A Tale of Two Ports: Dinoflagellate and Diatom Communities Found in the High Ship Traffic Region of Galveston Bay, Texas (USA) Jamie L. Steichen † *, Alexandra Denby ‡ , Rachel Windham ‡ , Robin Brinkmeyer †§ , and Antonietta Quigg †‡ † Department of Oceanography Texas A&M University College Station, TX 77843, U.S.A. ‡ Department of Marine Biology Texas A&M University at Galveston Galveston, TX 77553, U.S.A. § Department of Marine Science Texas A&M University at Galveston Galveston, TX 77553, U.S.A. ABSTRACT Steichen, J.L.; Denby, A.; Windham, R.; Brinkmeyer, R., and Quigg, A., 0000. A tale of two ports: Dinoflagellate and diatom communities found in the high ship traffic region of Galveston Bay, Texas (USA). Journal of Coastal Research, 00(0), 000–000. Coconut Creek (Florida), ISSN 0749-0208. Ballast water (BW) discharge by shipping vessels is a known transport vector of harmful species of dinoflagellates and diatoms. With a steady growth in global commerce, ship traffic to ports worldwide has intensified, increasing the risk of invasion by nonindigenous species. From 2008–12, .140 million metric tons of BW was discharged into Galveston Bay, Texas, much more than reported in other highly invaded Bays: San Francisco (96 3 10 6 mt) and Chesapeake (25 3 10 6 mt) during the same period. Studies conducted specifically on the dinoflagellate and diatom communities within Galveston Bay have been lacking until the present effort, which used both microscopic and genetic methods. Within one year of sampling, 35 genera of dinoflagellates and diatoms were identified from the two deepwater ports of Houston and Galveston. Seven of the genera are known toxin producers, three of which have formed harmful algal blooms within the Bay: Alexandrium, Gymnodinium, and Prorocentrum. Two genera identified from the ports (Takayama and Woloszynskia) have not been previously reported. This study provides a baseline of the phytoplankton community within these major ports in Galveston Bay before foreign shipping traffic increases due to the expansion of the Panama Canal. ADDITIONAL INDEX WORDS: Dinoflagellates, diatoms, invasive species, Galveston Bay, harmful algal blooms, ballast water. INTRODUCTION Maintaining biodiversity within natural systems is impor- tant to the resilience and in turn the stability of the communities within an ecosystem (Holling, 1973). However, phytoplankton communities within port waters around the world, connected by shipping routes, may be experiencing a decrease in genetic diversity as they approach biotic homoge- nization (Mckinney and Lockwood, 1999; Rahel, 2002). While biological invasions happen naturally, anthropogenic influenc- es, such as shipping, have increased the frequency and volume of these introductions as well as the degree of global biotic homogeneity (Lodge, 1993). Ballast water (BW) is the primary vector in the transportation and introduction of nonindigenous species (NIS) to ports around the world (Minton et al., 2005). Transportation of ships’ BW from port to port has also been attributed to an increase in the number and frequency of harmful algal blooms (HABs) occurring globally over the last several decades (Anderson, 2009; Anderson, Cembella, and Hallegraeff, 2012; Bolch and de Salas, 2007). New invasion pathways are developing because of increasing trade and expanding transport routes to regions around the world (Wonham, 2006). Ultimately, reduction of invasion frequency is only possible by decreasing the intensity of the propagule pressure placed onto these fragile ecosystems. Over the last century, as global commerce has grown, so too has the number of ships travelling worldwide, resulting in increased propagule pressure of NIS (Minton et al., 2005; Verling et al., 2005), especially in estuaries and coastal waters, where ports are typically located. Propagule pressure can be defined as the quantity, quality, and frequency of organisms arriving to areas outside their native region (Wonham, 2006). After multiple introductions, which are thought to be a major force determining invasion success, a species is more likely to become an established NIS or even an invasive species (Carlton, 1985; Wonham, 2006). NIS pose a threat to their newly inhabited waters by creating an invasive pressure on the native species. Phytoplankton community assemblages in BW are poorly studied, and previous surveys have focused mostly on those organisms causing HABs (Bienfang et al., 2011; Bolch and de Salas, 2007; Burkholder et al., 2007; Hallegraeff and Bolch, 1992; Roy et al., 2012; Steichen et al., 2012). However, invasive species, other than HABs, can also affect aquatic ecosystems by out competing and out numbering native communities. The introduction of any NIS phytoplankton should be considered a threat whether or not they are known harmful species (Hallegraeff and Gollasch, 2006). Natural latitudinal dispersal of phytoplankton may occur when these organisms become entrained and transported within coastal currents (Smayda, DOI: 10.2112/JCOASTRES-D-13-00225.1 received 18 December 2013; accepted in revision 7 April 2014; corrected proofs received 13 May 2014; published pre-print online 16 January 2015. *Corresponding author: jls4513@tamu.edu Ó Coastal Education and Research Foundation, Inc. 2015 Journal of Coastal Research 00 0 000–000 Coconut Creek, Florida Month 0000