Effects of a bacteria-produced algicide on non-target marine animal species
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Harmful algal blooms (HABs) are a topic of concern in both freshwater and marine systems. In the Delaware Inland Bays (USA), blooms of dinoflagellates such as Karlodinium veneficum can cause fish kills and render waters unsafe for recreational use. Laboratory experiments suggest an algicidal exudate produced by a local isolate of the bacterium Shewanella could be used to combat blooms. Before this exudate can be tested in a real-world scenario, its effects on non-target organisms need to be determined. In this study, the algicide (IRI-160AA) was tested on the copepod Acartia tonsa, the crab Callinectes sapidus, the shellfish Crassostrea virginica, the fish Fundulus heteroclitus, and the fish Menidia menidia. ☐ Mortality experiments with A. tonsa revealed that the 24hr LC50 was 13.4% (95% CI: 12.1 – 14.7%) for adult females and 5.96% (CI: 4.54 – 7.29%) for early-stage nauplii. For C. sapidus, the LC50 for first-stage zoea was 16.8% (CI: 13.5 – 22.6%) and for megalopae was beyond the concentrations tested. The 24-hour LC50 for C. virginica pediveliger larvae and adults was beyond the concentrations tested, however the larvae 48-hour LC50 was determined to be 10.9% (CI: 8.56 – 13.2%). ☐ A series of sub-lethal effects studies were also conducted. Respiration rates for A. tonsa adult females and nauplii were measured in a microrespirometer and found to be unaffected by most sub-lethal concentrations of algicide tested but did increase in the 11% v/v concentration for the nauplii only. For C. sapidus, rates increased for the zoea in the 11% and 17% concentrations, and the megalopae were unaffected at all concentrations. Pediveliger respiration for C. virginica was unaffected at all concentrations. Activity levels were determined using locomotor activity monitors (LAMs) over a 24h light:dark cycle. Levels were not affected for adult female copepods. Activity was affected for zoea in the 1%, 11%, and 17% treatments but not in the 7% treatment, however this difference only occurred during the first light phase and disappeared after more time in algicide-free water. Pediveliger larvae were affected at the 17% level, but this difference also disappeared with more time in clean seawater. Additional assays with C. sapidus revealed no effects of the algicide on molting, or abdomen pumping and grooming. ☐ To examine algicide effects on fish, two species of fish – Fundulus heteroclitus and Menidia menidia – were exposed to different treatments at 25 and 30˚C to test for a primary stress response, indicated by increased cortisol production. Treatments were: a) algicide (1%), b) algicide-free control, c) algicide-free media control (1%), d) diel-cycling hypoxia as a potential secondary stressor, e) diel-cycling pH as a potential secondary stressor, f) algicide with diel-cycling hypoxia, g) algicide with diel-cycling pH, h) diel-cycling hypoxia and pH, and i) algicide plus diel-cycling hypoxia and pH. Neither fish had a statistically significant increase in blood cortisol when exposed to the algicide, even when in conjunction with multiple other stressors. ☐ Collectively, my results demonstrated that all animals assayed here were tolerant to the bacterial algicide at concentrations required for dinoflagellate mortality (EC50 = ~1% v/v). Thus, IRI-160AA remains a promising tool for mitigating HABs in the Delaware Inland Bays and elsewhere in the region.