil Rh filter. Samples were irradiated for 1000 live seconds with 35 | kV x-rays with an x-ray tube current of 30 mA. Net intensities of 100 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 fluorescent x-rays, |,, which vary in direct proportion to the mass of a given element in a sample, were obtained by subtracting the back- ground radiation and integrating the K, peak for As, and the L, and L peaks for Pb. The intensity of the Compton scatter peak, |_., which varied in proportion to the mass of the total sample, was integrated in a window of 19.80 keV to 20.40 keV according to Webb and Dawkins (1998). The net intensity of fluorescent x-rays to the intensity of the integrated portion of the Compton scatter peak (I,./l_, ratio) was then used to determine the concentrations of the elements under study. The fluorescent x-rays produced by the sample were detected with a lithium drifted silicon detector and digitized by the EDAX PV9800. Determination of the concentrations of Pb and As present obstacles that must be overcome when using EDXRF. To begin, Pbis larger | than Rh so primary x-rays from a Rh target are not energetic enough to elicit K,, or K, peaks from Pb. Consequently, the less desirable L lines must be used to quantify Pb. Additionally, the Pb L, peak is centered at 10. 549 keV and the As K_peak is centered at 10. 532 keV. Their spectral lines interfere with each other when both elements are present. ) The relationship of I,/I,, to concentration is linear for both Pb and As to a concentration of 150 ppm. The following method was used to determine the concentrations of Pb and As in tissue when both elements were present in a sample at concentrations of less than 150 ppm. Multiple samples of standard reference material bovine albumin _ (U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD) were analyzed. Blank values for each element are generated by analyzing the matrix without adding any standards. The blank values are subtracted from the I,/I,, ratios. It is assumed hereafter that, when discussing I,/I_., blank values have already been subtracted and the I,/I., reported is the corrected value. Next albumin samples were spiked with 50.00 ppm Pb and the mean I,/I_., ratio for the L. peak was discovered to be 1.5210. The |,/I,, ratio for the As K, peak is 3.244 when Pb is not present and the As concentration is 90.00 ppm. When 50.00 ppm Pb and 50.00 ppm As are present in the same tissue sample the resulting |,/I,, ratio for the Pb L, peak is 1.168. For simplicity, let the I_/I_, ratio for the Pb L, peak equal x and I,/I,, ratio for the Pb L_ plus As K_peak equal y. Also, let (Pb) equal the concentration of Pb in a sample in ppm and (As) equal the concentra- 101 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 tion of As in a sample in ppm. Let C,, C,, C, be constants and the following equations can be used to describe the concentrations of Pb and As in tissue: x = C,(Pb) equation 1 y = C,(Pb) + C,(As) equation 2 These equations are true when: : C, = x/(Pb) = 1.168/50.00 = 0.02336, equation 3 C, = Y-C,(As)/(Pb)=1.521-0/50.00=0.03042 equation 4 C,= Y-C,(Pb)/As=3.244-0/50.00=0.06488 equation 5 Substituting C, from equation 3 into equation 1 and substituting C, and C, from equations four and five respectively into equation 2, one has machine formulas that can be employed to determine the concen- trations of As and Pb in tissue samples: x = 0.02336(Pb) equation 6 y = 0.03042(Pb) + 0.06488(AS) | equation 7 The value ofk was detem hed by integiatng the Pbl, peak ina window of 12.40 keV to 12.05 keV and the value of y was determined by integrating the additive Pb L_, As K, peak in a window of 10.30 keV to 10.81 keV. RESULTS Concentrations (ppm dry weight) from each of the three EDXRF spectra/animal were averaged and recorded as a single concentration measurement (Tables 2 and 3). Concentrations of each element, from each animal, were then averaged and recorded (Table 4). T-tests were employed to determine if the difference in the concentra- tion of each element was significant between Corbicula fluminea and Quadrula apiculata. SYSTAT 5.2.1 (Statistical Products and Service Solutions Inc., Chicago, IL) was used to determine t-test scores. A separate variance tscore and a pooled variance t-score were calcu- lated for the means of each species. An F-score was calulated to test the variance of the concentration of each element in each species. Though pooled variance t-tests are very robust to differences in variance (Zar 1996), the separate variance t-test was referred to when the differences in variance were significant. At an alpha value of 0.05, there was a significant difference in the variances of the mean concentrations of As and Pb (Table 4). T-tests confirm that Corbicula 102 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 fluminea gills contain significantly greater concentrations of As and Pb than do the gills of Quadrula apiculata. Consequently, Corbicula fluminea is a better bioindicator of these elements than Quadrula apiculata. DISCUSSION The primary focus of this study was to determine which of two com- mon bivalve species, Corbicula fluminea and Quadrula apiculata, would make a better bioindicator of arsenic and lead. This was determined solely on their relative abilities to concentrate those elements. The study was also undertaken to determine the presence, or absence, and bioavailability of As and Pb in the Concho River. FUTURE RESEARCH An earlier study of Corbicula sp. collected from the same site on the Concho River found the genus to have significantly higher concentra- tions of Br, Cu, Ni, P, Se, and Zn than the background concentrations of those elements in the river sediment (Webb & ]Dawkins, 1998). This study concludes that Corbicula fluminea concentrates As and Pb more readily than Quaclrula apiculata and would make a better bioindicator of those two elements. A follow-up study would determine if it would be feasible to use Corbicula fluminea as an indicator of those metals or whether it would be better to use the sediment instead. Such a study would possibly help determine the ultimate source of the As as well; Corbicula fluminea only have a three year lifespan and arsenic acid, a cotton defoliant and the assumed source of As in the bivalve, has been banned for more than five years. It is unlikely that As will be found in the Concho River sediment unless it is coming from anothersounce because the K,, of arsenic acid is 6 x 1O-""and all of the As used as a cotton defoliant should be in an ionic form (most as HAsO,”) at a pH of 8. A study of the sediment would reveal whether the As at the study site is a recent phenomena or possibly incorpo- rated into the sediment in a manner that is unknown at this time. ACKNOWLEDGEMENTS The author wishes to thank Ned Strenth, J. Kelley McCoy, Ross C. Dawkins, Jack C. Eli, George E. Shankle, Edgar N. Drake, and John D. Beatty of Angelo State University. The author also wishes to thank 103 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 Robert G. Howells of the Texas Parks and Wildlife Department. This study was made possible through funding from the Houston Conchol- ogy Society, Inc. LITERATURE CITED Buhrke, V.E., R. Jenkins, & D.K. Smith. 1998. A practical guide for the preparation of specimens for x-ray fluorescence and x-ray dif fraction analysis. John Wiley & Sons, Inc., New York, 333 pp. Dare, P.J. & D.B. Edwards. 1975. Seasonal changes in flesh weight and biochemical composition of mussels (Mytilus edulus L.) in the Conwy Estuary, North Wales.J. Exp. Mar. Biol. Ecol. 18: 89-97. Heit, M., C.S. Klusek, & K.M. Miller. 1980. Trace element, radionuclide, and polynuclear aromatic hydrocarbon concen- trations in unionidae mussels from Northern Lake George. Environ. Sci. Technol. 14: 465-468. Howells, R.G., R.W. Neck, & H.D. Murray. 1996. Freshwater mussels of Texas. Texas Parks and Wildlife Press, Austin, 218 pp. Lower Colorado River Authority, Upper Colorado River Author ity, Colorado River Municipal Water District, & Colorado River Basin Steering Committee. 1996. Regional assessment of wa- ter quality Colorado River basin & Colorado/Lavaca coastal plain- technical report. Austin, 176 pp. Neves, R.J. & S. N. Moyer. 1988. Evaluation of techniques for age determination of freshwater mussels (Unionidae). Amer. Malacological Bull.6(2): 179-188. Vaughn, C.C., C.M. Webb, D.E. & R.C. Dawkins. 1998. A comparison of trace element concentrations in Corbicula sp. (Bivalvia:Corbiculidae) and sedi- ment from the Concho river by energy dispersive x-ray fluores- cence. Texas Journal of Science 50(2): 149-154. Zar, J.H. 1996. Biostatistical analysis third edition.Prentice Hall. Upper Saddle River, New Jersey, 662 pp. 104 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 Table 1. Whole animal weight of Q. apiculata (QA) and C. fluminea (C) analyzed with EDXRF. Weight (g) Weight (g) Sample Number (shell & Sample Number (shell & tissue) tissue) QA1 113..0 Cl 22.8 QA2 116.1 C2 2025 QA3 B0-3 C3 25.8 QaA4 #26 23. c4 2378 QA5 108.9 cs es QA6. 141.4 C6 25.6 QA7 56.8 CF 24.6 QA8 421.8 C8 24.8 QA9 [alge 1 cg 19.9 QA10 eee inc | C10 25.5 QA11 5 a aia Cid 30 4 QA12 120.8 C12 23 36 QA13 156.2 C13 21.8 QA14 LO? . 2 C14 20.6 QA15 132.6 CLS 24.3 QA16 127.0 C16 23 26 QA17 98.2 C17 $3.7 Average ; Average Weight & SD L26.407~+-29-0 Weight & SD 23.9--.3.6 (g) (g) 105 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 Table 2. Mean Concentration of As in 17 C. fluminea and 17 Q. apiculata. C. fluminea Q. apiculata ID Number Concentration & ID Number Concentration & SD (ppm dry SD(ppm dry weight) weight) Cl 20.71 = 3.99 QA1 7.29 =2.17 C2 11.68 - 3.89 QA2 1.78 = 1.56 C3 15.02 = 3.67 QA3 5.26 = 2.62 C4 tba Ll = 3206 QA4 4.24 -1.52 C5 17.16 = 3.20 QA5 2.05 =1.95 C6 20.45 = 3.30 QA6 2.8502 3.58 Cr 16.74 = 4.77 QA7 6.61 = 2.53 C8 14.29 =1.27 QA8 4.90 - 0.74 C9 18.12 *1.73 QA8 4.45 =2.41 C10 14.62 =2.14 QA9 3.84 = 2.87 Git 24.69 ='2.35 QA10 2.34 -2.11 C12 11.19 +1.66 QA11 3.14 + 0.48 ¢13 20.29 = 0.52 QA12 6.71, =. 49 c14 1 eee Me QaA13 2.44 > 2 69 C15 16.61 22.75 QA14 2.48 =2.99 C16 13250'—. 3:05 QA15 5.43 = 3.98 C17 18.35 =5.44 QA16 6.08 = 3.53 106 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 Table 3. Mean Concentration of Pb in 17 C. fluminea and 17 Q. apiculata. C. fluminea Q. apiculata ID Number Concentration ID Number Concentration & SD (ppm dry & SD (ppm dry weight) weight) Cl 42 230° >=, 2.25 QAl 19.76 * 2.61 C2 38.65 + 5.76 QA2 22.23) > 3.28 oF. 29.38 =.7 18 QA3 23..55)— 5.26 c4 27.68 = 6.56 QA4 25.49) ~ 358 Sto 29.92 = 3.49 QA5 24.01 = 6.94 C6 29.27 - 3.94 QA6 23.59 =~ 1.64 C7 37.65 + 11.31 QA7 21.91 * 4.43 C8 40.75 = 3.42 QA8 23.49 = 2.94 cS 30.88 = 1.82 QA9 30.80 = 3.82 C10 33,725. -.6'..52 QA10 23.26 71>, 2.52 C11 33234: — 3. 5a: QA11 23.99 = 4.97 C12 37.89 = 3.72 QA12 26,19 = 2.30 C13 23:323 =°0'.95 QA13 26.81 = 2.64 c14 36.28;< 5520 QA14 22.58 — 8.20 crs 39.19 + 5.96 QA1S 23.78 = 4.99 C16 45.20 = 4.69 QA16 27 .397-"5.99 Ci7 34.41 = 5.05 QA17 21.59 = 2.08 107 TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE 1999 00°0=G9%d 900° 0=G014d ce=dd aL *Cc@ae..~. 8S°.0-5 a aN SEC 80°S c8°9 c8°9 VL ve 99; Pe Gd 00°0=G0%d 00°0=qoz2q ce=dd €°€c=dd oL' TF bs Sore Te Loy OV°cr OV°cT ae | 67° 9T SW SsoueTARPA sBOUeTIPA eIeTNIOTde POUTUMNTF “QTID YJ paeqerno{pted Pe ToOog os jerzedas x6) ts qusUIS TA Ser0ds-J S8100S- (3u5teM Arp wdd) UOTIeAWUSIUOD ‘SeIODS-J pue saezo0os-q ere papntout osty ‘eQeTNOTde *O pue PeuTUMTZJ *D UT qd pue SW JO SUOTJeIRqUaDUOD ‘FP aTaey 108 HOUSTON CONCHOLOGY SOCIETY, INC. Officers 1998-1999 President: Constance E. Boone Program Vice president Virginia Joiner Field Trip Vice-President: Mary Martin Treasurer: Angela Doucette Recording Secretary: Carol Andrews: Corresponding Secretary: Cathy Betley Directors: Alex Bermudez | Allison McHenry Dave Green Cheryl Hood Frank & Tina Petway Ruth Anne Sparlin Immediate Past President: Darwin G. Alder Co-Editor, Texas Conchologist Constance E. Boone Co-Editor, Texas Conchologist Darwin G. Alder Honorary Life Members Constance a Boone Dr. Helmer Odé Dr. John McHenry TEXAS CONCHOLOGIST Vol. XXXV, No. 2, JUNE, 1999 TT 3 9088 01294 7487 Table of Contents 7 Recent Harold W. Harry Memorial Award Winners: Christine Ritter David W. Hicks and Daniel E. Webb............. auseeusnatetsneacsedss ata 89 Estuarine Macrobenthic Community Succession: The influence of hypoxia, salinity fluctuations, sediment resuspension and disturbance frequency by Christine Ritter.............cccsssscdscscsceessenceeeeeea 92 The Effects of Environmental Factors on the Production and Strength of Byssal Threads in the Nonindigenous Marine Mussel, Perna perna by David W. Hicks. ........:::cccecssessaseseesscess eee 96 A Comparison of Arsenic and Lead Concentrations in the freshwater bivalves Corbicula fluminea (Corbiculidae) and Quadrula apiculata (Unionidae) from the Concho River, Texas, using Energy Dispersive X-ray Fluorescence by Daniel E. WebD............:2c:00c::sennn0ncceswea eee 98