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Approaches to setting organism-based ballast water discharge standards
Citation:
LEE, II, H., D. REUSSER, AND M. R. FRAZIER. Approaches to setting organism-based ballast water discharge standards. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 23(2):301-310, (2013).
Impact/Purpose:
Because of concerns that the ballast water standards promulgated by the International Maritime Organization (IMO) are not sufficient to control the continued introduction of invasive species, several state and national efforts are underway to develop more stringent standards. This includes a court-mandated effort by the U.S. EPA under NPDES permitting. To assist in developing scientifically defensible standards, we evaluated seven approaches to establishing ballasts water standards: (1) expert opinion/management consensus; (2) zero detectable living organisms; (3) natural invasion rates; (4) reaction-diffusion models; (5) population viability analysis (PVA) models; (6) per capita invasion probabilities (PCIP); and, (7) experimental studies. Because of the difficulty in synthesizing scientific knowledge in an unbiased and transparent fashion, we recommend the use of quantitative models instead of expert opinion. The “zero detectable organism” approach is being advocated by several states, including California. However, the actual organism concentration associated with such a standard is defined by the statistical rigor of its monitoring program and it is not clear whether such a standard is as stringent as those derived from other approaches. Of the remaining approaches, we conclude that natural invasion rate, reaction-diffusion, and experimental methodologies are not suitable for generating standards. In theory, PVA models can be used to predict the likelihood of invasion by introduced species but in reality are limited by a lack of population vital rates for potential invaders. The newly developed PCIP approach, which is based on historical invasion rates at a regional scale, appears to circumvent many of the indicated problems, although it may underestimate invasions by asexual and parthenogenic species.
Description:
As a major vector by which foreign species invade coastal and freshwater waterbodies, ballast water discharge from ships is recognized as a major environmental threat. The International Maritime Organization (IMO) drafted an international ballast water treaty establishing ballast water discharge standards based on number of viable organisms per cubic meter of ballast discharge for different organism size classes. Concerns that the IMO standards are not sufficiently protective have initiated several state and national regulatory efforts to develop more stringent standards. We evaluated seven approaches to establishing discharge standards for the >50 micron size class: (1) expert opinion/management consensus; (2) zero detectable living organisms; (3) natural invasion rates; (4) reaction-diffusion models; (5) population viability analysis (PVA) models; (6) per capita invasion probabilities (PCIP); and, (7) experimental studies. Because of the difficulty in synthesizing scientific knowledge in an unbiased and transparent fashion, we recommend the use of quantitative models instead of expert opinion. The actual organism concentration associated with a “zero detectable organisms” standard is defined by the statistical rigor of its monitoring program and it is not clear whether such a standard is as stringent as some of the other standards. For several reasons, the natural invasion rate, reaction-diffusion, and experimental approaches are not considered suitable for generating discharge standards. PVA models can be used to predict the likelihood of establishment of a newly introduced species but are limited by a lack of population vital rates for species characteristic of ballast water discharges. Until such rates become available, PVA models may be better used to evaluate relative efficiency of proposed standards rather than predicting probabilities of invasion. The newly developed PCIP approach, which is based on historical invasion rates at a regional scale, appears to circumvent many of the indicated problems, although it may underestimate invasions by asexual and parthenogenic species. Further research is needed to better define the propagule dose-response, densities at which Allee effects occur, and approaches to predicting the likelihood of invasion from multi-species introductions.
