Growth and competition of several harmful dinoﬂagellates under different nutrient and light conditions Ji Li a, *, Patricia M. Glibert a , Jeffrey A. Alexander a , Mayra E. Molina b a University of Maryland Center for Environmental Science, Horn Point Laboratory, P.O. Box 775, Cambridge, MD 21613, USA b P.O. Box 925, Lebec, CA 93243, USA 1. Introduction Prorocentrum spp. is one of the major groups of bloom forming harmful dinoﬂagellates that have been reported to develop harmful algal blooms (HABs) in coastal waters worldwide, and to cause ecological damage by high biomass and to have related effects (Heil et al., 2005; Glibert et al., 2008b, in press). Prorocentrum minimum is a common HAB species in coastal and estuarine systems in USA, and it is well documented in the Chesapeake Bay and many other parts of the world (Glibert et al., 2001; Heil et al., 2005; Tango et al., 2005). In the past two decades, over 800 events of P. minimum with cell density over 100,000 cell L 1 were recorded in the Chesapeake Bay by the State of Maryland Department of Natural Resources (MD DNR) monitoring program. Another Prorocentrum species, Prorocentrum donghaiense, is a major bloom species near the Changjiang River estuary and in the coastal area of East China Sea. Large scale P. donghaiense blooms have been observed in those waters in the past two decades (Zhou et al., 2006; Li et al., 2009, 2010). Another HAB species, which is increasing in both frequency and abundance in Chesapeake Bay, as well as numerous other waters in US and around the world, is Karlodinium veneﬁcum. K. veneﬁcum is a potentially toxic dinoﬂagellate and has been implicated in causing ﬁsh kill events (Heil et al., 2001; Deeds et al., 2002, 2006; Adolf et al., 2006a). Both P. minimum and K. veneﬁcum are recognized as dominant late spring and summer bloom species in the Chesa- peake Bay area, and often co-occur (Glibert et al., 2001; Tango et al., 2005). P. minimum has also been suggested responsible for shellﬁsh kills in Gulf of Mexico and Florida (Smith, 1975; Steidinger and Tangen, 1996), while Karenia brevis, a prevalent, potentially toxic dinoﬂagellate has long been observed in the southwest Florida shelf (Heil et al., 2007; Vargo et al., 2008; Vargo, 2009). In the East China Sea, the dinoﬂagellate Karenia mikimotoi was reported to bloom just before or contemporaneously with P. donghaiense blooms (Li et al., 2009). Thus, there are numerous questions with regard to relative success of Prorocentrum species in the presence of the competing dinoﬂagellates, Karlodinium or Karenia. In all of these cases, bloom areas were enriched by large terrestrial nutrient inputs. The relationships between nutrient loading and bloom development are very complex (Anderson et al., 2002; Glibert et al., 2005a, 2006, 2008a; Glibert and Burkholder, 2006). While dissolved inorganic nitrogen (DIN) is the major N Harmful Algae 13 (2012) 112–125 A R T I C L E I N F O Article history: Received 27 July 2011 Received in revised form 17 October 2011 Accepted 17 October 2011 Available online 22 October 2011 Keywords: Harmful dinoﬂagellates Prorocentrum Karlodinium Karenia Growth rate Competition N:P ratio Light A B S T R A C T Three near-shore type harmful dinoﬂagellates, Prorocentrum minimum, Prorocentrum donghaiense and Karlodinium veneﬁcum, and one off-shore dinoﬂagellate, Karenia brevis, were grown in laboratory monocultures and mixed batch cultures. The dinoﬂagellate cultures were grown on treatments of two ambient nitrogen (N):phosphorus (P) ratios; two N substrates (nitrate and urea) and two light intensities. The microalgae Rhodomonas and Synechococcus were also added in separate treatments to the mixed culture treatments as potential food sources. All tested species grew well on both N substrates. In mixed culture, P. minimum outgrew K. veneﬁcum, and P. donghaiense outgrew K. brevis in most treatments reaching higher growth rates and higher biomass. However, when a third algae, Rhodomonas, was added, the growth of P. minimum was inhibited relative to that of K. veneﬁcum. In contrast, when grown with K. brevis, the growth rate of P. donghaiense was not signiﬁcantly affected by the addition of potential prey. K. brevis had a longer growth phase, and kept growing after P. donghaiense reached stationary phase, suggesting better adaptation of K. brevis to low inorganic nutrient conditions. The growth of K. brevis was also signiﬁcantly limited in the low light treatment. K. veneﬁcum overgrew P. minimum in the presence of Rhodomonas, a potential nutrient source. The growth rates of both K. brevis and P. donghaiense were reduced with the presence of Synechococcus. In addition to nutrient competition, mixotrophy and allelopathy were likely mechanisms in determining the dominant species. ß 2011 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 410 221 8217. E-mail address: jili@hpl.umces.edu (J. Li). Contents lists available at SciVerse ScienceDirect Harmful Algae jo u rn al h om epag e: ww w.els evier.c o m/lo cat e/hal 1568-9883/$ – see front matter ß 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.hal.2011.10.005