Expansion of potentially harmful algal taxa in a Georgia Estuary (USA)

Evidence is widespread that species of harmful algae are showing up in new locations and that toxic bloom events may be increasing in magnitude and frequency. These trends are sometimes but not exclusively associated with cultural eutrophication. On the southeast coast of the USA, harmful species, bloom events, and deleterious ecosystem impacts were restricted to eutrophic estuaries and adjacent shelf waters of North Carolina and Florida prior to 2000. Specifically, Georgia and South Carolina waters either lacked HAB species or contained unremarkable concentrations. Beginning in 2000, however, numerous HAB taxa were collected in South Carolina coastal ponds and estuaries, and were associated with fish kills there. The present study documents the new appearance of HAB species in Georgia, in the Skidaway estuary, which has been sampled weekly for 22 years. Four HAB taxa were initially present when sampling began in 1986–1987, five new species appeared sporadically over the next 15 years, and then seven additional new taxa appeared between 2002 and 2008. Eleven of the sixteen taxa were dinoflagellates (species of Cochlodinium, Dinophysis, Gyrodinium, Heterocapsa, Karenia, Karlodinium, Kryptoperidinium, and Prorocentrum), four were raphidophytes (Chattonella, Fibrocapsa, and Heterosigma species), with one diatom (Pseudo-nitzschia). Notably, only two species occurred at concentrations exceeding 103 cells ml−1: Heterosigma akashiwo and Heterocapsa rotundata. One species, H. akashiwo, was present every spring/summer and in sufficient concentrations to discern temporal trends. H. exhibited significant increases in annual mean and peak abundances over the 22-year sample period. This increasing trend was significantly correlated with nutrient concentrations, specifically NH4 and DON. Whereas factors responsible for the initial appearance of new HAB taxa in these waters are unknown, the evidence suggests their establishment is related to cultural eutrophication. If current trends of increasing number and abundance of HAB species continue, estuaries in Georgia can expect to exhibit the detrimental ecological manifestations commonly observed elsewhere.