Temporal and spatial variability of an invasive toxigenic protist in a North American subtropical reservoir K. David Hambright a,b,c, *, Richard M. Zamor a,b,c , James D. Easton c , Karen L. Glenn c , Emily J. Remmel b,c , Anne C. Easton c a Program in Ecology and Evolutionary Biology, University of Oklahoma, Norman, OK, USA b Department of Zoology, University of Oklahoma, Norman, OK, USA c Plankton Ecology Laboratory, Biological Station, University of Oklahoma, Norman, OK, USA 1. Introduction Harmful algae are those that can cause a variety of deleterious effects on aquatic ecosystems, including beach fouling, water oxygen deficiency, clogging of fish gills, or poisoning of various organisms (Grane ´ li and Turner, 2006). Blooms of harmful algae (commonly referred to as HABs) are increasingly becoming a major impediment to the normal ecological and economical functioning of aquatic ecosystems world wide. For example, in coastal marine systems, blooms of Pseudo-nitzschia spp., Alexandrium spp., and Karenia brevis and their associated toxins (domoic acid, saxitoxin, and brevetoxin, respectively) have resulted in increasing numbers of cases of human shellfish poisoning, and blooms of Pfiesteria spp. and Heterosigma sp. have been linked to fish and bird mortalities (Burkholder, 1998; Grane ´ li and Turner, 2006; Shumway et al., 2003). Such dramatic events are not usually associated with harmful algae in freshwater systems. Rather, freshwater harmful algae are most commonly cyanobacteria and generally are associated more with aesthetics and nuisance, creating surface scums and imparting bad tastes and odors to water (Paerl, 1988). Fish kills can result from cyanobacterial blooms, but these tend to be related more to oxygen depletion, rather than direct toxicity. Notable and increasingly common exceptions to the marine- freshwater HAB dichotomy are freshwater blooms of golden algae of the genus Prymnesium. Although generally confined to coastal marine systems, Prymnesium, particularly P. parvum, have created havoc in freshwater aquaculture ponds in Israel and China, and in coastal broads in England since the 1950s, 1960s, and 1970s, and is now rapidly becoming a growing threat in freshwater ecosystems in North America (Grover et al., 2007; Roelke et al., 2007). Prymnesium parvum, hereafter Prymnesium, is a toxigenic marine haptophyte that has seemingly expanded its range into freshwater systems throughout the world (Edvardsen and Imai, 2006; Lutz-Carrillo et al., 2010). The first North American record of Prymnesium is from the 1980s in the Pecos River system of southern Texas (Baker et al., 2007). During the subsequent two decades, Prymnesium gradually expanded its distribution north- ward, reaching the Red River basin in 2001, the Canadian River basin in 2003, and Lake Texoma in 2004 (Watson, 2001). Prymnesium blooms and fish kills have also been reported as far eastward as North Carolina, and westward to Arizona (Texas Parks Harmful Algae 9 (2010) 568–577 ARTICLE INFO Article history: Received 8 November 2009 Received in revised form 9 April 2010 Accepted 9 April 2010 Keywords: Hydrology Lake Texoma Nutrients N:P ratio Prymnesium parvum Salinity ABSTRACT The toxigenic marine flagellate Prymnesium parvum was first recorded in Lake Texoma, OK-TX, USA, an impoundment of the Red and Washita Rivers, following a massive fish kill in January 2004. Results of a 4.5-year monitoring program, spanning five bloom periods, revealed that Prymnesium abundances in the lake were temporally and spatially variable—densities were higher in winter, near-shore, and in Red River-associated sampling sites; the largest blooms were in Lebanon Pool, a large backwater basin often disconnected from the main reservoir. Prymnesium blooms appeared to have been fueled by high nutrient concentrations, and winter-spring densities were positively correlated with chlorophyll a, conductivity, total phosphorus, total nitrogen, and microzooplankton biomass, and negatively correlated with molar total nitrogen:total phosphorus and cladoceran and total crustacean zooplankton biomass. Comparison of Prymnesium densities with hydrological data suggested that Prymnesium blooms in Lebanon Pool were highest when the pool was disconnected from the main reservoir; no bloom occurred in the winter of 2004–2005, the only year since the 2003–2004 invasion in which Lebanon Pool and Lake Texoma were connected during the winter months. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author at: Biological Station and Department of Zoology, University of Oklahoma, Norman, OK, USA. Tel.: +1 405 325 7435; fax: +1 405 325 0835. E-mail addresses: dhambright@ou.edu (K.D. Hambright), rmzamor@ou.edu (R.M. Zamor), jeaston@ou.edu (J.D. Easton), klooper@ou.edu (K.L. Glenn), Emily.J.Remmel-1@ou.edu (E.J. Remmel), anne@ou.edu (A.C. Easton). Contents lists available at ScienceDirect Harmful Algae journal homepage: www.elsevier.com/locate/hal 1568-9883/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.hal.2010.04.006