The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change J.M. O’Neil a, * , T.W. Davis b , M.A. Burford b , C.J. Gobler c a University of Maryland, Center for Environmental Science, Horn Point Laboratory, Cambridge, MD 21613, USA b GriffithUniversity, Australian Rivers Institute, Nathan, QLD4111, Australia c StonyBrookUniversity, School of Marineand Atmospheric Science, Stony Brook, NY, USA 1. Introduction While cyanobacterial harmful algal bloomshavebeenreported in the scientificliteraturefor morethan 130 years(Francis, 1878), in recentdecades, the incidence and intensityof theseblooms,as well aseconomic lossassociated with these events hasincreased in both fresh and marine waters (Chorus and Bartram, 1999; Carmichael, 2001, 2008; Hudnell, 2008; Heisler et al., 2008; Hoagland et al.,2002;Paerl, 2008; Paul,2008;Paerl and Huisman, 2008). Recently, there have been discoveries of previously unidentified cyanobacterial toxins, such as amino b-methyla- mino- L-alanine (BMAA), and of new genera of cyanobacteria capable of producing previouslydescribed toxins (Coxet al.,2003, 2005, 2009; Cox,2009; Brand, 2009; Kerbratet al., 2011). To date, factorsidentifiedas contributingtowards the global expansion of harmful cyanobacterial blooms have included increased nutrient inputs, the transportof cells or cystsvia anthropogenic activities, and increased aquaculture production and/or overfishing that altersfoodwebsandmaypermitharmfulspecies to dominate algal communities (GEOHAB, 2001; HARRNESS, 2005; Heisler et al., 2008). It has also been shown that an increasein surfacewater temperatures due to changing global climatecould play a role in the proliferationof cyanobacterial blooms (Peperzak, 2003; Paerl and Huisman,2008; Paul, 2008).Importantly,there is consensus thatharmfulalgalbloomsarecomplex events, typicallynot caused by a single environmental driver but rather multiple factors occurring simultaneously (Heisler et al., 2008). Finally, an improved ability to detect and monitor harmful cyanobacterial blooms, and their toxins as well as increased scientificand public awareness of theseevents has also led to betterdocumentation of these events (GEOHAB, 2001; HARRNESS,2005; Sivonen and Bo ¨rner, 2008). There have been several reviews of the intensification and global expansionof harmful cyanobacterial blooms in terms of Harmful Algae14 (2012) 313–334 A R T I C L E I N F O Articlehistory: Availableonline 29 October2011 Keywords: Climatechange Cyanobacteria CyanoHABs Eutrophication Harmful algaeblooms Toxins A B S T R A C T Cyanobacteria are the most ancient phytoplanktonon the planet and form harmful algal blooms in freshwater, estuarine, andmarineecosystems. Recent research suggests that eutrophication andclimate change are two processes that may promotethe proliferationand expansionof cyanobacterial harmful algal blooms.In this review, we specificallyexaminethe relationshipsbetweeneutrophication, climate change and representative cyanobacterial genera from freshwater (Microcystis, Anabaena, Cylindros- permopsis), estuarine (Nodularia, Aphanizomenon), and marine ecosystems(Lyngbya, Synechococcus, Trichodesmium). Commonalities amongcyanobacterial genera include beinghighly competitivefor low concentrations of inorganicP (DIP) and the ability to acquireorganicP compounds. Bothdiazotrophic(= nitrogen(N 2 ) fixers) and non-diazotrophiccyanobacteria display greatflexibility in the N sourcesthey exploit to form blooms. Hence,while some cyanobacterial blooms are associated with eutrophication, several form blooms when concentrationsof inorganic N and P are low. Cyanobacteria dominate phytoplankton assemblages under higher temperaturesdue to both physiological (e.g. more rapid growth) and physical factors (e.g. enhancedstratification),with individual speciesshowing different temperature optima. Significantly less is known regarding how increasing carbon dioxide (CO 2 ) concentrations will affect cyanobacteria, although some evidence suggests several genera of cyanobacteria are well-suited to bloom under low concentrations of CO 2 . While the interactiveeffects of futureeutrophication andclimatechange on harmful cyanobacterial bloomsarecomplex, much of the currentknowledgesuggests theseprocesses arelikely to enhance the magnitude and frequency of these events. ß 2011 ElsevierB.V. All rights reserved. * Corresponding author. E-mail address: joneil@hpl.umces.edu (J.M. O’Neil). Contents lists available at SciVerse ScienceDirect Harmful Algae j ou r n a l h om e p a g e : ww w . e l s e v i e r . c o m / l o c a t e / h a l 1568-9883/$ – seefront matterß 2011 ElsevierB.V. All rights reserved. doi:10.1016/j.hal.2011.10.027