Ballast water is a leading pathway for the global introduction of aquatic nonindigenous species. Most international ships are expected to install ballast water management systems (BWMS) by 2024 to ...treat ballast water before release. This study examines if ballast water discharges managed by BWMS are meeting standards for organisms ≥50 μm in minimum dimension (i.e., <10 organisms per m3; typically zooplankton). Representative samples of ballast water were collected from 29 ships (using 14 different BWMS) arriving to Canada during 2017–2018. Fourteen samples (48 %) had zooplankton concentrations clearly exceeding the standard (ranging from 18 to 3822 organisms per m3). Nonetheless, compared to earlier management strategies, BWMS appear to reduce the frequency of high-risk introduction events. BWMS filter mesh size was an important predictor of zooplankton concentration following treatment. Greater rates of compliance may be achieved as ship crews gain experience with operation and maintenance of BWMS.
•Ballast water is a main pathway for introduction of aquatic nonindigenous species.•Ships are using new ballast water management systems (BWMS) to treat ballast water.•Nearly 50 % of ballast water samples exceed treatment standards after using BWMS.•However, the frequency of high-risk introductions has been dramatically reduced.
The most effective way to manage species transfers is to prevent their introduction via vector regulation. Soon, international ships will be required to meet numeric ballast discharge standards using ...ballast water treatment (BWT) systems, and ballast water exchange (BWE), currently required by several countries, will be phased out. However, there are concerns that BWT systems may not function reliably in fresh and/or turbid water. A land-based evaluation of simulated “BWE plus BWT” versus “BWT alone” demonstrated potential benefits of combining BWE with BWT for protection of freshwater ecosystems. We conducted ship-based testing to compare the efficacy of “BWE plus BWT” versus “BWT alone” on voyages starting with freshwater ballast. We tested the hypotheses that there is an additional effect of “BWE plus BWT” compared to “BWT alone” on the reduction of plankton, and that taxa remaining after “BWE plus BWT” will be marine (low risk for establishment at freshwater recipient ports). Our study found that BWE has significant additional effect on the reduction of plankton, and this effect increases with initial abundance. As per expectations, “BWT alone” tanks contained higher risk freshwater or euryhaline taxa at discharge, while “BWE plus BWT” tanks contained mostly lower risk marine taxa unlikely to survive in recipient freshwater ecosystems.
The unintentional release of aquatic nonindigenous species (NIS) via ballast water has long been recognized as a primary vector of biological invasions. To reduce the risk of ballast-mediated ...invasions, the International Maritime Organization (IMO) will direct ships to meet standards regarding the maximum number of viable organisms discharged in ballast water, with most ships expected to install ballast water management systems (BWMSs). Currently, filtration + ultraviolet (UV) irradiation is utilized as a common BWMS. There are issues, however, with enumerating viable phytoplankton after treatment at the low UV doses used onboard ships because the physiological effect occurs at the DNA level—organisms are reproductively sterilized but may remain alive for hours or days after treatment. The objective of this study is to examine three techniques to measure the number of viable phytoplankton cells following filtration + UV treatment: pulse amplitude modulation (PAM) fluorometry, epifluorescence microscopy using fluorescein diacetate (FDA) stain, and the serial dilution culture most probable number (MPN) method. PAM and staining techniques demonstrated similar patterns of phytoplankton reduction after UV irradiation. After 14 days, the MPN method confirmed viability of treated samples in enriched culture medium incubations and may be used to indicate potential recovery of damaged cells (i.e., “re-growth”). All cells that survived treatment and showed detectable growth after 14 days of incubation were smaller than 10 µm, as determined by microscopy. Combinations of direct and/or indirect measurements and culture-based methods might be the best solution to improve detection strategies and eliminate nonindigenous species.
We studied forest cover and use by small mammals in the fall of 2001 and 2002 in patches of the industrially damaged landscape of Sudbury, Ontario, Canada (46°30′N, 81°00′W). Three common forest ...patch types in the region were surveyed: semi-barren terrain, a protected arboretum, and a 30-year-old conifer plantation. Each year, four sites per treatment were selected in a 10
km
2 area in the vicinity of the Laurentian University campus. At each site, plant cover (percent low-shrub-herbaceous layer (0–1
m); percent shrub layer (1–3
m); and stand height was surveyed in four 5-m radius plots while number of trees were tallied using a Basal Area Factor 2
prism. Small mammal plots (10
m
×
10
m) were set on site with mouse- and squirrel-size live traps for 3 days during 4 weeks in early fall. A total of 398 mammals of 9 species (deer mouse (
Peromyscus maniculatus); short-tailed shrew (
Blarina brevicauda); masked shrew (
Sorex cinereus), eastern chipmunk (
Tamias striatus), red squirrel (
Tamiasciurus hudsonicus), northern flying squirrel (
Glaucomys sabrinus); Gapper's red-backed vole (
Clethrionomys gapperi); meadow vole (
Microtus pennsylvanicus), house mouse (
Mus musculus)) were captured in 1265 trap-nights and 938 trap-days (for diurnal species). There were significant differences in the structural habitat variables among treatments, though corresponding trends in abundance, activity and diversity of mammals were not significant. At a smaller scale we found: (a) a significant positive relationship between site-specific stand height, tree basal area, mammal richness, diversity, short-tailed shrew abundance and flying squirrel activity; (b) a positive effect of percent shrub cover on red squirrel activity; and (c) a negative effect of shrub cover on deer mouse abundance. Our data provides evidence that habitat selection processes occurred at a small scale within the landscape; mammal diversity increased with forest cover recovery, though both positive and negative specific responses to patch structure were detected. We suggest that these small-scale effects may be meaningful for the recovery of fragmented landscapes where suitable (i.e. structured) forest patches are small, within a low quality habitat matrix.
PDF
