A decade of fish-killing Prymnesium parvum blooms in Texas: roles of inflow and salinity

Fish-killing Prymnesium parvum blooms have occurred in south-central USA for at least ∼30 years, with the last decade experiencing recurrent blooms of large magnitude. In the systems reported here, Lakes Possum Kingdom, Granbury and Whitney (Texas), P. parvum blooms were winter phenomena developing under conditions far from the growth optimum. Bloom thresholds of 10 × 10 6 cells L ―1 were observed as a function of inflow and salinity for the period 2000―2009. In Lake Possum Kingdom, blooms occurred only when 7-day accumulated inflows were 1.5 psu. For Lakes Granbury and Whitney, blooms occurred when 7-day accumulated inflows were 0.5 psu. Inflow to these lakes exceeded thresholds during the spring and early-summer months in 8 (Lake Possum Kingdom), 7 (Lake Granbury) and 6 (Lake Whitney) of the 10 years analyzed. Salinities typically exceeded these thresholds during the period of study prior to the spring of 2007. The spring of 2007 was a period of high precipitation, after which salinities were typically below thresholds. The linkage between incidence of P. parvum blooms, inflows and salinity is of concern because combined effects from human population increase and climate change could lead to periods of decreased inflow and increased salinity, which may then increase the frequency and magnitude of P. parvum blooms.