_ — CONCHOLOGIT Y, < 2 4 : ; 7 ; VOLUME XXXIV, No. 1 ISSN 0885-1263 ———" AUGUST 1997 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 reqular 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 Ode' 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 publication dates. Photos accompanying articles are welcomed. TEXAS CONCHOLOGIST Vol. XXXIV No. 1, August, 1997 FIELD NOTES ON THE SOUTHWARD DISPERSAL OF THE EXOTIC BROWN MUSSEL, PERNA PERNA, IN THE WESTERN GULF OF MEXICO BRENDEN S. HOLLAND Department of Oceanography College of Geoscience and Maritime Studies Texas A&M University, College Station, Texas INTRODUCTION The natural distributions of over one thousand marine species have been directly altered by human activity (Carlton, 1989). The brown mussel, Pema pema, represents a recent biological addition to the western Gulf of Mexico biofouling community. Prior to 1990, the range of the brown mussel included the South Atlantic, portions of the Indian Ocean, and the eastern Mediterranean Sea (Vakily, 1989; Bayne, 1976). The introduction and subsequent proliferation (Figure 1) of this marine mussel in the western Gulf of Mexico is by now familiar to most Texas conchologists, Gulf coast naturalists, marine scientists, beach comb- ers, and fishermen. Hicks and Tunnell first discovered this mussel inhabiting the South Jetty at Port Aransas, Texas, in early 1990 and were the first to document its presence in North American waters (Hicks and Tunnell, 1993). They have been studying its ecology, both in the field and in the laboratory, since that time (Figure 1). Moreover, Hicks and Tunnell speculate that the brown mussel arrived in the Gulf of Mexico as a result of ballast-water transport (Hicks personal communication; Hicks and Tunnell, 1993). At Texas A&M’s main campus, we are focus- ing on the population structure of P. perna. Using molecular markers we are working to determine the most probable geographic source of this exotic bivalve. We are testing genetic material from populations within the natural range of P. perna and then comparing it to popula- tions from the Texas and Mexican gulf coast. The introduction of P. pema to the Texas coast presents an opportunity to investigate and document this invasion as it happens. Using shipping records in con- junction with genetic data, we hope to reconstruct the most likely intro- duction scenario. Identification of the most likely geographic origin of this species should aid conservationists and marine resource manag- ers concerned with prevention of ballast water introductions. Further- more, by accurately identifying the anthropogenic source of biological introductions this study can be used by legislators and regulatory agen- cies charged with enforcement of “no introductions” policy. By dem- onstrating the ability to identify the source of human-mediated intro- l TEXAS CONCHOLOGIST Vol. XXXIV No. 1, August, 1997 ductions in coastal regions where ballast water regulations are in effect, we thereby provide a powerful legal tool which can be used to protect the natural marine communities and biodiversity. Historically, biological invasions have proven both economically and ecologically disastrous (Carlton and Geller, 1993; Hamer 1991; Hedgpeth, 1993; Locke et al., 1991; Mills et al., 1994). For example, the European zebra mussel, Dreissena polymorpha, was introduced in the mid-1980’s to Lake Erie. Its rapid colonization of the entire Great Lakes watershed is an ecologi- cal and financial disaster of unprecedented scope and magnitude. The zebra mussel has altered North America’s largest aquatic ecosystem irreversibly. Regional municipal water and utility plants have estimated zebra mussel removal costs at over 100 million dollars per year (Anony- mous, 1990; Carlton and Geller, 1993; Hamer 1991; Locke et al., 1991; Mills et al., 1994). Due to similarities between the zebra mussel and P. pema in terms of adaptability, fecundity and the capacity to alter the environment, the brown mussel should be closely monitored. Potential threats include health concerns for humans, displacement of endemic species, and biofouling of coastal structures and vessels (Carlton, 1989; Hamer, 1991). Due to paralytic shellfish poisoning (PSP) and accumulation of danger- ous levels of pathogenic bacteria, pesticides, and heavy metals in pol- luted areas (Bayne, 1976), mussels can be highly toxic to humans who consume them. Biofouling of coastal structures such as municipal water and utility intakes, petroleum exploration and production platforms, and navigation buoys leads to expensive cleaning operations and navi- gational hazards (Carlton, 1989; Hamner, 1991; Locke et al., 1993; Mills et al., 1994). FIELD SURVEY Pema pema has been reported on outer wave exposed regions of jet- ties and groins as far south as Playa Escondida in the southern portion of the Mexican state of Veracruz (Figure 2) (Hicks and Tunnell, 1995). Armed with this information, a Mexican vehicle permit, collection buck- ets, several gallons of ethanol (tissue preservative), and a four-wheel drive vehicle, we departed in early June, 1996, on a collecting effort that we hoped would take us as far south as the brown mussel had dispersed (Figure 2). We began our survey at the South Jetty in Port Aransas, Texas. Stop- ping frequently along the way, we found and collected P. perna samples along the Texas coast from Port Aransas to Brazos Santiago Pass, and Z. TEXAS CONCHOLOGIST Vol. XXXIV No. 1, August, 1997 along the Mexican Gulf as far south as the town of Tecolutla (Lat. 20° 33' N, Long. 97° OO’W), Mexico, about 170 km north of Veracruz City (Figure 2). We observed the healthiest looking and most abundant mussels at the Mansfield Pass jetties, Padre Island National Seashore, Texas (Lat. 26° 34’N, Long. 97° 17’W). At Mansfield, we found dense colonies of robust mussels, with individuals of up to 10 cm in length. The condition of the mussels at Brazos Santiago Pass (Lat. 26° 4’N, Long. 97° 9' W) was also very good, although colony density and average shell length were lower (no individuals over 7 cm were observed). There appeared to be some evidence of harvesting, possibly by local fishermen. Con- tinuing southward into Mexico,we did not find mussels as healthy or abundant as those observed at Mansfield and Brazos Santiago Passes in Texas. Well developed jetties at Barra Tuxpan (Lat. 20° 57’N, Long. 97° 26’W) protect the mouth of the Tuxpan River, 150 km south of Tampico, Mexico. Mussels at this locality were small, and beds were poorly developed (Figure 3). There was evidence of recent recruit- ment, as hundreds of tiny mussels (