Responses of phytoplankton and Pfiesteria-like dinoflagellate zoospores to nutrient enrichment in the Neuse River Estuary, North Carolina, USA

Abstract

The recently described toxic dinoflagellate Pfiestena piscicida and morphologically similar Pfiesteria-like dinoflageiiates have become a major water quality issue with possible fish mortality and reported human health implications. The linkages between accelerated nutrient loading, eutrophication, and the proliferation of this group of dinoflagellates, however, are not well established for natural Systems. Phytoplankton pnmary production may provide a key link between nutrient inputs and potential outbreaks of Pfiesteria-like biflagellated zoospores in the Neuse River Estuary, North Carolina. The impacts of nutrient (NO3--nitrogen and ~0,~--phosphorus) supply rates, sediment-water column exchange, water column m~xing, and phytoplankton prey on the abundance of Pfiesteria-like non-toxic biflagellated zoospores were examined seasonally over 18 mo in a region of the Neuse River Estuary where fish-kiils attnbuted to P piscicida have been reported. Phytoplankton community responses to the manipulated vanables indicated that biomass and productivity were consistently N limited. Dominant phytoplankton taxa, including chlorophytes, diatoms, and cyanobacteria, exhibited significant biomass increases in response to N (as NO3-) additions. Phosphate (as ennchments did not additionally influence the relative growth and abundance of individual algal groups. Pfiesterialike zoospores did not exhibit significant increases in abundance in response to mixing, sediment, or nutnent-addition treatments. Seasonally, the number of Pfiesteria-like zoospores was positively correlated with phytoplankton biomass and productivity. The abundance of Pfiesteria-like zoospores followed general trends in phytoplankton biomass and production in the estuary, suggesting that the source of organic nutrition supporting growth is likely phytoplankton based. Lowering of phytoplankton growth and bloom potentials through proposed nutrient-input reduction strategies should translate into broad-based water quality improvement, including declines in the frequency and magnitudes of nuisance algal blooms, 0, depletion, and associated fish and shellfish mortality in the Neuse &ver Estuary

Field ecology of toxic Pfiesteria complex species and a conservative analysis of their role in estuarine fish kills.

“…b From laboratory experiments (5,8,12,13,58,62) together with field data from North Carolina and Maryland estuaries (31,32,41,42). Note that in contrast to these studies, a recent short-term mesocosm study by Pinckney et al (63) found no apparent nutrient stimulation of pfiesteria-like organisms. From recent evaluation of that work, however, a national peerreview panel (40) concluded that "the study was compromised by serious experimental flaws (control populations usually died off) and taxonomic uncertainties, inadequate consideration of Pfiesteria life cycle stages and their trophic regulation, and a restricted data focus" [(40), p 22].…”

The role of nutrient loading and eutrophication in estuarine ecology.

“…Large amounts of N and other nutrients may be sequestered and stored in biomass (i.e., POM) and therefore not considered when budgets are constructed. Nutrient addition and dilution bioassays, in which natural samples are incubated under various nutrient concentrations, allow the phytoplankton to function as bioindicators to signal which nutrient(s) is limiting (46,47). This experimental approach offers a direct and reliable assessment of the identity and relative proportions of limiting nutrients.…”

Pfiesteria: Review of the Science and Identification of Research Gaps. Report for the National Center for Environmental Health, Centers for Disease Control and Prevention

“…Published comments include rejection of the idea that P. piscicida blooms cause fish kills, and strenuous denials that the organism may pose significant threats to natural fish stocks or human health (24,27,28). Some of these objections (27) are basically polemical arguments flawed by scientific misinterpretations that have been pointed out by Lewitus et al (29) and Oldach (30).…”

“…A Neuse River, North Carolina, experimental study was hampered by chronic low abundance of the biflagellate zoospore stage (frequently <6 cells mL -1 ). Abundance of other phytoplankton organisms of similar size ranged from 10 3 to 10 4 cells mL -1 (24). Dead fish often are carried to regions outside of the active kill area by tidal and other currents, blurring interpretations based on analyses of watermass properties in samples collected in the "dead zone.…”

“…Pinckney et al (24) concluded from mesocosm experiments that Pfiesteria-like organisms in the Neuse River do not respond to inorganic nitrogen and phosphorus nutrification, nor is their growth negatively influenced by water column mixing. The authors' interpretation of their findings directly contradicts laboratory experience with these ecophysiological factors (11,16), which Pinckney et al dismiss in extrapolating their results to P. piscicida.…”