Impact/Purpose:

GENERIC RARE OBJECTIVE: The Regional Applied Research Effort (RARE) provides the Regions with a mechanism to address near term research needs through an ORD Laboratory/Center. Any applied research project that a Region identifies and that an ORD laboratory has the expertise to carry out will be considered if the three following conditions are met: 1) projects must be funded through an ORD Laboratory or Center, 2) the project must fall within with defined mission of the selected ORD Laboratory/Center, and 3) proposals must be research-oriented.

Description:

This research proposes to experimentally assess the response of the toxic dinoflagellate, Pfiesteria piscicida, and representative zooplankton predators and algal prey to three EBDC fungicides that are commonly used on croplands and effluent spray fields, and two common heavy metal contaminants in swine wastes. The fungicide and metal effects will be tested alone and in combination. The information from these experiments will be used to design a final experimental series to assess how sublethal levels of EBDCs, alone or with heavy metals, interact with sublethal densities of toxic P. piscicida to affect zooplankton and fish health. Wastes from intensive swine operations and other agriculture also contain organic and inorganic nutrient forms that are known to stimulate P. piscicida both directly and indirectly, mediated through abundance of algal prey. A secondary project goal will be to examine the influence of prey-replete versus prey-limited conditions in the previous growing season on P. piscicida cell production and toxicity to fish following excystment in the subsequent growing season. The chemicals of focus in this study will be three commonly used EBDC fungicides as Dithane (pure ethylene bisdithiocarbamate), Maneb (manganese ethylene bisdithiocarbamate), and Zineb (zinc ethylene bisdithiocarbamate); and heavy metals copper and zinc. Series of short-term batch culture experiments using (i) potentially toxic Pfiesteria piscicida alone (i.e., a virulent clonal population confirmed as capable of producing toxin and killing fish, in tempor-arily nontoxic form without fish prey, with dominant flagellated and amoeboid stages quantified); (ii) potentially toxic P. piscicida and algal prey (e.g., mixed prey as representative cryptomonads [Cryptophyceae], chrysophyte flagellates [Prymnesiophyceae], and green algal flagellates; (iii) potentially toxic P. piscicida and predators as representative zooplankters (the copepod, Acartia tonsa, and the rotifer, Brachionus); and (iv) toxic P. piscicida with test fish will be completed to address these hypotheses: 1. EBDCs and metals, alone or in combination, reduce Pfiesteria cell production and toxicity, with differential severity of the effect depending on the specific fungicide and/or metal added. 2. EBDCs and metals, alone or in combination, reduce survival of representative microbial predators, with differential severity of the effect depending upon the specific fungicide and/or metal added. However, these chemicals, alone or in combination, adversely impact Pfiesteria predator populations at lower dosages than are required to adversely affect P. piscicida.When present together, EBDCs, metals and toxic Pftesteria act synergistically in adversely affecting microbial predator survival. 3. EBDCs and metals, alone or in combination, reduce survival of representative algal prey, with differential severity of the effect depending upon the specific fungicide and/or metal. But these chemicals, alone or in combination, adversely impact algal prey at lower dosages than are required to adversely affect P. piscicida. When present together, EBDCs, metals and toxic Pfesteria act synergistically in adversely affecting microbial predator survival. 4. Reduction of algal prey populations, in the absence of fish, induces P. piscicida to encyst (i.e., to transform to resistant, dormant resting stages). Cysts that were produced under prey-depleted conditions respond more strongly to the presence of live fish (e.g., with higher toxic zoospore production, or with more virulent toxic zoospores) than cysts that were pro-duced under prey-replete conditions. 5. EBDCs and metals, alone or in combination, reduce fish immunological function at lower dosages than are required to adversely affect P. piscicida populations (including toxic zoo-spores, amoebae, etc.). When present together, these chemicals + [sublethal levels of] toxic P. piscicida interact synergistically to reduce fish immunological function.

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