BIOFOULING OF WASTEWATER TREATMENT PLANTS BY THE FRESHWATER BRYOZOAN, PLUMATELLA VAIHIRIAE (HASTINGS, 1929) TIMOTHY S. WOOD 1 * and TERRENCE G. MARSH 2 1 Department of Biological Sciences, Wright State University, Dayton, OH 45435, U.S.A. and 2 Department of Biology, North Central College, Naperville, IL 60566-7063, U.S.A. (First received November 1997; accepted in revised form June 1998) AbstractÐWe report large growths of a phylactolaemate bryozoan, Plumatella vaihiriae [Hastings, A. (1929) Notes on some little-known phylactolaematous polyzoa and description of a new species from Tahiti. Ann. Mag. Nat. Hist., 10(3), 300±311], from three widely separated domestic wastewater treat- ment plants in the United States. This relatively uncommon species is previously known only from Tahiti, Hawaii, Utah, and Argentina. The bryozoan colonies are capable of plugging pipes and ®lters. Free statoblasts are suspected of interfering with ultraviolet disinfection of wastewater. Laboratory reared specimens exhibit rapid, aggressive growth and produce vast quantities of free statoblasts which either ¯oat or sink. Devising eective control methods is impeded by limited knowledge of bryozoan physiology. Given the widespread distribution of known wastewater treatment facilities aected by the bryozoan, the problem is probably a common one. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐbryozoa, Ectoprocta, Phylactolaemata, Plumattella, Hyalinella, vaihirial, biofouling, waste- water, sewage INTRODUCTION Several species of freshwater bryozoans are notor- ious for clogging pipes that carry un®ltered water from rivers and lakes. The branching, tubular ani- mal colonies attach ®rmly to any solid substrate, often appearing as clumps of brownish moss. In the last century major cities in Europe and the United States regularly experienced disruption of public water service due to blockages by bryozoans (Kraepelin, 1886). We now report a new bryozoan biofouling threat, this time in domestic wastewater treatment facilities in the United States. Although we are so far aware of only three such occurrences they are over 1200 km from each other and suggest the likelihood of a widespread problem. Bryozoans are tiny coelomate animals which form coherent colonies, often of surprisingly large size. Most freshwater species belong to the class phylactolaemata, and the species infesting waste- water treatment plants is Plumatella vaihiriae (Hastings, 1929). Individual units of the colony, termed zooids, ingest and digest suspended particles from the water. Each zooid is also capable of pro- ducing dormant buds, called statoblasts, which can resist harsh environmental conditions for several years. Plumatella vaihiriae and other species of the family plumatellidae produce two types of stato- blasts: a small ¯oatoblast (Fig. 1) released freely into the water, and a larger sessoblast (Fig. 2) cemented ®rmly to submerged surfaces. After an obligate period of dormancy these seed-like stato- blasts can ``germinate'' and produce a new gener- ation of colonies. Every ¯oatoblast has a central fenestra surrounded by an annulus of large cells (Fig. 1). The biology of freshwater bryozoans is summarized by Pennak (1990) and Wood (1989, 1991). Despite its wide geographical range the literature citing Plumatella vaihiriae is not extensive. The species was ®rst described as Hyalinella vaihiriae from material collected in Lake Vaihiria, a moun- tain pond in Tahiti (Hastings, 1929). Since then it has been found in Utah (Rogick, 1942), Hawaii (Baily-Brock and Hayward, 1984), and Argentina (Cazzaniga, 1988). Lacourt's (1986) report of Plumatella vaihiriae in Australia cannot be con- ®rmed by any known specimen (Wood, in press) and should be considered tentative. Because Plumatella vaihiriae is so poorly known our primary intent in this paper is to document its occurrence with the ®rst full description of the species. We also discuss the implications of what appears to be a serious biofouling hazard. Although we suggest several possible methods for suppressing bryozoan populations, thorough studies on the eectiveness of such measures are still under way. Wat. Res. Vol. 33, No. 3, pp. 609±614, 1999 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98/$ - see front matter PII: S0043-1354(98)00274-7 *Author to whom all correspondence should be addressed. [Tel: +1-937-7752542; Fax: +1-937-7753320, E-mail: twood@wright.edu]. 609