Testing Treatments Against Parasitic Scuticociliate (Philaster apodigitiformis) that Causes Mass Mortality Among Sea Urchins (Diadema antillarum) - Results

The information in this data release are those referenced in the journal article by Evans and others (2024) entitled “Evaluation of in vitro treatments against the causative agent of Diadema antillarum scuticociliatosis (DaSc).” They contain the results observed and collected during an experiment that tested the efficacy of nine compounds (2’4’ dihydroxychalcone, bithionol sulfoxide, carnidazole, furaltadone, plumbagin, oxyclozanide, quinacrine, tomatine, and toltrazuril), previously found to be effective against the parasitic ciliate family Philasteridae (Iglesias and others, 2002; Sueiro and others, 2022). One commercially available product (Kordon Ich Attack) was also tested, however was omitted from these data as it was not effective at the highest dosage trialed (100 microliters of the product in 900 microliter ciliate culture). The efficacy of the compounds was tested by applying each to subcultures of Philaster apodigitiformis (strain FWC2) originally isolated from coelomic fluid of Diadema antillarum specimen collected from a reef in Key Largo, Florida (FL) on June 15th, 2022 (Hewson and others, 2023).

The compounds were tested at the U.S. Geological Survey St. Petersburg Coastal and Marine Science Center (USGS SPCMSC), Coral Microbial Ecology Laboratory in St. Petersburg, FL, USA (Figure 1) between November 2022 and August 2023. Prior to treatment, the compounds were dissolved in either dimethyl sulfoxide (DMSO) or sterile deionized water (DI) to create 20 millimolar (mM) stocks, and further diluted in sterile artificial seawater (ASW) to generate 1 mM working stocks. These working stocks were then used to create final testing concentrations of 100 micromolar, 50 µM, 25 µM, 12.5 µM, 6.25 µM, and 3.13 µM for each run of the experiment. Controls included 1000 microliter (µL) of unamended culture and 900 µL culture plus either: 100 µL ASW, 100 µL DMSO diluted in ASW to the highest concentration used in the drug trials (i.e.,10 µL DMSO in 190 µL ASW), or 100 µL DI water diluted in ASW to the highest concentration used in the drug trials (i.e., 10 µL DI in 190 µL ASW). Compounds identified to be effective within 24 hours were then trialed for 15-minute exposure periods. Each potentially effective compound was tested at its highest dosage (100 µM) by mixing 90 µL of scuticociliate culture and 10 µL of 1 mM stock solution on a Sedgwick Rafter chamber and observing the mixture continuously for 15 minutes using a Meiji Techno EMZ-13 microscope. Each successful treatment was then trialed again for 15 minutes at 50% the previous concentration. During this experiment, only quinacrine and tomatine showed potential for further testing. For more information about this experiment, please see the results and metadata files.

Evans, J.S., Voelschow, J.J., Ritchie, I.T., Breitbart, M., Hewson, I., and Kellogg, C.A. 2024, Evaluation of in vitro treatments against the causative agent of Diadema antillarum scuticociliatosis (DaSc): Diseases of Aquatic Organisms, v. 157, p. 107-112, https://doi.org/10.3354/dao03776.