AME 75:55-68 (2015)  -  DOI: https://doi.org/10.3354/ame01748

ABSTRACT: Prymnesium parvum is a harmful algal bloom species present in many inland water bodies of the southcentral USA, but does not form fish-killing blooms in all of them. The present study tested the hypothesis that rotifer grazing of P. parvum might influence the incidence of blooms. Three-day in-lake experiments, which focused on the size fraction of zooplankton dominated by rotifers and natural phytoplankton assemblages inoculated with P. parvum, were conducted during the time of bloom development in 2 reservoirs of the southcentral USA: Lakes Somerville and Whitney, where the latter experiences P. parvum blooms and the former does not. Toxicity at a level lethal to fish was only occasionally observed during these experiments, so our experimental treatments are considered to be at a low-toxicity level. As a whole, rotifers in Lakes Somerville and Whitney selectively grazed P. parvum. Rotifers in Lake Somerville appeared to benefit from this selective grazing, while rotifers in Lake Whitney did not. The differences between rotifer communities from these lakes might be because rotifers from Lake Somerville historically have only been exposed to low levels of toxins produced by P. parvum and were able to develop resistance to these toxins, thus enabling them to persist and perhaps contribute to the suppression of blooms there. The opportunity for this type of microevolutionary adaptation may not occur in lakes where P. parvum blooms and waters reach high toxicity levels, such as those which have occurred historically in Lake Whitney.

KEY WORDS: Prymnesium parvum · Rotifer · Selective grazing · Microevolutionary adaptation