Beyond hydraulic flushing: Deep water mixing takes the harm out of a haptophyte algal bloom

Low pH preempts bloom development of a toxic haptophyte

“…Prymnesium parvum cell densities in the cove during our first experiment were 0.21 Â 10 6 , 0.76 Â 10 6 , 0.67 Â 10 6 , and 0.42 Â 10 6 cells/L at T0, T7, T14, and T21, respectively (Hayden et al, 2012). No acute toxicity to P. promelas was observed in the cove at any point during the first experiment.…”

“…Cells were counted in a minimum of 20 random fields of view at 400Â magnification. If less than 200 P. parvum cells were observed, a subsequent 20 random fields of view were then counted (Hayden et al, 2012).…”

“…Sub-samples of approximately 10 mL were removed from each field collected sample and settled for at least 24 h using Utermö hl algal settling chambers (Utermö hl, 1958). Zooplankton biovolume was determined by using the same microscopy and enumeration techniques as were used when determining P. parvum cell density, with additional measurements taken of appropriate dimensions of each individual that enabled geometric estimation of organism biovolume (Hayden et al, 2012).…”

“…No acute toxicity to P. promelas was observed in the cove at any point during the first experiment. Because cell densities did not exceed a designated bloom density level of 10 Â 10 6 cells/L and ambient toxicity was not observed, we refer to this period as pre-bloom (Hayden et al, 2012). During our second experiment, P. parvum cell densities in the cove were 1.1 Â 10 6 , 2.6 Â 10 6 , 0.46 Â 10 6 , and 0.08 Â 10 6 cells/L at T0, T7, T14, and T21, respectively.…”

“…Although cell densities did not exceed a designated bloom density threshold of 10 Â 10 6 cells/L, acute toxicity to P. promelas was observed by T14 with a 48 h LC 50 value of 77.5% of ambient cove water. Consequently, we refer to this period as bloom development (Hayden et al, 2012).…”