Multiple stressors on the potential toxicity of Heterosigma akashiwo, a fish-killing flagellate in the Salish Sea.

• Main Authors: Matheson, Julia, Cochlan, William, Trick, Charles
• Format: Text
• Language: English
• Published: Western CEDAR 2014
• Subjects: Terrestrial and Aquatic Ecology; Ocean acidification
• Online Access: https://cedar.wwu.edu/ssec/2014ssec/Day3/50; https://cedar.wwu.edu/cgi/viewcontent.cgi?article=1511&context=ssec

As a large, island rich, estuary, the Salish Sea is strongly influenced by a diversity of ocean water intrusions and by direct and indirect human activities. The consequences of these processes provide multiple stressors on incumbent species, such as the potentially economically damaging blooms of the fish-killing flagellate Heterosigma akashiwo. Here we present laboratory findings on the combination of increased ocean acidification (pH) and modified nutrient supply (N:P) on the toxicity of a Puget Sound isolate from the Salish Sea. The toxicity and growth responses of batch cultures, conducted at a range of initial concentrations of nitrate and phosphate (N:P ratios from 1:1 to 48:1) and two pH levels (8.1 & 7.4), were examined throughout the exponential and stationary phases of growth . A modified fish gill cell bioassay was used to quantify the ecotoxicological response, generally associated with the fish-killing potential. The toxicity of the H. akashiwo cultures varied strongly with culture conditions in two general ways. First, cells grown under lower pH conditions (pH 7.4) were less toxic than the cells grown at pH 8.1. Second, cells at the lower pH were more toxic during the exponential / early stationary growth phase compared with the cells grown at normal pH levels where levels of toxicity were greatest in the stationary phase. Similarly, modification of the initial N:P conditions of the growth medium had a significant influence on observed toxicity, with the greatest toxicity occurring at 12:1 and 15:1 during the late exponential growth phase. These laboratory results demonstrate the importance of understanding how multiple stressors potentially influence the toxicity of natural fish-killing blooms of H. akashiwo in the Salish Sea.