Control Method for Invasive Aquatic Species introduced via Ballast Water: Effects of Carbon Dioxide Supersaturation on Survivorship of Digesia tigrina (Planaria: Maculata) and Lirceus brachyurus (Isopoda: Crustacea)

Survivorship of an aquatic species of planaria (Digesia tigrina) and isopods (Lirceus barchyurus) to elevated levels of carbon dioxide (CO₂) was determined. Both planaria and isopods were exposed to levels of freshwater supersaturated with carbon dioxide, and percent mortality was calculated for various exposure durations, and at various pressure levels. The data collected were graphically analyzed to determine the time necessary to produce mortality in 50% (LT50) of any given sample of specimens tested at a certain pressure level. At 38.6 kPa, 103.4 kPa and 172.4 kPa, the LT50 for planaria was calculated to be 150.3 ± 10.1, 58.6 ± 11.1, and 27.8 ± 6.2 minutes, respectively. At 38.6 kPa, 103.4 kPa and 172.4 kPa , the LT50 for isopods was calculated to be 181.1 ± 52.5, 79.7 ± 21.9, and 40.5 ± 17.0 minutes, respectively. These results suggest that CO₂ supersaturation may be an easily applied, efficient method that would end the unwanted introduction of nonnative aquatic species to habitats via ballast water released from shipping vessels.

Effect of High Hydrostatic Pressure Processing on Freely Suspended and Shellfish Associated T7 Bacteriophage

The effectiveness of hydrostatic pressure processing (HPP) for inactivating viruses has only been evaluated in a limited number of studies and most of the work has been performed with freely suspended viruses. In this work, the inactivation of freely suspended, as well as shellfish associated bacteriophage T7, by HPP was studied. T7 was selected in hopes that it could potentially serve as a model for animal virus behavior. Both clams (Mercenaria mercenaria) and oysters (Crassostrea virginica) were homogeneously blended separately and inoculated with bacteriophage T7. The inoculated shellfish meat, as well as freely suspended virus samples, were subjected to HPP under the following conditions: 2, 4 and 6 min durations; 241.3, 275.8 and 344.7 Megapascals (MPa) pressure levels; and temperature ranges of 29.4 – 35, 37.8 – 43.3 and 46.1 – 51.7Ë C. Plaque forming unit (PFU) reductions of 7.8 log10 (100% inactivation) were achieved for freely suspended T7 at 344.7 MPa, 2 min and 37.8 – 43.3Ë C. At 46.1 – 51.7Ë C, T7 associated with either clams or oysters was inactivated at nearly 100% (> 4 log10) at all pressure levels and durations tested. The results indicated that T7 is readily inactivated by HPP under the proper conditions, may be protected or made more susceptible by shellfish meat, and may serve as a viable model for the response of several animal viruses to HPP.