Predicting the risk of toxic blooms of golden alga from cell abundance and environmental covariates

Abstract

Golden alga (Prymnesium parvum) is a toxic haptophyte that has caused considerable ecological damage to marine and inland aquatic ecosystems worldwide. Studies focused primarily on laboratory cultures have indicated that toxicity is poorly correlated with the abundance of golden alga cells. This relationship, however, has not been rigorously evaluated in the field where environmental conditions are much different. The ability to predict toxicity using readily measured environmental variables and golden alga abundance would allow managers rapid assessments of ichthyotoxicity potential without laboratory bioassay confirmation, which requires additional resources to accomplish. To assess the potential utility of these relationships, several a priori models relating lethal levels of golden alga ichthyotoxicity to golden alga abundance and environmental covariates were constructed. Model parameters were estimated using archived data from four river basins in Texas and New Mexico (Colorado, Brazos, Red, Pecos). Model predictive ability was quantified using cross-validation, sensitivity, and specificity, and the relative ranking of environmental covariate models was determined by Akaike Information Criterion values and Akaike weights. Overall, abundance was a generally good predictor of ichthyotoxicity as cross validation of golden alga abundance-only models ranged from 80% to 90% (leave-one-out cross-validation). Environmental covariates improved predictions, especially the ability to predict lethally toxic events (i.e., increased sensitivity), and top-ranked environmental covariate models differed among the four basins. These associations may be useful for monitoring as well as understanding the abiotic factors that influence toxicity during blooms.

Toxic Algae in Inland Waters of the Conterminous United States—A Review and Synthesis

“…A density of ≥10,000 cells mL −1 has been used as a quantitative criterion to define P. parvum bloom conditions [84]. However, the association between cell density and toxicity can vary among water bodies within and across river basins [85]. High-and low-toxicity strains of P. parvum can coexist in time and space [86], further complicating our understanding of the association between cell density and toxicity.…”

“…High-and low-toxicity strains of P. parvum can coexist in time and space [86], further complicating our understanding of the association between cell density and toxicity. Indeed, although they seem to be relatively uncommon, high-density blooms with no overt signs of ichthyotoxicity (e.g., dead or dying fish) have been reported in the USA [85,87,88] and in England [89]. The true frequency of non-toxic blooms is unknown because they can go unnoticed and unreported.…”

“…Toxic blooms of P. parvum in U.S. inland waters largely occur during the cooler months of the year, with peak bloom conditions often coinciding with temperatures in the range of 8 to 15 • C [36,85,87,88,94,135] Although rare, there are a few instances of toxic blooms occurring in the summer. For example, a highly toxic bloom was recorded in Moss Creek Lake, Texas, at a temperature of ~29 • C in the summer [135].…”