Effects of organic carbon, organic nitrogen, inorganic nutrients, and iron additions on the growth of phytoplankton and bacteria during a brown tide bloom

Abstract

Although nutrient inputs are the most commonly cited cause of brown tide blooms of Aureococcus anophagefferens on Long Island, New York, there is no consensus as to which nutrient(s) stimulates A. anophagefferens growth in the field. To evaluate the ability of dissolved organic carbon (DOC as glucose), dissolved organic nitrogen (DON as urea), nitrate, phosphate and iron to enhance A. anophagefferens growth during blooms, 10 nutrient enrichment experiments were conducted over the course of a brown-tide bloom during May, June and July of 1998 in West Neck Bay (WNB), Long Island, USA, using whole bay water. During the experiments, A. anophagefferens densities ranged from 1 × 10 4 to 5 × 10 5 cells ml -1, representing between 2 and 90% of algal biomass. Brown tide growth changed as a function of ambient nutrient levels during experiments, as the bloom shifted from organic carbon to N-limitation when nitrate levels in WNB decreased from elevated (2 to 20 µM) to low (< 0.5 µM) levels. Contrary to current hypotheses that organic nitrogen fuels A. anophagefferens bloom formation and inorganic nitrogen can repress it, brown tide growth in response to equimolar nitrate and urea additions was nearly identical during experiments. Additions of nitrate or urea either had no effect or significantly decreased the relative abundance of the brown tide among the algal community during experiments. In contrast, augmentation of A. anophagefferens growth and decreases in non-brown-tide phytoplankton (NBTP) growth during organic carbon (glucose) additions resulted in significant increases in the relative abundance of brown tide among phytoplankton. Simultaneous enhancement of bacterial growth by glucose additions indicated a possible A. anophagefferens-NBTPbacterial interaction by which monospecific brown tides may be initiated. Therefore, it is hypothesized that processes introducing copious amounts of labile DOC during A. anophagefferens blooms, such as leakage or remineralization of NBTP blooms, could promote monospecific brown tides.

Promotion of harmful algal blooms by zooplankton predatory activity

“…The initial presence of faster growing, more palatable algal prey can thus actually favour the development of the HAB. Indeed, typically HAB events follow the bloom of non-HAB species (figure 1b versus c, Smayda 1997; Gobler & Sanudo-Wilhelmy 2001).…”

Effect of the northern quahog Mercenaria mercenaria on the development of blooms of the brown tide alga Aureococcus anophagefferens

“…Numerous scenarios and specific growth factors have been proposed as possible 'causative agents' for these blooms including general eutrophication, increased availability of iron, urea, selenium or DON, or specific meteorological conditions or groundwater input (Cosper et al 1993, Gobler & Cosper 1996, Lomas et al 1996, Berg et al 1997, LaRoche et al 1997, Gobler & Sañudo-Wilhelmy 2001. These studies have provided valuable information relating to the growth requirements of A. anophagefferens, but they have not provided a predictive understanding of brown tides.…”

Extracellular enzyme activity and uptake of carbon and nitrogen along an estuarine salinity and nutrient gradient

“…Paerl 1988, Berg et al 1997, Lewitus et al 1999, Glibert et al 2001. In particular, many nuisance algal species exhibit positive growth responses to the addition of small organic compounds (Lewitus & Kana 1994, Berg et al 1997, Gobler & Sañudo-Wilhelmy 2001. Thus, an important question in productive, organic-rich systems is to what extent does organic matter contribute to auto-and heterotrophic microbial nutrition relative to inorganic nutrients?…”